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diff --git a/old/61773-0.txt b/old/61773-0.txt deleted file mode 100644 index 2b88fc3..0000000 --- a/old/61773-0.txt +++ /dev/null @@ -1,25538 +0,0 @@ -Project Gutenberg's Sewerage and Sewage Treatment, by Harold Eaton Babbitt - -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms -of the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you'll -have to check the laws of the country where you are located before using -this ebook. - - - -Title: Sewerage and Sewage Treatment - -Author: Harold Eaton Babbitt - -Release Date: April 7, 2020 [EBook #61773] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK SEWERAGE AND SEWAGE TREATMENT *** - - - - -Produced by Richard Tonsing and the Online Distributed -Proofreading Team at https://www.pgdp.net (This file was -produced from images generously made available by The -Internet Archive) - - - - - - -[Illustration: - - FIG. 1.—Construction of Peck’s Run Sewer, Baltimore, Maryland. - - _Frontispiece._ -] - - - - - SEWERAGE - AND - SEWAGE TREATMENT - - BY - - HAROLD E. BABBITT, M.S. - - _Assistant Professor, Municipal and Sanitary Engineering, University of - Illinois; Associate Member American Society of Civil Engineers_ - - - NEW YORK - JOHN WILEY & SONS, INC. - LONDON: CHAPMAN & HALL, LIMITED - 1922 - - - - - Copyright, 1922, by - HAROLD E. BABBITT, M.S. - - - PRESS OF - BRAUNWORTH & CO. - BOOK MANUFACTURERS - BROOKLYN, N. Y. - ------------------------------------------------------------------------- - - - - - PREFACE - - -This book is a development of class-room and lecture notes prepared by -the author for use in his classes at the University of Illinois. He has -found such notes necessary, since among the many books dealing with -sewerage and sewage treatment he has found none suitable as a text-book -designed to cover the entire subject. The need for a single book of the -character described has been expressed by engineers in practice, and by -students and teachers for use in the class-room. This book has been -prepared to meet both these needs. It is hoped that the searching -questions propounded by students in using the original notes, and the -suggestions and criticisms of engineers and teachers who have read the -manuscript, have resulted in a text which can be readily understood. - -The ground covered includes an exposition of the principles and methods -for the designing, construction and maintenance of sewerage works, and -also of the treatment of sewage. In covering so wide a field the author -has deemed it necessary to include some chapters which might equally -well appear in works on other branches of engineering, such as the -chapter on Pumps and Pumping Stations. Special stress has been laid on -the fundamentals of the subject rather than the details of practice, -although illustrations have been drawn freely from practical work. The -quotation of expert opinions which may be in controversy, or the -citation of examples of different methods of accomplishing the same -thing, has been avoided when possible in order to simplify explanations -and to avoid confusing the beginner. - -The work is to some extent a compilation of notes and quotations which -have been collected by the author during years of study and teaching the -subject. Credit has been given wherever due, and at the same time -references have pointed out the original sources whenever possible. -These references, which have been supplemented by brief bibliographies -at the end of certain chapters, will be useful to the student and -engineer interested in further study. Occasionally the original -reference has been lost or the phraseology of a quotation has been so -altered by class-room use, as to make it impossible to trace the -original source, so that in some few instances full credit may be -lacking. - -The author is indebted to many of his friends for their criticisms and -suggestions in the preparation of the manuscript; but he desires -particularly to acknowledge the assistance of Professor A. N. Talbot, -Professor of Municipal and Sanitary Engineering at the University of -Illinois, and of Professor M. L. Enger, Professor of Mechanics and -Hydraulics at the University of Illinois, in the entire work; also that -of Mr. T. D. Pitts, Principal Assistant Engineer of the Baltimore -Sewerage Commission during the construction of the Baltimore sewers, for -his suggestions on the first half of the book; and to Mr. Paul Hansen, -consulting engineer, of Chicago, and to Mr. Langdon Pearse, Sanitary -Engineer of the Sanitary District of Chicago, for their help on the -section covering the treatment of sewage; and to Professor Edward -Bartow, Professor of Chemistry at the University of Iowa, for his review -of the chapter on Activated Sludge; in general his thanks are due to all -others who have furnished suggestions, illustrations, or quotations, -acknowledgments of which have been included in the text. - - H. E. B. - - URBANA, ILLINOIS, 1922. - - - - - TABLE OF CONTENTS - - - CHAPTER I - - INTRODUCTION - - PAGES - 1. Sewerage and the Sanitary Engineer. 2. Historical. 3. - Methods of Collection. 4. Methods of Disposal. 5. Methods of - Treatment. 6. Definitions. 1–8 - - - CHAPTER II - - WORK PRELIMINARY TO DESIGN - - 7. Division of Work. 8. Preliminary. 9. Estimate of cost. - METHODS OF FINANCING. 10. Bond Issues. 11. Special - Assessment. 12. General Taxation. 13. Private Capital. - PRELIMINARY WORK. 14. Preparing for Design. 15. Underground - Surveys. 16. Borings. 9–23 - - - CHAPTER III - - QUANTITY OF SEWAGE - - 17. Dry Weather Flow. 18. Methods for Predicting Population. - 19. Extent of Prediction. 20. Sources of Information on - Population. 21. Density of Population. 22. Changes in Area. - 23. Relation between Population and Sewage Flow. 24. - Character of District. 25. Fluctuations in Rate of Sewage - Flow. 26. Effect of Ground Water. 27. Résumé of Method for - Determination of Quantity of Dry weather Sewage. QUANTITY OF - STORM WATER. 28. The Rational Method. 29. Rate of Rainfall. - 30. Time of Concentration. 31. Character of Surface. 32. - Empirical Formulas. 33. Extent and Intensity of Storms. 24–50 - - - CHAPTER IV - - HYDRAULICS OF SEWERS - - 34. Principles. 35. Formulas. 36. Solution of Formulas. 37. Use - of Diagrams. 38. Flow in Circular Pipes Partly Full. 39. - Sections Other than Circular. 40. Non-Uniform Flow. 51–77 - - - CHAPTER V - - DESIGN OF SEWERAGE SYSTEMS - - 41. The Plan. 42. Preliminary Map. 43. Layout of the Separate - System. 44. Location and Numbering of Manholes. 45. Drainage - Areas. 46. Quantity of Sewage. 47. Surface Profile. 48. Slope - and Diameter of Sewers. 49. The Sewer Profile. DESIGN OF A - STORM-WATER SEWER SYSTEM. 50. Planning the System. 51. - Location of Street Inlets. 52. Drainage Areas. 53. - Computation of Flood Flow by McMath Formula. 54. Computation - of Flood Flow by Rational Method. 78–98 - - - CHAPTER VI - - APPURTENANCES - - 55. General. 56. Manholes. 57. Lampholes. 58. Street Inlets. - 59. Catch-basins. 60. Grease Traps. 61. Flush-tanks. 62. - Siphons. 63. Regulators. 64. Junctions. 65. Outlets. 66. - Foundations. 67. Underdrains. 99–126 - - - CHAPTER VII - - PUMPS AND PUMPING STATIONS - - 68. Need. 69. Reliability. 70. Equipment. 71. The Building. 72. - Capacity of Pumps. 73. Capacity of Receiving Well. 74. Types - of Pumping Machinery. 75. Sizes and Descriptions of Pumps. - 76. Definitions of Duties and Efficiency. 77. Details of - Centrifugal Pumps. 78. Centrifugal Pump Characteristics. 79. - Setting of Centrifugal Pumps. 80. Steam Pumps and Pumping - Engines. 81. Steam Turbines. 82. Steam Boilers. 83. Air - Ejectors. 84. Electric Motors. 85. Internal Combustion - Engines. 86. Selection of Pumping Machinery. 87. Costs of - Pumping Machinery. 88. Cost Comparisons of Different Designs. - 89. Number and Capacity of Pumping Units. 127–163 - - - CHAPTER VIII - - MATERIALS FOR SEWERS - - 90. Materials. 91. Vitrified Clay Pipe. 92. Cement and Concrete - Pipe. 93. Proportioning of Concrete. 94. Waterproofing of - Concrete. 95. Mixing and Placing Concrete. 96. Sewer Brick. - 97. Vitrified Clay Sewer Block. 98. Cast Iron, Steel, and - Wood. 164–193 - - - CHAPTER IX - - DESIGN OF THE SEWER RING - - 99. Stresses in Buried Pipe. 100. Design of Steel Pipe. 101. - Design of Wood Stave Pipe. 102. External Loads on Buried - Pipe. 103. Stresses in Circular Ring. 104. Analysis of Sewer - Arches. 105. Reinforced Concrete Sewer Design. 194–210 - - - CHAPTER X - - CONTRACTS AND SPECIFICATIONS - - 106. Importance of the Subject. 107. Scope of the Subject. 108. - Types of Contracts. 109. The Agreement. 110. The - Advertisement. 111. Information and Instructions for Bidders. - 112. Proposal. 113. General Specifications. 114. Technical - Specifications. 115. Special Specifications. 116. The - Contract. 117. The Bond. 211–232 - - - CHAPTER XI - - CONSTRUCTION - - 118. Elements. WORK OF THE ENGINEER. 119. Duties. 120. - Inspection. 121. Interpretation of Contract. 122. Unexpected - Situations. 123. Cost Data and Estimates. 124. Progress - Reports. 125. Records. EXCAVATION. 126. Specifications. 127. - Hand Excavation. 128. Machine Excavation. 129. Types of - Machines. 130. Continuous Bucket Excavators. 131. Cableway - and Trestle Excavators. 132. Tower Cableways. 133. Steam - Shovels. 134. Drag Line and Bucket Excavators. 135. - Excavation in Quicksand. 136. Pumping and Drainage. 137. - Trench Pump. 138. Diaphragm Pump. 139. Jet Pump. 140. Steam - Vacuum Pumps. 141. Centrifugal and Reciprocating Pumps. 142. - Well Points. 143. Rock Excavation. 144. Power Drilling. 145. - Steam or Air for Power. 146. Depth of Drill Hole. 147. - Diameter of Drill Hole. 148. Spacing of Drill Holes. SHEETING - AND BRACING. 149. Purposes and Types. 150. Stay Bracing. 151. - Skeleton Sheeting. 152. Poling Boards. 153. Box Sheeting. - 154. Vertical Sheeting. 155. Pulling Wood Sheeting. 156. - Earth Pressures. 157. Design of Sheeting and Bracing. 158. - Steel Sheet Piling. LINE AND GRADE. 159. Locating the Trench. - 160. Final Line and Grade. 161. Transferring Grade and Line - to the Pipe. 162. Line and Grade in Tunnel. TUNNELLING. 163. - Depth. 164. Shafts. 165. Timbering. 166. Shields. 167. Tunnel - Machines. 168. Rock Tunnels. 169. Ventilation. 170. - Compressed Air. EXPLOSIVES AND BLASTING. 171. Requirements. - 172. Types of Explosives. 173. Permissible Explosives. 174. - Strength. 175. Fuses and Detonators. 176. Care in Handling. - 177. Priming, Loading, and Firing. 178. Quantity of - Explosive. PIPE SEWERS. 179. The Trench Bottom. 180. Laying - Pipe. 181. Joints. 182. Labor and Progress. BRICK AND BLOCK - SEWERS. 183. The Invert. 184. The Arch. 185. Block Sewers. - 186. Organization. 187. Rate of Progress. CONCRETE SEWERS. - 188. Construction in Open Cut. 189. Construction in Tunnels. - 190. Materials for Forms. 191. Design of Forms. 192. Wooden - Forms. 193. Steel-lined Wooden Forms. 194. Steel Forms. 195. - Reinforcement. 196. Cost of Concrete Sewers. BACKFILLING. - 197. Method. 233–331 - - - CHAPTER XII - - MAINTENANCE OF SEWERS - - 198. Work Involved. 199. Causes of Troubles. 200. Inspection. - 201. Repairs. 202. Cleaning of Sewers. 203. Flushing Sewers. - 204. Cleaning Catch-basins. 205. Protection of Sewers. 206. - Explosions in Sewers. 207. Valuation of Sewers. 332–351 - - - CHAPTER XIII - - COMPOSITION AND PROPERTIES OF SEWAGE - - 208. Physical Characteristics. 209. Chemical Composition. 210. - Significance of Chemical Constituents. 211. Sewage Bacteria. - 212. Organic Life in Sewage. 213. Decomposition of Sewage. - 214. The Nitrogen Cycle. 215. Plankton and Macroscopic - Organisms. 216. Variations in the Quality of Sewage. 217. - Sewage Disposal. 218. Methods of Sewage Treatment. 352–371 - - - CHAPTER XIV - - DISPOSAL BY DILUTION - - 219. Definition. 220. Conditions Required for Success. 221. - Self-purification of Running Streams. 222. Self-purification - of Lakes. 223. Dilution in Salt Water. 224. Quantity of - Diluting Water Needed. 225. Governmental Control. 226. - Preliminary Treatment. 227. Preliminary Investigations. 372–382 - - - CHAPTER XV - - SCREENING AND SEDIMENTATION - - 228. Purpose. 229. Types of Screens. 230. Sizes of Openings. - 231. Design of Fixed and Movable Screens. PLAIN - SEDIMENTATION. 232. Theory of Sedimentation. 233. Types of - Sedimentation Basins. 234. Limiting Velocities. 235. Quantity - and Character of Grit. 236. Dimensions of Grit Chambers. 237. - Existing Grit Chambers. 238. Number of Grit Chambers. 239. - Quantity and Characteristics of Sludge from Plain - Sedimentation. 240. Dimensions of Sedimentation Basins. - CHEMICAL PRECIPITATION. 241. The Process. 242. Chemicals. - 243. Preparation and Addition of Chemicals. 244. Results. 383–409 - - - CHAPTER XVI - - SEPTICIZATION - - 245. The Process. 246. The Septic Tank. 247. Results of Septic - Action. 248. Design of Septic Tanks. 249. Imhoff Tanks. 250. - Design of Imhoff Tanks. 251. Imhoff Tank Results. 252. Status - of Imhoff Tanks. 253. Operation of Imhoff Tanks. 254. Other - Tanks. 410–430 - - - CHAPTER XVII - - FILTRATION AND IRRIGATION - - 255. Theory. 256. The Contact Bed. 257. The Trickling Filter. - 258. Intermittent Sand Filter. 259. Cost of Filtration. - IRRIGATION. 260. The Process. 261. Status. 262. Preparation - and Operation. 263. Sanitary Aspects. 264. The Crop. 431–464 - - CHAPTER XVIII - - ACTIVATED SLUDGE - - 265. The Process. 266. Composition. 267. Advantages and - Disadvantages. 268. Historical. 269. Aëration Tank. 270. - Sedimentation Tank. 271. Reaëration Tank. 272. Air - Distribution. 273. Obtaining Activated Sludge. 274. Cost. 465–479 - - - CHAPTER XIX - - ACID PRECIPITATION, LIME AND ELECTRICITY, AND DISINFECTION - - 275. The Miles Acid Process. ELECTROLYTIC TREATMENT. 276. The - Process. DISINFECTION. 277. Disinfection of Sewage. 482–493 - - - CHAPTER XX - - SLUDGE - - 278. Methods of Disposal. 279. Lagooning. 280. Dilution. 281. - Burial. 282. Drying. 495–505 - - - CHAPTER XXI - - AUTOMATIC DOSING DEVICES - - 283. Types. 284. Operation. 285. Three Alternating Siphons. - 286. Four or More Alternating Siphons. 287. Timed Siphons. - 288. Multiple Alternating and Timed Siphons. 506–512 - - - - - SEWERAGE AND SEWAGE TREATMENT - - - - - CHAPTER I - INTRODUCTION - - -=1. Sewerage and the Sanitary Engineer.=—Present day conceptions of -sanitation are based on the scientific discoveries which have resulted -so much in the increased comfort and safety of human life during the -past century, in the increase of our material possessions, and the -extent of our knowledge. The danger to health in the accumulation of -filth, the spreading of disease by various agents, the germ theory of -disease, and other important principles of sanitation can be counted -among the more recent scientific discoveries and pronouncements. -Experience has shown, and continues to show, that the increase of -population may be inhibited by accumulations of human waste in populous -districts. The removal of these wastes is therefore essential to the -existence of our modern cities. - -The greatest need of a modern city is its water supply. Without it city -life would be impossible. The next most important need is the removal of -waste matters, particularly wastes containing human excreta or the germs -of disease. To exist without street lights, pavements, street cars, -telephones, and the many other attributes of modern city life might be -possible, although uncomfortable. To exist in a large city without -either water or sewerage would be impossible. The service rendered by -the sanitary engineer to the large municipality is indispensable. In -addition to the service necessary to the maintenance of life in large -cities, the sanitary engineer serves the smaller city, the rural -community, the isolated institution, and the private estate with -sanitary conveniences which make possible comfortable existence in them, -and which are frequently considered as of paramount necessity. Training -for service in municipal sanitation is training for a service which has -a more direct beneficial effect on humanity than any other engineering -work, or any other profession. W. P. Gerhard states: - - _A Sanitary Engineer_ is an engineer who carries out those works - of civil engineering which have for their object: - - (_a_) The promotion of the public and individual health; - - (_b_) The remedying of insanitary conditions; - - (_c_) The prevention of epidemic diseases. - - A well-educated sanitary engineer should have a thorough knowledge - of general civil engineering, of architecture, and of sanitary - science. The practice of the sanitary engineer embraces water - supply, sewerage, and sewage and garbage disposal for cities and - for single buildings; the prevention of river pollution, the - improvement of polluted water supplies; street paving and street - cleaning, municipal sanitation, city improvement plans, the laying - out of cities, the preparation of sanitary surveys, the regulation - of noxious trades, disinfection, cremation, and the sanitation of - buildings. - -The need of the work of the sanitary engineer in the provision of sewers -and drains is thrust upon us in our daily experience by the clogging of -sewers, the flooding of streets by heavy rains, filthy conditions in -unsewered districts, increased values of property and improved -conditions of living in sewered districts, and in many other ways. The -increasing demand for sewerage and the amount of money expended on sewer -construction is indicated by the information given in Table I. - - -=2. Historical.=—An ordinance passed by the Roman Senate in the name of -the Emperor about A.D. 80, states: - - I desire that nobody shall conduct away any excess water without - having received my permission or that of my representatives; for - it is necessary that a part of the supply flowing from the - delivery tanks shall be utilized not only for cleaning our city, - but also for flushing the sewers.[1] - -Neither the sewers mentioned nor the distributing pipes of the public -water supply were connected to individual residences. The contributions -to the sewers came from the ground and the street surface. The streets -were the receptacles of liquid and solid wastes and were often little -more than open sewers. A promenade after dark in an ancient, medieval, -or early modern city was accompanied not only by the underfoot dangers -of an uneven pavement or an encounter with a footpad, but with the -overhead danger from the emptying of slops into the streets from the -upper windows. Sewers were used for the collection of surface water; the -discharge of fecal matter into them was prohibited. The problem of the -collection of sewage remained unsolved until the Nineteenth Century. - - TABLE 1 - - POPULATION TRIBUTARY TO SEWERAGE SYSTEMS - - ──────────────────────────────────────┬──────────┬──────────┬────────── - │ 1905[2] │ 1915[3] │ 1920[4] - ──────────────────────────────────────┼──────────┼──────────┼────────── - Population discharging raw sewage into│ │ │ - the sea or tidal estuaries │ 6,500,000│ 8,500,000│ - Population discharging raw sewage into│ │ │ - inland streams or lakes │20,400,000│26,400,000│ - Population connected to systems where │ │ │ - sewage is treated in some way │ 1,100,000│ 6,900,000│ - Population connected with sewerage │ │ │ - systems │28,000,000│41,800,000│46,300,000 - ──────────────────────────────────────┴──────────┴──────────┴────────── - -The development of the London sewers was commenced early in the -Nineteenth Century. The sewerage system of Hamburg, Germany, was laid -out in 1842 by Lindley, an English engineer who with other English -engineers performed similar work in other German cities because of their -earlier experience in English communities. Berlin’s present system dates -from 1860. The construction of storm-water drains in Paris dates from -1663.[5] They were intended only as street drains but are now included -in the comprehensive system of the city. The first comprehensive -sewerage system in the United States was designed by E. S. Chesbrough -for the City of Chicago in 1855. Previous to this time sewers had been -installed in an indifferent manner and without definite plan. The -installation of a comprehensive sewerage system in Baltimore in 1915 -marks the completion of installation of sewerage systems in all large -American cities. - -In the early days of sewerage design it was considered unsafe to -discharge domestic wastes into the sewers as the concentration of so -much sewage was expected to create great nuisances and dangers to -health. That the fear that the concentration of large quantities of -sewage would create a nuisance was not ill founded is proven by the -conditions on the Thames at London in 1858–59. Dr. Budd states:[6] - - For the first time in the history of man, the sewage of nearly - three millions of people had been brought to seethe and ferment - under a burning sun in one vast open _cloaca_ lying in their - midst. - - The result we all know. Stench so foul we may well believe had - never before ascended to pollute this lower air. Never before at - least had a stink risen to the height of an historic event.... For - months together the topic almost monopolized the public prints.... - ‘India is in revolt and the Thames stinks’ were the two great - facts coupled together by a distinguished foreign writer, to mark - the climax of a national humiliation.[7] - -The problem of sewage disposal followed the more or less successful -solutions of the problem of sewage collection. In England the British -Royal Commission on Sewage Disposal was appointed in 1857 and issued its -first report in 1865. The first studies in the United States were -started in 1887 by the establishment of an experiment station at -Lawrence, Massachusetts, where valuable work has been done. The station -is under the State Board of Health, which issued its first report -containing the results of the work at the station, in 1890. - -Various methods of sewage treatment preparatory to disposal have been -devised from time to time. Some have fallen into disuse, such as the A. -B. C. (alum, blood and clay) process, and others have taken a permanent -place, such as the septic tank. The unsolved problems of sewage -collection, and the number of persons still unserved by sewerage and -sewage disposal opens a wide field to the study and construction of -sewerage works. - - -=3. Methods of Collection.=—The method of collection which involves the -removal of night soil from a privy vault, the pail system which involves -the collection of buckets of human excreta from closets and homes, -indoor chemical closets, and other makeshift methods of collection are -of extreme importance where no sewers exist, but they are not properly -considered as sewerage systems or sewerage works. These methods of -collection are generally confined to rural districts and to outlying -parts of urban communities. They require constant attention for their -proper conduct and little skill for their installation, the principal -requirements being to make the receptacles fly-proof. - -The pneumatic system was introduced by Liernur, a Dutch engineer.[8] It -is used in parts of a few cities in Europe, but it is not capable of use -on a large scale. It consists of a system of air-tight pipes, connecting -water closets, kitchen sinks, etc., with a central pumping station at -which an air-tight tank is provided from which the air is partly -exhausted. As little water as possible is allowed to mix with the fecal -matter and other wastes in order not to overtax the system. Solid and -liquid wastes are drawn to the central station when the waste valve on -the plumbing fixture is opened. - -The collection of sewage in a system of pipes through which it is -conducted by the buoyant effect and scouring velocity of water is known -as the water-carriage system. This is the only method of sewage -collection in general use in urban communities. In this system solid and -liquid wastes are so highly diluted with water as either to float or to -be suspended therein. The mixture resulting from this high dilution -follows the laws of hydraulics as applied to pure water, or water -containing suspended matter. It will flow freely through properly -designed conduits and will concentrate the sewage wastes at the point of -ultimate disposal. - - -=4. Methods of Disposal.=—Sewage is disposed of by dilution in water, by -treatment on land, or occasionally by discharging it into channels that -contain no diluting water. Some form of treatment to prepare sewage for -ultimate disposal is frequently necessary and will undoubtedly be -required in a comparatively short time for all sewage discharged into -watercourses. The solid matters removed by treatment may be buried, -burned, dumped into water, or used as a fertilizer. - -If the volume of diluting water, or the area and character of land used -for disposal are not as they should be, a nuisance will be created. The -aim of all methods of sewage treatment has so far been to produce an -effluent which could be disposed of without nuisance and in certain -exceptional cases to protect public water supplies from pollution. -Financial returns have been sought only as a secondary consideration. A -few sewage farms and irrigation projects might be considered as -exceptions to this as the value of the water in the sewage as an -irrigant has been the primary incentive to the promotion of the farm. - -It is to be remembered that since the aim of all sewage treatment is to -produce an effluent that can be disposed of without causing a nuisance, -the simplest process by which this result can be attained under the -conditions presented is the process to be adopted. No attempt is made to -_purify_ sewage completely, or on a practical scale to make drinking -water. - - -=5. Methods of Treatment.=—Screening and sedimentation are the primary -methods for the treatment of sewage. By these methods a portion of the -floating and settleable solids are removed, preventing the formation of -unsightly scum and putrefying sludge banks. Chemicals are sometimes -added to the sewage to form a heavy flocculent precipitate which hastens -sedimentation of the solid matters in the sewage. The process in these -methods is mechanical and the solid matters removed from the sewage must -be disposed of by other methods than dilution with the sewage effluent. -More complete methods of treatment are dependent on biologic action. -Under these methods of treatment complete stabilization of the effluent -is approached, and in the most complete treatment an effluent is -produced which is clear, sparkling, non-odorous, non-putrescible, and -sterile. Sterilization of sewage, usually with chlorine or some of its -compounds, has been used, not to reduce the amount of diluting water -necessary, but to reduce the number of pathogenic germs and to minimize -the danger of the transmission of disease. - - -=6. Definitions.=—Sewage and sewerage are not synonymous terms although -frequently confused. Sewage is the spent water supply of a community -containing the waste from domestic, industrial or commercial use, and -such surface and ground water as may enter the sewer.[9] Sewerage is the -name of the system of conduits and appurtenances designed to carry off -the sewage. It is also used to indicate anything pertaining to sewers. - -A difference is made between sanitary sewage, storm sewage, and -industrial wastes. Sanitary sewage, sometimes called domestic sewage, is -the liquid wastes discharged from residences or institutions, and -contains water closet, laundry and kitchen wastes. Storm sewage is the -surface run-off which reaches the sewers during and immediately after a -storm. Industrial wastes are the liquid waste products discharged from -industrial plants. - -A sewer is a conduit used for conveying sewage. - -The names of the conduits through which sewage may flow are: - -_Soil Stack._—A vertical pipe in a building through which waste water -containing fecal matter or urine is allowed to flow. - -_Waste Pipe._—A vertical pipe in a building through which waste water -containing no fecal matter is allowed to flow. - -_House Drain._—The approximately horizontal portion of a house drainage -system which conveys the drainage from the soil stack or waste pipe to -the point of discharge from the building. - -_House Sewer._—The pipe which leads from the outside wall of the -building to the sewer in the street. - -_Lateral Sewer._—The smallest branch in a sewerage system, exclusive of -the house sewers. - -_Sub-main or Branch Sewer._—A sewer from which the sewage from two or -more laterals is discharged.[10] - -_Main or Trunk Sewer._—A sewer into which the sewage from two or more -sub-main or branch sewers is discharged.[11] - -_Intercepting Sewer._—A sewer generally laid transversely to a sewerage -system to intercept some portion or all of the sewage collected by the -system. - -_Relief Sewer._—A sewer intended to carry a portion of the flow from a -district already provided with sewers of insufficient capacity and thus -preventing overtaxing the latter.[12] - -_Outfall Sewer._—That portion of a main or trunk sewer below all -branches. - -_Flushing Sewer._—A conduit through which water is conveyed for flushing -portions of a sewerage system. - -_Force Main._—A conduit through which sewage is pumped under pressure. - - - - - CHAPTER II - WORK PRELIMINARY TO DESIGN - - -=7. Division of Work.=—Engineering work on sewerage can be divided into -four parts, namely: preliminary, design, construction and maintenance. -An engineer may be engaged during any one or all of these periods on the -same sewerage system, and should therefore be acquainted with his duties -during each period. - - -=8. Preliminary.=—The demand for sewerage normally follows the -installation or extension of the public water supply. It may be caused -by: a lack of drainage on some otherwise desirable tract of real estate; -from a public realization of unpleasant or unhealthful conditions in a -built-up district; or through the realization by the municipal -administration of the necessity for caring for the future. In whatever -way the demand may be created the engineer should take an active part in -the promotion of the work. - -The engineer’s duties during the preliminary period are: to make a study -of the possible methods by which the demand for sewerage can be -satisfied; to present the results of this study in the form of a report -to the committee or organization responsible for the promotion of the -work; and so to familiarize himself with the conditions affecting the -installation of the proposed plans as to be able to answer all inquiries -concerning them. This work will require the general qualities of -character, judgment, efficiency and the understanding of men in -addressing interested persons individually and collectively on the -features of the proposed plans, and the exercise of engineering -technique in the survey and the drawing of the plans. The engineer -should assure himself that all legal requirements in the drawing of -petitions, advertising, permits, etc., have been complied with. This -requires some knowledge of national, state, and local laws. Although -none the less essential their description is not within the scope of -this book. - -The engineer’s preliminary report should contain a section devoted to -the feasibility of one or more plans which may be explained in more or -less detail with a statement of the cost and advantages of each. A -conclusion should be reached as to the most desirable plan and a -recommendation made that this plan be installed. Other sections of the -report may be devoted to a history of the growing demand, a description -of the conditions necessitating sewerage, possible methods of financing, -and such other subjects as may be pertinent. The making of the -preliminary plan and the design of sewerage works are described in -subsequent chapters. - - -=9. Estimate of Cost.=—In making an estimate of cost the information -should be presented in a readable and easily comprehended manner. It is -necessary that the items be clearly defined and that all items be -included. The method of determining the costs of doubtful items such as -depreciation, interest charges, labor, etc., and the probability of the -fluctuation of the costs of certain items should be explained. - -The engineer’s estimate may be divided somewhat as follows: - - Labor. - - Material. - - Overhead. This may include construction plant, office expense, - supervision, bond, interest on borrowed capital, insurance, - transportation, etc. The amount of the item is seldom less than 15 - per cent and is usually over 20 per cent of the contract price. - - Contingencies. This allowance is usually 10 to 15 per cent of the - contract price. - - Profit. This should be from 5 to 10 per cent of the sum of the - four preceding items. - -The contract price is the sum of these items. To this may be added: - - Engineering. 2 to 5 per cent of the contract price. - - Extra Work. Zero to 15 per cent of the contract price; dependent - on the character of the work, the completeness of the preliminary - information, the completeness of the plans, etc. - - Legal expense. - - Purchase of land, rights of way, etc., etc. - -The cost of the sewer may be stated as so much per linear foot for -different sizes of pipe, including all appurtenances such as manholes, -catch-basins, etc., or the items may be separated in great detail -somewhat as follows: - - Earth excavation, per cu. yd. - Rock excavation, per cu. yd. - Backfill, per cu. yd. - Brick manholes, 3 feet by 4 feet, per foot of depth. - Vitrified sewer pipe with cement joints, in place, - ... inches in diameter, 0 to 6 feet deep - 6 to 8 feet deep - 8 to 10 feet deep - Repaving, macadam per sq. yd. - asphalt per sq. yd. - Flush-tanks, ... gal. capacity, per tank. - Service pipes to flush-tanks, per linear foot., etc., etc. - -These methods represent the two extremes of presenting cost estimates. -Each method, or modification thereof, may have its use, dependent on -circumstances. - -Reliable cost data are difficult to obtain. Lists of prices of materials -and labor are published in certain engineering and trade periodicals. -The Handbook of Cost Data by H. P. Gillette contains lists of the amount -of material and labor used on certain specific jobs and types of -construction. The price of labor and materials on the local market can -be obtained from the local Chamber of Commerce, contractors and other -employers of labor, and dealers in the desired commodities. Contract -prices for sewerage work published in the construction news sections of -engineering periodicals may be a guide to the judgment of the probable -cost of proposed work, but are generally dangerous to rely upon as full -details are lacking in the description of the work. A wide experience in -the collection and use of cost data is the desirable qualification for -making estimates of cost. It is possessed by few and is not an -infallible aid to the judgment. - -Having completed the design and summary of the bills of material and -labor necessary for each structure or portion of the sewerage system, -the product of the unit cost and the amount of each item plus an -allowance for overhead will equal the cost of the item. The total cost -will be the sum of the costs of each item. The items should be so -grouped that the cost of the different portions of the system are -separated in order that the effect on the total cost resulting from -different combinations of items or the omission of any one item may be -readily computed. - -A method for estimating the approximate cost of sewers, devised by W. G. -Kirchoffer[13] depends upon the use of the diagram shown in Fig. 2. The -factors for local conditions are shown in Table 2. For example, let it -be required to find the cost of a 15–inch vitrified pipe sewer at a -depth of 9 feet, if the unit costs of labor and material and the -conditions are the same as shown in Table 3. - -[Illustration: - - FIG. 2.—Diagram for Estimating the Cost of Sewers. - - Eng. News, Vol. 76, p. 781. -] - - _Solution_ - - First: To find the factor depending on local conditions, enter the - diagram at the 10–inch diameter and continue down until the - intersection with the depth of trench at 8.2 feet is found. Now go - diagonally parallel to lines running from left to right upwards to - the intersection with the vertical line through a cost of 45 cents - per foot. The diagonal line running from left to right downwards - through this intersection corresponds to a factor of about 11. - - TABLE 2 - - FACTORS FOR COSTS OF SEWERS TO BE USED WITH FIGURE 2 - - ────────────────────────────────────────────────────────────────┬────── - Character of Material │Factor - ────────────────────────────────────────────────────────────────┼────── - Clay, gravel and boulders, Medford │22–26 - Mostly sand, deep trenches sheeted. Wages medium. Richland │ - Center. │21–22 - Sandy clay. Wages medium. Labor conditions good at Kiel. │15–20 - Sand. _Sandy_ clay, some water. Labor conditions good. Pipe │ - prices medium at Manston. │14–20 - Gravelly clay, ⅒th laid in concrete at Burlington. │13–22 - Sandy clay, some water, sheeting at La Farge. │17–23 - Sand with water. │ 20 - Gravel and boulders. High wages. │ 26 - Clay soil. Good digging. │ 17 - Sandy clay. Some water. │ 23 - Clay 2 miles inland. Laborers boarded at sanitarium, Wales │ 35 - Clay, gravel and boulders at Plymouth. │20–27 - Sand, clay and good digging at Lake Mills. │16–19 - Red clay. Machine work at North Milwaukee. │20–24 - Good digging. Wages medium at West Salem. │17–19 - Sandy soil, bracing only required. No water. Wages and pipe │ - medium. │ 14 - Red sticky clay. │ 24 - Good digging in any soil. Work scarce. │ 15 - Red clay. No bracing. │ 20 - Work inland from railroad. Boarding laborers _and_ other │ - expenses. │ 35 - ────────────────────────────────────────────────────────────────┴────── - - Second: To find the cost of 15–inch pipe at a depth of 9.0 feet, - enter the diagram at a diameter of 15 inches and continue down - until the intersection with a depth of trench at 9 feet is found. - Now go diagonally parallel to lines running from left to right - upwards to the intersection with the diagonal line running from - left to right downwards corresponding to the factor of 11 found - above. The vertical line passing through this point shows the cost - to be 67 cents per foot. - - TABLE 3 - - COST OF SEWER CONSTRUCTION AT ATLANTIC, IOWA - - (From Gillette’s Handbook of Cost Data) - - Material: Clay, not difficult to spade and requiring little or no - bracing and practically no pumping. All hand work except backfill which - was done by team and scraper. Depth of trench averaged 8.2 feet; width - 30 inches. Diameter of pipe 10 inches. - - ───────────────────────────────────────────────────────────┬─────┬───── - Item │Wage,│Cost, - │Cents│Cents - │ per │ per - │Hour │Foot. - ───────────────────────────────────────────────────────────┼─────┼───── - Pipe. │ │0.20 - Hauling team and driver. │ 30│ .003 - Hauling. Man helping. │ 17│ .001 - Cement and sand. │ │ .006 - Pipe layers. │ 22│ .014 - Pipe layer’s helper. │ 17│ .014 - Trenching. Top men. │ 17│ .027 - Trenching. Bottom men. │ 17│ .130 - Trenching. Scaffold men. │ 17│ .002 - Trenching. Bracing men. │ 17│ .002 - Backfilling. Shovel. │ 17│ .010 - Backfilling. Team and scraper. │ 30│ .008 - Backfilling. Man and scraper. │ 17│ .005 - Water boy. │ 10│ .006 - Foreman. │ 30│ .022 - ───────────────────────────────────────────────────────────┼─────┼───── - Total. │ │ .450 - ───────────────────────────────────────────────────────────┴─────┴───── - - - METHODS OF FINANCING - -The construction of sewerage works may be paid for by the issue of -municipal bonds, by special assessment, by funds available from the -general taxes, or by private enterprise. - - -=10. Bond Issues.=—A municipal bond is a promise by the municipality to -pay the face value of the bond to the holder at a certain specified -time, with interest at a stipulated rate during the interim. The -security on the bond is the taxable property in the municipality. The -legal restrictions thrown around municipal bond issues, the value of the -taxable property in the municipality, all of which may be used as -security for municipal bonds, and the fact that a municipality can be -sued in case of default, make municipal bonds desirable and provide a -good market for their sale. The funds available from a municipal bond -issue are limited by the amount that the legal limit is in excess of the -outstanding issues. The legal limit varies in different states from -about 5 to 15 per cent of the assessed value of the property in the -municipality. In some cases the amount available from municipal bonds -has been increased by forming a municipality within a municipality such -as a sanitary district, a park district, a drainage district, etc., -which comprises a large portion or all of an existing municipal -corporation. This case is well illustrated in some parts of the City of -Chicago where the municipal taxing powers are shared by the City -government, the Sanitary District, and Park Commissioners. The right to -create a new municipal corporation must be granted by the state -legislature. Knowledge of fixed bonds, serial bonds, life of bonds, -sinking funds, etc. is an important part of an engineer’s education.[14] - -Bond issues must usually be presented to the voters for approval at an -election. If approved, and other legal procedure has been followed, the -bonds may be bought by some of the many bonding houses, or by private -individuals, and the money is immediately available for construction. -The bonds are redeemed by general taxation spread over the period of the -issue. - - -=11. Special Assessment.=—A special assessment is levied against -property benefited directly by the structure being paid for. Special -assessments are used for the payment for the construction of lateral -sewers which are a direct benefit to separate districts but are without -general benefit to the city. In case the construction of an outfall -sewer or the erection of a treatment plant, which may be of some general -benefit, is necessary to care for a separate district, a part of the -expense may be borne by funds available from general taxation. The legal -procedure for the raising of funds by special assessment and the purpose -to which the funds so raised may be applied are stipulated in great -detail in different states and their directions must be followed -implicitly. Illinois procedure, which is similar to that in some other -states, is as follows: a meeting of the interested property owners is -called by a committee or board of the municipal government, as the -result of a petition by interested persons or through the independent -action of the Board. At this preliminary meeting or public hearing -arguments for and against the proposed improvement are heard. The -engineer is present at this meeting to answer questions and to advise -concerning the engineering features of the plan. If approval is given by -the Board the plan and specifications are prepared complete in every -detail and incorporated in an ordinance which is presented to the -legislative branch of the city government for passage. If the project is -adopted it is taken to the county court. An assessment roll is prepared -by a commissioner appointed by the court. This roll shows the amount to -be assessed against each piece of property benefited. A hearing is then -held in the county court at which the owner of any assessed property may -voice objections to the continuation of the project. The project may be -thrown out of court for many different reasons, such as the misspelling -of a street name, an error in an elevation, an error in the description -of a pavement, but most important of all is definite proof that the -benefit is not equal to the assessment. The many minor irregularities -which may nullify the procedure in a special assessment differ in -different states and in different courts in the same state, but in -general no court can approve an assessment greater than the benefits -given. After the project has passed through the county court and the -assessment roll has been approved, bonds may be issued for the payment -of the contractor. Special assessment bonds are liens against the -property assessed and have not the same security as a general municipal -bond. For this reason a city which has reached its legal limit of -municipal bond issues can still pay for work by special assessment. - -The funds available from special assessments are limited only by the -benefit to the property assessed. The amount of the benefit is difficult -to fix and may lead to much controversy. It should not exceed the amount -demanded for similar work in other localities, unless unusual and -well-understood reasons can be given. - - -=12. General Taxation.=—In paying for public improvements by general -taxation the money is taken from the general municipal funds which have -been apportioned for that purpose by the legislative department of the -municipal government. This method of raising funds for sewerage -construction is seldom used unless the political situation is -unfavorable to the success of a bond issue or special assessment and the -need for the improvement is great. It is usually difficult to -appropriate sufficient funds for new construction as the general tax is -apportioned to support only the operating expenses of the city, and -statutory provisions limit the amount of tax which can be levied. - - -=13. Private Capital.=—Private capital has been used for financing -sewerage works in some cases because of the aversion of the public in -some cities to the payment of a tax for the negative service performed -by a sewer. Sewers are buried, unseen, and frequently forgotten, but -knowledge of their necessity has spread and the number of privately -owned sewerage works is diminishing because of the better service which -can be provided by the municipality. - -Franchises are granted to private companies for the construction of -sewers only after the city has exhausted other methods for the raising -of capital. The return on the private capital invested is received from -a rental paid by the city, or paid directly by the users of the system, -an initial payment usually being demanded for connection to the system. -To be successful the enterprise must be popular and must fill a great -need. This method of financing sewerage works is seldom employed as -favorable conditions are not common. - - - PRELIMINARY WORK - - -=14. Preparing for Design.=—Methods for the design of sewerage systems -are given in Chapter V. Before the design is made certain information is -essential. A survey must be made from which the preliminary map can be -prepared as described in Art. 42. Other necessary information which is -the basis of subsequent estimates of the quantity of sewage to be cared -for must be obtained by a study of rates of water consumption and the -density and growth of population, the measurement of the discharge from -existing sewers, and the compilation of rainfall and run-off data. If no -rainfall data are available estimates must be made from the nearest -available data. Observations of rainfall or run-off for periods of less -than 10 to 20 years are likely to be misleading. Methods for gathering -and using this information are explained in subsequent chapters. - -Underground surveys are desirable along the lines of the proposed sewers -to learn of obstructions, difficult excavation and other conditions -which may be met. All such data are seldom gathered except for sewerage -systems involving the expenditure of a large amount of money. For -construction in small towns or small extensions to an existing system -the funds are usually insufficient for extensive preliminary -investigation. The saving in this respect is paid unknowingly to the -contractor as compensation for the risk in bidding without complete -information. - - -=15. Underground Surveys.=—These may be more or less extensive dependent -on the character of the district in which construction is to take place. -In built-up districts the survey should be more thorough than in -sparsely settled districts where only the character of the excavated -material is of interest and no obstructions are to be met. - -Underground surveys furnish to the engineer and to prospective bidders -on contract work information on which the design and estimate of cost -and the contractor’s bid may be based and without which no intelligent -work can be done. By removing much of the uncertainty of the conditions -to be met in the construction of the sewer, the design can be made more -economical and the contractor’s bid should be markedly lower, -sufficiently so to repay more than the expense of the survey. The -information to be obtained consists of the location of the ground-water -level, and the location and sizes of water, gas, and sewer pipes, -telephone and electric conduits, street-car tracks, steam pipes, and all -other structures which may in any way interfere with subsurface -construction. These structures should be located by reference to some -permanent point on the surface. The elevation of the top of the pipes, -except sewers, rather than the depth of cover should be recorded, as the -depth of cover is subject to change. The elevation of sewers should be -given to the invert rather than to the top of the pipe. - -A portion of the map of the subsurface conditions at Washington, D. C., -is shown in Fig. 3. Many of the dimensions and notations are not shown -to avoid confusion on this small reproduction.[15] Colors are generally -used instead of different forms of cross hatching to show the different -classes of pipe and structures. In addition to a record of the -underground structures the character of the ground and the pavement -should be recorded. A comprehensive underground survey is seldom -available nor does time usually permit its being made preliminary to the -design of a sewerage system. The character of the material through which -the sewer is to pass should be determined in all cases. - -[Illustration: - - FIG. 3.—Record Map of Underground Structures, Washington, D. C. - - Eng. Record, Vol. 74, p. 263. - - The various subsurface lines are differentiated by colors as follows: - _A_—Sewers, vermilion. _B_—Water mains, blue. _C_—Potomac Electric - Power Co., carmine. _D_—Washington Railway and Electric Co., - carmine. _E_—Capital Traction Co., violet. _F_—Chesapeake and - Potomac Telephone Co., green. _G_—Washington Gas Light Co., green. - _H_—Western Union Telegraph Co., orange. _I_—Postal Telegraph Co., - orange. _K_—Private vaults, black. _L_—City Electric Co., yellow. -] - -[Illustration: - - FIG. 4. - - Punch Drill. -] - -Underground pipes and structures are located by excavations, which may -be quite extensive in some cases. Their position is fixed by -measurements referred to manholes and other underground structures which -are somewhat permanent in position. A city engineer should grasp every -opportunity to record underground structures when excavations are made -in the streets. The character of the material through which the sewer is -to pass is determined by borings. - - -=16. Borings.=—Methods used for the investigation of subsurface -conditions preliminary to sewer construction are: punch drilling, boring -with earth auger, jet boring, wash boring, percussion drilling, abrasive -drilling, and hydraulic drilling. The last three methods named are used -only for unusually deep borings or in rock. - -Punch drills are of two sorts. The simplest punch drill consists of an -iron rod ⅞ of an inch to 1 inch in diameter, in sections about 4 feet -long. One section is sharpened at one end and threaded at the other so -that the next section can be screwed into it without increasing the -diameter of the rod, as shown in Fig. 4. The drill is driven by a sledge -striking upon a piece of wood held at the top of the drill to prevent -injury to the threads. The drill should be turned as it is driven to -prevent sticking. It is pulled out by a hook and lever as shown in Fig. -5. It is useful in soft ground for soundings up to 8 to 12 feet in -depth. Another form of punch drill described by A. C. Veatch[16] -consists of a cylinder of steel or iron, one to two feet long split -along one side and slightly spread. The lower portion is very slightly -expanded and tempered into a cutting edge. In use it is attached to a -rope or wooden poles and lifted and dropped in the hole by means of a -rope given a few turns about a windlass or drum. By this process the -material is forced up into the bit, slightly springs it, and so is held. -When the bit is filled it is raised to the surface and emptied. Much -deeper holes can be made with this than with the sharpened solid rod. - -[Illustration: - - FIG. 5.—Lever for Pulling Punch Drill. -] - -[Illustration: - - FIG. 6.—Earth Augers. -] - -Types of earth augers about 1½-inches in diameter are shown in Fig. 6. -They are screwed on to the end of a section of the pipe or rod and as -the hole is deepened successive lengths of pipe or rod are added. The -device is operated by two men. It is pulled by straight lifting or with -the assistance of a link and lever similar to that shown in Fig. 5. The -device is suitable for soft earth or sand free from stones, and can be -used for holes 15 to 25 feet in depth. For deeper holes a block and -tackle should be used for lifting the auger from the hole. It is not -suitable for holes deeper than about 35 feet. - -In the jetting method water is led into the hole through a ¾-inch or -1–inch pipe, and forced downward through the drill bit or nozzle against -the bottom of the hole. The complete equipment is shown in Fig. 7.[17] -It is not always necessary to case the hole as shown in the figure as -the muddy water and the vibration of the pipe puddle the sides so that -they will stand alone. The jet pipe may be churned in the hole by a rope -passing over a block and a revolving drum. In suitable soft materials -such as clay, sand, or gravel, holes can be bored to a depth of 100 feet -and samples collected of the material removed. An objection to the -method is the difficulty of obtaining sufficient water. - -[Illustration: - - FIG. 7.—Jetting Outfit. - - U. S. Geological Survey, Water Supply Paper, No. 257 - - 1. Simple Jetting Outfit. 2. Jetting Process. 3. Common Jetting Drill. - 4_a_ and 4_b_. Expansion Bit or Paddy. 5. Drive Shoe. -] - -Methods of drilling in rock up to depths of 20 feet are described in -Chapter XI under Rock Drilling. For deeper holes percussion, abrasive, -or hydraulic methods as used for deep well drilling must be employed. - - - - - CHAPTER III - QUANTITY OF SEWAGE - - -=17. Dry weather Flow.=—Estimates of the quantity of sewage flow to be -expected are ordinarily based on the population, the character of the -district, the rate of water consumption, and the probable ground-water -flow. Future conditions are estimated and provided for, as the sewers -should have sufficient capacity to care for the sewage delivered to them -during their period of usefulness. - - -=18. Methods for Predicting Population.=—Methods for the prediction of -future population are given in the following paragraphs. - -The method of _graphical extension_. This is the quickest and most -simple of all. In this method a curve is plotted on rectangular -coordinates to any convenient scale, with population as ordinates and -years as abscissas. The curve is extended into the future by judgment of -its general tendency. An example is given of the determination of the -population of Urbana, Illinois, in 1950. Table 4 contains the population -statistics which have been plotted on line A in Fig. 8 and extended to -1950. The probable population in 1950 is shown by this line to be about -21,000. - -The method of _geometrical progression_. In this method the rate of -increase during the past few years or decades is assumed to be constant -and this rate is applied to the present population to forecast the -population in the future. For example the rate of increase of population -in Urbana for the past 7 decades has varied widely, but indications are -that for the next few decades it will be about 20 per cent. Applying -this rate from 1920 to 1950 the population in 1950 is shown to be about -17,800. It is evident that this method may lead to serious error as -insufficient information is given in the table to make possible the -selection of the proper rate of increase. - - TABLE 4 - - POPULATION STUDIES - - ────┬──────────────────────────── - │ Urbana, Illinois - ────┼──────────┬────────┬──────── - Year│Population│Absolute│Per Cent - │ │Increase│Increase - │ │for Each│for Each - │ │ Decade │ Decade - ────┼──────────┼────────┼──────── - 1850│ 210│ │ - 1860│ 2,038│ 1828│ 85.6 - 1870│ 2,277│ 239│ 10.5 - 1880│ 2,942│ 665│ 22.6 - 1890│ 3,511│ 569│ 16.2 - 1900│ 5,728│ 2217│ 38.7 - 1910│ 8,245│ 2517│ 30.5 - 1920│ 10,230│ 1985│ 19.4 - ────┴──────────┴────────┴──────── - - ────┬─────────────────────────────────────────────────────────────── - │ Population of - ────┼───────┬────────┬─────────┬────────┬──────┬───────────┬──────── - Year│Decatur│Danville│Champaign│Kankakee│Peoria│Bloomington│ Ann, - │ │ │ │ │ │ │ Arbor - │ │ │ │ │ │ │Michigan - │ │ │ │ │ │ │ - ────┼───────┼────────┼─────────┼────────┼──────┼───────────┼──────── - 1850│ │ 736│ │ │ 5,095│ 1,594│ - 1860│ 3,839│ 1,632│ 1,727│ 2,984│14,045│ 7,075│ 5,097 - 1870│ 7,161│ 4,751│ 4,625│ 5,189│22,849│ 14,590│ 7,368 - 1880│ 9,547│ 7,733│ 5,103│ 5,651│29,259│ 17,180│ 8,061 - 1890│ 16,841│ 11,491│ 5,839│ 9,025│41,024│ 20,484│ 9,431 - 1900│ 20,754│ 16,354│ 9,098│ 13,595│56,100│ 23,286│ 14,509 - 1910│ 31,140│ 27,871│ 12,421│ 13,986│66,950│ 25,786│ 14,817 - 1920│ 43,818│ 33,750│ 15,873│ 16,721│76,121│ 28,638│ 19,516 - ────┴───────┴────────┴─────────┴────────┴──────┴───────────┴──────── - -[Illustration: - - FIG. 8.—Diagram Showing Methods for Estimating Future Population. -] - -The method of utilizing a _decreasing rate of increase_. This method -attempts to correct the error in the assumption of a constant rate of -increase. After a certain period of growth, as the age of a city -increases its rate of increase diminishes. In applying this knowledge to -a prediction of the future population of a city the population curve is -plotted, as in the graphical method and a straight line representing a -constant rate or increase is drawn tangent to the curve at its end. The -curve is then extended at a flatter rate in accordance with the rate of -change of a similar nearby larger city. This method has not been applied -to any of the cities included in Table 4, as none has reached that -limiting period where the rate of increase has begun to diminish. - -The method of utilizing an _arithmetical rate of increase_. This method -allows for the error of the geometrical progression which tends to give -too large results for old and slow-growing cities. This method generally -gives results that are too low. The absolute increase in the population -during the past decade or other period is assumed to continue throughout -the period of prediction. Applying this method to the same case, the -increase in the population during the past decade was 2,000. Adding -three times this amount to the population in 1920, the population of -Urbana in 1950 will be about 16,000. - -The method involving the _graphical comparison with other cities_ with -similar characteristics. In this method population curves of a number of -cities larger than Urbana but having similar characteristics, are -plotted with years as abscissas and population as ordinates, with the -present population of Urbana as the origin of coordinates. The -population curve for Urbana is first plotted. It will lie entirely in -the third quadrant as shown by the heavy full line in Fig. 8. The -population curves of some larger cities are then plotted in such a -manner that each curve passes through the origin at the time their -population was the same as that of the present population of Urbana. -These curves lie in the first and third quadrants. The population curve -of the city in question is then extended to conform with the curves of -older cities in the most probable manner as dictated by judgment. Such a -series of plots has been made in Fig. 8. The results indicate that the -population of Urbana in 1950 will be about 25,500. - -The last method described will give the most probable result as it is -the most rational. For quick approximations the geometrical progression -is used. The arithmetical progression is useful only as an approximate -estimate for old cities. - - -=19. Extent of Prediction.=—The period for which a sewerage system -should be designed is such that each generation bears its share of the -cost of the system. It is unfair to the present generation to build and -pay for an extensive system that will not be utilized for 25 years. It -is likewise unfair to the next generation to construct a system -sufficient to comply with present needs only, and to postpone the -payment for it by a long term bond issue. An ideal solution would be to -plan a system which would satisfy present and future needs and to -construct only those portions which would be useful during the period of -the bond issue. Unfortunately this solution is not practical, because, -1st, it is less expensive to construct portions of the system such as -the outfall, the treatment plant, etc., to care for conditions in -advance of present needs, and 2nd, the life of practically all portions -of a sewerage system is greater than the legal or customary time limit -on bond issues. - -A compromise between the practical and the ideal is reached by the -design of a complete system to fulfill all probable demands, and the -construction of such portions as are needed now in accordance with this -plan. The payment should be made by bond issues with as long life as is -financially or legally practical, but which should not exceed the life -of the improvement. - -The prediction of the population should therefore be made such that a -comprehensive system can be designed with intelligence. Practice has -seldom called for predictions more than 50 years in the future. - - -=20. Sources of Information on Population.=—The United States decennial -census furnishes the most complete information on population. -Unfortunately it becomes somewhat old towards the end of a decade. More -recent information can be obtained from local sources. Practically every -community takes an annual school census the accuracy of which is fairly -reliable. The general tendencies of the population to change can be -learned by a study of the post office records showing the amount of mail -matter handled at various periods. Local chambers of commerce and -newspapers attempt to keep records of population, but they are often -inaccurate. Another source of information is the gross receipts of -public service companies, such as street railways, water, gas, -electricity, telephone, etc. The population can be assumed to have -increased almost directly as their receipts, with proper allowance for -change in rates, character of management, and other factors. - - -=21. Density of Population.=—So far the study of population has been -confined to the entire city. It is frequently necessary to predict the -population of a district or small section of a city. A direct census may -be taken, or more frequently its population is determined by estimating -its density based on a comparison with similar districts of known -density, and multiplying this density by the area of the district. In -determining the density, statistics of the population of the entire city -will be helpful but are insufficient for such a problem. A special -census of the area involved would be conclusive but is generally -considered too expensive. A count of the number of buildings in the -district can be made quickly, and the density determined by -approximating the number of persons per building. Statistics of the -population of various districts together with a description of the -character of the district are given in Table 5. - -[Illustration: - - FIG. 9.—Density, Area, and Population, Cincinnati, Ohio. 1850 to 1950. -] - - TABLE 5 - - DENSITIES OF POPULATION - - ────────────┬────────────────────────────────────────┬────────┬──────── - City │ Character of District │ Area, │Density - │ │ Acres │per Acre - ────────────┼────────────────────────────────────────┼────────┼──────── - Philadelphia│Thomas Run. Residential. Mostly pairs of│ │ - │ two and three-story houses. 1204 acres│ │ - │ settled. │ 1,840│ 59 - │Pine Street. Residential. Mostly solid │ │ - │ four to six-story houses. 156 acres │ │ - │ settled. │ 160│ 97 - │Shunk Street. Residential. Mostly pairs │ │ - │ of two and three-story houses. 539 │ │ - │ acres settled. │ 539│ 119 - │Lombard Street. Tenements and hotels, │ │ - │ 145 acres settled. │ 147│ 113 - │York Street. Residential and │ │ - │ manufacturing. 354 acres settled. │ 358│ 94 - │ │ │ - New York │Residential. Three-story dwellings with │ │ - City │ 18–foot frontage, and four-story flats│ │ - │ with 20–foot frontage. │ │ 100 - │Residential. Five-story flats. │ │520–670 - │Residential. Six-story flats. │ │800–1000 - │Residential. Six-story apartments. High │ │ - │ class. │ │ 300 - │ │ │ - Chicago │1st Ward. Retail and commercial. The │ │ - │ “Loop”. │ 1,440│ 20.5 - │2d Ward. Commercial and low-class │ │ - │ residential solidly built up. │ 800│ 53.5 - │3d Ward. Low-class residential. │ 960│ 48.1 - │5th Ward. Industrial. Some low-class │ │ - │ residences. Not solidly built up. │ 2,240│ 25.51 - │6th Ward. Residential. Four and │ │ - │ five-story apartments. A few detached │ │ - │ residences. │ 1,600│ 47.0 - │7th Ward. Same as Ward 6. Not solidly │ │ - │ built up. Contains a large park. │ 4,160│ 21.7 - │8th Ward. Industrial. Sparsely settled. │ 13,624│ 4.8 - │9th Ward. Industrial and low-class │ │ - │ residential. Solidly built up. │ 640│ 70.0 - │10th Ward. Same as Ward 9. │ 640│ 80.8 - │13th Ward. Low-class residential. │ │ - │ Solidly built with three and │ │ - │ four-story flats. │ 6,100│ 36.7 - │16th Ward. Middle-class residential. │ │ - │ Some industries. Well built up. │ 800│ 81.5 - │19th Ward. Industrial and commercial. │ │ - │ Some low-class residences. │ 640│ 90.7 - │20th Ward. Low-class residential. Some │ │ - │ industries. Entirely built up. │ 800│ 77.1 - │21st Ward. Industrial. Entirely built │ │ - │ up. │ 960│ 49.9 - │23d Ward. Industrial and residential. │ 800│ 55.4 - │24th Ward. Residential apartment houses │ │ - │ and middle-class residences. │ 1,120│ 46.8 - │25th Ward. Residential. High-class │ │ - │ apartments. Wealthy homes. Contains a │ │ - │ large park. │ 4,160│ 24.0 - │26th Ward. Residential. Middle-class │ │ - │ homes and apartments. Fairly well │ │ - │ built up. │ 4,640│ 16.1 - │27th Ward. Residential. Sparsely │ │ - │ settled. │ 20,480│ 5.5 - │29th Ward. Low-class residential. │ │ - │ Two-story frame houses. “Back of the │ │ - │ Yards”. │ 6,400│ 12.8 - │30th Ward. The Stock Yards. │ 1,280│ 40.1 - │32d Ward. Scattered residences. │ 8,480│ 8.3 - │33d Ward. Scattered residences. │ 12,944│ 5.5 - │35th Ward. Scattered residences. │ 4,960│ 12.0 - │ │ │ - General │The most crowded conditions with │ │ - average │ five-story and higher, contiguous │ │ - │ buildings in poor class districts. │ │750–1000 - │Five and six-story contiguous flat │ │ - │ buildings. │ │500–750 - │Six-story high-class apartments. │ │300–500 - │Three and four-story dwellings, business│ │ - │ blocks and industrial establishments. │ │ - │ Closely built up. │ │100–300 - │Separate residences, 50 to 75–foot │ │ - │ fronts, commercial districts, │ │ - │ moderately well built up. │ │ 50–100 - │Sparsely settled districts and scattered│ │ - │ frame dwellings for individual │ │ - │ families. │ │ 0–50 - ────────────┴────────────────────────────────────────┴────────┴──────── - -The density of population in Cincinnati from 1850 to 1913 with -predictions to 1950 is given in Fig. 9.[18] This shows the densities for -the entire city and is illustrative of the manner in which future -conditions were predicted for the design of an intercepting sewer. The -data given in Table 5 are of value in estimating the densities of -population in various districts. The Committee on City Plan of the Board -of Estimate and Apportionment of New York City obtained some valuable -information on this point, especially in Manhattan. Three-story -dwellings with 18–foot frontage, or four-story flats with 20–foot -frontage, presumably contiguous, were found to hold 100 persons to the -acre. Five-story flats held 520 to 670 persons per acre. Six-story flats -held 800 to 1,000 persons per acre, and high-class six-story apartments -held less than 300 per acre. - - -=22. Changes in Area.=—In order to determine the probable extent of a -proposed sewerage system it is important to estimate the changes in the -area of a city as well as the changes in the population. With the same -population and an increased area the quantity of sewage will be -increased because of the larger amount of ground water which will enter -the sewers. Predictions of the area of a city are less accurate than -predictions of population because the factors affecting changes cannot -be so easily predicted. An area curve plotted against time would be -helpful in guiding the judgment, but its extension into the future based -on past occurrences would be futile. A knowledge of the city, its -political tendencies, possibilities of extension, and other factors must -be weighed and judged. The engineer, if he is ignorant of the city for -which he is making provision, is dependent upon the testimony of real -estate men, business men and others acquainted with the local situation. - - -=23. Relation between Population and Sewage Flow.=—The amount of sewage -discharged into a sewerage system is generally equal to the amount of -water supplied to a community, exclusive of ground water. The entire -public water supply does not reach the sewers, but the losses due to -leakage, lawn sprinkling, manufacturing processes, etc., are made up by -additions from private water supplies, surface drainage, etc. The -estimated quantity of water used but which did not reach the sewers in -Cincinnati is shown in Table 6. The amount shown represents 38 per cent -of the total consumption. Unless direct observations have been made on -existing sewers or other factors are known which will affect the -relation between water supply and sewage, the average sewage flow -exclusive of ground water, should be taken as the average rate of water -consumption. Experience has shown that water consumption increases after -the installation of sewers. - - TABLE 6 - - ESTIMATED QUANTITY OF WATER USED BUT NOT DISCHARGED INTO THE SEWERS IN - CINCINNATI - - Expressed in gallons per capita per day, and based on a total - consumption of 125 to 150 gallons per capita per day. - - ──────────────────────────────────────────────────────────────┬──────── - Steam railroads. │6 to 7 - Street sprinklers. │6 to 7 - Consumers not sewered. │9 to 10½ - Manufacturing and mechanical. │6 to 7 - Lawn sprinklers. │3 to 3½ - Leakage. │18 to 21 - ──────────────────────────────────────────────────────────────┴──────── - -The public water supply is generally installed before the sewerage -system. By collecting statistics on the rate of supply of water a fair -prediction can be made of the quantity of sewage which must be cared -for. The rate of water supply varies widely in different cities. It is -controlled by many factors such as meters, cost and availability of -water, quality of water, climate, population, etc. In American cities a -rough average of consumption is 100 gallons per capita per day. Other -factors being equal the rate of consumption after meters have been -installed will be about one-half the rate before the meters were -installed. Low cost, good quantity and good quality will increase the -rate of consumption, and the rate will increase slowly with increasing -population. Statistics of rates of water consumption are given in Table -7. - - -=24. Character of District.=—The various sections of a city are -classified as commercial, industrial, or residential. The residential -districts can be subdivided into sparsely populated, moderately -populated, crowded, wealthy, poor, etc. Commercial districts may be -either retail stores, office buildings, or wholesale houses. Industrial -districts may be either large factories, foundries, etc., or they may be -made up of small industries housed in loft buildings. - -In cities of less than 30,000 population the refinement of such -subdivisions is generally unnecessary in the study of sewage flow, all -districts being considered the same. The data given in Tables 8 and 9 -indicate the difference to be found in different districts of large -cities. The Milwaukee data are presented in a form available for -estimates on different bases. These data are shown in Table 10. - - TABLE 7 - - RATES OF WATER CONSUMPTION - - From Journals of American and New England Water Works Associations - ───────────────────────────────────┬───────────┬───────────┬─────────── - City │Population │ Per Cent │Consumption, - │ in │ Metered │ Gal. per - │ Thousands │ │Capita per - │ │ │ Day - ───────────────────────────────────┼───────────┼───────────┼─────────── - Tacoma, Wash. │ 100 │ 11.6│ 460 - Buffalo, N. Y. │ 450 │ 4.9│ 310 - Cheyenne, Wyo. │ 13 │ │ 270 - Erie, Pa. │ 72 │ 3.0│ 198 - Philadelphia, Pa. │ 1611 │ 4.6│ 180 - St. Catherines, Ont. │ 17 │ 3.2│ 160 - Port Arthur, Ont. │ 18 │ 14.7│ 145 - Ogdensburg, N. Y. │ 18 │ 0.2│ 140 - Los Angeles, Cal. │ 516 │ 77.9│ 140 - Wilmington, Del. │ 92 │ 43.7│ 125 - Lancaster Pa. │ 60 │ 34.6│ 120 - Richmond, Va. │ 120 │ 75.2│ 115 - St. Louis, Mo. │ 730 │ 6.7│ 110 - Springfield, Mass. │ 100 │ 94.4│ 110 - Keokuk, Ia. │ 14 │ 64.5│ 105 - Jefferson City, Mo. │ 13.5│ 34.4│ 100 - Muncie, Ind. │ 30 │ 23.8│ 95 - Burlington, Ia. │ 24 │ 4.5│ 90 - Council Bluffs, Ia. │ 32 │ 75.5│ 80 - San Diego, Cal. │ 85 │ 100 │ 80 - Monroe, Wis. │ 3 │ 100 │ 80 - Yazoo City, Miss. │ 7 │ 84.1│ 75 - Oak Park, Illinois. │ 26 │ 100 │ 70 - Portsmouth, Va. │ 75 │ 8.1│ 65 - New Orleans, La. │ 360 │ 99.7│ 60 - Rockford, Ill. │ 53 │ 93.0│ 55 - Fort Dodge, Ia. │ 20 │ 96.0│ 50 - Manchester, Vt. │ 1.5│ 69.0│ 45 - Woonsocket, R. I. │ 47.5│ 95.6│ 35 - ───────────────────────────────────┴───────────┴───────────┴─────────── - -Attempts have been made to express the rate of sewage flow in different -units other than in gallons per capita per day. A unit in terms of -gallons per square foot of floor area tributary has been suggested for -commercial and industrial districts. It has not been generally adopted. -The rates of flow in New York City as reported in this unit by W. S. -McGrane are given in Table 11. - -The most successful way to predict the flow from commercial or -industrial districts is to study the character of the district’s -activities and to base the prediction on the quantity of water demanded -by the commerce and industry of the district affected. - - -=25. Fluctuations in Rate of Sewage Flow.=—The rate of flow of sewage -from any district varies with the season of the year, the day of the -week, and the hour of the day. The maximum and minimum rates of sewage -flow are the controlling factors in the design of sewers. The sewers -must be of sufficient capacity to carry the maximum load which may be -put upon them, and they must be on such a grade that deposits will not -occur during periods of minimum flow. The maximum and minimum rates of -flow are usually expressed as percentages of the average rate of flow. - - TABLE 8 - - SEWAGE FLOW FROM DIFFERENT CLASSES OF DISTRICTS - - Arranged from data by Kenneth Allen in Municipal Engineer’s Journal, - Feb., 1918. - - ──────────────────────────────────────────────────────┬───────┬─────── - District │Gallons│Gallons - │ per │ per - │Capita │ Acre - │per Day│per Day - ──────────────────────────────────────────────────────┼───────┼─────── - Buffalo, N. Y. From Report of International Joint │ │ - Commission on the Pollution of Boundary Waters: │ │ - Industrial: Metal and automobile plants. Maximum. │ │ 13,000 - Industrial: Meat packing, chemical and soap. │ │ 16,000 - Commercial: Hotels, stores and office buildings. │ │ 60,000 - Domestic: Average. │ 80 │ - Domestic: Apartment houses. │ 147 │ - Domestic: First-class dwellings. │ 129 │ - Domestic: Middle-class dwellings. │ 81 │ - Domestic: Lowest-class dwellings. │ 35.5│ - │ │ - Cincinnati, Ohio. 1913 Report on Sewerage Plan: │ │ - Industrial, in addition to residential and ground │ │ - water. │ │ 9,000 - Commercial, in addition to residential and ground │ │ - water. │ │ 40,000 - Domestic. │ 135 │ - │ │ - Detroit, Mich.: │ │ - Domestic. │ 228 │ - Industrial, in addition to residential and ground │ │ - water. │ │ 12,000 - Commercial, in addition to residential and ground │ │ - water. │ │ 50,000 - │ │ - Milwaukee, Wis. 1915 Report of Sewerage Commission: │ │ - Industrial, maximum. │ 81 │ 16,600 - Industrial, average. │ 31 │ 8,300 - Commercial, maximum. │ │ 60,500 - Commercial, average. │ │ 37,400 - Wholesale commercial, maximum. │ │ 20,000 - Wholesale commercial, average. │ │ 9,650 - ──────────────────────────────────────────────────────┴───────┴─────── - - TABLE 9 - - OBSERVED WATER CONSUMPTION IN DIFFERENT CLASSES OF DISTRICTS IN NEW YORK CITY - - From data by Kenneth Allen in Municipal Engineers Journal, for 1918 - ─────────────┬─────────────┬──────────┬─────────────┬───────────┬───────────── - Hotels │ Daily Cons. │Tenements │ Daily Cons. │Office and │ Daily Cons. - │ Gals. per │ │ Gals. per │ Loft │ Gals. per - │1000 Sq. Ft. │ │1000 Sq. Ft. │ Buildings │1000 Sq. Ft. - │ Floor Area │ │ Floor Area │ │ Floor Area - ─────────────┼────────┬────┼──────────┼────────┬────┼───────────┼────────┬──── - Building │Max.[19]│Avg.│ Location │Max.[19]│Avg.│ Building │Max.[19]│Avg. - ─────────────┼────────┼────┼──────────┼────────┼────┼───────────┼────────┼──── - Hotel │ │ │78th–79th │ │ │McGraw │ │ - Biltmore. │ │ │ St. and │ │ │ Bldg. │ │ - │ 470 │368 │ B’way. │ 256 │192 │ │ 309 │206 - Hotel │ │ │410 E. │ │ │N. Y. │ │ - McAlpin. │ │ │ 65th St.│ │ │ Telephone│ │ - │ 753 │694 │ │ 350 │295 │ Bldg. │ │194 - Hotel Plaza. │ │ │30th St. │ │ │Met. Life │ │ - │ │ │ and │ │ │ Bldg. │ │ - │ │ │ Madison │ │ │ │ │ - │ 630 │578 │ Ave │ 306 │188 │ │ │256 - Hotel Waldorf│ │ │27 Lewis │ │ │42d St. │ │ - Astoria. │ 618 │482 │ St. │ 307 │250 │ Bldg │ │271 - Hotel Astor. │ │ │258 │ │ │Municipal │ │ - │ │ │ Delancey│ │ │ Bldg. │ │ - │ 732 │492 │ St. │ 267 │226 │ │ │118 - Hotel │ │ │ │ │ │Equitable │ │ - Vanderbilt.│ 604 │545 │ │ │ │ Bldg. │ 366 │268 - ─────────────┼────────┼────┼──────────┼────────┼────┼───────────┼────────┼──── - Average │ 634 │526 │ Average │ 297 │230 │ Average │ 338 │219 - ─────────────┴────────┴────┴──────────┴────────┴────┴───────────┴────────┴──── - - TABLE 10 - - SEWAGE FLOW FROM DIFFERENT CLASSES OF DISTRICTS BASED ON 1915 REPORT OF - MILWAUKEE SEWERAGE COMMISSION - - ────────────────────────────────────────────────────────────────┬────── - Ratio of maximum to average rate for department store district. │ 1.755 - Ratio of maximum to average rate for hotel district. │ 1.65 - Ratio of maximum to average rate for office building district. │ 1.51 - Ratio of maximum to average rate for wholesale commercial │ - district. │ 2.1 - │ - │——————│—————— - Average and maximum gallons per thousand square feet of │ │ - floor area: │ Avg. │ Max. - │——————│—————— - For department store district. │ 232│ 407 - For office building district. │ 541│ 891 - For wholesale commercial district. │ 164│ 344 - For all districts except wholesale commercial. │ 381│ 618 - │ │ - Average and maximum gallons per day: │ │ - For all districts except wholesale commercial. │17,700│29,800 - For wholesale commercial district. │ 9,650│20,000 - ─────────────────────────────────────────────────────────┴──────┴────── - - TABLE 11 - - RATES OF CONSUMPTION PREDICTED FOR DIFFERENT DISTRICTS IN NEW YORK CITY - - ────────────┬───────────┬──────┬────────┬────────┬───────── - │ Net Bldg. │ │Observed│Observed│ - │Area in Sq.│ Avg. │Cons. in│Cons. in│Predicted - District │ Ft. per │Number│ g.p.d. │ g.p.d. │ Mean - │ Acre for │ of │per 1000│per 1000│ Cons. - │ Ultimate │Floors│Sq. Ft. │Sq. Ft. │ - │Consumption│ │ Max. │ Avg. │ - ────────────┼───────────┼──────┼────────┼────────┼───────── - Hotel and │ 24,800│ 15│ 634│ 526│ 500 - midtown. │ │ │ │ │ - Midtown and │ 24,800│ 15│ 338│ 219│ 300 - financial.│ │ │ │ │ - East and │ │ │ │ │ - West of │ 24,800│ 10│ 297│ 230│ 300 - midtown. │ │ │ │ │ - Apartment, │ │ │ │ │ - 59th to │ 20,400│ 7│ │ 230│ 300 - 155th Sts.│ │ │ │ │ - Manhattan │ │ │ │ │ - north of │ 20,400│ 5│ │ 230│ 300 - 155th St. │ │ │ │ │ - ────────────┴───────────┴──────┴────────┴────────┴───────── - - ────────────┬─────────┬─────────┬─────────┬────────┬──────── - │Predicted│Predicted│Predicted│Measured│Measured - │ Mean in │ Dry │Max. Dry │Avg. Dry│Max. Dry - District │ Million │ Weather │ Weather │Weather │Weather - │Gals. per│ Flow, │ Flow, │ Flow, │ Flow, - │Acre per │ c.f.s. │ c.f.s. │ c.f.s. │ c.f.s. - │ Day │per Acre │per Acre │per Acre│per Acre - ────────────┼─────────┼─────────┼─────────┼────────┼──────── - Hotel and │ .20 │ .29│ .34│ 1.04 │ .146 - midtown. │ │ │ │ │ - Midtown and │ .12 │ .18│ .23│ .078│ .110 - financial.│ │ │ │ │ - East and │ │ │ │ │ - West of │ .074│ .12│ .15│ .057│ .097 - midtown. │ │ │ │ │ - Apartment, │ │ │ │ │ - 59th to │ .043│ .06│ .09│ │ - 155th Sts.│ │ │ │ │ - Manhattan │ │ │ │ │ - north of │ .031│ .05│ .08│ │ - 155th St. │ │ │ │ │ - ────────────┴─────────┴─────────┴─────────┴────────┴──────── - -Midtown district consists of department stores, large railroad -terminals, industrial and loft buildings, and sky-scraper office -buildings. - -It is difficult to set any definite figure for the percentage which the -maximum rate of flow is of the average. Fluctuations above and below the -average are greater the smaller the tributary population. This relation -can be expressed empirically as - - _M_ = 500⁄_P_^⅕, - -in which _M_ represents the per cent which the maximum flow is of the -average, and _P_ represents the tributary population in thousands. The -expression should not be used for populations below 1,000 nor above -1,000,000. Having determined the expected average flow of sewage by a -study of the population, water consumption, etc., the maximum quantity -of sewage is determined by multiplying the average flow by the per cent -which the maximum is of the average. In this connection W. G. Harmon[20] -offers the relation - - _M_ = 1 + 14⁄(4 + √(_P_)), - -which was used in the design of the Ten Mile Creek intercepting sewer at -Toledo, Ohio. For rough estimates and for comparative purposes the ratio -of the average to the minimum flow can be taken the same as the ratio of -the maximum to the average flow, unless direct gaugings or other -information show it to be otherwise. - -[Illustration: - - Fig. 10.—Daily and Hourly Variations of Sewage Flow. -] - - 1. Toledo, O.; Manufacturing average. - - 2. Toledo, O.; Manufacturing, Monday. - - 3. Toledo, O.; Manufacturing, Sunday. - - 4. Toledo, O.; Residential, average. - - 5. Toledo, O.; Residential, Monday. - - 6. Toledo, O.; Residential, Sunday. - - 7. Cincinnati, O., Industrial, average. - - 8. Cincinnati, O.; Residential, average. - - 9. Cincinnati, O.; Commercial, average. - - 10. Average of 7 cities. - -The fluctuations of flow in commercial and industrial districts are so -different from those in residential districts that the formulas given -should not be used in the design of sewers other than those draining -residential areas. It is reasonable to suppose that fluctuations in -rates of flow from industrial districts are dependent upon the character -of the tributary industries. A study of these industries will give -valuable light on the maximum and minimum rates at which sewage will be -delivered to the sewers. - -Hourly, daily, and seasonal fluctuations in rates of sewage flow are of -interest in the design of pumping stations to give knowledge of the -rates at which the pumps must operate at various periods. The -fluctuations in rates of sewage flow during various hours and days in -different cities and districts are shown in Fig. 10. Fluctuations in -rate of flow of sewage lag behind fluctuations in rate of water -consumption, the time being dependent on the distance through which the -wave of change must travel in the sewer. - - -=26. Effect of Ground Water.=—Sewers are seldom laid with water-tight -joints. Since they usually lie below the ground water level it is -inevitable that a certain amount of ground water will enter. Various -units have been suggested for the expression of the inflow of ground -water in an attempt to include all of the many factors. Some of these -units are: gallons per acre drained by the sewer per day, gallons per -mile of pipe per day, gallons per inch diameter per mile of pipe per -day, etc. Since the ground water enters pipe sewers at the joints, the -longer the joints the greater the probability of the entrance of ground -water. The last unit is therefore the most logical but the accuracy of -the result is scarcely worthy of such refinement and the unit usually -adopted is gallons per mile of pipe per day. - -No definite figure can be given for the amount of ground water to be -expected in sewers since the character of the soil and the ground water -pressure must be considered. Relatively normal infiltration may be found -from 5,000 to 80,000 gallons per mile of pipe per day. The minimum is -seldom reached in wet ground and the maximum is frequently exceeded. -Table 12 shows the amount of ground water measured in various sewers as -given by Brooks.[21] - - -=27. Résumé of Method for Determination of Quantity of Dry weather -Sewage.=—The steps in the determination of the quantity of sewage are: -determine the period in the future for which the sewers are to be -designed; estimate the population and tributary area at the end of this -period; estimate the rate of water consumption and assume the sewage -flow to equal the water consumption; determine the maximum and minimum -rates of sewage flow; and finally, estimate the maximum rate of ground -water seepage and add it to the maximum rate of sewage flow to give the -total quantity of sewage to be carried by the proposed sewers. - - TABLE 12 - - DATA ON THE INFILTRATION OF GROUND WATER INTO SEWERS - - Abstracted from paper by J. N. Brooks in Transactions Am. Society of Civil - Engineers, Vol. 76, p. 1909. - ───────────┬─────┬──────┬─────┬───────┬──────┬─────┬────────────────────── - Place │ │Diam- │ │ │ │ │ - │ │ eter │ │ Wet │ Avg. │ │ - │ │ or │ │Trench,│ Head │Char-│ - │ │Dimen-│ │ Per │ of │acter│ - │ │sions │ │Cent of│Ground│ of │ - │ │ in │Mate-│ Total │Water,│Sub- │ - │Shape│Inches│rial │Length │ Fee │grade│ Gallons per 24 Hours - ───────────┼─────┼──────┼─────┼───────┼──────┼─────┼─────┬──────┬───────── - │ │ │ │ │ │ │ │ Per │ - │ │ │ │ │ │ │ │ Inch │ - │ │ │ │ │ │ │ │Diam- │ - │ │ │ │ │ │ │ │ eter │ - │ │ │ │ │ │ │ Per │ Per │ - │ │ │ │ │ │ │Foot │ Mile │ - │ │ │ │ │ │ │ of │ of │Per Mile - │ │ │ │ │ │ │Joint│ Pipe │ of Pipe - ───────────┼─────┼──────┼─────┼───────┼──────┼─────┼─────┼──────┼───────── - Boston, │ │ 8 to │ │ │ │ │ │ │ - Mass. │Circ.│ 36 │V.P. │ │ │ │ 2.6│ 1,818│ 40,000 - East │ │ │ │ │ │ │ │ │ - Orange, │ │ │ │ │ │ │ │ │ - N. J. │ │ │ │ │ 10│ Q. │ │ │ 22,400 - East │ │ │ │ │ │ │ │ │ - Orange, │ │ 8 to │ │ │ │ │ │ │ - N. J. │ │ 24 │V.P. │ │ │ │ 0.8│ 540│ 8,650 - Joint trunk│ │ │ │ │ │ │ │ │ - sewer, │ │ │ │ │ │ │ │ │ - New │ │ │ │ │ │G. & │ │ │ - Jersey │ │ │ │ │ │ Q. │ │ │ 25,000 - Rogers │ │ │ │ │ │ │ │ │ - Park, │ │ │ │ │ │ │ │ │ - Ill. │ │ 6 │ │ │ │ │ 0.3│ 207│ 1,240 - Altoona, │ │ │ │ │ │ │ │ │ - Pa. │ │ 30 │ │ │ │ │ 5.0│ 2,890│ 86,592 - Concord, │ │ │ │ │ │ │ │ │ - Mass. │ │ │ │ 18│ 8│ │ │ │ 43,000 - Malden, │ │ │ │ │ │ │ │ │ - Mass. │Circ.│ │V.P. │ 60│ │ │ │ │ 50,000 - Westboro, │ │ │ │ │ │ │ │ │ - Mass. │ │ 15 │V.P. │ 100│ │ │ │88,100│1,320,300 - Fond du │ │ │ │ │ │ │ │ │ - Lac, Wis.│Circ.│ 24 │V.P. │ 100│ 5│ C. │ 1.5│ 1,010│ 24,370 - East │ │ │ │ │ │ │ │ │ - Orange, │ │10 to │ │ │ │ │ │ │ - N. J. │Circ.│ 24 │V.P. │ 100│ │ │ 4.7│ 2,540│ 43,250 - Ocean │ │ │ │ │ │ │ │ │ - Grove, N.│ │ 4 to │ │ │ │ │ │ │ - J. │Circ.│ 12 │V.P. │ 100│ 3│S.C. │ 2.7│ 1,890│ 15,126 - Ocean │ │ │ │ │ │ │ │ │ - Grove, N.│ │ 4 to │ │ │ │ │ │ │ - J. │Circ.│ 12 │V.P. │ 100│ 4│S.C. │ 7.9│ 5,480│ 43,764 - East │ │ │ │ │ │ │ │ │ - Orange, │ │ 24 × │ │ │ │ │ │ │ - N. J. │Rect.│ 36 │Brick│ 100│ │ │ │ │ 570,000 - Westboro, │ │ │ │ │ │ │ │ │ - Mass. │ │ │Brick│ │ │ │ │ │ 415,850 - Altoona, │ │ 33 × │B. & │ │ │ │ │ │ - Pa. │Rect.│ 44 │ C. │ │ │ │ │ 5,390│ 264,000 - Columbus, │ │ 42 × │Con- │ │ │ │ │ │ - Ohio. │H.S. │ 42 │crete│ │ │ │ │ 120│ 6,340 - Bronx │ │ │ │ │ │ │ │ │ - Valley, │ │44 to │Con- │ │ │ │ │ │ - N. Y. │Circ.│ 72 │crete│ │ │ G. │ │ 123│ 7,266 - Cincinnati,│ Estimated in design. Data not │ │ │ │ - Ohio. │ from Brooks │ │ │ │ 67,500 - Milwaukee, │ Residential districts, gals. per acre per │ │ 1460 to - Wis. │ day. Not taken from Brooks │ │ 2200 - ───────────┴─────────────────────────────────────────────┴──────┴───────── - - Abbreviations: H.S. = horseshoe shaped; B. & C = Brick and concrete; V.P. - = vitrified pipe; G. = gravel; Q. = quicksand; S. C. = sand clay; C. = - clay. - - - QUANTITY OF STORM WATER - - -=28. The Rational Method.=—The water which falls during a storm must be -removed rapidly in order to prevent the flooding of streets and -basements, and other damages. The quantity of water to be cared for is -dependent upon: the rate of rainfall, the character and slope of the -surface, and the area to be drained. All methods for the determination -of storm-water run-off, whether rational or empirical, depend upon these -factors. - -The so-called Rational Method can be expressed algebraically, as, - - _Q_ = _AIR_, - - in which _Q_ = rate of run-off in cubic feet per second; - - _A_ = area to be drained expressed in acres; - - _I_ = percentage imperviousness of the area; - - _R_ = maximum average rate of rainfall over the entire - drainage area, expressed in inches per hour, which - may occur during the time of concentration. - -The area to be drained is determined by a survey. A discussion of _R_ -and _I_ follows in the next two sections. An example of the use of the -Rational Method is given on page 95. - - -=29. Rate of Rainfall.=—Rainfall observations have been made over a long -period of time by United States Weather Bureau observers and others. -Continuous records are available in a few places in this country showing -rainfall observations covering more than a century. Such records have -been the bases for a number of empirical formulas for expressing the -probable maximum rate of rainfall in inches per hour, having given the -duration of the storm. Table 13 is a collection of these formulas with a -statement as to the conditions under which each formula is applicable. -The formula most suitable to the problem in hand should be selected for -its solution.[22] - - TABLE 13 - - RAINFALL FORMULAS - - ────────────┬─────────────────────────┬──────────────────────────────── - Name of │ Conditions for which │ Formula - Originator │ Formula is Suitable │ - ────────────┼─────────────────────────┼──────────────────────────────── - E. S. Dorr │ │_i_ = 150⁄(_t_ + 30) - A. N. Talbot│Maximum storms in Eastern│_i_ = 360⁄(_t_ + 30) - │ United States │ - A. N. Talbot│Ordinary storms in │_i_ = 105⁄(_t_ + 15) - │ Eastern United States │ - Emil │Heavy rainfall near New │_i_ = 120⁄(_t_ + 20), etc. - Kuichling │ York City │ - L. J. Le │For San Francisco. See T.│ - Conte │ A. S. C. E. v. 54, p. │_i_ = 7⁄_t_^½ - │ 198 │ - Sherman │Maximum for Boston, Mass.│_i_ = 25.12⁄_t_^{.687} - Sherman │Extraordinary for Boston,│_i_ = 18⁄_t_ ^½ - │ Mass. │ - Webster │Ordinary for │_i_ = 12⁄_t_^{0.6} - │ Philadelphia, Pa. │ - │Ordinary storms for │ - Hendrick │ Baltimore. Eng. & │_i_ = 105⁄(_t_ + 10) - │ Cont., Aug. 9. 1911 │ - J. de │Ordinary storms for │_i_ = 163⁄(_t_ + 27) - Bruyn-Kops│ Savannah, Ga. │ - C. D. Hill │For Chicago, Ill. │_i_ = 120⁄(_t_ + 15) - Metcalf and │Louisville, Ky. Am. Sew. │_i_ = 14⁄_t_^½ - Eddy │ Prac., Vol I. │ - W. W. Horner│St. Louis, Mo. Eng. News,│_i_ = 56⁄(_t_ + 5)^{.85} - │ Sept. 29, 1910 │ - R. A. │For Spokane, Wash. Eng. │_i_ = 23.92⁄(_t_ + 2.15) + 0.154 - Brackenbuy│ Record, Aug. 10, 1912 │ - Metcalf and │New Orleans │_i_ = 19⁄_t_^½ - Eddy │ │ - Metcalf and │For Denver, Colo. │_i_ = 84⁄(_t_ + 4) - Eddy │ │ - │Central Park, N. Y. │ - Kenneth │ 51–Year Record. Eng. │_i_ = 400⁄(2_t_ + 40)[23] - Allen │ News-Record, April 7, │ - │ 1921, p. 588 │ - ────────────┴─────────────────────────┴──────────────────────────────── - - -=30. Time of Concentration.=—By the time of concentration is meant the -longest time without unreasonable delay that will be required for a drop -of water[24] to flow from the upper limit of a drainage area to the -outlet. Assuming a rainfall to start suddenly and to continue at a -constant rate and to be evenly distributed over a drainage area of 100 -per cent imperviousness and even slope towards one point, the rate of -run-off would increase constantly until the drop of water from the upper -limit of the area reached the outlet, after which the rate of run-off -would remain constant. In nature the rate of rainfall is not constant. -The shorter the duration of a storm the greater the intensity of -rainfall. Therefore the maximum run-off during a storm will occur at the -moment when the upper limit of the area has commenced to contribute. -From that time on the rate of run-off will decrease. - -The time of concentration can be measured fairly well by observing the -moment of the commencement of a rainfall, and the time of maximum -run-off from an area on which the rain is falling. A prediction of the -time of concentration is more or less guess work. As the result of -measurements some engineers assume the time of concentration on a city -block built up with impervious roofs and walks, and on a moderate slope, -is about 5 to 10 minutes. This is used as a basis for the judgment of -the time of concentration on other areas. For relatively large drainage -areas such a method cannot be used. The procedure is to measure the -length of flow through the drainage channels of the area, to assume the -velocity of the flood crest through these channels and thus to determine -the time of concentration. Table 14 shows the flood crest velocities in -various streams of the Ohio River Basin under flood conditions. The -velocity over the surface of the ground may be approximated by the use -of the formula[25] - - _V_ = 2,000_I_√(_S_), - - in which _V_ = the velocity of flow over the surface of the ground in - feet per minute; - - _I_ = the percentage imperviousness of the ground; - - _S_ = the slope of the ground. - -For areas up to 100 acres where natural drainage channels are not -existent this formula will give more satisfactory results than guesses -based on the time of concentration of certain known areas. - -Having determined the time of concentration, the rate of rainfall _R_ to -be used in the Rational Method is found by substitution in some one of -the rainfall formulas given in Table 13. - - TABLE 14 - - FLOOD CREST VELOCITIES IN OHIO RIVER BASIN IN MARCH, 1913 - - From Table 12. U. S. G. S., Water Supply Paper. No. 334 - ───────────┬───────────────┬────────┬────────┬───────────────┬─────────┬───────────┬──────── - River │ Stations │ │Distance│ Distance of │Velocity │ Velocity │ - │ │Distance│to Mouth│ Lower Station │ between │ from │ Time - │ │between │ of │ below │Stations,│Pittsburgh,│between - │ │Stations│ River, │Starting-point,│Miles per│ Miles per │Stations - │ │in Miles│ Miles │ Miles │ Hour │ Hour │in Hours - ───────────┼───────────────┼────────┼────────┼───────────────┼─────────┼───────────┼──────── - Ohio │Pittsburgh, │ │ │ │ │ │ - │ Pa., to │ │ │ │ │ │ - │ Wheeling, W. │ │ │ │ │ │ - │ Va. │ 90│ 967│ 90│ 9.0│ 9.0│ 10.0 - Ohio │Wheeling, W. │ │ │ │ │ │ - │ Va., to │ │ │ │ │ │ - │ Marietta, │ │ │ │ │ │ - │ Ohio │ 82│ 877│ 172│ 5.9│ 7.2│ 14 - Ohio │Marietta, Ohio,│ │ │ │ │ │ - │ to │ │ │ │ │ │ - │ Parkersburg, │ │ │ │ │ │ - │ W. Va. │ 12│ 795│ 184│ 0.9│ 4.8│ 14 - Ohio │Parkersburg to │ │ │ │ │ │ - │ Point │ │ │ │ │ │ - │ Pleasant, W. │ │ │ │ │ │ - │ Va. │ 80│ 783│ 264│ 6.7│ 5.3│ 12 - Ohio │Point Pleasant │ │ │ │ │ │ - │ to │ │ │ │ │ │ - │ Huntington, │ │ │ │ │ │ - │ W. Va. │ 44│ 703│ 308│ 11.0│ 5.7│ 4 - Ohio │Huntington to │ │ │ │ │ │ - │ Catlettsburg,│ │ │ │ │ │ - │ W. Va. │ 9│ 659│ 317│ 0.8│ 4.1│ 11 - Ohio │Catlettsburg, │ │ │ │ │ │ - │ W. Va., to │ │ │ │ │ │ - │ Portsmouth, │ │ │ │ │ │ - │ Ohio │ 38│ 650│ 355│ │ 5.0│ - Ohio │Portsmouth │ │ │ │ │ │ - │ Ohio, to │ │ │ │ │ │ - │ Maysville, │ │ │ │ │ │ - │ Ky. │ 52│ 612│ 407│ 5.2│ 5.0│ 10 - Ohio │Maysville, Ky.,│ │ │ │ │ │ - │ to │ │ │ │ │ │ - │ Cincinnati, │ │ │ │ │ │ - │ Ohio │ 61│ 560│ 468│ 6.8│ 5.2│ 9 - Ohio │Cincinnati, │ │ │ │ │ │ - │ Ohio, to │ │ │ │ │ │ - │ Louisville, │ │ │ │ │ │ - │ Ky. │ 136│ 499│ 604│ 11.4│ 5.9│ 12 - Ohio │Louisville, │ │ │ │ │ │ - │ Ky., to │ │ │ │ │ │ - │ Evansville, │ │ │ │ │ │ - │ Ind. │ 183│ 363│ 787│ 1.9│ 5.3│ 96 - Ohio │Evansville, │ │ │ │ │ │ - │ Ind., to Mt. │ │ │ │ │ │ - │ Vernon Ind. │ 36│ 180│ 823│ 9.0│ 5.3│ 4 - Ohio │Mt. Vernon, │ │ │ │ │ │ - │ Ind., to │ │ │ │ │ │ - │ Paducah, Ky.│ 101│ 144│ 924│ 2.1│ 4.6│ 48 - Ohio │Paducah, Ky. to│ │ │ │ │ │ - │ Cairo, Ill. │ 43│ 43│ 967│ 2.9│ 4.2│ 15 - Monongahela│Fairmont, W. │ │ │ │ │ │ - │ Va., to Lock │ │ │ │ │ │ - │ No. 2 Pa. │ │ │ │ │ │ - │ (Upper) │ 107│ 119│ 107│ 6.7│ │ 16 - Little │Creston, W. │ │ │ │ │ │ - Kanawha │ Va., to Dam. │ │ │ │ │ │ - │ No. 4 W. Va. │ │ │ │ │ │ - │ (Upper) │ 16│ 48│ 16│ 16.0│ │ 1 - New │Radford, W. │ │ │ │ │ │ - │ Va., to │ │ │ │ │ │ - │ Hinton, W. │ │ │ │ │ │ - │ Va. │ 78│ 139│ 78│ 3.0│ │ 26 - Kanawha │Kanawha Falls, │ │ │ │ │ │ - │ W. Va. to │ │ │ │ │ │ - │ Charleston, │ │ │ │ │ │ - │ W. Va. │ 37│ 95│ 37│ 2.6│ │ 14 - Scioto │Columbus, Ohio,│ │ │ │ │ │ - │ to │ │ │ │ │ │ - │ Chillicothe, │ │ │ │ │ │ - │ Ohio │ 52│ 110│ 52│ 4.7│ │ 11 - Miami │Dayton, Ohio, │ │ │ │ │ │ - │ to Hamilton, │ │ │ │ │ │ - │ Ohio │ 44│ 77│ 44│ 14.7│ │ 3 - Kentucky │Highbridge, │ │ │ │ │ │ - │ Ky., to │ │ │ │ │ │ - │ Frankfort, │ │ │ │ │ │ - │ Ky. │ 52│ 117│ 52│ 5.2│ │ 10 - Cumberland │Celina, Tenn. │ │ │ │ │ │ - │ to Nashville,│ │ │ │ │ │ - │ Tenn. │ 190│ 383│ 190│ 2.9│ │ 64.5 - Tennessee │Knoxville to │ │ │ │ │ │ - │ Chattanooga, │ │ │ │ │ │ - │ Tenn. │ 183│ 635│ 183│ 3.2│ │ 57 - ───────────┴───────────────┴────────┴────────┴───────────────┴─────────┴───────────┴──────── - NOTE.—The velocities shown are the velocities of the crest of the flood wave and are not the - average velocity of the flow of the river. The velocity of the crest of the flood wave - should be used in determining the time of concentration. The flood crest velocity is slower - then that of the river because of the storage in the river basin. - - -=31. Character of Surface.=—The proportion of total rainfall which will -reach the sewers depends on the relative porosity, or imperviousness, -and the slope of the surface. Absolutely impervious surfaces such as -asphalt pavements or roofs of buildings will give nearly 100 per cent -run-off regardless of the slope, after the surfaces have become -thoroughly wet. For unpaved streets, lawns, and gardens the steeper the -slope the greater the per cent of run-off. When the ground is already -water soaked or is frozen the per cent of run-off is high, and in the -event of a warm rain on snow covered or frozen ground, the run-off may -be greater than the rainfall. The run-off during the flood of March, -1913, at Columbus, Ohio, was over 100 per cent of the rainfall. Table -15[26] shows the relative imperviousness of various types of surfaces -when dry and on low slopes. The estimates for relative imperviousness -used in the design of the Cincinnati intercepter are given in Table 16. - - TABLE 15 - - VALUES OF RELATIVE IMPERVIOUSNESS - - Roof surfaces assumed to be water-tight 0.70– 0.95 - Asphalt pavements in good order .85– .90 - Stone, brick, and wood-block pavements with tightly cemented - joints .75– .85 - The same with open or uncemented joints .50– .70 - Inferior block pavements with open joints .40– .50 - Macadamized roadways .25– .60 - Gravel roadways and walks .15– .30 - Unpaved surfaces, railroad yards, and vacant lots .10– .30 - Parks, gardens, lawns, and meadows, depending on surface - slope and character of subsoil .05– .25 - Wooded areas or forest land, depending on surface slope and - character of subsoil .01– .20 - Most densely populated or built up portion of a city .70– .90 - - TABLE 16 - - COEFFICIENTS OF IMPERVIOUSNESS USED IN THE DESIGN OF THE CINCINNATI SEWERS - - ──────────────┬─────────────────────────────┬──────────────────┬─────────── - Character of │ │ │Residential, - Improvement │ │ │291.1 A. 20 - │ │ │ per Acre, - │ │ │ Middle - │ │ │ Class, - │ │ │ Detached - │ │ │Dwellings, - │ │ │Yellow and - │ │Combined Tenement │ Blue Clay - │ │ and Industrial. │ Overlying - │Typical Commercial Area, 30.4│ 35.6 A., 55 per │ Beds of - │A. None Undeveloped. Sand and│ Acre. Clay, Sand │ Shale and - │ Gravel │ and Gravel │ Sandstone - ──────────────┼──────┬─────┬─────┬──────────┼──────┬─────┬─────┼─────┬───── - │ Area │ │ │Equivalent│ Area │ │ │ Per │ - │ in │ Per │ │Imp. Area,│ in │ Per │ │Cent │ - │1000’s│Cent │ I, │ 1000’s │1000’s│Cent │ I, │ of │ I, - │Square│Total│Esti-│ Square │Square│Total│Esti-│Total│Esti- - │ Feet │Area │mated│ Feet │ Feet │Area │mated│Area │mated - ──────────────┼──────┼─────┼─────┼──────────┼──────┼─────┼─────┼─────┼───── - Roofs: │ │ │ │ │ │ │ │ │ - Public and │ │ │ │ │ │ │ │ │ - commercial│ 881.2│ 66.5│ 0.90│ 793.0│ 66.8│ 4.3│ 0.40│ 4.8│ 0.40 - Residences │ │ │ │ │ 289.2│ 18.6│ .90│ 13.1│ .90 - Barns and │ │ │ │ │ │ │ │ │ - sheds │ │ │ │ │ 79.2│ 5.1│ .75│ 1.4│ .75 - │ │ │ │ │ │ │ │ │ - Interior │ │ │ │ │ │ │ │ │ - Walks: │ │ │ │ │ │ │ │ │ - Brick │ 7.5│ 0.6│ .40│ 3.0│ 35.6│ 2.3│ .40│ 0.6│ .40 - Cement │ 10.0│ 0.7│ .75│ 7.5│ 22.6│ 1.5│ .75│ 2.6│ .75 - │ │ │ │ │ │ │ │ │ - Street Walks: │ │ │ │ │ │ │ │ │ - Brick │ 6.1│ 0.5│ .40│ 2.4│ 48.2│ 3.1│ .40│ 1.0│ .40 - Cement │ 139.3│ 10.5│ .75│ 104.5│ 78.1│ 5.0│ .75│ 3.4│ .75 - │ │ │ │ │ │ │ │ │ - Street │ │ │ │ │ │ │ │ │ - Pavements: │ │ │ │ │ │ │ │ │ - Asphalt, │ │ │ │ │ │ │ │ │ - brick, │ │ │ │ │ │ │ │ │ - wood block│ 145.5│ 11.0│ .85│ 123.7│ │ │ │ 5.0│ .85 - Granite │ │ │ │ │ │ │ │ │ - block │ 111.4│ 8.4│ .75│ 83.6│ │ │ │ 1.0│ .75 - Macadam and │ │ │ │ │ │ │ │ │ - cobble │ 23.2│ 1.8│ .40│ 9.3│ 238.6│ 15.4│ .40│ 4.8│ .40 - Granite and │ │ │ │ │ │ │ │ │ - poor │ │ │ │ │ │ │ │ │ - macadam │ │ │ │ │ │ │ │ 0.4│ .20 - │ │ │ │ │ │ │ │ │ - Unimproved │ │ │ │ │ │ │ │ │ - yards and │ │ │ │ │ │ │ │ │ - lawns: │ │ │ │ │ 692.4│ 44.7│ .15│ │ - Tributary to│ │ │ │ │ │ │ │ │ - paved │ │ │ │ │ │ │ │ │ - gutters │ │ │ │ │ │ │ │ 57.1│ .15 - Not │ │ │ │ │ │ │ │ │ - tributary │ │ │ │ │ │ │ │ │ - to paved │ │ │ │ │ │ │ │ │ - gutters │ │ │ │ │ │ │ │ 7.9│ .10 - ──────────────┼──────┼─────┼─────┼──────────┼──────┼─────┼─────┼─────┼───── - Total │1324.2│100.0│ │ 1127.0│1550.7│100.0│ │100.0│ - ──────────────┼──────┴─────┴─────┴──────────┼──────┴─────┴─────┼─────┴───── - Impervious │ │ │ - coefficient │ │ │ - for the │ │ │ - district │ 85.1 │ 44.4 │ 35.9 - ──────────────┴─────────────────────────────┴──────────────────┴─────────── - -C. E. Gregory[27] states that _I_, in the expression _Q_ = _AIR_ is a -function of the time of concentration or the duration of the storm. If -_t_ represents the time of concentration and _T_ represents the duration -of the storm, then when _T_ is less than _t_ - - _I_ = 0.175_t_^⅓, - -but when _T_ is greater than _t_, - - _I_ = 0.175⁄_t_(_T_^{4/3} − (_T_ − _t_)^{4/3}). - -Gregory condenses Kuichling’s rules with regard to the per cent run-off, -as follows: - - 1. The per cent of rainfall discharged from any given drainage - area is nearly constant for heavy rains lasting equal periods of - time. - - 2. This per cent varies directly with the area of impervious - surface. - - 3. This per cent increases rapidly and directly or uniformly with - the duration of the maximum intensity of the rainfall until a - period is reached which is equal to the time required for the - concentration of the drainage waters from the entire area at the - point of observation, but if the rainfall continues at the same - intensity for a longer period this per cent will continue to - increase at a much smaller rate. - - 4. This per cent becomes larger when a moderate rain has - immediately preceded a heavy shower on a partially permeable - territory. - -Gregory’s formulas have not been generally accepted and are not widely -used in practice. Marston stated:[28] - - All that engineers are at present, warranted in doing is to make - some deduction from 100 per cent run-off ... the deduction ... - being at present left to the engineer in view of his general - knowledge and his familiarity with local conditions. - -Burger states[29] in the same connection: - - In its application there will usually be as many results - (differing widely from each other) as the number of men using it. - -In spite of these objections the Rational Method is in more favor with -engineers than any other method. - - -=32. Empirical Formulas.=—The difficulty of determining run-off with -accuracy has led to the production by engineers of many empirical -formulas for their own use. Some of these formulas have attracted wide -attention and have been used extensively, in some cases under conditions -to which they are not applicable. In general these formulas are -expressions for the run-off in terms of the area drained, the relative -imperviousness, the slope of the land, and the rate of rainfall. - -The Burkli-Ziegler formula, devised by a Swiss engineer for Swiss -conditions and introduced into the United States by Rudolph Hering, was -one of the earliest of the empirical formulas to attract attention in -this country. It has been used extensively in the form - - _Q_ = _CiA_∜(_S_⁄_A_), - - in which_Q_ = the run-off in cubic feet per second; - - _i_ = the maximum rate of rainfall in inches per hour over - the entire area. This is determined only by - experience in the particular locality, and is usually - taken at from 1 to 3 inches per hour; - - _S_ = the slope of the ground surface in feet per thousand, - - _A_ = the area in acres; - - _C_ = an expression for the character of the ground surface, - or relative imperviousness. In this form of the - expression _C_ is recommended as 0.7. - -The McMath formula was developed for St. Louis conditions and was first -published in Transactions of the American Society of Civil Engineers, -Vol. 16, 1887, p. 183. Using the same notation as above, the formula is, - - _Q_ = _CiA_⁵√(_S_⁄_A_), - -McMath recommended the use of _C_ equal to 0.75, _i_ as 2.75 inches per -hour, and _S_ equal to 15. The formula has been extended for use with -all values of _C_, _i_, _S_, and _A_ ordinarily met in sewerage -practice. Fig. 11 is presented as an aid to the rapid solution of the -formula. - -[Illustration: - - FIG. 11.—Diagram for the Solution of McMath’s Formula, - _Q_ = _Aci_⁵√_S_⁄_A_. -] - -Other formulas have been devised which are more applicable to drainage -areas of more than 1,000 acres.[30] Such areas are met in the design of -sewers to enclose existing stream channels draining large areas. -Kuichling’s formulas, published in 1901 in the report of the New York -State Barge Canal, were devised for areas greater than 100 square miles. -The following modification of these formulas for ordinary storms on -smaller areas was published for the first time in American Sewerage -Practice, Volume I, by Metcalf and Eddy: - - _Q_ = 25,000⁄(_A_ + 125) + 15. - -[Illustration: - - FIG. 12.—Comparison of Empirical Run-off Formulas. -] - -It is to be noted that the only factor taken into consideration is the -area of the watershed. It is obvious that other factors such as the rate -of rainfall, slope, imperviousness, etc., will have a marked effect on -the run-off. - -There are other run-off formulas devised for particular conditions, some -of which are of as general applicability as those quoted. Two formulas -which are frequently quoted are: Fanning’s, _Q_ = 200_M_^⅝ and Talbot’s -_Q_ = 500_M_^¼, in which _M_ is the area of the watershed in square -miles. A comprehensive treatment of the subject is given in American -Sewerage Practice, Vol. I, by Metcalf and Eddy. - -A comparison of the results obtained by the application of a few -formulas to the same conditions is shown graphically in Fig. 12. It is -to be noted that the divergence between the smallest and largest results -is over 100 per cent. As these formulas are not all applicable to the -same conditions, the differences shown are due partially to an extension -of some of them beyond the limits for which they were prepared. - - -=33. Extent and Intensity of Storms.=—In the design of storm sewers it -is necessary to decide how heavy a storm must be provided for. The very -heaviest storms occur infrequently. To build a sewer capable of caring -for all storms would involve a prohibitive expense over the investment -necessary to care for the ordinary heavy storms encountered annually or -once in a decade. This extra investment would lie idle for a long period -entailing a considerable interest charge for which no return is easily -seen. The alternative is to construct only for such heavy storms as are -of ordinary occurrence and to allow the sewers to overflow on -exceptional occasions. The result will be a more frequent use of the -sewerage system to its capacity, a saving in the cost of the system, and -an occasional flooding of the district in excessive storms. The amount -of damage caused by inundations must be balanced against the extra cost -of a sewerage system to avoid the damage. A municipality which does not -provide adequate storm drainage is liable, under certain circumstances, -for damages occasioned by this neglect. It is not liable if no drainage -exists, nor is it liable if the storm is of such unusual character as to -be classed legally as an act of God. - -Kuichling’s studies of the probabilities of the occurrence of heavy -storms are published in Transactions of the American Society of Civil -Engineers, Vol. 54, 1905, p. 192. Information on the extent of rain -storms is given by Francis in Vol. 7, 1878, p. 224, of the same -publication. Kuichling expresses the intensity of storms which will -occur, - - once in 10 years as _i_ = 105⁄(_t_ + 20), - - once in 15 years as _i_ = 120⁄(_t_ + 20), - -in which _i_ is the intensity of rainfall in inches per hour and _t_ is -the duration of the storm in minutes. - - - - - CHAPTER IV - THE HYDRAULICS OF SEWERS - - -=34. Principles.=—The hydraulics of sewers deals with the application of -the laws of hydraulics to the flow of water through conduits and open -channels. In so far as its hydraulic properties are concerned the -characteristics of sewage are so similar to those of water that the same -physical laws are applicable to both. In general it is assumed that the -energy lost due to friction between the liquid and the sides of the -channel varies as some function of the velocity, usually the square, and -that the total energy passing any section of the stream differs from the -energy passing any other section only by the loss of energy due to -friction. - -The general expression for the flow of sewage would then be, - - _h_ = (_f_)_V_^n, - -in which _h_ is the head or energy lost between any two sections, and -_V_ is the average velocity of flow between these sections. It is to be -noted in this general expression that the quantity and rate of flow past -all sections is assumed to be constant. This condition is known as -_steady flow_. Problems are encountered in sewerage design which involve -conditions of unsteady flow, and methods of solution of them have been -developed based on modifications of this general expression. The average -velocity of flow is computed by dividing the rate (quantity) of flow -past any section by the cross-sectional area of the stream at that -section. This does not represent the true velocity at any particular -point in the stream, as the velocity near the center is faster than that -near the sides of the channel. The distribution of velocities in a -closed circular channel is somewhat in the form of a paraboloid -superimposed on a cylinder. - -The laws of flow are expressed as formulas the constants of which have -been determined by experiment. It has been found that these constants -depend on the character of the material forming the channel and the -hydraulic radius. The _hydraulic radius_ is defined as the ratio of the -cross-sectional area of the stream to the length of the wetted -perimeter, or line of contact between the liquid and the channel, -exclusive of the horizontal line between the air and the liquid. - - -=35. Formulas.=—The loss of head due to friction caused by flow through -circular pipes flowing full as expressed by Darcy is, - - _h_ = _f_(_l_⁄_d_) (_V_^2⁄2_g_), - -in which _h_ is the head lost due to friction in the distance _l_, _V_ -is the velocity of flow, _g_ is the acceleration due to gravity, and _f_ -is a factor dependent on _d_ and the material of which the pipe is made. -A formula for _f_ expressed by Darcy as the result of experiments on -cast-iron pipe is, - - _f_ = 0.0199 + 0.00166⁄_d_, - -in which _d_ is the diameter in feet. In using the formula with this -factor the units used must be feet and seconds. - -Another form of the same expression is known as the Chezy formula. It is -an algebraic transformation of the Darcy formula, but in the form shown -here, by the use of the hydraulic radius, it is made applicable to any -shape of conduit either full or partly full. The Chezy formula is, - - _V_ = _C_√(_RS_), - -in which _R_ is the hydraulic radius, _S_ the slope ratio of the -hydraulic gradient, and _C_ a factor similar to _f_ in the Darcy -formula. - -Kutter’s formula was derived by the Swiss engineers, Ganguillet and -Kutter, as the result of a series of experimental observations. It was -introduced into the United States by Rudolph Hering and its derivation -is given in Hering and Trautwine’s translation of “The Flow of Water in -Open Channels by Ganguillet and Kutter.” In English units it is, - - _V_ = {(1.81/_n_ + 41.67 + .0028/_S_)/(1 + (_n_/√_R_)(41.67 + - (.0028/_S_)))}√(_RS_), - -in which _n_ is a factor expressing the character of the surface of the -conduit and the other notation is as in the Chezy formula. _V_ is the -velocity in feet per second, _S_ is the slope ratio, and _R_ the -hydraulic radius in feet. The values of _n_ to be used in all cases are -not agreed upon, but in general the values shown below are used in -practice. - - VALUES OF _n_ IN KUTTER’S FORMULA - - _n_ CHARACTER OF THE MATERIALS - - 0.009 Well-planed timber. - - 0.010 Neat cement or very smooth pipe. - - 0.012 Unplaned timber. Best concrete. - - Smooth masonry or brickwork, or concrete sewers under ordinary - 0.013 conditions. - - 0.015 Vitrified pipe or ordinary brickwork. - - 0.017 Rubble masonry or rough brickwork. - - 0.020 } Smooth earth. - 0.035 - - 0.030 } Rough channels overgrown with grass. - 0.050 - -Kutter’s formula is of general application to all classes of material -and to all shapes of conduits. It is the most generally used formula in -sewerage design. - -The cumbersomeness of Kutter’s formula is caused somewhat by the attempt -to allow for the effect of the low slopes of the Mississippi River -experiments on the coefficients. The correctness of these experiments -has not been well established and the slopes are so flat that the -omission of the term 0.0028⁄_S_ will have no appreciable effect on the -value of _V_ ordinarily used in sewer design. The difference between the -value of _V_ determined by the omission of this term and the value of -_V_ found by including it is less than 1 per cent for all slopes greater -than 1 in 1,000 for 8 inch pipe (_R_ = 0.167 feet). As the diameter of -the pipe or the hydraulic radius of the channel increases up to a -diameter of 13.02 feet (_R_ = 3.28 feet), the difference becomes less -and at this value of _R_ there is no difference whether the slope is -included or not. For larger pipes the difference increases slowly. For a -16 foot pipe (_R_ = 4 feet) on a slope of 1 in 1,000 the difference is -less than 0.2 per cent, and on a slope of 1 in 10,000 the difference is -approximately 1 per cent. Flatter slopes than these are seldom used in -sewer design, except for very large sewers where careful determinations -of the hydraulic slope are necessary. It is therefore safe in sewer -design to use Kutter’s formula in the modified form shown below in which -the term (.0028)⁄_S_ has been omitted. - - _V_ = (1.81 + 41.67_n_)_R_√_S_/_n_(√_R_ + 41.67_n_). - -Bazin’s formula is - - _V_ = √(_RS_)/√(α + β/_d_) - -in which α and β are constants for different classes of material. For -cast-iron pipe α is 0.00007726 and β is 0.00000647. This formula is -seldom used in sewerage design. - -Exponential formulas have been developed as the result of experiments -which have demonstrated that _V_ does not vary as the one-half power of -_R_ and _S_ but that the relation should be expressed as, - - _V_ = _CR_^{_p_}_S_^{_q_}, - -in which _p_ and _q_ are constants and _C_ is a factor dependent on the -character of the material. The various formulas coming under this -classification have been given the names of the experimenters proposing -them. Examples of these formulas are: Flamant’s, in English units, for -new cast-iron pipe, which is, - - _V_ = 232_R_^{.715}_S_^{.572}, - -and Lampé’s for the same material which is, - - _V_ = 203.3_R_^{.694}_S_^{.555}. - -These formulas are useful only for the material to which they apply, but -they can be used for conduits of any shape. A. V. Saph and E. W. Schoder -have shown[31] that the general formula for all materials lies between -the limits, - - _V_ = (93 to 142)_S_^{.50 to .55}_R_^{.63 to .69}. - -Hazen and Williams’ formula is in the form, - - _V_ = 1.31_CR_^{.63}_S_^{.54}, - -in which _C_ is a factor dependent on the character of the material of -the conduit. The values of _C_ as given by Hazen and Williams are, - - _C_ CHARACTER OF MATERIAL - 95 Steel pipe under future conditions. (Riveted steel.) - Cast iron under ordinary future conditions and brick - 100 sewers in good condition. - 110 New riveted steel, and cement pipe. - 120 Smooth wood or masonry conduits under ordinary conditions. - Masonry conduits after some time and for very smooth pipes - such as glass, brass, lead, etc., when old, and for new - 130 cast-iron pipe under ordinary conditions. - -This formula is of as general application as Kutter’s formula and is -easier of solution, but being more recently in the field and because of -the ease of the solution of Kutter’s formula by diagrams it is not in -such general use. Exponential formulas are used more in waterworks than -in sewerage practice. - -Manning’s formula is in the form, - - _V_ = 1.486⁄_n__R_^⅔_S_^½ - -in which _n_ is the same as for Kutter’s formula. Charts for the -solution of Manning’s formula are given in Eng. News-Record, Vol. 85, -1920, p. 837. - - -=36. Solution of Formulas.=—The solution of even the simplest of these -formulas, such as Flamant’s, is laborious because of the exponents -involved. Darcy’s and Kutter’s formulas are even more cumbersome because -of the character of the coefficient. The labor involved in the solution -of these formulas has resulted in the development of a number of -diagrams and other short cuts. Since each formula involves three or more -variables it cannot be represented by a single straight line on -rectangular coordinate paper. The simplest form of diagram for the -solution of three or more variables is the nomograph, an example of -which is shown in Fig. 13 for the solution of Flamant’s formula. A -straight-edge placed on any two points of the scales of two different -vertical lines will cross the other line at a point on the scale -corresponding to its correct value in the formula. Such a diagram is in -common use for the solution of problems for the flow of water in -cast-iron pipe. - -[Illustration: - - FIG. 13.—Diagram for the Solution of Flamant’s Formula for the Flow of - Water in Cast-iron Pipe. -] - -Fig. 14 has been prepared to simplify the solution of Hazen and -Williams’ formula. The scales of slope for different classes of material -are shown on vertical lines to the left of the slope line. For use these -scales must be projected horizontally on the slope line. The scales for -other factors are shown on independent reference lines. - - For example let it be required to find the loss of head in a 12 - inch pipe carrying 1 cubic foot per second when the coefficient of - roughness is 100. A straight-edge placed at 1.0 cubic feet per - second on the quantity scale, and 12 inches on the diameter scale - crosses the slope line at .00092 opposite the slope scale for _c_ - = 100. It crosses the velocity line at 1.31 feet per second. - -Kutter’s formula is the most commonly used for sewer design and has been -generally accepted as a standard in spite of its cumbersomeness. Fig. 15 -is a graphical solution of Kutter’s formula for small pipes, and Fig. 16 -for larger pipes. The diagrams are drawn on the nomographic principle -and give solutions for a wide range of materials, but they are specially -prepared for the solution of problems in which _n_ = .015. In their -preparation the effect of the slope on the coefficient has been -neglected. Fig. 17 is drawn on ordinary rectangular coordinate paper and -can be used only for the solution of problems in which _n_ = .015. Both -diagrams are given for practice in the use of the different types. - -[Illustration: - - FIG. 14.—Diagram for the Solution of Hazen and Williams’ Formula. -] - -[Illustration: - - FIG. 15.—Diagram for the Solution of Kutter’s Formula. - - For values of _n_ between 0.010 and 0.020. Specially arranged for _n_ - = 0.015. Values of Q from 0.1 to 10 second-feet. -] - -[Illustration: - - FIG. 16.—Diagram for the Solution of Kutter’s Formula. - - For values of _n_ between 0.010 and 0.020. Specially arranged for _n_ - = 0.015. Values of Q from 10 to 1,000 second-feet. -] - -[Illustration: - - FIG. 17.—Diagram for the Solution of Kutter’s Formula. -] - -[Illustration: - - FIG. 18.—Conversion Factors for Kutter’s Formula. -] - -In Figs. 15 and 16 the diameter scales are varied for different values -of the roughness coefficient _n_. The velocity scale is shown _only for -a value of n = .015_. The velocity for other values of _n_ can be -determined by the method given in the following paragraphs. - -37. =Use of Diagrams.=—There are five factors in Kutter’s formula: _n_, -_Q_, _V_, _d_ (or _R_), and _S_. If any three of these are given the -other two can be determined, except when the three given are _Q_, _V_, -and _d_. These three are related in the form _Q_ = _AV_, which is -independent of slope or the character of the material. There are only -nine different combinations possible with these five factors, which will -be met in the solution of Kutter’s formula. The solution of the problems -by means of the diagrams is simple when the data given include _n_ -= .015. For other given values of _n_ the solution is more complicated. -Results of the solution of types of each of the nine problems are given -in Table 17 and the explanatory text below. - -_If n is given and is equal to .015_, the solution is simple. - - For example in Table 17 _case 1, example 1_; to be solved on Fig. - 15. Place a straight-edge at 1.0 on the _Q_ line and at 6 inches - on the diameter line for _n_ = .015. The slope and the velocity - will be found at the intersection of the straight-edge with these - respective scales. - -All problems in which _n_ is given as .015 and the solution for which -falls within the limits of Fig. 15 or 16 should be solved by placing a -straight-edge on the two known scales and reading the two unknown -results at the intersection of the straight-edge and the remaining -scales. - - For example in _case 1_, _example 2_ find the intersection of the - horizontal line representing _Q_ = 100 with the sloping diameter - line representing _d_ = 48 inches. The vertical slope line passing - through this point represents _S_ = .0065 and the sloping velocity - line passing through this point represents 8.5 feet per second. - -In general problems in which _n_ = .015, can be solved on Fig. 17 by -finding the intersection of the two lines representing the given data, -and reading the values of the remaining variables represented by the -other two lines passing through this point. - - TABLE 17 - - SOLUTIONS OF PROBLEMS BY KUTTER’S FORMULA - - ─────┬───────┬────────────────────────────┬──────────────────────────── - Case │Example│ Given │ Found - ─────┼───────┼─────┬─────┬────┬────┬──────┼─────┬─────┬────┬────┬────── - │ │ _n_ │ _Q_ │_V_ │_d_ │ _S_ │ _n_ │ _Q_ │_V_ │_d_ │ _S_ - ─────┼───────┼─────┼─────┼────┼────┼──────┼─────┼─────┼────┼────┼────── - 1 │ 1 │0.015│ 1.0│ 2.5│ 6│ │ │ │5.0 │ │0.0575 - 1 │ 2 │ .015│100.0│ │ │ │ │ │8.5 │ │.0065 - 1 │ 3 │ .020│ 1.0│ │ 6│ │ │ │5.0 │ │.13 - 1 │ 4 │ .020│100.0│ │ 48│ │ │ │8.5 │ │.0125 - 2 │ 1 │ .015│ 5.0│ │ │0.0003│ │ │1.2 │28 │ - 2 │ 2 │ .010│ 5.0│ │ │.0003 │ │ │1.7 │23.5│ - 3 │ 1 │ .015│ │ │ 18│.002 │ │ 4.0│2.25│ │ - 3 │ 2 │ .018│ │ │ 18│.0008 │ │ 2.0│1.1 │ │ - 4 │ 1 │ .015│ 2.0│ 2.5│ │ │ │ │ │12 │.00475 - 4 │ 2 │ .011│ 2.0│ 2.5│ │ │ │ │ │12 │.0022 - 5 │ 1 │ .015│ │ 5.0│ 36│ │ │ 35.0│ │ │.0038 - 6 │ 1 │ .018│ │ 5.0│ │.001 │ │185.0│ │80 │ - 7 │ 1 │ │ 3.0│ │ 18│.002 │0.019│ │1.7 │ │ - 7 │ 2 │ │ 50.0│ │ 36│.005 │ .012│ │7.0 │ │ - 8 │ 1 │ │ 6.0│ 2.5│ │.003 │ .018│ │ │21 │ - 9 │ 1 │ │ │ 4.2│ 66│.00059│ .011│100.0│ │ │ - ─────┴───────┴─────┴─────┴────┴────┴──────┴─────┴─────┴────┴────┴────── - -_If n is given and is not equal to .015_ the solution is not so simple. -In Fig. 15 and 16 the diagram is so drawn that the _position_ of the -diameter scales for all values of _n_ is fixed on the vertical -“diameter” line. The _scales_ of diameter change for each value of _n_. -These scales of diameter are shown for each value of _n_ from .010 -to .020 on vertical lines to the left of the “diameter” line. For use, -the proper diameter scale for any given value of _n_ must be projected -horizontally upon the vertical “diameter” line. The velocity can be -determined on Fig. 15 and 16, _only when the diameter has been -determined_ and then _only when the diameter scale for n equal .015 is -used, since the only scale shown for velocity is for n = .015._ - - For example, in _Case 1_, _Example 3_ there are given _n_ = .020, - _Q_, and _d_. Find the intersection of the vertical line for _n_ = - .020 with the sloping diameter line for _d_ = 6 inches. Project - the intersection horizontally to the right to the vertical - “diameter” line. Place a straight-edge at this point and at _Q_ = - 1.0 on the quantity scale. The required value of _S_ is read at - the intersection of the straight-edge and the slope scale and is - equal to 0.13. The intersection of the straight-edge in this - position with the velocity scale is not the required value of the - velocity since the velocity scale is made out for _n_ = .015 and - not .020. It is necessary to change the position of the - straight-edge so that it may lie on _Q_ equal 1.0 and on _d_ equal - 6 inches for _n_ equal .015. The value of _V_ is shown in this - position as 5 feet per second. - - The reverse process for Fig. 15 and 16 is illustrated _by Case 4_, - _Example 2_ in which _n_ = .011 and _Q_ and _V_ are also given. - When _Q_ and _V_ are given the value of _d_ is fixed independent - of all other factors. Therefore the value of _d_ can be read from - the scale with _n_ = .015 and is found to be 12 inches. Now find - the value of _d_ = 12 inches on the scale for _n_ = .011 and - project on to the “diameter” line. Place the straight-edge at this - point and at _Q_ = 2. The required slope is read as .0022. - -Fig. 17 is prepared for the solution of problems in which _n_ = .015 -only. For problems in which _n_ has some other value it is necessary to -transform the data to equivalent conditions in which _n_ = .015. This is -done by means of the conversion factors shown in Fig. 18. The given -slope or velocity is multiplied by the proper factor to convert from or -to the value of _n_ = .015. - - For example in _Case 1_, _Example 4_ there are given _n_ = .020, - _Q_, and _d_. With _Q_ and _d_ given the value of _V_ can be read - from Fig. 17 without conversion. The corresponding value of _S_ - for _n_ = .015 is .0065. It is now necessary to use the - transformation diagram Fig. 18. The hydraulic radius of the given - pipe is one foot. On Fig. 18 at the intersection of the slope line - for _R_ = 1.0 foot and _n_ = .020 the value of the factor is read - as 1.92. Since the given _n_ is for rougher material than that - represented by _n_ = .015 the required slope must be greater than - for _n_ = .015 to give the same velocity. It is therefore - necessary to multiply .0065 × 1.92 and the required slope is - .0125. - - In _Case 6_, _Example 1_ there are given _n_ = .018, _d_, and _S_. - The remaining factors are to be solved by Fig. 17. Solve first as - though _n_ = .015 in order to find an approximate value of _d_ or - _R_. In this case it is evident that _d_ is greater than 57 - inches. The value of _R_ is therefore about 1.25. Referring to - Fig. 18 the conversion factor for the slope for _n_ = .018 is - about 1.52. Since the given slope for _n_ = .018 is .001, for an - equal velocity and for _n_ = .015 the slope should be less. - Therefore in reading Fig. 17 it is necessary to use a slope of - .001⁄1.52 = .00066. The diameter is found to be about 80 inches. - Since this is nearer to the correct diameter the value of the - conversion factor must be corrected for this approximation. The - hydraulic radius for an 80 inch pipe is 1.67 feet, and the - conversion factor from Fig. 18 is about 1.48. The slope for _n_ = - .015 should be therefore .001⁄1.48 = .000675 and from Fig. 17 the - required diameter and quantity are read as 80 inches and 185 - second-feet, respectively. - -_If n is not given_ but must be solved for, the solution on Fig. 15 and -16 is relatively simple. The desired value of _n_ is read at the -intersection of the sloping diameter line representing the known -diameter and the horizontal projection of the intersection of the -straight-edge with the vertical “diameter” line. - - For example in _Case 7_, _Example 1_ there are given _Q_, _d_, and - _S_. Lay the straight-edge on the given values of _Q_ = 3 and _S_ - = .002. At the point where the straight-edge crosses the vertical - “diameter” line project a horizontal line to the sloping diameter - line for _d_ = 18 inches. The vertical line passing through this - point represents a value of _n_ = .019. In order to find the value - of _V_ lay the straight-edge on _Q_ = 3 and _d_ = 18 inches for - _n_ = .015. The value of _V_ is read as 1.7. - - A slightly different condition is illustrated in the solution of - _Case 8_, _Example 1_ in which _Q_, _V_ and _S_ are given. - Determine first the value of _d_ as though _n_ = .015. Then - proceed to determine _n_ as in the preceding examples. - -The solution for an unknown value of _n_ on Fig. 17 is not so simple. It -must be determined by working backwards from the conversion factor. - - For example in _Case 7_, _Example 2_ there are given _Q_, _d_, and - _S_. The value of _V_ is read directly as though _n_ = .015 as 7 - feet per second. The value of _S_ read for _n_ = .015 is .0075. - But the given slope is .005. Since the given slope is flatter than - that for _n_ = .015 the conversion factor is less than unity and - is therefore .005⁄.0075 = 0.67. With this value of the conversion - factor and the value of _R_ given as 0.75 the value of _n_ is read - from Fig. 18 as slightly greater than .012. - - -=38. Flow in Circular Pipes Partly Full.=—The preceding examples have -involved the flow in circular pipes completely filled. The same methods -of solution can be used for pipes flowing partly full except that the -hydraulic radius of the wetted section is used instead of the diameter -of the pipe. Diagrams are used to save labor in finding the hydraulic -radius and the other hydraulic elements of conduits flowing partly full. - -The hydraulic elements of a conduit for any depth of flow are: (_a_) The -hydraulic radius, (_b_) the area, (_c_) the velocity of flow, and (_d_) -the quantity or rate of discharge. The velocity and quantity when partly -full as expressed in terms of the velocity and quantity when full as -calculated by Kutter’s formula will vary slightly with different -diameters, slopes and coefficients of roughness. The other elements are -constant for all conditions for the same type of cross-section. The -hydraulic elements for all depths of a circular section for two -different diameters and slopes are shown in Fig. 19. The differences -between the velocity and quantity under the different conditions are -shown to be slight, and in practice allowance is seldom made for this -discrepancy. - -In the solution of a problem involving part full flow in a circular -conduit the method followed is to solve the problem as though it were -for full flow conditions and then to convert to partial flow conditions -by means of Fig. 19, or to convert from partial flow conditions to full -flow conditions and solve as in the preceding section. - - For example let it be required to determine the quantity of flow - in a 12–inch diameter pipe with _n_ = .015 when on a slope of .005 - and the depth of flow is 3 inches. First find the quantity for - full flow. From Fig. 15 this is 2.0 cubic feet per second. The - depth of flow of 3 inches is one-fourth or 0.25 of the full depth - of 12 inches. From Fig. 19, running horizontally on the 0.25 depth - line to meet the quantity curve, the proportionate quantity at - this depth is found to be on the 0.13 vertical line, and the - quantity of flow is therefore 2 × 0.13 = 0.26 cubic feet per - second. - -[Illustration: - - FIG. 19.—Hydraulic Elements of Circular Sections. -] - - _d_ = 12′ 0″ _s_ = .0004 _n_ = .015 - _d_ = 1′ 0″ _s_ = .01 _n_ = .013 - -Another problem, involving the reversal of this process is illustrated -by the following example: - - Let it be required to determine the diameter and full capacity of - a vitrified pipe sewer on a grade of 0.002 if the velocity of flow - is 3.0 feet per second when the sewer is discharging at 30 per - cent of its full capacity, the depth of flow being 12 inches. From - Fig. 19 the depth of flow when the sewer is carrying 30 per cent - of its full capacity is 0.38 of its full depth. Since the partial - depth is 12 inches the full diameter is 12⁄.038 = 31.6 inches. The - velocity of flow at 38 per cent depth is 86 per cent of the full - velocity. Since the velocity given is 3.0 feet per second, the - full velocity is 3.0⁄.86 = 3.5 feet per second. With a full - velocity of 3.5 feet per second and a diameter of 31.6 inches from - Fig. 16 the full capacity of the sewer is 18 cubic feet per - second. - - -=39. Sections Other than Circular.=—The ordinary shape used for small -sewers is circular. The difficulty of constructing large sewers in a -circular shape, special conditions of construction such as small head -room, soft foundations, etc., or widely fluctuating conditions of flow -have led to the development of other shapes. For conduits flowing full -at all times a circular section will carry more water with the same loss -of head than any other section under the same conditions. In any section -the smaller the flow the slower the velocity, an undesirable condition. -The ideal section for fluctuating flows would be one that would give the -same velocity of flow for all quantities. Such a section is yet to be -developed. Sections have been developed that will give relatively higher -velocities for small quantities of flow than are given by a circular -section. The best known of these sections is the egg shape, the -proportions and hydraulic elements of which are shown in Fig. 20. Other -shapes that have the same property, but which were not developed for the -same purpose are the rectangular, the U-shape, and the section with a -cunette. The egg-shaped section has been more widely used than any other -special section. It is, however, more difficult and expensive to build -under certain conditions, and has a smaller capacity when full than a -circular sewer of the same area of cross-section. Various sections are -illustrated in Fig. 22 and 23. - -The U-shaped section is suitable where the cover is small, or close -under obstructions where a flat top is desirable and the fluctuations of -flow are so great as to make advantageous a special shape to increase -the velocity of low flows. The proportions of a U-shaped section are -shown in Fig. 23 (6). Other sections used for the same purpose are the -semicircular and special forms of the rectangular section. - -The proportions and the hydraulic elements of the square-shaped section -are shown in Fig. 21. This is useful under low heads where a flat roof -is required to carry heavy loads, and the fluctuations of flow are not -large. - -Sections with cunettes have not been standardized. A cunette is a small -channel in the bottom of a sewer to concentrate the low flows, as shown -in Fig. 22 (7). A cunette can be used in any shape of sewer. - -[Illustration: - - FIG. 20.—Hydraulic Elements of an Egg-shaped Section. - - _d_ = 6′ 0″ _s_ = .00065 _n_ = .015 -] - -[Illustration: - - FIG. 21.—Hydraulic Elements of a Square Section. - - _d_ = 10′ 0″ _s_ = .0004 _n_ = .015 -] - -Sections developed mainly because of the greater ease of construction -under certain conditions are the basket handle, the gothic, the -catenary, and the horse shoe. Some of these shapes are shown in Fig. 22 -and 23. They are suitable for large sewers on soft foundations, where it -is desirable to build the sewer in three portions, such as invert, side -walls, and arch. They are also suitable for construction in tunnels -where the shape of the sewer conforms to the shape of the timbering, or -in open cut work where the shape of the forms are easier to support. - -Problems of flow in all sections can be solved by determining the -hydraulic radius involved, and substituting directly in the desired -formula, or by the use of one of the diagrams after converting to the -equivalent circular diameter. The determination of the hydraulic radius -of these special sections is laborious, and hence other less difficult -methods are followed. Problems are more commonly solved by converting -the given data into an equivalent circular sewer, solving for the -elements of this circular sewer and then reconverting into the original -terms, or by working in the other direction. The hydraulic elements of -various sections when full are given in Table 18. - - TABLE 18 - - HYDRAULIC ELEMENTS OF SEWER SECTIONS. SEWERS FLOWING FULL. - - ───────────────┬─────────────┬─────────────┬─────────────┬────────────── - Section │Area in Terms│ Hydraulic │ Vert. Dia. │ Source - │ Vertical │ Radius in │_D_ in Terms │ - │ Diameter │ terms of │ of Dia. _d_ │ - │Squared _D_^2│Vertical Dia.│of Equivalent│ - │ │ _D_ │ Circular │ - │ │ │ Section │ - ───────────────┼─────────────┼─────────────┼─────────────┼────────────── - Circular │ 0.7854│ 0.250 │1.000 │ - Egg │ 0.5150│ .1931│1.295 │Eng. Record, - │ │ │ │ Vol. 72: 608 - Ovoid │ 0.5650│ .2070│1.208 │Eng. Record, - │ │ │ │ Vol. 72: 608 - Semi-elliptical│ 0.8176│ .2487│1.041 │Eng. News, - │ │ │ │ Vol. 71: 552 - Catenary │ 0.6625│ .2237│1.1175 │Eng. Record, - │ │ │ │ Vol. 72: 608 - Horseshoe │ 0.8472│ .2536│0.985 │Eng. Record, - │ │ │ │ Vol. 72: 608 - Basket handle │ 0.8313│ .2553│0.979 │Eng. Record, - │ │ │ │ Vol. 72: 608 - Rectangular │ 1.3125│ .2865│0.7968 │Hydraulic - │ │ │ │ Dgms. and - │ │ │ │ Tbls. - │ │ │ │ Garrett - Square (3 sides│ 1.0000│ .333 │0.7500 │Eng. Record, - wet) │ │ │ │ Vol. 72: 608 - Square (4 sides│ 1.0000│ .250 │1.0000 │Eng. Record, - wet) │ │ │ │ Vol. 72: 608 - ───────────────┴─────────────┴─────────────┴─────────────┴────────────── - -[Illustration: - - 1. Standard Egg-shaped Section, North Shore Intercepter, Chicago, - Illinois. -] - -[Illustration: - - 2. Rectangular Section, Omaha, Nebraska, Eng. Contracting, Vol. 46, p. - 49. -] - -[Illustration: - - 3. Trench in firm ground. 4. Trench in Rock. - - NOTE.—Underdrains and Wedges to be used only when Ordered by the - Engineer. -] - -[Illustration: - - 7. Brick and Concrete Sewer showing cunette. -] - -[Illustration: - - 5. Soft Foundation. 6. Wet ground. -] - -[Illustration: - - 8. Brick and Concrete Sewer, Evanston, Ill., Eng. Contracting, Vol. - 46, p. 227. -] - - FIG. 22. - -[Illustration] - - 1. Tunnel Sections. 2. Open Cut Sections. - ─────────────────────────────────────────────────────────────────────── - Type A. Type B. Type C. Type D. - Where Rock Where Rock Where Rock Where Rock 16′ 6″ Where Rock - is more is more is between drops below Sewer. 25′ is above - than 16′ than 7′ Springing Springing Fill Springing - above and less Line and 7′ Line on Line - Springing than 16′ above either - Line. above Springing Side. - Springing Line on - Line on both Sides. - both Sides. - - Mill Creek Sewer, St. Louis, Eng. Record, Vol. 70, pp. 434, 435. - -[Illustration: - - 3. Circular Concrete Section in Soft and Hard Ground, Eng. Record, - Vol. 59, p. 570. -] - -[Illustration: - - 4. Semi-Elliptical Section, Louisville, Ky., Eng. News, Vol. 62, p. - 416. -] - -[Illustration: - - 5. Reinforced Concrete Sewer, Harlem Creek, St. Louis, Eng. News, Vol. - 60, p. 131. -] - -[Illustration: - - 6. U-Shaped Section, San Francisco, Eng. News, Vol. 73, p. 310. -] - - FIG. 23. - -Equivalent sections are sections of the same capacity for the same slope -and coefficient of roughness. They have not necessarily the same -dimensions, shape, nor area. The diameter of the equivalent circular -section in terms of the diameter of each special section shown is given -in Table 18. The inside height of a sewer is spoken of as its diameter. - - For example let it be required to determine the rate of flow in a - 54–inch egg-shaped sewer on a slope of 0.001 when _n_ = .015. - First convert to the equivalent circle. From Table 18 the diameter - of the equivalent circle is 1⁄1.295 times the diameter of the - egg-shaped sewer, which becomes in this case 43 inches. From Fig. - 16 the capacity of a circular sewer of this diameter with _S_ = - 0.001 and _n_ = .015 is 28 cubic feet per second, which by - definition is the flow in the egg-shaped sewer. - - As an example of the reverse process let it be required to find - the velocity of flow in an egg-shaped sewer flowing full and - equivalent to a 48–inch circular sewer. Both sewers are on a slope - of 0.005 and have a roughness coefficient of _n_ = .015. It is - first necessary to find the quantity of flow in the circular - sewer, which by definition is the quantity of flow in the - equivalent egg-shaped sewer. The velocity of flow in the - egg-shaped sewer is found by dividing this quantity by the area of - the egg-shaped section. As read from the diagram the quantity of - flow is 90 cubic feet per second. From Table 18 the area of the - egg-shaped sewer is 0.51_D_^2 where _D_ is the diameter of the - egg-shaped sewer, and _D_ = 1.295_d_ where _d_ is the diameter of - the equivalent circular sewer. Therefore the area equals (0.51) × - (1.295 × 4)^2 = 13.5 square feet and the velocity of flow is - 90⁄13.5 = 6.7 feet per second. This is slightly less than the - velocity in the circular section. - -Some lines for egg-shaped sewers have been shown on Fig. 17 by which -solutions can be made directly. For other shapes, and for sizes of -egg-shaped sewers not found on Fig. 17 the preceding method or the -original formula must be used for solution. Problems in partial flow in -special sections are solved similarly to partial flow in circular -sections, by converting first to the conditions of full flow or by -working in the opposite direction. - - -=40. Non-uniform Flow.=—In the preceding articles it is assumed that the -mean velocity and the rate of flow past all sections are constant. This -condition is known as steady, uniform flow. In this article it will be -assumed that conditions of steady non-uniform flow exist, that is, the -rate of flow past all sections is constant, but the velocity of flow -past these sections is different for different sections. Under such -conditions the surface of the stream is not parallel to the invert of -the channel. If the velocity of flow is increasing down stream the -surface curve is known as the drop-down curve. If the velocity of flow -is decreasing down stream the surface curve is known as the backwater -curve. The hydraulic jump represents a condition of non-uniform flow in -which the velocity of flow decreases down stream in such a manner that -the surface of the stream stands normal to the invert of the channel at -the point where the change in velocity occurs. Above and below this -point conditions of uniform flow may exist. - -Conditions of non-uniform flow exist at the outlet of all sewers, except -under the unusual conditions where the depth of flow in the sewer under -conditions of steady, uniform flow with the given rate of discharge -would raise the surface of water in the sewer, at the point of -discharge, to the same elevation as the surface of the body of water -into which discharge is taking place. By an application of the -principles of non-uniform flow to the design of outfall sewers, smaller -sewers, steeper grades, greater depth of cover, and other advantages can -be obtained. - -The backwater curve is caused by an obstruction in the sewer, by a -flattening of the slope of the invert, or by allowing the sewer to -discharge into a body of water whose surface elevation would be above -the surface of the water in the sewer, at the point of discharge, under -conditions of steady, uniform flow with the given rate of discharge. - -The drop-down curve is caused by a sudden steepening of the slope of the -invert; by allowing a free discharge; or by allowing a discharge into a -body of water whose surface elevation would be below the surface of the -water in the sewer, at the point of discharge, under conditions of -steady, uniform flow with the given rate of discharge. The last -described condition is common at the outlet of many sewers, hence the -common occurrence of the drop-down curve. - -The hydraulic jump is a phenomenon which is seldom considered in sewer -design. If not guarded against it may cause trouble at overflow weirs -and at other control devices, in grit chambers, and at unexpected -places. The causes of the hydraulic jump are sufficiently well -understood to permit designs that will avoid its occurrence, but if it -is allowed to occur the exact place of the occurrence of the jump and -its height are difficult, if not impossible, to determine under the -present state of knowledge concerning them. The hydraulic jump will -occur when a high velocity of flow is interrupted by an obstruction in -the channel, by a change in grade of the invert, or the approach of the -velocity to the “critical” velocity. The “critical” velocity is equal to -√(_gh_), where _h_ is the depth of flow and _g_ is the acceleration due -to gravity. The velocity in the channel above the jump must be greater -than √(_gh__{1}), where _h__{1} is the depth of flow in the channel -above the jump. The velocity in the channel below the jump must be -greater than √(_gh__{2}), where _h__{2} is the depth of flow below the -jump. The jump will not take place unless the slope of the invert of the -channel is greater than _g_⁄_C_^2,in which _C_ is the coefficient in the -Chezy formula. With this information it is possible to avoid the jump by -slowing down the velocity by the installation of drop manholes, flight -sewers, or by other expedients. - -The shape of the drop-down curve can be expressed, in some cases, by -mathematical formulas of more or less simplicity, dependent on the shape -of the conduit. The formula for a circular conduit is complicated. Due -to the assumptions which must be made in the deduction of these -formulas, the results obtained by their use are of no greater value than -those obtained by approximate methods. A method for the determination of -the drop-down curve is given by C. D. Hill.[32] In this method it is -necessary that the rate of flow past all sections shall be the same; -that the depth of submergence at the outlet shall be known; and that the -depth of flow at some unknown distance up the stream shall be assumed. -The shape and material of construction of the sewer and the slope of the -invert should also be known. The problem is then to determine the -distance between cross-sections, one where the depth of flow is known, -and the other where the depth of flow has been assumed. This distance -can be expressed as follows: - - _L_ = ((_d__{2} − _d__{1}) − (_H__{1} − _H__{2}))⁄(_S_ − S_{1}) = (_d_′ - − _H_′)⁄_S_′, - - in which _L_ = the distance between cross-sections; - - _d__{1} = the depth of flow at the lower section; - - _d__{2} = the depth of flow at the upper section; - - _H__{1} = the velocity head at the lower section; - - _H__{2} = the velocity head at the upper section; - - _S_ = the hydraulic slope of the stream surface; - - _S__{1} = the slope of the invert of the sewer. - -In order to solve such problems with a satisfactory degree of accuracy -the difference between _d__{1} and _d__{2} should be taken sufficiently -small to divide the entire length of the sewer to be investigated into a -large number of sections. The solution of the problem requires the -determination of the wetted area, the hydraulic radius, and other -hydraulic elements at many sections. The labor involved can be -simplified by the use of diagrams, such as Fig. 19, or by specially -prepared diagrams such as those accompanying the original article by C. -D. Hill. The solution of the problem can be simplified by tabulating the -computations as follows: - - DROP-DOWN CURVE COMPUTATION SHEET - - Uniform discharge. Varying depth - - ┌───────────────────────────────────────────────────────────────────────┐ - │ _D_ = _Q_ = _A_ = _V_ = │ - │ _Q_⁄_A_ = _S__{1} = _L_ = (_d__{1} − _H__{1})⁄_S__{1} │ - ├───┬───┬───────┬───┬───┬───────┬───────┬───┬───┬───────┬───┬─────┬─────┤ - │ 1 │ 2 │ 3 │ 4 │ 5 │ 6 │ 7 │ 8 │ 9 │ 10 │11 │ 12 │ 13 │ - ├───┴───┴───────┼───┼───┼───────┼───────┼───┼───┼───────┼───┼─────┴─────┤ - │ Depth │_R_│_H_│_H__{1}│_d__{1}│_V_│_S_│_S__{1}│_L_│ Elevation │ - │ │ │ │ │ − │ │ │ │ │ │ - │ │ │ │ │_H__{1}│ │ │ │ │ │ - ├───┬───┬───────┼───┼───┼───────┼───────┼───┼───┼───────┼───┼─────┬─────┤ - │_D_│_d_│_d__{1}│ │ │ │ │ │ │ │ │Sewer│W. L.│ - ├───┼───┼───────┼───┼───┼───────┼───────┼───┼───┼───────┼───┼─────┼─────┤ - │ │ │ │ │ │ │ │ │ │ │ │ │ │ - ├───┼───┼───────┼───┼───┼───────┼───────┼───┼───┼───────┼───┼─────┼─────┤ - │ │ │ │ │ │ │ │ │ │ │ │ │ │ - ├───┼───┼───────┼───┼───┼───────┼───────┼───┼───┼───────┼───┼─────┼─────┤ - │ │ │ │ │ │ │ │ │ │ │ │ │ │ - -At the head of the computation sheet should be recorded the diameter of -the sewer in feet, the assumed volume of flow, the area of the full -cross-section of the sewer, the velocity of the assumed volume flowing -through the full bore of the sewer, and the gradient or slope of the -invert. In the 1st column enter the assumed depth in decimal parts of -the diameter for each cross-section; in the 2nd column enter the same -depth in feet; in the 3rd column enter the difference in feet between -the successive cross-sections; in the 4th column enter the hydraulic -radius corresponding to the depth at each cross-section; in the 8th -column enter the velocity, equal to the volume divided by the wetted -area, for each cross-section; in the 5th column enter the corresponding -velocity head; in the 6th column enter the difference between the -velocity heads at successive cross-sections; in the 7th column enter the -difference between the quantities in the third and in the sixth columns; -in the 9th column enter the hydraulic slope corresponding to the -velocity and hydraulic radius of each cross-section; in the 10th column -enter the difference between the hydraulic slope and the slope or -gradient of the sewer; in the 11th column enter the computed distance -between successive cross-sections; in the 12th column enter the -elevation of the bottom of the sewer at each cross-section; and in the -13th column enter the corresponding elevation of the surface of the -water. - -The table should be filled in until the distance to the required section -is determined, or if the distance is known, it should be filled in until -the depth of flow with the assumed rate of discharge has been checked. - -If only the depth of flow at some section is known and it is required to -know the maximum rate of flow with a free discharge, or a discharge with -a submergence at the outlet less than the depth of flow with the maximum -rate of discharge, it is necessary to make a preliminary estimate of the -maximum rate of flow in order to fill in the quantity _Q_ at the head of -the table. The procedure should be as follows: - - 1st. Assume a depth of flow at the outlet. - - 2nd. Compute the area (_A_) and the hydraulic radius (_R_) at the known - section and at the outlet. - - 3rd. Determine the area and the hydraulic radius half way between these - two sections as the mean of the areas and the hydraulic radii of - the two sections. - - 4th. Determine the rate of flow through the sewer from the condition - that the difference in head at the two sections is the head lost - due to friction caused by the average velocity of flow between - the sections (equals (_lV_^2)⁄(_C_^2_R_)) plus the gain in - velocity head (equals _V__{2}^2 − (_V__{1}^2)⁄(2_g_)), which - then combined and transposed result in the expression: - - _Q_ = _AA__{1}_A__{2} √(2_Rgh_⁄(2_A__{1}^2_A__{2}^2_gl_ + (_A__{1} - − _A__{2})(_A_^2_C_^2_R_))) - - - - in which _Q_ = rate of flow; - - _A_ = the area determined in the 3rd step; - - _A__{1} = the area at the upper cross-section; - - _A__{2} = the area at the lower cross-section; - - _C_ = the coefficient in the Chezy formula; - - _g_ = the acceleration due to gravity; - - _h_ = the difference in elevation of the surface of the - stream at the two cross-sections; - - _l_ = the distance between the cross-sections; - - _R_ = the hydraulic radius determined in the third step. - - 5th. Continue this process by assuming different depths at the outlet - until the maximum rate of discharge has been found by trial. - -With this rate of discharge and depth of flow at the outlet, the depth -of flow at the known section can be checked. If appreciably in error a -correction should be made by the assumption of a different depth of flow -at the outlet. The approximate character of the method is scarcely -worthy of the refinement in the results which will be obtained by -checking back for the depth of flow at the known section. It will be -sufficiently accurate to assume the rate of flow obtained by trial from -the preceding expression, as the maximum rate of discharge from the -sewer. - - - - - CHAPTER V - DESIGN OF SEWERAGE SYSTEMS - - -=41. The Plan.=—Good practice demands that a comprehensive plan for a -sewerage system be provided for the needs of a community for the entire -extent of its probable future growth, and that sewers be constructed as -needed in accordance with this plan. - -Sewerage systems may be laid out on any one of three systems: separate, -storm, or combined. A separate system of sewers is one in which only -sanitary sewage or industrial wastes or both are allowed to flow. Storm -sewers carry only surface drainage, exclusive of sanitary sewage. -Combined sewers carry both sanitary and storm sewage. The use of a -combined or a separate system of sewerage is a question of expediency. -Portions of the same system may be either separate, combined, or storm -sewers. - -Some conditions favorable to the adoption of the separate system are -where: - - _a._ The sanitary sewage must be concentrated at one outlet, such - as at a treatment plant, and other outlets are available for the - storm drainage. - - _b._ The topography is flat necessitating deep excavation and - steeper grades for the larger combined sewers. - - _c._ The sanitary sewers must be placed materially deeper than the - necessary depth for the storm-water drains. - - _d._ The sewers are to be laid in rock, necessitating more - difficult excavation for the larger combined sewers. - - _e._ An existing sewerage system can be used to convey the dry - weather flow, but is not large enough for the storm sewage. - - _f._ The city finances are such that the greater cost of the - combined system cannot be met and sanitary drainage is imperative. - - _g._ The district to be sewered is an old residential section - where property values are not increasing and the assessment must - be kept down. - -Some additional points given in a report by Alvord and Burdick to the -city of Billings, Montana, are: - -The separate system of sewerage should be used, where: - - 1st. Storm water does not require extensive underground removal, - or where it can be concentrated in a few shallow underground - channels. - - 2nd. Drainage areas are short and steep facilitating rapid flow of - water over street surfaces to the natural water courses. - - 3rd. The sanitary sewage must be pumped. - - 4th. Sewers are being built in advance of the city’s development - to encourage its growth. - - 5th. The existing sewer is laid at grades unsuitable for sanitary - sewage, it can be used as a storm sewer. - - A combined system must be relatively larger than a separate storm - sewer as the latter may overflow on exceptional occasions, but the - former never. - - - A combined system of sewerage should be used where: - - 1st. It is evident that storm and sanitary sewerage must be - provided soon. - - 2nd. Both sanitary and storm sewage must be pumped. - - 3rd. The district is densely built up. - - -=42. Preliminary Map.=—The first step in the design of a sewerage system -is the preparation of a map of the district to be served within the -limits of its probable growth. The map should be on a scale of at least -200 feet to the inch in the built up sections or other areas where it is -anticipated that sewers may be built, and where much detail is to be -shown a scale as large as 40 feet to the inch may have to be used. The -adoption of so large a scale will usually necessitate the division of -the city or sewer district into sections. A key map should be drawn to -such a scale that the various sections represented by separate drawings -can all be shown upon it. In preparing the enlarged portions of the map -it is not necessary to include these portions of the city in which it is -improbable that sewers will be constructed, such as parks and -cemeteries. - -The contour interval should depend on the character of the district and -the slope of the land. In those sections drawn to a scale of 200 feet to -the inch for slopes over 5 per cent, the contour interval need not be -closer than 10 feet. For slopes between 1 and 5 per cent the contour -interval should be 5 feet. For flatter slopes the interval should not -exceed 2 feet, and a one foot interval is sometimes desirable. In -general the horizontal distances between contours should not exceed 400 -feet and they should be close enough to show important features of the -natural drainage. Elevations should also be given at street -intersections, and at abrupt changes in grade. For portions of the map -on a smaller scale the contours need be sufficiently close to show only -the drainage lines and the general slope of the land. - -The following may be shown on the preliminary map: the elevation of lots -and cellars; the character of the built up districts, whether cheap -frame residences, flat-roof buildings, manufacturing plants, etc.; -property lines; width of streets between property lines and between curb -lines; the width and character of the sidewalks and pavements; street -car and railroad tracks; existing underground structures such as sewers, -water pipes, telephone conduits, etc.; the location of important -structures which may have a bearing on the design of the sewers such as -bridges, railroad tunnels, deep cuts, culverts, etc.; and the location -of possible sewer outlets and the sites for sewage disposal plants. - -Fig. 24 shows a preliminary map for a section of a city, on which the -necessary information has been entered. The map is made from survey -notes. All streets are paved with brick. The alleys are unpaved. The -entire section is built up with high-class detached residences averaging -one to each lot. The lots vary from 1 to 3 feet above the elevation of -the street. - - -=43. Layout of the Separate System.=—Upon completion of the preliminary -map a tentative plan of the system is laid out. The lines of the sewer -pipe are drawn in pencil, usually along the center line of the street or -alley in such a manner that a sewer will be provided within 50 feet or -less of every lot. The location of the sewers should be such as to give -the most desirable combination of low cost, short house connections, -proper depth for cellar drainage, and avoidance of paved streets. Some -dispute arises among engineers as to the advisability of placing pipes -in alleys, although there is less opposition to so placing sewers than -any other utility conduit. The principal advantage in placing sewers in -alleys is to avoid disturbing the pavement of the street, but if both -street and alley are paved it is usually more economical to place the -sewer in the street as the house connections will be shorter. On -boulevards and other wide streets such as Meridian Avenue in Fig. 24, -the sewers are placed in the parking on each side of the street, rather -than to disturb the pavement and lay long house connections to the -center of the street. - -All pipes should be made to slope, where possible, in the direction of -the natural slope of the ground. The preliminary layout of the system is -shown in Fig. 24. The lowest point in the portion of the system shown is -in the alley between Alabama and Tennessee Streets. The flow in all -pipes is towards this point, and only one pipe drains away from any -junction, except that more than one pipe may drain from a terminal -manhole on a summit. - - -=44. Location and Numbering of Manholes.=—Manholes are next located on -the pipes of this tentative layout. Good practice calls for the location -of a manhole at every change in direction, grade, elevation, or size of -pipe, except in sewers 60 inches in diameter or larger. The manholes -should not be more than 300 to 500 feet apart, and preferably as close -as 200 to 300 feet. In sewers too small for a man to enter the distance -is fixed by the length of sewer rods which can be worked successfully. -In the larger sewers the distances are sometimes made greater but -inadvisedly so, since quick means of escape should be provided for -workmen from a sudden rise of water in the sewer, or the effect of an -asphyxiating gas. In the preliminary layout the manholes are located at -pipe intersections, changes in direction, and not over 300 to 500 feet -apart on long straight runs at convenient points such as opposite street -intersections where other sewers may enter. - -No standard system of manhole numbering has been adopted. A system which -avoids confusion and is subject to unlimited extension is to number the -manholes consecutively upwards from the outlet, beginning a new series -of numbers prefixed by some index number or letter for each branch or -lateral. This system has been followed with the manholes on Fig. 24. - -[Illustration: - - FIG. 24.—Typical Map Used in the Design of a Separate Sewer System. -] - -[Illustration: - - FIG. 25.—Typical Map Used in the Design of a Storm Sewer System. -] - - -=45. Drainage Areas.=—The quantity of dry weather sewage is determined -by the population rather than the topography. Lot lines and street -intersections or other artificial lines marking the boundaries between -districts are therefore taken as watershed lines for sanitary sewers. -The quantity of sewage to be carried and the available slope are the -determining factors in fixing the diameter of the sewer. Since there may -be no change in diameter or slope between manholes the quantity of -sewage delivered by a sewer into any manhole will determine the diameter -of the sewer between it and the next manhole above. In order to -determine the additional amount contributed between manholes a line is -drawn around the drainage area tributary to each manhole. This line -generally follows property lines and the center lines of streets or -alleys, its position being such that it includes all the area draining -into one manhole, and excludes all areas draining elsewhere. An entire -lot is usually assumed to lie within the drainage area into which the -building on the lot drains. In laying out these areas it is best to -commence at the upper end of a lateral and work down to a junction. Then -start again at the upper end of another lateral entering this junction, -and continue thus until the map has been covered. - -The areas are given the same numbers as the manholes into which they -drain. The dividing lines for the drainage areas on Fig. 24 are shown as -dot and dash lines, and the areas enclosed are appropriately numbered. -If more than one sewer drains into the same manhole the area should be -subdivided so that each subdivision encloses only the area contributing -through one sewer. Such a condition is shown at manhole _C_2. The areas -are designated by subletters or symbols corresponding to the symbol used -for the sewer into which they drain. For example, the two areas -contributing to manhole _C_2 are lettered _C_2_{_K_} and _C_2_{_D_}. The -sewer from manhole _C_3 to _C_2 receives no addition, it being assumed -that all the lots adjacent to it drain into the sewer on the alley. -There is therefore no area _C_2. Likewise there is no area _A_1_{_C_}. - - -=46. Quantity of Sewage.=—The remaining work in the computation of the -quantity of sewage is best kept in order by a tabulation. Table 19 shows -the computations for the sewers discharging from the east into manhole -No. 142. The computation should begin at the upper end of a lateral, -continue to a junction, and then start again at the upper end of another -lateral entering this junction. Each line in the table should be filled -in completely from left to right before proceeding with the computations -on the next line. In the illustrative solution in Table 19, computations -for quantity have not been made between manholes where it was apparent -that there would be an insufficient additional quantity to necessitate a -change in the size of the pipe. - -In making these computations the assumptions of quantity and other -factors given below indicate the sort of assumptions which must be made, -based on such studies as are given in Chapter III. The density of -population was taken as 20 persons per acre, the assumption being based -on the census and the character of the district. The average sanitary -sewage flow was taken as 100 gallons per capita per day. The per cent -which the maximum dry weather flow is of the average was taken as _M_ = -500⁄_P_^⅕, in which _P_ is the population in thousands. The per cent is -not to exceed 500 nor to be less than 150. The rate of infiltration of -ground water was assumed as 50,000 gallons per mile of pipe per day. - -In the first line of Table 19, the entries in columns (1) to (6) are -self-explanatory. There are no entries in columns (7) to (10), as no -additional sewage is contributed between manholes 3.5 and 3.4. In column -(11), 2250 persons are recorded as the number tributary to manhole No. -3.5 in the district to the north and west. These people contribute an -average of 100 gallons per person per day, or a total of 0.346 second -foot. This quantity is entered in column (13). The figure in column (14) -is obtained from the expression _M_ = (500)⁄_P_^⅕. Column (15) is .01 of -the product of columns (13) and (14). Column (16) is the product of the -length of pipe between manholes 3.5 and 3.4, and the ground water unit -reduced to cubic feet per second. Column (17) is the sum of column (16), -and all of the ground water tributary to manhole 3.5, which is not -recorded in the table. Column (18) is the sum of columns (15) and (17). - -No new principle is represented in the second and third lines. - -In the fourth line the first 10 columns need no further explanation. The -(11th) column is the sum of the (10th) column, and the (11th) column in -the third line. It represents the total number of persons tributary to -manhole 3.4 on lateral No. 8. Column (13) in the fourth line is the sum -of column (13) in the third line and the (12th) column in the fourth -line, and the (15th) column in the fourth line is the product of the 2 -preceding columns in the fourth line. Note that in no case is the figure -in column (15) the sum of any previous figures in column (15). With this -introduction the student should be able to check the remaining figures -in the table, and should compute the quantity of sewage entering manhole -No. 142 from the west, making reasonable assumptions for the tributary -quantities from beyond the limits of the map. - - TABLE 19 - - COMPUTATIONS FOR QUANTITY OF SEWAGE FOR A SEPARATE SEWERAGE SYSTEM - - ──────────┬──────────┬──────────┬───────┬───────┬──────┬───────┬───── - On Street │ From │To Street │ From │ To │Length│Mark of│Area, - │ Street │ │Manhole│Manhole│ Feet │ Added │Acres - │ │ │ │ │ │ Areas │ - │ │ │ │ │ │ │ - │ │ │ │ │ │ │ - ──────────┼──────────┼──────────┼───────┼───────┼──────┼───────┼───── - Nebraska │Map margin│Alley S. │ 3.5│ 3.4│ 338│ │ - St. │ │ Grant │ │ │ │ │ - │ │ St. │ │ │ │ │ - Alley S. │Railroad │E. of │ 8.3│ 8.2│ 328│ 8.2│ 2.7 - of Grant│ │ Missouri│ │ │ │ │ - St. │ │ St. │ │ │ │ │ - Alley S. │E. of │E. of │ 8.2│ 8.1│ 355│ 8.1│ 3.41 - of Grant│ Missouri│ Kansas │ │ │ │ │ - St. │ St. │ St. │ │ │ │ │ - Alley S. │E. of │Nebraska │ 8.1│ 3.4│ 340│3.4_{8}│ 2.68 - of Grant│ Kansas │ St. │ │ │ │ │ - St. │ St. │ │ │ │ │ │ - Nebraska │Alley S. │Alley S. │ 3.4│ 3.3│ 380│ │ - St. │ of Grant│ of │ │ │ │ │ - │ St. │ Meridian│ │ │ │ │ - │ │ │ │ │ │ 7.1│ - Alley S. │Railroad │Nebraska │ 7.2│ 3.3│ 800│3.3_{7}│ 7.14 - of │ │ St. │ │ │ │ │ - Meridian│ │ │ │ │ │ │ - Nebraska │Alley S. │Alley S. │ 3.3│ 3.2│ 304│ │ - St. │ of │ of Smith│ │ │ │ │ - │ Meridian│ Av. │ │ │ │ │ - │ │ │ │ │ │ 6.1│ - Alley S. │Railroad │Nebraska │ 6.2│ 3.2│ 609│3.2_{6}│ 3.82 - of Smith│ │ St. │ │ │ │ │ - Ave. │ │ │ │ │ │ │ - Nebraska │Alley S. │S. of │ 3.2│ 3.1│ 300│ │ - St. │ of Smith│ Cordovez│ │ │ │ │ - │ Ave. │ St. │ │ │ │ │ - S. of │Railroad │Nebraska │ 4.1│ 3.1│ 410│3.1_{4}│ 3.10 - Cordovez│ │ St. │ │ │ │ │ - St. │ │ │ │ │ │ │ - S. of │Map margin│Nebraska │ 5.1│ 3.1│ 380│3.1_{5}│ 2.69 - Cordovez│ │ St. │ │ │ │ │ - St. │ │ │ │ │ │ │ - Nebraska │S. of │Long St. │ 3.1│ 148│ 172│ │ - St. │ Cordovez│ │ │ │ │ │ - │ St. │ │ │ │ │ │ - Long St. │Map margin│Nebraska │ 149│ 148│ 380│ 148│ 1.53 - │ │ St. │ │ │ │ │ - Long St. │Nebraska │N. │ 148│ 147│ 492│ │ - │ St. │ Carolina│ │ │ │ │ - │ │ St. │ │ │ │ │ - Long St. │N. │Georgia │ 147│ 146│ 430│ │ - │ Carolina│ St. │ │ │ │ │ - │ St. │ │ │ │ │ │ - Long St. │Georgia │Harris St.│ 146│ 145│ 419│ 146│ 0.81 - │ St. │ │ │ │ │ │ - │ │ │ │ │ │ 2.1│ - Long St. │Harris St.│Tennessee │ 145│ 143│ 725│143–145│ 6.6 - │ │ St. │ │ │ │ │ - │ │ │ │ │ │ │ - Column No.│ (2) │ (3) │ (4) │ (5) │ (6) │ (7) │ (8) - (1) │ │ │ │ │ │ │ - ──────────┴──────────┴──────────┴───────┴───────┴──────┴───────┴───── - - ──────────┬──────────┬──────────┬──────────┬───────┬─────────┬───────── - On Street │ From │To Street │Population│Number │ Total │ Avg. - │ Street │ │ per Acre │ of │ Persons │Sanitary - │ │ │ │Persons│Tributary│ Flow, - │ │ │ │ │ │ C.F.S. - │ │ │ │ │ │ - ──────────┼──────────┼──────────┼──────────┼───────┼─────────┼───────── - Nebraska │Map margin│Alley S. │ │ │ 2250│ 0.0000 - St. │ │ Grant │ │ │ │ - │ │ St. │ │ │ │ - Alley S. │Railroad │E. of │ 20│ 54│ 54│ .0084 - of Grant│ │ Missouri│ │ │ │ - St. │ │ St. │ │ │ │ - Alley S. │E. of │E. of │ 20│ 68│ 122│ .0106 - of Grant│ Missouri│ Kansas │ │ │ │ - St. │ St. │ St. │ │ │ │ - Alley S. │E. of │Nebraska │ 20│ 54│ 176│ .0084 - of Grant│ Kansas │ St. │ │ │ │ - St. │ St. │ │ │ │ │ - Nebraska │Alley S. │Alley S. │ │ │ 2428│ .0000 - St. │ of Grant│ of │ │ │ │ - │ St. │ Meridian│ │ │ │ - │ │ │ │ │ │ - Alley S. │Railroad │Nebraska │ 20│ 142│ 142│ .0221 - of │ │ St. │ │ │ │ - Meridian│ │ │ │ │ │ - Nebraska │Alley S. │Alley S. │ │ │ 2568│ .0000 - St. │ of │ of Smith│ │ │ │ - │ Meridian│ Av. │ │ │ │ - │ │ │ │ │ │ - Alley S. │Railroad │Nebraska │ 20│ 76│ 76│ .0119 - of Smith│ │ St. │ │ │ │ - Ave. │ │ │ │ │ │ - Nebraska │Alley S. │S. of │ │ │ 2644│ .0000 - St. │ of Smith│ Cordovez│ │ │ │ - │ Ave. │ St. │ │ │ │ - S. of │Railroad │Nebraska │ 20│ 62│ 62│ .0096 - Cordovez│ │ St. │ │ │ │ - St. │ │ │ │ │ │ - S. of │Map margin│Nebraska │ 20│ 54│ 54│ .0084 - Cordovez│ │ St. │ │ │ │ - St. │ │ │ │ │ │ - Nebraska │S. of │Long St. │ │ │ 2760│ .0000 - St. │ Cordovez│ │ │ │ │ - │ St. │ │ │ │ │ - Long St. │Map margin│Nebraska │ 20│ 31│ 31│ .0048 - │ │ St. │ │ │ │ - Long St. │Nebraska │N. │ │ │ 2791│ .0000 - │ St. │ Carolina│ │ │ │ - │ │ St. │ │ │ │ - Long St. │N. │Georgia │ │ │ 2791│1.000[33] - │ Carolina│ St. │ │ │ │ - │ St. │ │ │ │ │ - Long St. │Georgia │Harris St.│ 20│ 16│ 2807│ .0025 - │ St. │ │ │ │ │ - │ │ │ │ │ │ - Long St. │Harris St.│Tennessee │ 20│ 132│ 2936│ .0205 - │ │ St. │ │ │ │ - │ │ │ │ │ │ - Column No.│ (2) │ (3) │ (9) │ (10) │ (11) │ (12) - (1) │ │ │ │ │ │ - ──────────┴──────────┴──────────┴──────────┴───────┴─────────┴───────── - - ──────────┬──────────┬──────────┬──────────┬────────┬───────── - On Street │ From │To Street │Cumulative│Per cent│ Total - │ Street │ │ Avg. │ Max. │ Max. - │ │ │ Sanitary │Sanitary│Sanitary, - │ │ │ Flow, │ is of │ C.F.S. - │ │ │ C.F.S. │Average │ - ──────────┼──────────┼──────────┼──────────┼────────┼───────── - Nebraska │Map margin│Alley S. │ 0.346│ 425│ 1.47 - St. │ │ Grant │ │ │ - │ │ St. │ │ │ - Alley S. │Railroad │E. of │ .0084│ 500│ 0.041 - of Grant│ │ Missouri│ │ │ - St. │ │ St. │ │ │ - Alley S. │E. of │E. of │ .0190│ 500│ 0.095 - of Grant│ Missouri│ Kansas │ │ │ - St. │ St. │ St. │ │ │ - Alley S. │E. of │Nebraska │ .0274│ 500│ 0.137 - of Grant│ Kansas │ St. │ │ │ - St. │ St. │ │ │ │ - Nebraska │Alley S. │Alley S. │ .373│ 423│ 1.58 - St. │ of Grant│ of │ │ │ - │ St. │ Meridian│ │ │ - │ │ │ │ │ - Alley S. │Railroad │Nebraska │ .0221│ 500│ 0.111 - of │ │ St. │ │ │ - Meridian│ │ │ │ │ - Nebraska │Alley S. │Alley S. │ .395│ 414│ 1.63 - St. │ of │ of Smith│ │ │ - │ Meridian│ Av. │ │ │ - │ │ │ │ │ - Alley S. │Railroad │Nebraska │ .0119│ 500│ 0.060 - of Smith│ │ St. │ │ │ - Ave. │ │ │ │ │ - Nebraska │Alley S. │S. of │ .407│ 414│ 1.68 - St. │ of Smith│ Cordovez│ │ │ - │ Ave. │ St. │ │ │ - S. of │Railroad │Nebraska │ .0096│ 500│ 0.048 - Cordovez│ │ St. │ │ │ - St. │ │ │ │ │ - S. of │Map margin│Nebraska │ .0084│ 500│ 0.042 - Cordovez│ │ St. │ │ │ - St. │ │ │ │ │ - Nebraska │S. of │Long St. │ .425│ 409│ 1.74 - St. │ Cordovez│ │ │ │ - │ St. │ │ │ │ - Long St. │Map margin│Nebraska │ .0048│ 500│ 0.024 - │ │ St. │ │ │ - Long St. │Nebraska │N. │ .430│ 409│ 1.76 - │ St. │ Carolina│ │ │ - │ │ St. │ │ │ - Long St. │N. │Georgia │ .430│ 409│ 1.76 - │ Carolina│ St. │ │ │ - │ St. │ │ │ │ - Long St. │Georgia │Harris St.│ .433│ 407│ 1.76 - │ St. │ │ │ │ - │ │ │ │ │ - Long St. │Harris St.│Tennessee │ .454│ 403│ 1.83 - │ │ St. │ │ │ - │ │ │ │ │ - Column No.│ (2) │ (3) │ (13) │ (14) │ (15) - (1) │ │ │ │ │ - ──────────┴──────────┴──────────┴──────────┴────────┴───────── - - ──────────┬──────────┬──────────┬─────────┬──────────┬──────┬────── - On Street │ From │To Street │Increment│Cumulative│Total │ Line - │ Street │ │of Ground│ Ground │Flow, │Number - │ │ │ Water, │ Water, │C.F.S.│ - │ │ │ C.F.S. │ C.F.S. │ │ - │ │ │ │ │ │ - ──────────┼──────────┼──────────┼─────────┼──────────┼──────┼────── - Nebraska │Map margin│Alley S. │ 0.005│ 0.0187│ 1.66│ 1 - St. │ │ Grant │ │ │ │ - │ │ St. │ │ │ │ - Alley S. │Railroad │E. of │ .0048│ .0048│ 0.046│ 2 - of Grant│ │ Missouri│ │ │ │ - St. │ │ St. │ │ │ │ - Alley S. │E. of │E. of │ .0052│ .010│ 0.105│ 3 - of Grant│ Missouri│ Kansas │ │ │ │ - St. │ St. │ St. │ │ │ │ - Alley S. │E. of │Nebraska │ .0050│ .015│ 0.152│ 4 - of Grant│ Kansas │ St. │ │ │ │ - St. │ St. │ │ │ │ │ - Nebraska │Alley S. │Alley S. │ .0058│ .208│ 1.79│ 5 - St. │ of Grant│ of │ │ │ │ - │ St. │ Meridian│ │ │ │ - │ │ │ │ │ │ - Alley S. │Railroad │Nebraska │ .0117│ .0117│ 0.123│ 6 - of │ │ St. │ │ │ │ - Meridian│ │ │ │ │ │ - Nebraska │Alley S. │Alley S. │ .0045│ .224│ 1.85│ 7 - St. │ of │ of Smith│ │ │ │ - │ Meridian│ Av. │ │ │ │ - │ │ │ │ │ │ - Alley S. │Railroad │Nebraska │ .0089│ .0089│ 0.069│ 8 - of Smith│ │ St. │ │ │ │ - Ave. │ │ │ │ │ │ - Nebraska │Alley S. │S. of │ .0044│ .237│ 1.92│ 9 - St. │ of Smith│ Cordovez│ │ │ │ - │ Ave. │ St. │ │ │ │ - S. of │Railroad │Nebraska │ .006│ .006│ 0.054│ 10 - Cordovez│ │ St. │ │ │ │ - St. │ │ │ │ │ │ - S. of │Map margin│Nebraska │ .0056│ .0056│ 0.048│ 11 - Cordovez│ │ St. │ │ │ │ - St. │ │ │ │ │ │ - Nebraska │S. of │Long St. │ .0025│ .251│ 1.99│ 12 - St. │ Cordovez│ │ │ │ │ - │ St. │ │ │ │ │ - Long St. │Map margin│Nebraska │ .0056│ .0056│ 0.030│ 13 - │ │ St. │ │ │ │ - Long St. │Nebraska │N. │ .0072│ .264│ 2.02│ 14 - │ St. │ Carolina│ │ │ │ - │ │ St. │ │ │ │ - Long St. │N. │Georgia │ .0064│ 1.27│ 3.03│ 15 - │ Carolina│ St. │ │ │ │ - │ St. │ │ │ │ │ - Long St. │Georgia │Harris St.│ .0061│ 1.28│ 3.04│ 16 - │ St. │ │ │ │ │ - │ │ │ │ │ │ - Long St. │Harris St.│Tennessee │ .024│ 1.30│ 3.13│ 17 - │ │ St. │ │ │ │ - │ │ │ │ │ │ - Column No.│ (2) │ (3) │ (16) │ (17) │ (18) │ - (1) │ │ │ │ │ │ - ──────────┴──────────┴──────────┴─────────┴──────────┴──────┴────── - TABLE 20 - - COMPUTATIONS FOR SLOPE AND DIAMETER OF PIPES FOR A SEPARATE SEWERAGE - SYSTEM - - ──────────┬──────────┬──────────┬───────┬───────┬──────┬─────────────── - On Street │ From │To Street │ From │ To │Length│El. of Surface - │ Street │ │Manhole│Manhole│ Feet │ - │ │ │ │ │ │ - │ │ │ │ │ │ - │ │ │ │ │ │ - ──────────┼──────────┼──────────┼───────┼───────┼──────┼───────┬─────── - │ │ │ │ │ │ Upper │ Lower - │ │ │ │ │ │Manhole│Manhole - ──────────┼──────────┼──────────┼───────┼───────┼──────┼───────┼─────── - Nebraska │Map margin│Alley S. │ 3.5│ 3.4│ 338│ 105.8│ 102.4 - St. │ │ Grant │ │ │ │ │ - │ │ St. │ │ │ │ │ - Alley S. │Railroad │E. of │ 8.3│ 8.2│ 328│ 113.5│ 112.0 - of Grant│ │ Missouri│ │ │ │ │ - St. │ │ St. │ │ │ │ │ - Alley S. │E. of │E. of │ 8.2│ 8.1│ 355│ 112.0│ 107.7 - of Grant│ Missouri│ Kansas │ │ │ │ │ - St. │ St. │ St. │ │ │ │ │ - Alley S. │E. of │Nebraska │ 8.1│ 3.4│ 340│ 107.7│ 102.4 - of Grant│ Kansas │ St. │ │ │ │ │ - St. │ St. │ │ │ │ │ │ - Nebraska │Alley S. │Alley S. │ 3.4│ 3.3│ 380│ 102.4│ 100.7 - St. │ of Grant│ of │ │ │ │ │ - │ St. │ Meridian│ │ │ │ │ - Alley S. │Railroad │Kansas St.│ 7.2│ 7.1│ 400│ 111.8│ 107.0 - of │ │ │ │ │ │ │ - Meridian│ │ │ │ │ │ │ - Alley S. │Kansas St.│Nebraska │ 7.1│ 3.3│ 400│ 107.0│ 100.7 - of │ │ St. │ │ │ │ │ - Meridian│ │ │ │ │ │ │ - Nebraska │Alley S. │Alley S. │ 3.3│ 3.2│ 304│ 100.7│ 99.3 - St. │ of │ of Smith│ │ │ │ │ - │ Meridian│ Av. │ │ │ │ │ - Alley S. │Railroad │East of │ 6.2│ 6.1│ 305│ 109.3│ 105.3 - of Smith│ │ Kansas │ │ │ │ │ - Ave. │ │ St. │ │ │ │ │ - Alley S. │East of │Nebraska │ 6.1│ 3.2│ 304│ 105.3│ 99.3 - of Smith│ Kansas │ St. │ │ │ │ │ - Ave. │ St. │ │ │ │ │ │ - Nebraska │Alley S. │S. of │ 3.2│ 3.1│ 300│ 99.3│ 101.1 - St. │ of Smith│ Cordovez│ │ │ │ │ - │ Ave. │ St. │ │ │ │ │ - S. of │Railroad │Nebraska │ 4.1│ 3.1│ 410│ 100.8│ 101.1 - Cordovez│ │ St. │ │ │ │ │ - St. │ │ │ │ │ │ │ - S. of │Map margin│Nebraska │ 5.1│ 3.1│ 380│ 104.6│ 101.1 - Cordovez│ │ St. │ │ │ │ │ - St. │ │ │ │ │ │ │ - Nebraska │S. of │Long St. │ 3.1│ 148│ 172│ 101.1│ 98.7 - St. │ Cordovez│ │ │ │ │ │ - │ St. │ │ │ │ │ │ - Long St. │Map margin│Nebraska │ 149│ 148│ 380│ 103.8│ 98.7 - │ │ St. │ │ │ │ │ - Long St. │Nebraska │N. │ 148│ 147│ 492│ 98.7│ 103.8 - │ St. │ Carolina│ │ │ │ │ - │ │ St. │ │ │ │ │ - Long St. │N. │Georgia │ 147│ 146│ 430│ 103.8│ 99.1 - │ Carolina│ St. │ │ │ │ │ - │ St. │ │ │ │ │ │ - Long St. │Georgia │Harris St.│ 146│ 145│ 419│ 99.1│ 96.9 - │ St. │ │ │ │ │ │ - Alley S. │End of │Harris St.│ 2.2│ 2.1│ 350│ 105.2│ 98.1 - of Janis│ Janis │ │ │ │ │ │ - St. │ St. │ │ │ │ │ │ - Harris St.│Alley N. │Long St. │ 2.1│ 145│ 135│ 98.1│ 96.9 - │ of Janis│ │ │ │ │ │ - │ St. │ │ │ │ │ │ - Long St. │Harris St.│Kentucky │ 145│ 144│ 258│ 96.9│ 94.4 - │ │ St. │ │ │ │ │ - Long St. │Kentucky │Tennessee │ 144│ 143│ 282│ 94.4│ 93.6 - │ St. │ St. │ │ │ │ │ - Tarbell │Harris St.│Long St. │ 1.1│ 143│ 417│ 98.7│ 92.6 - Ave. │ │ │ │ │ │ │ - Long St. │Tennessee │Alley W. │ 143│ 142│ 185│ 92.6│ 92.3 - │ St. │ of Tenn.│ │ │ │ │ - │ │ St. │ │ │ │ │ - │ │ │ │ │ │ │ - Column No.│ (2) │ (3) │ (4) │ (5) │ (6) │ (7) │ (8) - (1) │ │ │ │ │ │ │ - ──────────┴──────────┴──────────┴───────┴───────┴──────┴───────┴─────── - - ──────────┬──────────┬──────────┬──────┬──────┬──────┬────────┬──────── - On Street │ From │To Street │Total │Slope │ Dia. │Velocity│Capacity - │ Street │ │Flow, │ │ of │ when │ when - │ │ │C.F.S.│ │Pipe, │ Full, │ Full, - │ │ │ │ │Inches│Ft. per │ Second - │ │ │ │ │ │ Second │ Feet - ──────────┼──────────┼──────────┼──────┼──────┼──────┼────────┼──────── - │ │ │ │ │ │ │ - │ │ │ │ │ │ │ - ──────────┼──────────┼──────────┼──────┼──────┼──────┼────────┼──────── - Nebraska │Map margin│Alley S. │ 1.66│0.0108│ 10│ 3.25│ 1.78 - St. │ │ Grant │ │ │ │ │ - │ │ St. │ │ │ │ │ - Alley S. │Railroad │E. of │ 0.046│.00575│ 8│ 2.00│ 0.71 - of Grant│ │ Missouri│ │ │ │ │ - St. │ │ St. │ │ │ │ │ - Alley S. │E. of │E. of │ 0.105│ .0110│ 8│ 2.78│ 0.98 - of Grant│ Missouri│ Kansas │ │ │ │ │ - St. │ St. │ St. │ │ │ │ │ - Alley S. │E. of │Nebraska │ 0.152│ .0156│ 8│ 3.27│ 1.18 - of Grant│ Kansas │ St. │ │ │ │ │ - St. │ St. │ │ │ │ │ │ - Nebraska │Alley S. │Alley S. │ 1.79│.00385│ 12│ 2.28│ 1.79 - St. │ of Grant│ of │ │ │ │ │ - │ St. │ Meridian│ │ │ │ │ - Alley S. │Railroad │Kansas St.│ │ .0120│ 8│ 2.90│ 1.03 - of │ │ │ │ │ │ │ - Meridian│ │ │ │ │ │ │ - Alley S. │Kansas St.│Nebraska │ 0.123│ .0157│ 8│ 3.28│ 1.18 - of │ │ St. │ │ │ │ │ - Meridian│ │ │ │ │ │ │ - Nebraska │Alley S. │Alley S. │ 1.85│ .0042│ 12│ 2.36│ 1.85 - St. │ of │ of Smith│ │ │ │ │ - │ Meridian│ Av. │ │ │ │ │ - Alley S. │Railroad │East of │ │ .0131│ 8│ 3.00│ 1.08 - of Smith│ │ Kansas │ │ │ │ │ - Ave. │ │ St. │ │ │ │ │ - Alley S. │East of │Nebraska │ 0.069│ .0197│ 8│ 3.70│ 1.32 - of Smith│ Kansas │ St. │ │ │ │ │ - Ave. │ St. │ │ │ │ │ │ - Nebraska │Alley S. │S. of │ 1.92│.00213│ 15│ 2.00│ 2.45 - St. │ of Smith│ Cordovez│ │ │ │ │ - │ Ave. │ St. │ │ │ │ │ - S. of │Railroad │Nebraska │ │.00574│ 8│ 2.00│ 0.71 - Cordovez│ │ St. │ │ │ │ │ - St. │ │ │ │ │ │ │ - S. of │Map margin│Nebraska │ 0.054│.00854│ 8│ 2.46│ 0.87 - Cordovez│ │ St. │ │ │ │ │ - St. │ │ │ │ │ │ │ - Nebraska │S. of │Long St. │ 1.99│.00213│ 15│ 2.00│ 2.45 - St. │ Cordovez│ │ │ │ │ │ - │ St. │ │ │ │ │ │ - Long St. │Map margin│Nebraska │ 0.030│ .0134│ 8│ 3.04│ 1.08 - │ │ St. │ │ │ │ │ - Long St. │Nebraska │N. │ 2.02│.00213│ 15│ 2.00│ 2.45 - │ St. │ Carolina│ │ │ │ │ - │ │ St. │ │ │ │ │ - Long St. │N. │Georgia │ 3.03│ .0016│ 18│ 2.00│ 3.50 - │ Carolina│ St. │ │ │ │ │ - │ St. │ │ │ │ │ │ - Long St. │Georgia │Harris St.│ 3.04│ .0016│ 18│ 2.00│ 3.50 - │ St. │ │ │ │ │ │ - Alley S. │End of │Harris St.│ │ .0203│ 8│ 3.78│ 1.35 - of Janis│ Janis │ │ │ │ │ │ - St. │ St. │ │ │ │ │ │ - Harris St.│Alley N. │Long St. │ │ .0088│ 8│ 2.53│ 0.89 - │ of Janis│ │ │ │ │ │ - │ St. │ │ │ │ │ │ - Long St. │Harris St.│Kentucky │ │.00353│ 18│ 2.98│ 5.20 - │ │ St. │ │ │ │ │ - Long St. │Kentucky │Tennessee │ │.00635│ 18│ 4.00│ 7.00 - │ St. │ St. │ │ │ │ │ - Tarbell │Harris St.│Long St. │ │ .0146│ 8│ 3.18│ 1.14 - Ave. │ │ │ │ │ │ │ - Long St. │Tennessee │Alley W. │ 3.13│ .0016│ 18│ 2.00│ 3.50 - │ St. │ of Tenn.│ │ │ │ │ - │ │ St. │ │ │ │ │ - │ │ │ │ │ │ │ - Column No.│ (2) │ (3) │ (9) │ (10) │ (11) │ (12) │ (13) - (1) │ │ │ │ │ │ │ - ──────────┴──────────┴──────────┴──────┴──────┴──────┴────────┴──────── - - ──────────┬──────────┬──────────┬───────────────┬────── - On Street │ From │To Street │ El. of Invert │ Line - │ Street │ │ │Number - │ │ │ │ - │ │ │ │ - │ │ │ │ - ──────────┼──────────┼──────────┼───────┬───────┼────── - │ │ │ Upper │ Lower │ - │ │ │Manhole│Manhole│ - ──────────┼──────────┼──────────┼───────┼───────┼────── - Nebraska │Map margin│Alley S. │ 97.80│ 94.40│ 1 - St. │ │ Grant │ │ │ - │ │ St. │ │ │ - Alley S. │Railroad │E. of │ 105.50│ 103.62│ 2 - of Grant│ │ Missouri│ │ │ - St. │ │ St. │ │ │ - Alley S. │E. of │E. of │ 103.61│ 99.70│ 3 - of Grant│ Missouri│ Kansas │ │ │ - St. │ St. │ St. │ │ │ - Alley S. │E. of │Nebraska │ 99.69│ 94.40│ 4 - of Grant│ Kansas │ St. │ │ │ - St. │ St. │ │ │ │ - Nebraska │Alley S. │Alley S. │ 94.07│ 92.61│ 5 - St. │ of Grant│ of │ │ │ - │ St. │ Meridian│ │ │ - Alley S. │Railroad │Kansas St.│ 103.80│ 99.00│ 6 - of │ │ │ │ │ - Meridian│ │ │ │ │ - Alley S. │Kansas St.│Nebraska │ 98.99│ 92.70│ 7 - of │ │ St. │ │ │ - Meridian│ │ │ │ │ - Nebraska │Alley S. │Alley S. │ 92.37│ 91.09│ 8 - St. │ of │ of Smith│ │ │ - │ Meridian│ Av. │ │ │ - Alley S. │Railroad │East of │ 101.30│ 97.30│ 9 - of Smith│ │ Kansas │ │ │ - Ave. │ │ St. │ │ │ - Alley S. │East of │Nebraska │ 97.29│ 91.30│ 10 - of Smith│ Kansas │ St. │ │ │ - Ave. │ St. │ │ │ │ - Nebraska │Alley S. │S. of │ 90.84│ 90.20│ 11 - St. │ of Smith│ Cordovez│ │ │ - │ Ave. │ St. │ │ │ - S. of │Railroad │Nebraska │ 92.80│ 90.62│ 12 - Cordovez│ │ St. │ │ │ - St. │ │ │ │ │ - S. of │Map margin│Nebraska │ 96.60│ 93.10│ 13 - Cordovez│ │ St. │ │ │ - St. │ │ │ │ │ - Nebraska │S. of │Long St. │ 90.04│ 89.87│ 14 - St. │ Cordovez│ │ │ │ - │ St. │ │ │ │ - Long St. │Map margin│Nebraska │ 95.80│ 90.70│ 15 - │ │ St. │ │ │ - Long St. │Nebraska │N. │ 89.86│ 88.94│ 16 - │ St. │ Carolina│ │ │ - │ │ St. │ │ │ - Long St. │N. │Georgia │ 88.69│ 88.00│ 17 - │ Carolina│ St. │ │ │ - │ St. │ │ │ │ - Long St. │Georgia │Harris St.│ 87.99│ 87.32│ 18 - │ St. │ │ │ │ - Alley S. │End of │Harris St.│ 97.20│ 90.10│ 19 - of Janis│ Janis │ │ │ │ - St. │ St. │ │ │ │ - Harris St.│Alley N. │Long St. │ 90.09│ 88.90│ 20 - │ of Janis│ │ │ │ - │ St. │ │ │ │ - Long St. │Harris St.│Kentucky │ 87.31│ 86.40│ 21 - │ │ St. │ │ │ - Long St. │Kentucky │Tennessee │ 86.39│ 84.60│ 22 - │ St. │ St. │ │ │ - Tarbell │Harris St.│Long St. │ 90.70│ 84.60│ 23 - Ave. │ │ │ │ │ - Long St. │Tennessee │Alley W. │ 83.77│ 83.47│ 24 - │ St. │ of Tenn.│ │ │ - │ │ St. │ │ │ - │ │ │ │ │ - Column No.│ (2) │ (3) │ (14) │ (15) │ - (1) │ │ │ │ │ - ──────────┴──────────┴──────────┴───────┴───────┴────── - - -=47. Surface Profile.=—A profile of the surface of the ground along the -proposed lines of the sewers should be drawn after the completion of the -computations for quantity. An example of a profile is shown in Fig. 26 -for the line between manholes No. 3.5 and No. 147. The vertical scale -should be at least 10 times the horizontal. A horizontal scale of 1 inch -to 200 feet can be used where not much detail is to be shown, but a -scale of one 1 to 100 feet is more common and more satisfactory and even -one inch to 10 feet has been used. The information to be given and the -method of showing it are illustrated on Fig. 26. The profile should show -the character of the material to be passed through and the location of -underground obstacles which may be encountered. The method of obtaining -this information is taken up in Chapter II. The collection of the -information should be completed as far as possible previous to design, -and borings and other investigations made as soon as the tentative -routes for the sewers have been selected. - - -=48. Slope and Diameter of Sewers.=—After the quantity of sewage to be -carried has been determined, and the profile of the ground surface has -been drawn, it is possible to determine the slope and diameter of the -sewer. A table such as No. 20 is made up somewhat similar to No. 19, or -which may be an extension of Table 19 since the first 6 columns in both -tables are the same. The elevation of the surface at the upper and lower -manholes is read from the profile. - -The depth of the sewer below the ground surface is first determined. -Sewers should be sufficiently deep to drain cellars of ordinary depth. -In residential districts cellars are seldom more than 5 feet below the -ground surface. To this depth must be added the drop necessary for the -grade of the house sewer. Six-inch pipe laid on a minimum grade of 1.67 -per cent is a common size and slope restriction for house drains or -sewers. An additional 12 inches should be allowed for the bends in the -pipe and the depth of the pipe under the cellar floor. Where the -elevation of the street and lots is about the same, and the street is -not over 80 feet in width between property lines, a minimum depth of 8 -feet to the invert of sewers, 24 inches or less in diameter is -satisfactory. This is on the assumption that the axes of the house drain -and the sewer intersect. For larger pipes the depth should be increased -so that when the street sewer is flowing full, sewage will not back up -into the cellars or for any great distance into the tributary pipes. - -[Illustration: - - FIG. 26.—Typical Profile Used in the Design of a Separate Sewer - System. -] - -The grade or slope at which a sewer shall be may be fixed by: the slope -of the ground surface; the minimum permissible self-cleansing velocity; -a combination of diameter, velocity, and quantity; or the maximum -permissible velocity of flow. Sewers are laid either parallel to the -ground surface where the slope is sufficient or where possible without -coming too near the surface they are laid on a flatter grade to avoid -unnecessary excavation. The minimum permissible slope is fixed by the -minimum permissible velocity. - -The velocity of flow in a sewer should be sufficient to prevent the -sedimentation of sludge and light mineral matter. Such a velocity is in -the neighborhood of 1 foot per second. Since sewers seldom flow full -this velocity should be available under ordinary conditions of dry -weather flow. The minimum velocity when full should therefore be about 2 -feet per second. Under this condition, the velocity of 1 foot per second -is not reached until the sewer is less than 18 per cent full. The -velocity in small sewers should be made somewhat faster than in large -sewers since the velocity of flow for small depths in small pipes is -less than for the same proportionate depth in large pipes. The maximum -permissible velocity of flow is fixed at about 10 feet per second in -order to avoid excessive erosion of the invert. If the sewer is -carefully laid this limit may be exceeded in sanitary sewers. - -The method for determining the grade and diameter of sewers is best -explained through an illustrative problem which is worked out in Table -20 for the profile shown on Fig. 26. The figures are inserted in the -table from left to right in each line, one line being completed before -the next one is commenced. The headings in the first 6 columns are -self-explanatory. The elevations of the surface at the upper and lower -manholes are read from the profile. The total flow is read from column -(18) in Table 19. The slope of the ground surface is then computed, and -with the quantity, slope, and coefficient of roughness, the diameter of -the pipe and the velocity of flow are read from Fig. 15. - -The following conditions may arise: - - (1) The diameter required is less than 8 inches. Use a diameter of - 8 inches as experience has shown that the use of smaller diameters - is unsatisfactory. - - (2) The velocity of flow when the sewer is full is less than 2 - feet per second. Increase the slope until the velocity when full - is 2 feet per second. - - (3) The diameter of the pipe required is not one of the commercial - sizes shown in Fig. 15. Use the next largest commercial size. - - (4) The slope of the ground surface is steeper than necessary to - maintain the required minimum velocity and the upper end of the - sewer is deeper than the required minimum depth. Place the sewer - on the minimum permissible grade, or upon such a grade that its - lower end will be at the minimum permissible depth. - - (5) The slope of the ground surface is so steep as to make the - velocity of flow greater than the maximum rate permissible. Reduce - the grade by deepening the sewer at the upper manhole and using a - drop manhole at this point. - -It is not permissible to use a pipe larger than that called for by the -above conditions. This is attempted sometimes in order to reduce the -grade and thereby save excavation, under the rule of a minimum velocity -of 2 feet per second when full. It is better to use the smaller pipe on -the flat grade as the quantity of sewage is insufficient to fill the -larger sewer and the minimum permissible velocity is more quickly -reached. - -Having determined the slope, the diameter, and the capacity of the pipe -to be used, these values are entered in the table. The elevations of the -invert of the pipe at the upper and lower manholes are next computed and -entered in the table. This method is followed until all of the -diameters, slopes, and elevations have been determined. - -The slopes are computed from center to center of manholes, but an extra -allowance of 0.01 of a foot is allowed by some designers for the -increased loss in head in passing through the manhole. When it becomes -necessary to increase the diameter of the sewer the top of the outgoing -sewer is placed at the same elevation or below the top of the lowest -incoming sewer. No extra allowance is made to compensate for loss in -head in the manhole in this case. This case is illustrated in columns -(14) and (15) in lines (16) and (17) of Table 20. All of the conditions -listed above are illustrated in Table 20, except the condition for a -velocity greater than 10 feet per second. - -The first condition is met at the head of practically every lateral, and -is illustrated in the second line. - -The second condition is also illustrated in the second line. The slope -of the ground surface is 0.0046, which gives a velocity of only 1.8 feet -per second in an 8–inch pipe. The slope is therefore increased to -0.00575, on which the full velocity is 2 feet per second. - -The third condition is met in the first line. The diameter called for to -carry 1.66 cubic feet per second on a slope of 0.0108 is slightly less -than 10 inches. A 10–inch pipe is therefore used and its full capacity -and velocity are recorded. - -The fourth condition is illustrated in the fourteenth line. The cut at -manhole No. 3.1 is 11.1 feet. The slope of the ground is 0.014, much -steeper than is necessary to maintain the minimum velocity in a 15–inch -pipe. The pipe is therefore placed on the minimum permissible slope, and -excavation is saved. The student should check the figures in Table 20 -and be sure that they are understood before an attempt is made to make a -design independently. - - -=49. The Sewer Profile.=—The profile is next completed as shown in Fig. -26, the pipe line being drawn in as the computations are made. The cut -is recorded to the nearest ⅒th of a foot at each manhole, or change in -grade. It should not be given elsewhere as it invites controversy with -the contractor. The cut is the difference of the elevation of the invert -of the lowest pipe in the trench at the point in question, and the -surface of the ground. - -The stationing should be shown to the nearest ⅒th of a foot. It should -commence at 0 + 00 at the outlet and increase up the sewer. The station -of any point on the sewer may show the distance from it to the outlet, -or a new system of stationing may be commenced at important junctions or -at each junction. - -Elevations of the surface of the ground should be shown to the nearest -⅒th of a foot, and the invert elevation to the nearest 1/100th of a -foot. - -Only the main line sewer is shown in profile in Fig. 26. The profiles of -the laterals computed in Table 20, have not been shown. The approximate -location of all house inlets are shown on the profile and located -exactly, and are made a matter of record during construction. - - - DESIGN OF A STORM WATER SEWER SYSTEM - - -=50. Planning the System.=—Storm sewer systems are seldom as extensive -as separate or combined sewer systems, since storm sewage can be -discharged into the nearest suitable point in a flowing stream or other -drainage channel, whereas dry weather or combined sewage must be -conducted to some point where its discharge will be inoffensive. The -need of a comprehensive general plan of a storm sewer system is quite as -great, however, as for a separate system. The haphazard construction of -sewers at the points most needed for the moment results in the -duplication of forgotten drains, expense in increasing the capacity of -inadequate sewers, and difficult construction due to underground -structures thoughtlessly located. A comprehensive plan permits the -construction of sewers where they are needed as they are required, and -enables all probable future needs to be cared for at a minimum of -expense. - -The same preliminary survey, map, and underground information are -necessary for the design of a storm sewer system as for a separate sewer -system. The map shown on Fig. 25 has been used for the design of a -storm-water sewer system. - -The steps in the design of a storm-water sewer system are: - -1st. Note the most advantageous points to locate the inlets and lay out -the system to drain these inlets. 2nd. Determine the required capacity -of the sewers by a study of the run-off from the different drainage -areas. 3rd. Draw the profile and compute the diameter and slope of the -pipes required. - - -=51. Location of Street Inlets.=—The location of storm sewers is -determined mainly by the desirable location of the street inlets. The -inlets must therefore be located before the system can be planned. In -general the inlets should be located so that no water will flow across a -street or sidewalk, in order to reach the sewer. This requires that -inlets be placed on the high corners at street intersections, in -depressions between street intersections, and at sufficiently frequent -intervals that the gutters may not be overloaded. City blocks are seldom -so long as to necessitate the location of inlets between crossings -solely on account of inadequate gutter capacity. The capacity of a -gutter can be computed approximately by the application of Kutter’s -formula. Inlet capacities are discussed in Chapter VI. When the area -drained is sufficiently large to tax the capacity of the gutter or -inlet, an inlet should be installed regardless of the location of the -street intersections. - -The street inlets are located on the map as shown in Fig. 25. The sewer -lines are then located so as to make the length of pipe to pass near to -all inlets a minimum. Storm sewers are seldom placed near the center of -a street because of the frequent crowded condition on this line. - - -=52. Drainage Areas.=—The outline of a drainage area is drawn so that -all water falling within the area outlined will enter the same inlet, -and water falling on any point beyond the outline will enter some other -inlet. This requires that the outline follow true drainage lines rather -than the artificial land divisions used in locating the drainage lines -in the design of sanitary sewers. The drainage lines are determined by -pavement slopes, location of downspouts, paved or unpaved yards, grading -of lawns and the many other features of the natural drainage which are -altered by the building up of a city. The location of the drainage lines -is fixed as the result of a study of local conditions. - -The watershed or drainage lines are shown on Fig. 25 by means of dot and -dash lines. A drainage line passes down the middle of each street -because the crown of the street throws the water to either side and -directs it to different inlets. A watershed line is drawn about 50 feet -west of such streets as Kentucky St., Florida St., etc., because the -downspouts from the houses on those streets discharge or will discharge -into the street on which they face. The location of any watershed line -within 20 feet more or less is, in most cases, a matter of judgment -rather than exactness. Each area is given an identifying number or mark -which is useful only in design. It usually corresponds to the inlet -number. - - -=53. Computation of Flood Flow by McMath Formula.=—McMath’s Formula is -used as an example of the method pursued when an empirical formula is -adopted for the computation of run-off, and because of its frequent use -in practice. Other formulas may be more satisfactory under favorable -conditions. - -Computations should be kept in order by a tabulation such as is shown in -Table 21, in which the quantity of storm flow discharged from the sewer -at the foot of Tennessee St., on Fig. 25, has been computed by means of -the McMath Formula, using the constants suggested for St. Louis -conditions, _i_ = 2.75, and _c_ = 0.75. The solutions of the formula -have been made by means of Fig. 11. The column headings in the Table are -explanatory of the figures as recorded. The computation should begin at -the upper end of a lateral, proceed to the first junction and then -return to the head of another lateral tributary to this junction. They -should be continued in the same manner until all tributary areas have -been covered. Special computations will be necessary for the -determination of the maximum quantity of storm water entering each inlet -to avoid the flooding of an inlet or gutter. These computations have not -been shown as they are so easily made by the application of McMath’s -Formula to each area concerned. - -The determination of the average slope ratio is a matter of judgment, -based on the average natural slope of the surface of the ground and an -estimate of the probable future conditions. - - -=54. Computation of Flood Flow by Rational Method.=—The rational method -for the computation of storm-water run-off is described in Chapter III. -An example of its application to storm sewer design is given here for -the district shown in Fig. 25.[34] The computations are shown in Table -21. As in the preceding designs the table has been filled in from left -to right and line by line. Computations have started at the upper end of -laterals tributary to each junction. The column headed _I_ represents -the imperviousness factor in the expression _Q_ = _AIR_. It is based on -judgment guided by the constants given in Chapter III concerning -imperviousness. The column headed “Equivalent 100 per cent _I_ acres” is -the product of the two preceding columns. It reduces all areas to the -same terms so that they can be added for entry in the column headed -“Total 100 per cent _I_ acres.” It may be necessary to record the values -for this column on several lines where the imperviousnesses of the -tributary areas are different. This condition is illustrated in the last -line of the table, for the length of sewer nearest the outlet. In the -preceding lines the imperviousness recorded represents an average for -all the tributary areas. - - TABLE 21 - -COMPUTATIONS FOR THE QUANTITY OF STORM SEWAGE AT THE FOOT OF TENNESSEE - STREET ON FIGURE 25 - - ─────────┬──────────┬──────────┬───────────┬───────────────────────────────── - On Street│ From │To Street │Identifying│ By McMath’s Formula - │ Street │ │ Number of │ - │ │ │ Acres │ - │ │ │ Drained │ - ─────────┼──────────┼──────────┼───────────┼──────────┬───────┬───────┬────── - │ │ │ │Additional│ Total │ Slope │ Run - │ │ │ │ Acres │ Acres │ of │Off in - │ │ │ │ Drained │Drained│Surface│C.F.S. - │ │ │ │ │ │ │ - │ │ │ │ │ │ │ - │ │ │ │ │ │ │ - ─────────┼──────────┼──────────┼───────────┼──────────┼───────┼───────┼────── - State │N. │S. │ 91 and 92 │2.35 │ 2.35│ 0.005│ 5.5 - │ Carolina│ Carolina│ │ │ │ │ - State │S. │Georgia │88, 89 and │3.0 │ 5.35│ .005│ 10.8 - │ Carolina│ │ 90 │ │ │ │ - State │Georgia │Florida │85, 86 and │3.0 │ 8.35│ .007│ 16.5 - │ │ │ 87 │ │ │ │ - State │Florida │Kentucky │81, 83 and │3.0 │ 11.35│ .009│ 22.0 - │ │ │ 84 │ │ │ │ - State │Kentucky │Tennessee │79, 80 and │3.0 │ 14.35│ .010│ 28.0 - │ │ │ 82 │ │ │ │ - State │Texas │Louisiana │ 76 and │3.8 │ 3.8│ .005│ 8.3 - │ │ │ others │ │ │ │ - State │Louisiana │Alabama │73, 74 and │3.7 │ 7.5│ .007│ 15.0 - │ │ │ 75 │ │ │ │ - State │Alabama │Tennessee │70, 71 and │3.0 │ 10.5│ .006│ 19.0 - │ │ │ 72 │ │ │ │ - Tennessee│State │Talon │68, 69, 77 │4.3 │ 29.15│ .15│ 52 - │ │ │ and 78 │ │ │ │ - Talon │Albemarle │Tennessee │65, 66 and │2.8 │ 2.8│ .018│ 8.4 - │ │ │ 67 │ │ │ │ - Tennessee│Talon │Burnside │ 64 and │0.7 │ 29.85│ .15│ 55 - │ │ │ 64_a_ │ │ │ │ - Burnside │N. │S. │57, 58 and │2.84 │ 2.84│ .008│ 7.2 - │ Carolina│ Carolina│ 59 │ │ │ │ - Burnside │S. │Georgia │54, 55 and │3.88 │ 6.72│ .010│ 14.9 - │ Carolina│ │ 56 │ │ │ │ - Burnside │Georgia │Florida │50, 52 and │3.88 │ 10.60│ .012│ 22 - │ │ │ 53 │ │ │ │ - Burnside │Florida │Kentucky │47, 48 and │3.88 │ 14.48│ .013│ 30 - │ │ │ 51 │ │ │ │ - Burnside │Kentucky │Tennessee │44, 45 and │3.88 │ 18.36│ .013│ 36 - │ │ │ 46 │ │ │ │ - Tennessee│Burnside │Elm │ 42 and 43 │2.84 │ 51.05│ .015│ 82 - Elm │Above │Chetwood │ Included in next line below │ │ - │ Chetwood│ │ │ │ - Elm │Chetwood │Albemarle │31, 32 and │2.75 │ 2.75│ .007│ 7.0 - │ │ │ 33 │ │ │ │ - Elm │Albemarle │Tennessee │27, 28, 29 │5.75 │ 8.50│ .016│ 20 - │ │ │ and 30 │ │ │ │ - Tennessee│Elm │Varennes │25, 26 and │2.62 │ 62.17│ .017│ 100 - │ │ │ 41 │ │ │ │ - Varennes │S. │Georgia │17, 18 and │3.17 │ 3.17│ .010│ 8.3 - │ Carolina│ │ 19 │ │ │ │ - Varennes │Georgia │Florida │14, 15 and │3.17 │ 6.34│ .011│ 14.5 - │ │ │ 16 │ │ │ │ - Varennes │Florida │Kentucky │11, 12 and │3.17 │ 9.51│ .013│ 21 - │ │ │ 13 │ │ │ │ - Varennes │Kentucky │Tennessee │8, 9 and 10│3.17 │ 12.68│ .013│ 26 - Tennessee│Varennes │Boulevard │ 6 and 7 │2.32 │ 77.17│ .017│ 120 - Tennessee│Boulevard │Outlet │1, 2, 3, 4,│4.72 │ 81.89│ .017│ 122 - │ │ │ and 5 │ │ │ │ - │ │ │ │ │ │ │ - │ │ │ │ │ │ │ - │ │ │ │ │ │ │ - │ │ │ │ │ │ │ - ─────────┴──────────┴──────────┴───────────┴──────────┴───────┴───────┴────── - - ─────────┬──────────┬──────────┬─────────────────────────────────────────── - On Street│ From │To Street │ By Rational Method - │ Street │ │ - │ │ │ - │ │ │ - ─────────┼──────────┼──────────┼─────┬─────┬──────────┬─────┬────────────── - │ │ │Area,│ _I_ │Equivalent│Total│ Time of - │ │ │Acres│ │ 100 Per │ 100 │Concentration, - │ │ │ │ │ Cent _I_ │ Per │ Minutes - │ │ │ │ │ Acres │Cent │ - │ │ │ │ │ │ _I_ │ - │ │ │ │ │ │Acres│ - ─────────┼──────────┼──────────┼─────┼─────┼──────────┼─────┼────────────── - State │N. │S. │ 2.35│ 0.50│ 1.17│ 1.17│ 7.0 - │ Carolina│ Carolina│ │ │ │ │ - State │S. │Georgia │ 3.00│ .50│ 1.50│ 2.67│ 8.1 - │ Carolina│ │ │ │ │ │ - State │Georgia │Florida │ 3.00│ .50│ 1.50│ 4.17│ 9.0 - │ │ │ │ │ │ │ - State │Florida │Kentucky │ 3.00│ .50│ 1.50│ 5.67│ 9.9 - │ │ │ │ │ │ │ - State │Kentucky │Tennessee │ 3.00│ .50│ 1.50│ 7.17│ 10.7 - │ │ │ │ │ │ │ - State │Texas │Louisiana │ 3.80│ .35│ 1.33│ 1.33│ 10.0 - │ │ │ │ │ │ │ - State │Louisiana │Alabama │ 3.70│ .40│ 1.48│ 2.81│ 11.9 - │ │ │ │ │ │ │ - State │Alabama │Tennessee │ 3.00│ .45│ 1.35│ 4.16│ 12.9 - │ │ │ │ │ │ │ - Tennessee│State │Talon │ 4.30│ .50│ 2.15│13.48│ 14.5 - │ │ │ │ │ │ │ - Talon │Albemarle │Tennessee │ 2.80│ .40│ 1.12│ 1.12│ 8.0 - │ │ │ │ │ │ │ - Tennessee│Talon │Burnside │ 0.70│ .20│ 0.14│14.74│ 15.3 - │ │ │ │ │ │ │ - Burnside │N. │S. │ 2.84│ .55│ 1.56│ 1.56│ 10.0 - │ Carolina│ Carolina│ │ │ │ │ - Burnside │S. │Georgia │ 3.88│ .55│ 2.13│ 3.69│ 11.1 - │ Carolina│ │ │ │ │ │ - Burnside │Georgia │Florida │ 3.88│ .55│ 2.13│ 5.82│ 12.2 - │ │ │ │ │ │ │ - Burnside │Florida │Kentucky │ 3.88│ .55│ 2.13│ 7.95│ 13.1 - │ │ │ │ │ │ │ - Burnside │Kentucky │Tennessee │ 3.88│ .55│ 2.13│10.08│ 13.8 - │ │ │ │ │ │ │ - Tennessee│Burnside │Elm │ 2.84│ .45│ 2.28│26.10│ 15.7 - Elm │Above │Chetwood │ │ │ │ │ - │ Chetwood│ │ │ │ │ │ - Elm │Chetwood │Albemarle │ 2.75│ .40│ 1.10│ 1.10│ 8.0 - │ │ │ │ │ │ │ - Elm │Albemarle │Tennessee │ 5.75│ .45│ 2.59│ 3.69│ 9.5 - │ │ │ │ │ │ │ - Tennessee│Elm │Varennes │ 2.62│ .50│ 1.31│30.00│ 16.2 - │ │ │ │ │ │ │ - Varennes │S. │Georgia │ 3.17│ .55│ 1.74│ 1.74│ 9.0 - │ Carolina│ │ │ │ │ │ - Varennes │Georgia │Florida │ 3.17│ .55│ 1.74│ 3.48│ 9.9 - │ │ │ │ │ │ │ - Varennes │Florida │Kentucky │ 3.17│ .55│ 1.74│ 5.22│ 10.8 - │ │ │ │ │ │ │ - Varennes │Kentucky │Tennessee │ 3.17│ .55│ 1.74│ 6.96│ 11.4 - Tennessee│Varennes │Boulevard │ 2.32│ .55│ 1.28│32.84│ 16.5 - Tennessee│Boulevard │Outlet │ 0.18│ .80│ 0.14│ Area No. 1 - │ │ │ │ │ │ - │ │ │ 1.38│ .50│ 0.69│ Area No. 2 - │ │ │ 2.80│ .55│ 1.54│ Areas No. 3 and 4 - │ │ │ 0.36│ .75│ 0.27│35.48│ 16.9 - │ │ │ │ │ │ │ - ─────────┴──────────┴──────────┴─────┴─────┴──────────┴─────┴────────────── - - ─────────┬──────────┬──────────┬─────────────────────────────────┬────── - On Street│ From │To Street │ By Rational Method │ Line - │ Street │ │ │Number - │ │ │ │ - │ │ │ │ - ─────────┼──────────┼──────────┼───┬────┬─────┬────┬───────┬─────┼────── - │ │ │_R_│_Q_ │ _S_ │_V_ │ Sewer │Time │ - │ │ │ │ │ │ │Length,│ in │ - │ │ │ │ │ │ │ Feet │Sewer│ - │ │ │ │ │ │ │ │ │ - │ │ │ │ │ │ │ │ │ - │ │ │ │ │ │ │ │ │ - ─────────┼──────────┼──────────┼───┼────┼─────┼────┼───────┼─────┼────── - State │N. │S. │4.8│ 5.6│0.011│ 4.6│ 300│ 1.1│ 1 - │ Carolina│ Carolina│ │ │ │ │ │ │ - State │S. │Georgia │4.6│12.2│ .010│ 5.5│ 300│ 0.9│ 2 - │ Carolina│ │ │ │ │ │ │ │ - State │Georgia │Florida │4.4│18.3│ .012│ 5.8│ 300│ 0.9│ 3 - │ │ │ │ │ │ │ │ │ - State │Florida │Kentucky │4.2│23.9│ .009│ 6.0│ 300│ 0.8│ 4 - │ │ │ │ │ │ │ │ │ - State │Kentucky │Tennessee │4.1│29.3│ .009│ 6.2│ 300│ 0.8│ 5 - │ │ │ │ │ │ │ │ │ - State │Texas │Louisiana │4.2│ 5.6│ .009│ 3.2│ 370│ 1.9│ 6 - │ │ │ │ │ │ │ │ │ - State │Louisiana │Alabama │3.9│11.0│ .011│ 5.2│ 300│ 1.0│ 7 - │ │ │ │ │ │ │ │ │ - State │Alabama │Tennessee │3.8│15.8│ .002│ 3.2│ 300│ 1.6│ 8 - │ │ │ │ │ │ │ │ │ - Tennessee│State │Talon │3.6│48.5│ .019│ 9.8│ 450│ 0.8│ 9 - │ │ │ │ │ │ │ │ │ - Talon │Albemarle │Tennessee │4.6│ 5.2│ .004│ 3.0│ 210│ 1.2│ 10 - │ │ │ │ │ │ │ │ │ - Tennessee│Talon │Burnside │3.5│51.5│ .006│ 5.0│ 120│ 0.4│ 11 - │ │ │ │ │ │ │ │ │ - Burnside │N. │S. │4.2│ 6.5│ .008│ 4.5│ 300│ 1.1│ 12 - │ Carolina│ Carolina│ │ │ │ │ │ │ - Burnside │S. │Georgia │4.0│14.8│ .007│ 4.7│ 300│ 1.1│ 13 - │ Carolina│ │ │ │ │ │ │ │ - Burnside │Georgia │Florida │3.9│22.7│ .011│ 5.8│ 300│ 0.9│ 14 - │ │ │ │ │ │ │ │ │ - Burnside │Florida │Kentucky │3.7│29.4│ .016│ 7.5│ 300│ 0.7│ 15 - │ │ │ │ │ │ │ │ │ - Burnside │Kentucky │Tennessee │3.7│37.3│ .019│ 9.2│ 300│ 0.5│ 16 - │ │ │ │ │ │ │ │ │ - Tennessee│Burnside │Elm │3.4│88.8│ .015│10.2│ 280.│ 0.5│ 17 - Elm │Above │Chetwood │ │ │ │ │ │ │ 18 - │ Chetwood│ │ │ │ │ │ │ │ - Elm │Chetwood │Albemarle │4.6│ 5.1│ .020│ 5.3│ 480│ 1.5│ 19 - │ │ │ │ │ │ │ │ │ - Elm │Albemarle │Tennessee │4.3│15.8│ .012│ 6.1│ 410│ 1.1│ 20 - │ │ │ │ │ │ │ │ │ - Tennessee│Elm │Varennes │3.4│ 102│ .012│10.2│ 180│ 0.3│ 21 - │ │ │ │ │ │ │ │ │ - Varennes │S. │Georgia │4.4│ 7.7│ .012│ 5.2│ 270│ 0.9│ 22 - │ Carolina│ │ │ │ │ │ │ │ - Varennes │Georgia │Florida │4.2│14.5│ .010│ 5.7│ 300│ 0.9│ 23 - │ │ │ │ │ │ │ │ │ - Varennes │Florida │Kentucky │4.1│21.4│ .017│ 7.7│ 300│ 0.6│ 24 - │ │ │ │ │ │ │ │ │ - Varennes │Kentucky │Tennessee │4.0│27.8│ .015│ 7.8│ 300│ 0.6│ 25 - Tennessee│Varennes │Boulevard │3.3│ 108│ .012│10.2│ 230│ 0.4│ 26 - Tennessee│Boulevard │Outlet │ │ │ │ │ │ │ 27 - │ │ │ │ │ │ │ │ │ - │ │ │ │ │ │ │ │ │ 28 - │ │ │ │ │ │ │ │ 29 - │ │ │3.3│ 117│Areas No. 1–5 inclusive │ 30 - │ │ │ │ │ │ │ │ │ - ─────────┴──────────┴──────────┴───┴────┴─────┴────┴───────┴─────┴────── - -The time of concentration in minutes is assumed by judgment for the -first area. For all subsequent areas it is the sum of the time of -concentration for the area or areas tributary to the inlet next above -and the time of flow in the sewer from the inlet next above to the inlet -in question. For example, in line 2 the time 8.1 minutes is the sum of -7.0 minutes time of concentration to the inlet at the corner of State -and North Carolina St., and the time of flow of 1.1 minute in the sewer -on State St. from North Carolina St. to South Carolina St. Where two -sewers are converging as at the corner of Varennes Road and Tennessee -St. the longest time is taken. For example, the time of concentration -down Varennes Road to Tennessee St. is shown in line 25 as 11.4 + 0.6 = -12.0 minutes. The time to the same point down Tennessee St. is shown in -line 21 as 16.2 + 0.3 = 16.5 minutes. This time is therefore used in -line 26. - -_R_, the rate of rainfall in inches per hour is determined by Talbot’s -formula. - -_Q_, is in cubic feet per second and is the product of the 8th and 10th -columns. Since the 8th column is the sum of the products of the 5th and -the 6th columns for the lines representing tributary areas, then the -11th column is the product of _A_, _I_, and _R_. - -_S_, is the slope on which it is assumed that the sewer will be laid. It -is usually assumed as parallel to the ground surface unless the velocity -for this slope becomes less than 2 feet per second. In such a case the -slope is taken as one which will cause this velocity. - -_V_, the velocity in feet per second, is computed from diagrams for the -solution of Kutter’s formula. The length in feet is scaled from the map -as the distance between inlets or groups of inlets, and the time is the -length in feet divided by the velocity in feet per minute. - -Having computed the quantity of flow to be carried in the sewer, the -design is completed by drawing the profile and computing the diameters -and slopes by the same method as used in the design of separate sewers. - - - - - CHAPTER VI - APPURTENANCES - - -=55. General.=—The appurtenances to a sewerage system are those devices -which, in addition to the pipes and conduits, are essential to or are of -assistance in the operation of the system. Under this heading are -included such structures and devices as: manholes, lampholes, -flush-tanks, catch-basins, street inlets, regulators, siphons, -junctions, outlets, grease traps, foundations and underdrains. - - -=56. Manholes.=—A manhole is an opening constructed in a sewer, of -sufficient size to permit a man to gain access to the sewer. Manholes -are the most common appurtenances to sewerage systems and are used to -permit inspection and the removal of obstructions from the pipes. The -details of the Baltimore standard manholes are shown in Fig. 27 and a -manhole on a large sewer in Omaha is shown in Fig. 28. The features of -these designs which should be noted are the size of the opening and -working space, and the strength of the structure. Manhole openings are -seldom made less than 20 inches in diameter and openings 24 inches in -diameter are preferable. A man can pass through any opening that he can -get his hips through provided he can bend his knees and twist his -shoulders immediately on passing the hole. For this reason the manhole -should widen out rapidly immediately below the opening, as shown in Fig. -27 and 38. - -The walls of the manhole may be built either of brick or of concrete. -Brick is more commonly used, as the forms necessary for concrete make -the work more expensive unless they can be used a number of times. The -walls of the manhole should be at least 8 inches thick. Greater -thicknesses are used in treacherous soils and for deep manholes, or to -exclude moisture. A rough expression for the thickness of the walls of a -brick manhole more than 12 feet deep in ordinary firm material is _t_ = -_d_⁄2 + 2, in which _t_ is the thickness in inches and _d_ is the depth -in feet. The thickness of brick walls may be changed every 5 to 10 feet -or so. Concrete walls may be built thinner than brick walls. - -[Illustration: - - FIG. 27.—Baltimore Standard Manhole Details. -] - -The bottoms of brick manholes are frequently made of concrete as shown -in Fig. 27. The floor slopes towards the center and is constructed so -that the sewage flows in a half round or U-shaped channel of greater -capacity than the tributary sewers. The sides of the channel should be -high enough to prevent the overflow of sewage onto the sloping floor, -which should have a pitch of about one vertical to 10 or 12 horizontal. -In manholes where two or more sewers join at approximately the same -level the channels in the bottom should join with smooth easy curves. -Where the inlet and outlet pipes are not of the same diameter the tops -of the pipes should ordinarily be placed at the same elevation to -prevent back flow in the smaller pipes when the larger pipes are flowing -full. - -The dimensions of the manhole should not be less than 3 feet wide by 4 -feet long for a height of at least 4 feet, when built in the form of an -ellipse, or 4 feet in diameter when built circular. No standard method -for the reduction of the diameter of the manhole near the top is -observed, the rate being more or less dependent on the depth of the -manhole. The use of sloping sides above the frost line is desirable as -such a form is more resistant to heaving by frost action. - -For sewers up to 48 inches in diameter the manhole is usually centered -over the intersection of the pipes and has a special foundation. For -larger sewers the manhole walls spring from the walls of the sewer as -shown in Fig. 28. - -[Illustration: - - FIG. 28.—Details of a Manhole and a Well Hole. -] - -In the case of a decided drop in the elevation of a sewer, or of a -tributary sewer appreciably higher than an outlet in any manhole, the -sewage is allowed to drop vertically at the manhole, hence the name drop -manhole. The Baltimore standard drop manhole is shown in Fig. 27. A well -hole is an unusually deep drop manhole in which the force of the -vertical drop of sewage is broken by a series of baffle plates, or by a -sump at the bottom of the well hole. Fig. 28 shows a well hole at St. -Paul, Minn. The use of drop manholes can be avoided in large sewers by -the construction of a flight of steps or flight sewer as shown in Fig. -29, which allows the use of a steep grade and serves to break the -velocity of the sewage. - -The specifications of the Sanitary District of Chicago, covering the -construction of manhole covers and frames are: - - All castings shall be of tough, close grained, gray iron, free - from blow holes, shrinkage and cold shuts, and sound, smooth, - clean and free from blisters and all defects. - - All castings shall be made accurately to dimensions to be - furnished and shall be planed where marked or where otherwise - necessary to secure perfectly flat and true surfaces. Allowance - shall be made in the patterns so that the specified thickness - shall not be reduced. - - All castings shall be thoroughly cleaned and painted before - rusting begins and before leaving the shop with two coats of high - grade asphaltum or any other varnish that the Engineer may direct. - After the castings have been placed in a satisfactory manner, all - foreign adhering substances shall be removed and the castings - given one additional coat of asphaltum. No castings shall be - accepted the weight of which shall be less than that due to its - dimensions by more than 5 per cent. - -[Illustration: - - FIG. 29.—Flight Sewer at Baltimore. - - Eng. Record, Vol. 59, p. 161. -] - -[Illustration: - - FIG. 30.—Baltimore Standard Manhole Frame and Cover. -] - -The weights of frames and covers in use vary from 200 to 600 pounds, the -weight of the frame being about 5 times that of the cover. The lightest -weights are used where no traffic other than an occasional pedestrian -will pass over the manhole. Frames and covers weighing about 400 pounds -are commonly used on residential streets, whereas 600 pound frames and -covers are desirable in streets on which the traffic is heavy. The -frames should be so designed that the pavement will rest firmly against -it and wear at the same rate as the surrounding street surface. -Experience has shown that vertical sides should be used for the outside -of the frame to approach this condition, and that the frame should not -be less than 8 inches high. The cover should be roughened in some -desirable pattern as shown in Fig. 30. Smooth covers become dangerously -slippery. Where the ventilation of the sewers is not satisfactory the -manhole covers are sometimes perforated. This is undesirable from other -points of view as the rising odors and vapors are obnoxious at the -surface and the entering dirt and water are detrimental to the operation -of the sewer. The stealing and destruction of manhole covers and the -unauthorized entering of sewers has occasionally required the locking of -the covers to the frame when in place. The locks commonly used consist -of a tumbler which falls into place when the manhole is closed, and -which can be opened only by a special wrench or hook. Adjustable frames -are sometimes used where the street grade is settling, or may be raised -in order that the elevation of the top of the cover may be made to -conform to that of the street surface, without reconstructing the top of -the manhole. One type of adjustable cover is shown in Fig. 31. Manhole -covers should be so marked that the sanitary sewer can be distinguished -from the storm-water sewer, and both from the telephone conduit, etc. - -[Illustration: - - FIG. 31.—Adjustable Manhole Frame and Cover. -] - -Iron steps are set into the walls of the manhole about 15 inches apart -vertically to allow entrance and exit to and from the manhole. -Galvanized iron is preferable to unprotected metal as the action of rust -is particularly rapid in the moist air of the sewer. One type of these -manhole steps is shown in Fig. 27. The steps should have a firm grip in -the wall as a loose step is a source of danger. - -[Illustration: - - FIG. 32.—Baltimore Standard Lamphole. -] - - -=57. Lampholes.=—A lamphole is an opening from the surface of the ground -into a sewer, large enough to permit the lowering of a lantern into the -sewer. Lampholes are used in the place of manholes to permit the -inspection or the flushing of sewers, and to avoid the expense of a -manhole. They are located from 300 to 400 feet from the nearest manhole -in such a manner that a lamp lowered in the lamp hole can be seen from -the two nearest manholes. - -Lampholes should be constructed of 8– to 12–inch tile or cast-iron pipe. -The lower section should be a cast-iron T on a firm foundation, but if -constructed of tile it should be reinforced with concrete to take up the -weight of the shaft. The details of the Baltimore standard lamphole are -shown in Fig. 32. Lampholes are not commonly used on sewerage systems on -account of their lack of real usefulness and the troubles encountered by -breaking of the pipe below the shaft. - - -=58. Street Inlets.=—A street inlet is an opening in the gutter through -which storm water gains access to the sewer. The types used in different -cities vary widely. Details of an inlet in successful use are shown in -Fig. 33. The figure shows also a common form of connection to the sewer. -A water-seal trap is sometimes used to prevent the escape of odors from -the sewer. Care must be taken in design that such traps do not freeze in -winter nor dry out in summer, although it is not always possible to -prevent these contingencies. - -[Illustration: - - FIG. 33.—Details of an Untrapped Street Inlet, without Catch-Basin. -] - -The important features to be observed in the design of a street inlet -are: height and length of opening, character of grating, and location. -The general location of inlets is discussed in Chapter V. The clear -height of opening commonly used is from 5 to 6 inches, with a clear -length of 24 to 30 inches or longer. Inlets of this size have given -satisfaction on paved streets with moderate slopes, where the drainage -area is not greater than 10,000 to 12,000 square feet of pavement. W. W. -Horner states:[35] - - The St. Louis type of inlet “old” style was a vertical opening in - the curb 8 inches high and 4 feet in length with a horizontal bar - making the net opening about 5 inches. It has a broad sill - extending under the sidewalk. The “new” style inlet is 4½ feet - long with a clear opening of 6 inches and no bar. The sill is done - away with and the opening drops down directly from the curb. Tests - were made of the capacity of this inlet on pavements on different - slopes with sumps of depths varying from 0 to 6 inches in front of - the inlet, extending out 3 feet from the gutter, and returning to - the elevation of the gutter at a slope of 3 inches to the foot. - The results of these tests are shown in Table 22. The capacity of - the inlet is expressed as the amount of water entering just before - some water begins to lap past. If a large amount of water is - allowed to flow past much more water will enter the inlet thus - furnishing a factor of safety for large storms. It was noted that - by beginning the rise in the pavement about opposite the middle of - the inlet the capacity of the inlet was increased from 20 to 50 - per cent. - - TABLE 22 - - CAPACITIES OF ST. LOUIS STREET INLETS - - From tests by W. W. Horner. Cubic feet per second - ─────────┬───────────────────┬─────────────────── - Slope in │ 0.42 │ 1.5 - Per Ct. │ │ - ─────────┼────┬────┬────┬────┼────┬────┬────┬──── - Depth of │ 0.0│ 2│ 4│ 6│ 0│ 2│ 4│ 6 - Sump, │ │ │ │ │ │ │ │ - Inches │ │ │ │ │ │ │ │ - Capacity,│ │ │1.27│ │ │ │ │ - old │ │ │ │ │ │ │ │ - style │ │ │ │ │ │ │ │ - Capacity,│ 0.1│ 0.5│ 1.5│ 2.5│0.08│ 0.4│ 1.1│ 2.1 - new │ │ │ │ │ │ │ │ - style │ │ │ │ │ │ │ │ - ─────────┴────┴────┴────┴────┴────┴────┴────┴──── - - ─────────┬───────────────────┬─────────────────── - Slope in │ 2.85 │ 4.5 - Per Ct. │ │ - ─────────┼────┬────┬────┬────┼────┬────┬────┬──── - Depth of │ 0│ 2│ 4│ 6│ 0│ 2│ 4│ 6 - Sump, │ │ │ │ │ │ │ │ - Inches │ │ │ │ │ │ │ │ - Capacity,│0.03│0.25│0.78│1.49│ │ │ │ - old │ │ │ │ │ │ │ │ - style │ │ │ │ │ │ │ │ - Capacity,│0.03│0.28│0.87│1.62│0.02│0.15│0.45│ 1.0 - new │ │ │ │ │ │ │ │ - style │ │ │ │ │ │ │ │ - ─────────┴────┴────┴────┴────┴────┴────┴────┴──── - -Gratings with horizontal bars will admit more water than gratings with -vertical bars, but they will also admit more rubbish such as sticks, -papers, leaves, etc., which serve to clog the sewers. Vertical barred -gratings and gratings in the bottom of the gutter clog more quickly than -other types. In the selection of the type of grating to be used a -decision must be made as to whether it is more desirable to clean the -sewer or catch-basin, or to flood the street as a result of clogged -inlets. Where catch-basins are used or the sewers are large, horizontal -bars are more satisfactory. The openings between bars should be small -enough to prevent the entrance of a horse’s hoof or objects of -sufficient size to clog the sewer. Four inches in the clear for vertical -openings and 6 inches for horizontal openings are reasonable sizes. - -The location of the inlets at the intersection of the two curb lines at -a corner results in a lower first cost but on heavily traveled streets -this may result in a higher maintenance cost than for other locations -because of the concentration of traffic at street corners, hammering the -inlet casting out of shape or position. Vehicles making short turns will -tend to climb the curb and will intensify the wear upon the inlet. These -objections can be overcome by the use of two inlets at each corner, set -back far enough from the curb intersection to avoid interference with -the cross-walks. This also makes it possible to raise the cross-walks -without the use of gutters under them. - -The size of the pipe from the inlet to the catch-basin or sewer should -be large enough to care for all of the water which may enter the inlet. -As the capacity of the inlet is seldom known with accuracy and the -capacity of the pipe is difficult of determination, it has become -customary to use a 10–inch or a 12–inch connecting pipe for each -ordinary independent inlet. - - -=59. Catch-basins.=—Catch-basins are used to interrupt the velocity of -sewage before entering the sewer, causing the deposition of suspended -grit and sludge and the detention of floating rubbish which might enter -and clog the sewer. A separate catch-basin may be used for each inlet, -or to save expense, the pipes from several inlets may discharge into one -catch-basin. - -[Illustration: - - FIG. 34.—Catch-basin. - - Outlets are not always trapped. -] - -The types in successful use are extremely varied, but the distinguishing -feature of all is an outlet located above the floor of the basin. A -common form of catch-basin is shown in Fig. 34. It is constructed -similar to a manhole with a diameter of about 4 or 4½ feet and a depth -of retained water from 3 to 4 feet. Catch-basins of this size will care -for the sewage from the inlets at the four corners of a street -intersection, each draining a city block. In unusual situations it may -be necessary to install a larger basin, but too large a catch-basin is -less desirable than one which is too small, as the former stinks and the -latter is useless. Traps are sometimes used to prevent the escape of -odors from the sewer into the street, but odors are often created in the -catch-basins themselves. Some engineers arrange the trap so that it can -be opened for observation down the sewer as in Fig. 34, thus combining -the advantages of a manhole with the catch-basin. - -The use of catch-basins is objectionable because: they furnish a -breeding place for mosquitoes and other flying insects; the septic -action in them produces offensive odors; if on a combined sewer they -permit the escape of offensive odors in dry weather when the water seal -in the trap has evaporated; and the freezing of the water seal in the -trap prevents the entrance of water to the sewer. The sole advantage -lies in the prevention of the clogging of the sewers, but this may be -sufficient to overbalance all of the disadvantages. In general -catch-basins should be provided on paved streets which are cleaned by -flushing the material into the sewers, or where the drainage is from an -unimproved or macadamized street, sandy country, or into sewers in which -the velocity of flow is less than 2 feet per second. - -[Illustration: - - FIG. 35.—Diagrammatic Section through a Grease Trap. -] - - -=60. Grease Traps.=—The presence of grease in sewers results in the -formation of incrustations which are difficult to remove and which cause -a material loss in the capacity of the sewer. The presence of oil and -gasoline has resulted in violent and destructive explosions as is -described in Chapter XII. A type of grease trap used on the drains from -hotels, restaurants, or other large grease producing industries is shown -in Fig. 35. The trap is similar to a catch-basin except that it is too -small for a man to enter, and the outlet is necessarily trapped in order -to prevent the escape of grease. The details of a gasoline and oil -separator approved by the New York City Fire Department are shown in -Fig. 36.[36] - -[Illustration: - - FIG. 36.—Gasoline and Oil Separator. -] - - -=61. Flush-Tanks.=—These are devices to hold water used in flushing -sewers. They are required only on sanitary and combined sewers. Their -use tends to prevent the clogging of sewers laid on flat grades and -permits flatter grades in construction than could otherwise be adopted. -Flush-tanks may be operated either by hand or automatically. Automatic -operation is more common than hand operation. The hand-operated tanks -are similar to manholes so arranged that the inlet and outlet sewers can -be plugged while the manhole or tank is being filled with water either -from a hose or a special service connection. When sufficient water has -been accumulated the outlet is opened and the sewer is flushed by the -rush of water. A sluice gate, flap valve, or a specially fitted board is -sufficient to fit over the mouth of the inlet and outlet during the -filling of the tank. Such an arrangement has the advantage of being -cheap, simple, and satisfactory, though somewhat crude. In some cases -water is run into the tank at the same rate that it is discharged -through the open outlet, maintaining a depth of 4 or 5 feet in the tank -until the water passing the manhole below runs clean. The volume of -water required by this method is large. Flushing water under a -relatively high head is sometimes obtained by the use of tank wagons -which are quickly emptied into the sewer through a canvas pipe dropped -down a manhole. In all such cases if not well constructed the manhole is -subject to caving due to the rush of water around the outlet. -Precautions should be taken to minimize this danger by limiting the -depth of water which may be accumulated. This can be done by -constructing an overflow at a height of 4 or 5 feet above the bottom of -the manhole, discharging into the sewer through an outside drain. - -Automatic flush-tanks are constructed similar to a manhole, but special -care should be taken to make them water-tight. The apparatus for -providing the automatic discharge may operate either with or without -moving parts, the latter being preferable as they require less attention -and are not so liable to get out of order. An automatic flush-tank of -the Miller type is shown in Fig. 37. It is a patented device -manufactured by the Pacific Flush Tank Company. The small pipe at the -left is a service connection to the water main. Water is allowed to flow -continuously into the tank at such a rate as to fill it in the required -interval between discharges. The tanks are discharged as nearly once a -day as it is practicable to regulate them. The rate of flow into the -tank is determined by trial and varies to some extent with the water -pressure. The regulator shown in the figure is desirable as the -continuous flow through the ordinary cock soon wears it away. Some -waters will cause deposits to form in the small passages of the cocks or -regulators, thus cutting off the flow. - -[Illustration: - - FIG. 37.—Automatic Flush-Tank. - - Pacific Flush Tank Co. -] - -The tank operates as follows: when the water rising in the tank reaches -the bottom of the bell, air is trapped in the bell and prevented from -escaping through the main trap by the water at _A_. As the water -continues to rise in the tank the air in the bell is compressed, the -water level at _A_ is driven down and water trickles from the siphon at -_C_. The height of the water in the tank above the level of the water in -the bell is equal at all times to the height of _C_ above the lowering -position of _A_. When _A_ reaches the position of _B_ a small amount of -air is released through the short leg of the trap and a corresponding -volume of water enters the bell. The head of water above the bell then -becomes greater than the head of water in the short leg of the trap, -which results in the discharge of all of the air in the long leg of the -trap and the rapid discharge of the water in the tank through the -siphon. The discharge is continued until the siphonic action is broken -by the admission of air when the water level in the tank is lowered to -the bottom of the bell. The size of the siphons is fixed by the diameter -of the leg of the siphon. Table 23 shows the capacity and size of sewers -for which the different sizes of siphons are recommended by the -manufacturers.[37] - - TABLE 23 - - SIZES OF SIPHONS TO BE USED WITH AUTOMATIC FLUSH-TANKS - - ──────────┬───────────┬───────────┬───────────┬───────────┬──────────── - │ │ │ │ │ Height of - │Diameter of│ Total │ │ │ the - │Tank at the│ Discharge │ Average │ │ Discharge - Diameter │ Discharge │ for One │ Rate of │Diameter of│ Line above - of Siphon │ Line in │ Flush in │ Discharge │ Sewer in │the Edge of - in Inches │ Feet │ Gallons │in Sec.-ft.│ Inches │ the Bell - ──────────┼───────────┼───────────┼───────────┼───────────┼──────────── - 4│ 3│ 60│ 0.35│ 4 to 6│1 ft. 2 in. - 5│ 3│ 100│ 0.73│ 6 to 8│1 ft. 11 in. - 6│ 4│ 240│ 1.06│ 8 to 10│2 ft. 6 in. - 8│ 4│ 280│ 2.12│ 12 to 15│2 ft. 11 in. - ──────────┴───────────┴───────────┴───────────┴───────────┴──────────── - -When flush-tanks are placed at the upper end of laterals provision -should be made for inspecting and cleaning the sewer by the construction -of a separate manhole, or by combining the features of a manhole and a -flush-tank in the same structure. Such a combination is shown in Fig. 38 -from a design by Alexander Potter. - -Except under unusual conditions flush-tanks are used only on separate -sewers. They should be placed at the upper end of laterals in which the -velocity of flow when full is less than 2 to 4 feet per second. The -capacity of the tank or the volume of the dose is dependent on the -diameter and slope of the sewer. The most effective flush is obtained by -a volume of water traveling at a high velocity and completely filling -the sewer. A large volume allowed to run slowly through the sewer will -have but little if any flushing action. Data on the quantity of flushing -water needed are given in Table 24.[38] As the result of a series of -experiments conducted by Prof. H. N. Ogden on the flushing of -sewers,[39] the conclusion was reached that the effect of a flush of -about 300 gallons in an 8–inch sewer on a grade less than 1 per cent -would not be effective beyond 800 to 1,000 feet, but that on steeper -grades much smaller quantities of water would produce equally good -results. - -[Illustration: - - FIG. 38.—Automatic Flush-Tank and Manhole. - - Miller-Potter Design. Pacific Flush Tank Co. -] - - TABLE 24 - - GALLONS OF WATER NEEDED FOR FLUSHING SEWERS - - ─────────────────┬───────────────────────────────────────────────────── - Slope │ Diameter of Sewer in Inches - ─────────────────┼─────────────────┬─────────────────┬───────────────── - │ 8│ 10│ 12 - ─────────────────┼─────────────────┼─────────────────┼───────────────── - 0.005 │ 80│ 90│ 100 - .0075 │ 55│ 65│ 80 - .01 │ 45│ 55│ 70 - .02 │ 20│ 30│ 35 - .03 │ 15│ 20│ 24 - ─────────────────┴─────────────────┴─────────────────┴───────────────── - -Engineers do not agree upon the advisability of the use of automatic -flush-tanks, some believing that they are a needless expense that can be -avoided by hand flushing, and others feeling that a flush-tank should be -placed at the upper end of every lateral. These diverse opinions are the -result of different experiences in different cities. - - -=62. Siphons.=—There are two forms of siphons used in sewerage practice, -a true siphon and an inverted siphon. A true siphon is a bent tube -through which liquid will flow at a pressure less than atmospheric, -first upwards and then downwards, entering and leaving at atmospheric -pressure. An inverted siphon is a bent tube through which liquid will -flow at a pressure greater than atmospheric first downwards and then -upwards, entering and leaving at atmospheric pressure. - -In sewerage practice the word siphon refers to an inverted siphon unless -otherwise qualified. Siphons, both true and inverted, are used in -sewerage systems to pass above or below obstacles. True siphons are -seldom used as they must be kept constantly filled with liquid.[40] -Accumulated gas must be removed in order to prevent the breaking of the -siphon which results in the cessation of flow. By the breaking of a true -siphon is meant the stoppage of siphonic action due to the accumulation -of air or gas at the peak of the siphon. Since the rate of flow of -sewage fluctuates widely it is extremely difficult to control the flow -so that a true siphon may be completely filled with liquid at all times. - -In the design of inverted siphons care must be taken to prevent -sedimentation, and to permit inspection and cleaning. Sedimentation is -prevented by maintaining a velocity greater than a fixed minimum, -usually taken at about 2 feet per second. This minimum is attained by -providing a number of channels. The smallest channel is designed to -convey the least expected flow at the minimum velocity. Each of the -other channels is made as small as possible, within the limits of -economy and simplicity, in order that the minimum velocity shall be -exceeded quickly after flow has commenced in them. The last channel or -channels to be filled are made somewhat larger, because the sewage -conveyed in them contains less settleable matter than is contained in -the more concentrated dry weather flow. The type of siphon used in New -York to pass under the subway is shown in Fig. 39. Note should be taken -of the clean-out manhole provided on the 14–inch pipe. The other pipes -are large enough for a man to enter and clean. - -[Illustration: - - FIG. 39.—Sewer Siphon under New York Subway. - - Eng. News Vol. 76, p. 443. -] - -The computations involved in the design of a siphon are illustrated in -the following example, in which it is desired to construct a siphon to -pass under the railway cut shown in Fig. 40. The first step is to -determine the limiting diameter and slope of the smallest pipe in the -siphon. One-sixth of the capacity of the 6–foot approach sewer or 19 -cubic feet per second will be assumed as the minimum flow. The diameter -of the pipe necessary to carry 19 cubic feet per second at a velocity of -2 feet per second is 42 inches. The hydraulic gradient should have a -slope of 0.0005 if the material used has a roughness coefficient -of .015. This is the minimum permissible slope of the siphon. The -selection of a steeper slope will necessitate the laying of the sewer at -a greater depth, and will permit the use of smaller pipes for the -siphon. The selection of the exact slope must then be based on judgment -with the minimum limitation above placed. The slope will be arbitrarily -selected as 0.001, the same as that of the approach sewer. The diameter -of the dry weather pipe will therefore be 36 inches, with a capacity of -18 second-feet, which is approximately the assumed dry weather flow. The -velocity of flow will be 2.5 feet per second. The length of flow along -the siphon is 150 feet. - -[Illustration: - - FIG. 40.—Diagram for the Design of an Inverted Siphon. -] - -The next step should be the determination of the elevation at the lower -end of the 36–inch pipe. This is done by multiplying the assumed grade -by the equivalent length of straight pipe, and subtracting the product -from the elevation at the upper end. The length of straight pipe which -will give the same loss of head as the siphon is called the equivalent -pipe. It is determined as follows: - -First, determine the head loss at entrance. This will vary between -nothing and one velocity head, dependent on the arrangement at the -entrance.[41] The length of straight pipe which will give this same loss -can be computed from the expression _l_ = _h_⁄_S_, using for _S_ the -assumed slope of the hydraulic gradient. - -Second, determine the head loss due to the bends, This is determined -from the expression - - _h_ = (_fl_)⁄(_d_) (_V_^2)⁄(2_g_) - - in which _h_ = the head loss in the bend; - - _l_ = the length of the bend; - - _d_ = the diameter of the pipe; - - _v_ = the average velocity of flow; - - _g_ = the acceleration due to gravity; - - _f_ = a factor dependent on the radius (_R_) of the bend and - _d_. - -The relation between _f_, _R_, and _d_, for 90° bends is shown as -follows:[42] - - _R_⁄_d_ 24 16 10 6 4 2.4 - - _f_ 0.036 0.037 0.047 0.060 0.062 0.072 - -After the head loss has been determined, the equivalent length of -straight pipe is determined as above. - -Third. The equivalent length of pipe will be the sum of the actual -length of pipe and the equivalent lengths as found above. - -In the problem in hand the head lost at the entrance will be assumed as -one-third of a velocity head, or 0.0324 foot. With the assumed slope of -0.001 this is equivalent to 32 feet of pipe. The radius of the bend is -about 20 feet and the length for a 45° central angle is about 16 feet. -The head loss for this angle will probably be a little more than -one-half that for a 90° angle. The expression will therefore be taken as -about 0.2(_V_^2)⁄(2_g_) and for two bends is equivalent to about 40 feet -of pipe. The equivalent length of pipe is therefore 150 + 32 + 40 = 222 -feet. The elevation at the lower end should therefore be: the elevation -at the upper end, 92.07 − 222 × .001 = 91.85. - -The diameters of the remaining pipes in the siphon are determined so -that the sewage in the approach sewer is backed up as little as is -consistent with good judgment before each pipe comes into action. This -is done satisfactorily by a method of cut and try. Let it be assumed -that the siphon will be composed of three pipes: the dry weather pipe -taking 18 second-feet, the second pipe taking 28 second-feet, and the -third pipe taking the remaining 70 second-feet. The diameters of the two -larger pipes on the assumed slope of 0.001 will therefore be 42 inches -and 60 inches respectively. Other combinations might be used which would -be equally satisfactory. There are many methods by which the sewage can -be diverted into the different channels of the siphon. For example, the -openings into the different pipes may be placed at the same elevation, -and the sewage allowed to enter them in turn through automatically or -hand-controlled gates, or in another method of control the openings may -be placed at such elevations that when the capacity of one pipe has been -exceeded the sewage will flow into the next largest pipe as shown in -Fig. 40. The outlets from the different pipes are ordinarily placed at -the same elevation, thus leaving each pipe standing full of sewage. Stop -planks should be provided at the outlet in order that the pipes may be -pumped out for cleaning. The objection to this arrangement is that the -larger pipes may operate at a velocity less than 2 feet per second, and -they will be standing full of sewage which might become septic. However, -as they will take nothing but the storm flow near the top of the sewer -no difficulty should be encountered from sedimentation in them, and all -are large enough for a man to enter for inspection or cleaning. - -[Illustration: - - FIG. 41.—Coffin Sewer Regulator. -] - - -=63. Regulators.=—Regulators are commonly used to divert the direction -of flow of sewage in order to prevent the overcharging of a sewer or to -regulate the flow to a treatment plant. Sewer regulators are of two -types, those with moving parts and those without moving parts. An -example of the moving part type is shown in Fig. 41. In this type as the -sewage rises the float closes the gate to the inlet sewer, thus -preventing the entrance of sewage under head from the larger sewer. -There are many variations in the details of float controlled regulators, -but the principle of operation is similar in all. These regulators can -be adjusted to fix the maximum rate of flow to a relief channel or -sewage treatment plant, or during times of storm to cut off the outlet -to the dry weather channel. Another form of the moving part type is -shown in Fig. 42.[43] It has been used extensively by the Milwaukee -Sewerage Commission. In its operation the dry weather flow is diverted -by the dam into the intercepter. It passes under the movable gate on its -way to the treatment plant. As the flow increases the dam is overtopped -and flood waters are discharged down the storm channel. The movable gate -is hung on a pivot placed below center. As the water rises in the -intercepter, the pressure against the upper portion of the gate becomes -greater than that against the lower portion, and the gate closes. An -opening is left at the bottom to allow an amount of sewage equal to the -dry weather flow to escape beneath the gate to prevent clogging or -sedimentation in the intercepter channel. - -Objections to all moving part regulators are their need of attention and -liability to become clogged. - -[Illustration: - - FIG. 42.—Moving Part Regulator without Float. -] - -[Illustration: - - FIG. 43.—Leaping Weir at Danville, Illinois. -] - -[Illustration: - - FIG. 44.—Overflow Weir at San Francisco. - - Eng. News, Vol. 73, p. 307. -] - -[Illustration: - - FIG. 45.—Overflow Weir in Action. - - Shadow of steel knife edge which forms the lip of the weir can be seen - through the falling sewage. -] - -The overflow weir and the leaping weir have no moving parts and are used -for the regulation of the flow in sewers. A leaping weir is formed by a -gap in the invert of a sewer through which the dry weather flow will -fall and over which a portion or all of the storm flow will leap. One -form of leaping weir is shown in Fig. 43. An overflow weir is formed by -an opening in the side of a sewer high enough to permit the discharge of -excess flow into a relief channel. A weir at San Francisco is shown in -Fig. 44. A series of tests were run on leaping weirs and overflow weirs -in the hydraulic laboratory of the University of Illinois. The type of -leaping weir tested was formed by the smooth spigot end of a standard -vitrified sewer pipe. The overflow weirs were formed by a steel knife -edge in the side of the pipe parallel to its axis as shown in Fig. 45. -Tests were made in 18–inch and 24–inch pipes on various slopes from -0.018 to 0.005, for both leaping weirs and overflow weirs. The overflow -weirs were varied in length from 16 inches to 42 inches and were placed -at various heights from 25 per cent to 50 per cent of the diameter above -the invert of the sewer. As the result of the observations the following -formulas were developed. For the leaping weir the expressions for the -coordinates of the curve of the surfaces of the falling stream, are: - - For the outside surface _x_ = 0.53_V_^⅔ + _y_^{4⁄7} - - For the inside surface _x_ = 0.30_V_^{4⁄7} + _y_^¾ - -in which _x_ and _y_ are the coordinates. The origin is in the upper -surface of the stream vertically above the end of the invert of the -pipe. The ordinate _y_ is measured vertically downwards. _V_ is the -velocity of approach in feet per second. These expressions are -applicable to any diameter of sewer up to 10 or 15 feet. They should -_not_ be used for depths of flow greater than about 14 inches; nor for -slopes of more than 25 per 1,000; nor for velocities less than 1 foot -per second nor more than 10 feet per second. The expression for the -ordinate of the inside curve is not good for less than 6 inches nor more -than 5 feet. The expression for the ordinate of the outside curve is -limited to values between the origin and 5 feet below it. - -The expression for the length of an overflow weir of the type shown in -Fig. 45, necessary to discharge a given quantity, is in the form, - - _l_ = 2.3_Vd_ log _h__{1}⁄_h__{2} - - in which _l_ = the length of the weir in feet; - - _V_ = the velocity of approach in feet per second; - - _d_ = the diameter of the pipe in feet; - - _h__{1} = the head of water on the upper end of the weir; - - _h__{2} = the head of water on the lower end of the weir. - -In the design of an overflow weir by this formula the height of the weir -above the invert of the sewer and the flow over the weir should be -determined arbitrarily. The height should be subtracted from the -computed depth of water above the weir to determine the value of -_h__{1}. The difference between the flow over the weir and the flow -above the weir will represent the rate of flow in the sewer below the -weir. The value of _h__{2} can then be computed as the difference in the -depth of flow below the weir and the height of the weir above the -invert. The value of _V_ is computed from Kutter’s formula. The length -of the weir is determined by substituting these values in the formula. - - -=64. Junctions.=—At the junction of two or more sewers the elevation of -the inverts should be such that the normal flow lines are at the same -elevation in all sewers. The sewers should approach the junction on a -steep grade to prevent sewage backing up in one when the other is -flowing full. The velocity of flow at the junction should not be -decreased and turbulence should be avoided in order to prevent -sedimentation and loss of head. The junction should be effected on -smooth easy curves with radii at least five times the diameter of the -sewer where possible. Curves with short radii cause backing up of sewage -thus reducing the capacity of the sewers. - -The terms bellmouth or trumpet arch are sometimes applied to the -junction of sewers large enough to be entered by a man. In small sewers -the Y branches and special junctions are manufactured so that the center -lines of the pipes intersect, and the junctions of mains and laterals -are made in manholes. In the construction of a bellmouth the arch is -carried over all the sewers. A manhole should be constructed at these -junctions as clogging frequently occurs there, due to swirling and back -eddies which cannot be avoided. - - -=65. Outlets.=—The outlets to a sewerage system discharging into a -swiftly running stream must be protected against wash and floating -debris. In a stream or other body of water subject to wide variations in -elevation the backing up of the sewage during high water should be -avoided. Where tidal flats or low ground about the outlet may be -alternately submerged and uncovered the discharge should always be into -swiftly running water. In quiescent bodies of water such as lakes and -harbors, and in rivers where the dilution is low, and in many other -cases, the sewer outlet should be submerged. - -[Illustration: - - FIG. 46.—Tide Gate. -] - -Outlets are protected against wash and the impact of debris by the -construction of deep foundations and heavy protecting walls. Although -the construction of an outlet in a slow current or a back eddy would -avoid danger from wash and debris, the discharge of the sewage into the -most rapid current possible aids in the prevention of a local nuisance. -A row of batter piles on the upstream or exposed side of the sewer is -desirable, or it may be necessary to construct a break-water to prevent -the wash of the current from dislodging the pipe. These break-waters are -low dams of wood or broken stone, more or less loosely thrown together. -The backing up of water into the sewer can be prevented by constructing -the sewer above the outlet on a steep grade. Where this is not possible -the use of tide gates will be helpful. A tide gate, one form of which is -shown in Fig. 46, is a special form of check valve placed on the end of -the sewer. - -[Illustration: - - FIG. 47.—Sewer Outlet on a Trestle. - - Eng. News, Vol. 49, p. 9. -] - -Sewer outlets are sometimes constructed on long trestles in order to -reach deep or running water. Such a trestle is shown in Fig. 47. In -Boston the outlet sewers are submerged under the harbor and discharge -through outlets well out in the tidal currents. The sewage is discharged -under pressure and the pumps are operated at some of the stations only -at such times as the tidal currents will carry the sewage away from the -harbor. It is not always necessary in a combined sewerage system to -carry the storm flow to a distant submerged outlet. A double outlet can -be constructed as shown in Fig. 48 in which the dry weather flow is -carried to the channel in a submerged sewer and the storm flow is -discharged on the bank.[44] Cast-iron pipe should be used for submerged -outlets as the sewer is subject to disturbance by the currents, anchors, -ice, and other causes. - -[Illustration: - - FIG. 48.—Dry Weather and Storm Sewer Outlet at Minneapolis, Minnesota. - - Eng. Record, Vol. 63, p. 383. -] - - -=66. Foundations.=—Sewers constructed in firm dry soil require no -special foundation to distribute the weight over the supporting medium. -In soft materials the lower half of the sewer ring may be spread as -shown in Fig. 22, and in rock the pressures on sewer pipes are evenly -distributed by a cushion of sand. In wet ground such as quicksand, mud, -swamp land, etc., a foundation must be constructed if the water cannot -be drained off. - -The permissible intensities of pressure on foundations in various -classes of material allowed by the building codes in different cities -are given in Table 25. These figures are based on the assumption that -the material is restrained laterally, which is generally the condition -in sewer construction. In the softer materials it becomes necessary to -spread the foundations not only to reduce the intensity of pressure, but -also to care for the thrust of the sewer arch. The arch thrust may be -found by one of the methods of arch analysis, and the haunches spread to -care for this, or the sewer invert may be transversally reinforced to -assist in caring for this action. Some sewer sections in hard and soft -material are shown in Fig. 22 and 23. - - TABLE 25 - - ALLOWABLE BEARING VALUE ON SOILS IN VARIOUS CITIES - - From Proc. Am. Soc. Civil Engrs., Vol. 46, 1920, p. 906 - - ─────────────────────────┬───────────────────────────────────────────── - Quicksand and alluvial │½ to 1 ton per sq. ft. for Providence, R. I., - soil │ ½ ton per sq. ft. for 6 cities - ─────────────────────────┼───────────────────────────────────────────── - Soft clay │1 ton per sq. ft. for 27 cities, ¾ ton per - │ sq. ft. for New Orleans, 2 to 3 tons for - │ Providence, R. I. - ─────────────────────────┼───────────────────────────────────────────── - Moderately dry clay and │2 tons for 7 cities, 1¾ to 2¼ for Chicago, 2½ - fine sand, clean and │ tons for Louisville, 2 to 4 tons for - dry │ Providence, 3 tons for Grand Rapids and Los - │ Angeles - ─────────────────────────┼───────────────────────────────────────────── - Clay and sand in │2 tons for 19 cities, 1¾ to 2¼ for Chicago, 3 - alternate layers │ to 5 tons for Providence - ─────────────────────────┼───────────────────────────────────────────── - Firm and dry loam or │3 tons for 24 cities, 2½ tons for 2 cities, 2 - clay, or hard dry clay │ to 3 tons for Atlanta, 3½ tons for - or fine sand │ Philadelphia, 4 tons for 6 cities - ─────────────────────────┼───────────────────────────────────────────── - Compact coarse sand, │4 tons for 25 cities, 3½ tons for Buffalo, 3 - stiff gravel or natural│ to 4 tons for Atlanta, 4 to 5 tons for - earth │ Cincinnati, 5 tons for Denver, 4 to 6 tons - │ for 3 cities, 6 tons for Rochester, N. Y. - ─────────────────────────┼───────────────────────────────────────────── - Coarse gravel, stratified│6 tons for 3 cities, 5 tons for 2 cities, 8 - stone and clay, or rock│ tons for 1 city - inferior to best brick │ - masonry │ - ─────────────────────────┼───────────────────────────────────────────── - Gravel and sand well │8 tons for 5 cities, 6 tons for 2 cities, 8 - cemented │ to 10 tons for 1 city - ─────────────────────────┼───────────────────────────────────────────── - Good hard pan or hard │10 tons for 4 cities, 6 tons for 2 cities, 8 - shale │ tons for 1 city - ─────────────────────────┼───────────────────────────────────────────── - Good hard pan or hard │8 tons for 1 city, 10 to 15 tons for 1 city, - shale unexposed to air,│ 12 to 18 tons for 1 city - frost or water │ - ─────────────────────────┼───────────────────────────────────────────── - Very hard native bed rock│20 tons for 5 cities, 15 tons for 1 city, 10 - │ tons for 1 city, 25 to 50 tons for 1 city - ─────────────────────────┼───────────────────────────────────────────── - Rock under caisson │24 tons for Baltimore, 25 tons for Cleveland - ─────────────────────────┴───────────────────────────────────────────── - -On soft foundations such as swamps or for outfalls on the muck bottom of -rivers the sewer may be carried on a platform. For small sewers 2–inch -planks, 2 to 4 feet longer than the diameter of the pipe are laid across -the trench, and the sewer rests directly upon them. For large sewers -imposing a heavy concentrated load, a pile foundation should be -constructed. The foundation may consist of piles alone, pile bents, or a -wooden platform supported on pile bents. The load which can be carried -by a pile is determined with accuracy only by driving a test pile and -placing a load on it. Where piles do not penetrate to a firm stratum the -load they will support can be determined by any one of the various -formulas, either theoretical or empirical, which have been devised. -Probably the best known of these formulas are the so-called Engineering -News formulas one of which is: - - _P_ = 2_Wh_⁄(_S_ + 1) for a pile driven by a drop hammer, - - in which _P_ = the safe load on the pile in pounds. The factor of - safety is 6; - - _W_ = the weight of the hammer in pounds; - - _h_ = the fall of the hammer in feet; - - _S_ = the penetration of the pile in inches at the last - driving blow. The blow is assumed to be driven on - sound wood without rebound of the hammer. - -Reference should be made to engineering handbooks for other forms of -pile formulas. The accuracy of all of these formulas is not of a high -degree. - -The piles are driven at about 2 to 4 feet centers, to a depth of from 8 -to 20 feet, unless hard bottom is struck at a lesser depth. The butt -diameter of the piles used for the smallest sewers is about 6 to 8 -inches. If bents are used, 2 or 3 piles are driven in a row across the -line of the sewer and are capped with a timber. For brick, block, pipe, -and some concrete sewers, a wooden platform must be constructed between -the pile bents for the support of the sewer. - - -=67. Underdrains.=—The construction of special foundations can sometimes -be avoided by laying drains under the sewers, thus removing the water -held in the soil. The laying of the underdrains facilitates the -construction of the sewer and reduces the amount of ground water -entering the sewer. The underdrains usually consist of 6– or 8–inch -vitrified tile laid with open joints from 1 to 2 feet below the bottom -of the sewer as shown in Fig. 1. If the sewers are large, parallel lines -of drains may be laid beneath them. An observation hole should be -constructed from the bottom of the manhole to each underdrain. This hole -usually consists of a 6– or 8–inch pipe, embedded in concrete, connected -to the drain and open at the top. It is too small to permit effective -cleaning of the underdrains, which are usually neglected after -construction, and which as a result clog and cease to function. Since -the principal period of usefulness of the drains is during construction, -their stoppage after the work is completed is not serious. The hollow -tile used in vitrified block sewers serve as underdrains after -construction, but are of little or no assistance to the draining of the -trench during construction. - - - - - CHAPTER VII - PUMPS AND PUMPING STATIONS - - -=68. Need.=—In the design of a sewerage system it is occasionally -necessary to concentrate the sewage of a low-lying district at some -convenient point from which it must be lifted by pumps. In the -construction of sewers in flat topography the grade required to cause -proper velocity of sewage flow necessitates deep excavation. It is -sometimes less expensive to raise the sewage by pumping than to continue -the construction of the sewers with deep excavation. - -In the operation of a sewage-treatment plant a certain amount of head is -necessary. If the sewage is delivered to the plant at a depth too great -to make possible the utilization of gravity for the required head, pumps -must be installed to lift the sewage. In the construction of large -office buildings, business blocks, etc., the sub-basements are -frequently constructed below the sewer level. The sewage and other -drainage from the low portion of the building must therefore be removed -by pumping. Because pumps are often an essential part of a sewerage -system, their details should be understood by the engineer who must -write the specifications under which they are purchased and installed. - - -=69. Reliability.=—If the only outlet from a sewerage system is through -a pumping station, the inability of the pumps to handle all of the -sewage delivered to them may so back up the sewage as to flood streets -and basements, endangering lives and health and destroying property. -Such an occurrence should be guarded against by providing sufficient -pumping capacity and machinery of the greatest reliability. - - -=70. Equipment.=—The equipment of a sewage pumping station, in addition -to pumping machinery, may include a grit chamber, a screen, and a -receiving well. The grit chamber and screen are necessary to protect the -pumps from wear and clogging. Grit chambers are not necessary in sewage -devoid of gritty matter, such as the average domestic sewage, unless -reciprocating pumps are used. Sufficient gritty matter is found in -average domestic sewage to have an undesirable effect on reciprocating -pumps. Receiving wells are used in small pumping stations where the -capacity of the pumps is greater than the average rate of sewage flow. -The pumps are then operated intermittently, the pumps standing idle -during the time that the receiving well is filling. - -Except for a few types of pumps of which the valve openings are -unsuitable, any machine capable of pumping water is capable of pumping -sewage which has been properly screened. The principles of sewage pumps -are then similar to principles of water pumps. The conditions under -which these principles are applied differ but slightly in the character -of the liquid, and a smaller range of discharge pressures. Pumps with -large passages, discharging under low heads are more commonly found -among sewage pumps. - -[Illustration: - - FIG. 49.—Calumet Sewage Pumping Station, Chicago, Illinois. -] - - -=71. The Building.=—The pumping station should, if possible, be of -pleasing design and should be surrounded by attractive grounds. The -Calumet Sewage Pumping Station in Chicago is shown in Fig. 49. Its -architecture is pleasing particularly in contrast with its location and -immediate surroundings. Such structures tend to remove the popular -prejudice from sewerage and to arouse interest in sewerage questions. -Service to the public is of value. It can be rendered more easily by -arousing public interest and cooperation by the erection of attractive -structures, than by feeding popular prejudice by the construction of -miserable eyesores. - - -=72. Capacity of Pumps.=—The capacity of the pumping equipment should be -sufficient to care for the maximum quantity of sewage delivered to it, -with the largest pumping unit shut down, and the provision of such -additional capacity as, in the opinion of the designer, will provide the -necessary factor of safety. - -Pumps can usually be operated under more or less overload. Power pumps -and centrifugal pumps driven by constant speed electric motors have no -overload capacity. A power pump or a centrifugal pump may be overloaded -up to the maximum horse-power of any variable speed motor or steam -engine driving it, provided the pump has been designed to permit it. -Direct-acting steam pumps which are designed for proper piston speed and -valve action at normal loads, can carry a 50 per cent overload for short -periods, although the strain on the pump is great. They will carry a 20 -to 25 per cent overload for about eight hours with less vibration and -strain. The use of pumps capable of working at an appreciable overload -is somewhat of an additional factor of safety, but the overload factor -should not be taken into consideration in determining the capacity of -the pumping equipment. - -The load on a pumping station consists of the quantity of sewage to be -pumped and the height it must be lifted. Variations in the quantity are -discussed in Chapter III. The head against which the pumps must operate -fluctuates with the level in the tributary sewer or pump well, and in -the discharge conduit. For a free discharge or discharge into a short -force main the greater the rate of sewage flow the smaller the lift, as -the depth of flow in the tributary sewer increases more rapidly than -that in the discharge conduit. If the discharge is into a large body of -water or under other conditions where the discharge head is -approximately constant, the fluctuations in total head should not exceed -the diameter of the tributary sewer. Such fluctuations are of minor -importance in the operation of direct-acting steam pumps, but may be of -great importance in the operation of centrifugal pumps, as is brought -out in Art. 78. - - -=73. Capacity of Receiving Well.=—The use of receiving wells is -restricted to small installations which require, in addition to the -standby unit, only one pump, the capacity of which is equal to the -maximum rate of sewage flow. When the receiving well has been pumped dry -the pump stops, allowing the well to fill again. Although the use of a -large receiving well, or an equalizing reservoir, for a large pumping -station would permit the operation of the pumps under more economical -conditions, the storage of sewage for the length of time required would -not be feasible. The sewage would probably become septic, creating odors -and corroding the pumps. The extra cost of the reservoir might not -compensate for the saving in the capacity and operation of the pumps. - -The capacity of the receiving well should be so designed that the pump -when operating will be working at its maximum capacity, and the period -of rest during conditions of average rate of flow should be in the -neighborhood of 15 to 20 minutes. For example, assume an average rate of -flow of 2 cubic feet per second, with a maximum rate of double this -amount. The pump should have a capacity of 4 cubic feet per second, and -if the receiving well is to be filled in 15 minutes by the average rate -of sewage flow its capacity should be 15 × 5 × 60 × 7.5 or 14,000 -gallons. Under these circumstances the pump will operate 15 minutes and -rest 15 minutes, during average conditions of flow. - - -=74. Types of Pumping Machinery.=—The two principal types of pumping -machines for lifting sewage are centrifugal pumps and reciprocating -pumps. A centrifugal pump is, in general, any pump which raises a liquid -by the centrifugal force created by a wheel, called the impeller, -revolving in a tight casing, as shown in Fig. 50. A reciprocating pump -is one in which there is a periodic reversal of motion of the parts of -the pump. - -Centrifugal pumps are sometimes classified as volute pumps and turbine -pumps. A volute pump is a centrifugal pump with a spiral casing into -which the water is discharged from the impeller with the same velocity -at all points around the circumference, as shown in Fig. 51. A turbine -pump is a centrifugal pump in which the water is discharged from the -impeller through guide passages into a collecting chamber, in such a -manner as to prevent loss of energy in changing from kinetic head to -pressure head. A turbine pump is shown in section in Fig. 51. -Centrifugal pumps are sometimes classified as single stage and -multi-stage. A centrifugal pump from which the water is discharged at -the pressure created by a single impeller is called a single-stage pump. -If the water in the pump is discharged from one impeller into the -suction of another impeller the pump is known as a multi-stage pump. The -number of impellers operating at different pressures determines the -number of stages of the pump. A three-stage pump is shown in Fig. 52. - -[Illustration: - - FIG. 50.—Section through de Laval Single-Stage, Double Suction - Centrifugal Pump. -] - - 375 Lubricating ring. - - 380 Oil hole cap. - - 383 Oil drain tube. - - 404 Shaft sleeve lock nut. - - 440 Driving coupling. - - 441 Driven coupling. - - 443 Coupling check nut. - - 450 Coupling bolt. - - 451 Coupling bolt nut. - - 452 Coupling rubber. - - 453 Coupling rubber steel tube. - - 500 Pump case. - - 550 Bearing bracket cap. - - 551 Bearing. - - 552 Shaft. - - 553 Shaft sleeve, right hand thread. - - PW Impeller. - - 554 Shaft sleeve, left hand thread. - - 555 Shaft stop collar, inner. - - 555–1 Shaft stop collar, outer. - - 556 Guide ring. - - 560 Packing gland. - - 563 Bearing. - - 567R Impeller protecting ring, right hand thread. - - 567L Impeller protecting ring, left hand thread. - - 583 Pump case protecting ring. - - 567 Labyrinth packing. - - 583 Labyrinth packing. - - 600 Pump case cover. - - 692 Impeller key. - - 815 Bearing bracket, outer. - - 815–1 Bearing bracket, inner. - -[Illustration: - - FIG. 51.—Types of Centrifugal Pumps. -] - -[Illustration: - - FIG. 52.—Section of a Multi-Stage Centrifugal Pump. - - Courtesy DeLaval Steam Turbine Co. -] - -Reciprocating pumps are generally driven by steam and are either -direct-acting, or of the crank-and-fly-wheel type. Power pumps are -reciprocating machines which may be driven by any form of motor, to -which they are connected by belt, chain or shaft. A Deming triplex -power pump is shown in Fig. 53. Power pumps can be used only where the -character of the sewage will not clog the valves nor corrode the pump. -A direct-acting steam pump is one in which the steam and water -cylinders are in the same straight line and the steam is used at full -boiler pressure throughout the full length of the stroke. The -crank-and-fly-wheel type of pumping engine permits the use of steam -expansively during a part of the stroke, the energy stored in the -flywheel carrying the machine through the remainder of the stroke. -Reciprocating pumps are sometimes classified as plunger pumps and -piston pumps. In the action of a plunger pump the water is expelled -from the water cylinder, by the action of a plunger which only partly -fills the water cylinder, as shown in Figs. 54 and 55. In a piston -pump the water is expelled from the water cylinder by the action of a -piston which completely fills the water cylinder, as shown in Fig. 63, -which illustrates a direct-acting piston pump. - -[Illustration: - - FIG. 53.—Triplex Power Pump. - - Courtesy, The Deming Co. -] - -Plungers are better than pistons for pumping sewage as the wear between -the pistons and the inside face of the cylinder soon reduces the -efficiency of the pump. Outside packed plungers are better than the -inside packed type because the packing can be taken up without stopping -the pump and the leakage from the pump is visible at all times. Outside -packed pumps are more expensive in first cost, but are easier to -maintain and have a longer life than piston pumps. - -[Illustration: - - FIG. 54.—Water End of Inside Center-Packed Plunger Pump. -] - -In selecting a pump to perform certain work the size of the water -cylinder and the speed of the travel of the piston should be -investigated to insure proper capacity. The average linear travel of the -piston for slow speed pumps is estimated at about 100 feet per minute, -dependent on the length of stroke and the valve area. For short strokes -and small valve areas the speed may be as low as 40 feet per minute, and -for long stroke fire pumps with large valves the piston can be operated -at a speed of 200 feet per minute.[45] Vertical, triple-expansion, -crank-and-fly-wheel, outside packed plunger pumps with flap valves can -be operated at speeds of 200 feet per minute when lifting sewage, and -when equipped with mechanically operated valves and lifting water they -can be run at speeds of 400 to 500 feet per minute. The speed of travel -multiplied by the volume of piston or plunger displacement, with proper -allowance for slippage, will give the capacity of the pump. The slippage -allowance may be from 3 to 8 per cent for the best pumps, and for pumps -in poor conditions it may be a high as 30 to 40 per cent. - -[Illustration: - - FIG. 55—Water End of Outside Center-Packed Plunger Pump. - - Courtesy Allis-Chalmers Co. -] - -There are two types of ejector pumps used for lifting sewage. One of -these depends on the vacuum created by the velocity of a stream of water -or steam passing through a small nozzle. The operation of this pump is -described in Art. 139 and it is illustrated in Fig. 97. The other type -of ejector pump is known as the compressed-air ejector. It is operated -by means of compressed air which is turned into a receptacle containing -sewage. The details of this type are explained in Art. 83 and are -illustrated in Fig. 68. - - -=75. Sizes and Description of Pumps.=—The size of a centrifugal pump is -expressed as the diameter of the discharge pipe in inches. It has -nothing to do with the head for which the pump is suited. On the -assumption of a velocity of flow of 10 feet per second through the -discharge pipe the capacity of the pump can be approximated. - -The size of a reciprocating pump involves the expression of the -diameters of the steam cylinders, the water cylinder, and the length of -the stroke in inches, in the order named, beginning with the steam -cylinder with the highest pressure. A complete description of a steam -pumping engine might be; compound, duplex, horizontal, condensing, -crank-and-fly-wheel, outside-center-packed, 12″ × 24″ × 18″ × 24″ pump. -The word compound means that there are a high-pressure and a -low-pressure steam cylinder; the word duplex means that there are two of -each of these cylinders; the word horizontal means that the axes of -these cylinders are in a horizontal plane; the word condensing means -that the steam is discharged from the low-pressure cylinders into a -condenser; the name crank-and-fly-wheel is self-explanatory; the name -outside-center-packed means that the water cylinder is divided into two -portions between which the plunger is exposed to the atmosphere, and -that the packing rings are on the outside of the two portions of the -cylinder as shown in Fig. 55; the figures shown mean that the -high-pressure steam cylinder is 12 inches in diameter, the low-pressure -24 inches in diameter, the water cylinder is 18 inches in diameter, and -the stroke of the pump is 24 inches. - - -=76. Definitions of Duty and Efficiency.=—The duty of a pump is the -number of foot-pounds of work done by the pump per million B.T.U., per -thousand pounds of steam, or per hundred pounds of coal, consumed in -performing the work. These units are only approximately equal as 100 -pounds of coal or 1,000 pounds of steam do not always contain the same -number of B.T.U. and may only approximately equal 1,000,000 B.T.U. - -Since 1,000,000 B.T.U. are equal to 778,000,000 foot-pounds of work, a -pump with a duty of 778,000,000 will have an efficiency of 100 per cent. -The efficiency of a pump is therefore its duty based on B.T.U. divided -by 778,000,000. The efficiencies or duties of various types of pumps are -given in Table 26.[46] - - TABLE 26 - - APPROXIMATE DUTIES OF STEAM PUMPS - - Small duplex, non-condensing 10,000,000 - Large duplex, non-condensing 25,000,000 - Small simple, flywheel, condensing 50,000,000 - Large simple, flywheel, condensing 65,000,000 - Small compound, flywheel, condensing 65,000,000 - Large compound, flywheel, condensing 120,000,000 - Small triple, flywheel, condensing 150,000,000 - Large triple, flywheel, condensing 165,000,000 - - -=77. Details of Centrifugal Pumps.=—A section of a centrifugal pump with -the names of the parts marked thereon is shown in Fig. 50. Among the -important parts which require the attention of the purchaser are: the -impeller (_PW_), the impeller packing rings (567 _R_ & _L_), the -bearings (551, 563), the thrust bearings (555–1), the shaft (552), and -the shaft coupling (440). - -The impeller should be of bronze, gun metal, or other alloy, because -there is no rusting or roughening of the surface, and the efficiency -does not fall with age. Normal fresh sewage is not corrosive, but septic -sewage and sludge are usually so corrosive that iron parts cannot be -used with success in contact with them. The impeller should be machined -and polished to reduce the friction with the liquid. Impellers are made -either closed or open, i.e., either with or without plates on the sides -connecting the blades to avoid the friction of the liquid against the -side of the casing. The closed type of impeller is shown in Fig. 50. -Closed impellers are slightly more expensive, but generally give better -service and higher efficiencies than the open type. Single impeller -pumps should have an inlet on each side of the impeller to aid in -balancing the machine, unless the plane of the impeller is to be -horizontal when operating. Multi-impeller pumps usually have single -inlet openings for each impeller. Vibration in the pump is sometimes -caused by an unbalanced impeller. The moving parts may be balanced at -one speed and unbalanced at another. To determine if the moving parts -are balanced the pump should be run free at different speeds and the -amount of vibration observed. If the impeller is removed from the pump -its balance when at rest can be studied by resting it on horizontal -knife edges. If there is a tendency to rotate in any direction from any -position the impeller is not perfectly balanced. - -Packing rings are used to prevent the escape of water from the discharge -chamber back into the suction chamber. These rings should be made of the -same material as the impeller. Labyrinth type rings, as shown in Fig. -50, are sometimes used as the long tortuous passages are efficient in -preventing leakage. - -The bearings must be carefully made because of the high speed of the -pump. They are usually made of cast iron with babbitt lining. They -should be placed on the ends of the shaft on the outside of the pump -casing, as shown in Fig. 50, and should be split horizontally so as to -be easily renewed. Exterior bearings are oil lubricated by means of ring -or chain oilers with deep oil wells. Where interior bearings are -necessary, because of the length of the shaft, they should be made of -hard brass and should be water lubricated. - -[Illustration: - - FIG. 56.—Marine Type Thrust Bearing. - - Courtesy, DeLaval Steam Turbine Co. -] - -Thrust bearings or thrust balancing devices are used to take up the end -thrust which occurs in even the best designed pumps. To overcome this -pumps are designed with double suction, opposed impellers, or two pumps -with their impellers opposed may be placed on the same shaft. Due to -inequalities in wear, workmanship or other conditions, end thrust will -occur and must be cared for. Various types of thrust bearings are in -successful use, such as: the piston, ball, roller or marine types. The -marine type thrust bearing is shown in Fig. 56. The piston type of -hydraulic balancing device is shown in Fig. 57. In the figure _A_ -represents the impeller, and _B_ a piston fixed to the shaft and -revolving with it. There is a passage for water through the openings -(1), (2), and (3) leading from the impeller chamber to the atmosphere or -to the suction of the pump. If the impeller tends to move to the right -opening (1) is closed resulting in pressure on the right of the impeller -forcing it to the left. If the impeller moves to the left (1) is opened -thus transmitting pressure to the piston _B_ forcing the impeller to the -right. The flange _C_ is not essential, but is advantageous in pumps -handling gritty matter. As the channel (2) wears larger the pressure -against the piston decreases allowing it to move to the left. This -partially closes (3) building up the pressure again. - -[Illustration: - - FIG. 57.—Piston Type of Thrust Balancing Device. -] - -Flexible shaft couplings should be used if the shaft of the driving -motor and the pump are in the same line, as direct alignment is -difficult to obtain or to maintain. Where connected to steam turbines, -reduction gearing and rigid couplings are usually used on sewage pumps -to obtain slow speed and permit large passages. Flexible couplings are -of various types, one of which is shown in Fig. 50. A rigid coupling -would be formed by bolting the flanges firmly together. Shaft couplings -are usually not necessary where the pump is driven by belt connection to -the engine or motor, or where the pump and pulley rest on only two -bearings. - -The stuffing box shown in Fig. 50 is packed loosely with two layers of -hemp between which is a lantern gland, in order to permit a small amount -of leakage. A drip box is placed below this gland to catch the leakage -and return it to the pump. The leakage is permitted as it aids in -lubrication and the tightening of the gland will cause binding of the -shaft. The gland on the suction side of the pump should be connected by -a small pipe to the discharge chamber in order to keep a constant supply -of water for lubrication and to prevent the entrance of air to the -suction end of the pump. - - -=78. Centrifugal Pump Characteristics.=—The capacity of a centrifugal -pump is fixed by the size and type of its impeller and by the speed of -revolution. Roughly, the capacity of a pump, for maximum efficiency, -varies directly as the speed of revolution, the discharge pressure -varies as the square of the speed, and the power varies as the cube of -the speed. These relations are found not to hold exactly in tests -because of internal hydraulic friction in the pump. - -The characteristic curves for a centrifugal pump, or the so-called pump -characteristics, are represented graphically by the relation between -quantity and efficiency, quantity and power necessary to drive, and -quantity and head, all at the same speed. The quantities are plotted as -abscissas in every case. The curve whose ordinates are head and whose -abscissas are quantities is known as “the characteristic.” The curve -showing the relation between quantities and speeds is sometimes included -among the characteristics. Characteristics of pumps with different -styles of impellers are shown in Fig. 58. Fig. 59 shows the -characteristics of a pump run at different speeds, the efficiencies at -these speeds when pumping at different rates, and the maximum efficiency -at different speeds. It is to be noted that the information given in -this figure is more extensive than that in Fig. 58. The operating -conditions under any head, rate of discharge, and speed are given. The -curves of constant speed are parallel, and their distances apart vary as -the square of the speed. The line of maximum efficiency is approximately -a parabola. - -[Illustration: - - FIG. 58.—Characteristics of Centrifugal Pumps with Different Styles of - Impellers at Constant Speed. -] - -A study of the characteristics of any particular pump should be made -with a view to its selection for the load and conditions under which it -is to be used. Among the important things to be considered in the -selection of a centrifugal pump for the expected conditions of load are: -the capacity required, the maximum and minimum total head to be pumped -against, the maximum variations in suction and discharge heads, and the -nature of the drive. For example, the pump, whose characteristics are -shown in Fig. 59, should be operated at about 800 revolutions per -minute. Under total heads between 40 and 50 feet, the discharge for the -best efficiency will vary between 600 and 670 gallons per minute. - -[Illustration: - - FIG. 59.—Efficiency and Characteristic Curves of a Centrifugal Pump at - Different Speeds. -] - -[Illustration: - - FIG. 60.—Efficiencies of Centrifugal Pumps. -] - -The efficiencies of centrifugal pumps increase with their capacities as -is shown approximately in Fig. 60. - - -=79. Setting of Centrifugal Pumps.=—In setting a centrifugal pump, care -should be taken to provide a firm foundation to hold the shafts of the -pump and the electric motor or the reduction gearing in good alignment, -or to prevent the pump from being displaced by the pull of a belt. It is -desirable that the foundation be level. Centrifugal pumps should be set -submerged for small pumping stations automatically controlled. Sludge -pumps must be set submerged as otherwise they will not prime -successfully. Provision should be made by which the pump can be lifted -from the sewage, or sludge, for inspection and repair. In many cases the -pump can be made self-priming by setting it in a dry, water-tight vault -below the low level of sewage flow. Where possible it is desirable not -to set the pump submerged as it will receive better care when easily -accessible. - -[Illustration: - - FIG. 61.—Centrifugal Pump in Manhole at Duluth, Minn. - - Eng. Contracting, Vol. 43, 1915, p. 310. -] - -The suction pipe should be free from vertical bends where air might -collect and should be straight for at least 18 to 24 inches from the -pump casing. An elbow on the suction pipe, attached directly to the -casing of the pump gives a lower efficiency than a suction pipe with a -short straight run. Centrifugal pumps will operate with as high a -suction lift as reciprocating pumps, but at the start they must be -primed and some provision must be made for priming them. The suction -pipe should be equipped with foot valves to hold the priming, or some -method may be provided for exhausting the air from the suction pipe. The -foot valves should be so installed as to form no appreciable obstruction -to the flow of water. They should have an area of opening at least 50 -per cent greater than the cross-section of the suction pipe. A strainer -on the suction pipe is undesirable as it becomes clogged and is usually -in an inaccessible position for cleaning. A screen should be placed at -the entrance to the suction well to prevent the entrance of objects that -are likely to clog the pump. A gate-valve and a check-valve should be -provided on the discharge pipe, the former to assist in controlling the -rate of discharge and the latter to prevent back flow into the pump when -it is not operating. - -Centrifugal pumps are well adapted to service in either large or small -units. An installation in a manhole at Park Point, Duluth, is shown in -Fig. 61. This station is controlled by an automatic electric device -which is operated by a float in the suction pit. Such automatic control -is an added advantage of the use of electrically driven centrifugal -pumps. The Calumet Pumping Station in Chicago, shown in Fig. 49, has a -capacity of approximately 1,000 cubic feet per second. The simplicity of -the layout of this station is shown in Fig. 62. - -[Illustration: - - FIG. 62.—Interior Arrangement of the Calumet Sewage Pumping Station, - Chicago. - - Eng. News-Record, Vol. 85, 1920, p. 872. -] - - -=80. Steam Pumps and Pumping Engines.=—The direct-acting steam pump, one -type of which is shown in Fig. 63, is adapted to pumping sewage the -character of which will not corrode or clog the valves. In this form of -pump it is necessary to utilize the steam at full pressure throughout -the entire length of the stroke, which results in high steam -consumption. A flywheel permits the use of steam expansively during a -part of the stroke, thus increasing the economy of operation. Other -devices used for the same purpose are known as compensators. They are -not in general use. - -Steam engines are classified in many different ways, for example; -according to the type of valve gear, as, plain slide valve, Corliss, -Lentz, etc.; or according to the number of steam expansions, as, simple, -compound, triple-expansion, etc.; or according to the efficiency of the -machine as low duty or high duty; or as - -[Illustration: - - FIG. 63.—Section of Duplex Piston Steam Pump. - - Courtesy, The John H. McGowan Co. -] - - STEAM END - - 2 Steam cylinder and housing combined. - - 8 Steam piston head. - - 9 Steam piston follower. - - 10 Steam piston inside ring. - - 11 Steam piston outside ring (2). - - 12 Steam cylinder head. - - 14 Steam chest. - - 16 Steam chest cover. - - 17 Steam slide valve. - - 18 Steam valve rod. - - 20 Steam valve rod, pin and nut. - - 22 Steam valve rod, collar and set screw. - - 23 Steam valve rod, stuffing box. - - 24 Steam valve rod, stuffing box, nut and gland. - - 38 Piston rod. - - 47 Piston rod stuffing box. - - 48 Piston rod, stuffing box, nut and gland. - - 49 Valve gear stand. - - 51 Long valve crank and shaft. - - 52 Short valve crank and shaft. - - PUMP END - - 115 Pump body. - - 127 Brass liner. - - 129 Water piston head. - - 130 Water piston follower. - - 137 Cylinder head. - - 139 Valve plate. - - 140 Cap. - - 152 Suction flange. - - 161 Discharge flange. - - 162 Valve seat, suction or discharge. - - 163 Valve, suction or discharge. - - 164 Suction valve spring. - - 167 Discharge valve spring. - - 168 Valve plate, suction or discharge. - - 169 Valve stem, suction or discharge. - - STEAM END - - 55 Crank pin. - - 56 Valve rod link. - - 61 Long rocker arm. - - 62 Short rocker arm. - - 63 Rocker arm wiper. - - 69 Cross head. - -condensing or non-condensing, etc. Throttling engines or automatic -engines refer to the method of control of the steam by the governor. In -throttling engines the governor controls the amount of opening of the -throttle valve, in automatic engines the governor controls the position -of the cut-off. - -The simple slide valve, low-duty, non-condensing, throttling engine, is -the lowest in first cost and the most expensive in the consumption of -fuel. The triple-expansion Corliss, or the non-releasing Corliss, -high-duty pumping engine is the most expensive in first cost but -consumes less steam for the power delivered than any other form of -reciprocating engine. For pumps of very small capacity the cost of fuel -is not so important an item as the first cost of the machine. For this -reason and because of the lower cost of attendance low-duty pumps are -more frequently found in small pumping stations. - -[Illustration: - - FIG. 64.—Diagram Showing Rates of Steam Consumption for Different Size - Units under Different Loads. -] - - TABLE 27 - - WATER RATES OF PRIME MOVERS AT FULL AND PART LOADS - - ───────────────────────────────┬──────┬─────────────────────────┬────── - Type of Engine │ │ │Boiler - │Power,│ │Press. - │ K.W. │ Per Cent of Full Load │ Lbs. - ───────────────────────────────┼──────┼────┬────┬────┬─────┬────┼────── - │ │ 25 │ 50 │ 75 │ 100 │125 │ - ───────────────────────────────┼──────┼────┼────┼────┼─────┼────┼────── - Single cylinder, high speed, │ │ │ │ │ │ │100 to - non-condensing │ 25│ 33│ 27│26.3│ 27.0│27.5│ 150 - │ 250│ 42│37.5│ 35│ 34.0│34.0│ - │ │ │ │ │ │ │ - Automatic, flat four valve, │ │ │ │ │ │ │100 to - high speed │ 150│ │ 32│ 30│ 26.5│29.0│ 125 - │ 250│ │ 33│ 31│ 28│30.0│ - │ │ │ │ │ │ │ - Tandem compound condensing, │ │ │ │ │ │ │100 to - high speed │ 125│ │ 23│ 19│ 17│ 18│ 150 - │ │ │ 25│ 20│ 19.5│ 21│ - │ │ │ │ │ │ │ - Cross compound, condensing, │ │ │ │ │ │ │ 125 - high speed │ │ 30│ 26│ 24│ 23│23.5│ - │ │ │ │ │ │ │ - Cross compound, non-condensing,│ │ │ │ │ │ │ 125 - high speed │ │ 39│ 31│ 27│ 26│27.5│ - │ │ │ │ │ │ │ - Single cylinder Corliss, │ │ │ │ │ │ │ 100 - condensing │ 120│23.7│20.4│ 19│ 18.5│19.0│ - │ 500│26.3│22.8│21.3│ 20.8│21.3│ 125 - │ │ │ │ │ │ │ - Compound Corliss, condensing │ │16.5│ 14│12.5│ 12.1│12.5│ 100 - │ │22.2│ 19│17.0│ 16.5│17.0│ 150 - │ │ │ │ │ │ │ - Single cylinder, rotary four │ │ │ │ │ │ │ 100 - valve, non-condensing │ 75│26.2│22.3│21.3│ 21.6│22.8│ - │ 400│35.0│27.2│26.4│ 26.0│26.8│ 180 - │ │ │ │ │ │ │ - Rotary four valve, tandem │ │ │ │ │ │ │ 100 - compound non-condensing │ 125│32.0│22.0│ 20│18.25│18.5│ - │ 600│40.0│28.3│23.2│ 22.5│22.7│ 150 - │ │ │ │ │ │ │ - Cross compound, non-condensing │ │ │ │ │ │ │ 100 - rotary four valve │ 125│ 25│ 21│19.1│ 18.5│19.0│ - │ 600│39.4│ 28│22.3│ 20.6│20.7│ 150 - │ │ │ │ │ │ │ - Single cylinder, poppett valve,│ │ │ │ │ │ │ 100 - non-condensing │ 120│22.7│20.5│19.7│ 19.1│20.1│ - │ 600│28.5│26.0│25.0│ 24.3│25.5│ 150 - │ │ │ │ │ │ │ - Single cylinder, poppett valve,│ │ │ │ │ │ │ 100 - condensing │ 120│18.5│16.7│16.1│ 15.6│16.4│ - │ 600│24.6│22.3│21.4│ 20.8│21.9│ 150 - │ │ │ │ │ │ │ - Compound condensing, poppett │ │ │ │ │ │ │ 100 - valve │ 200│14.2│13.0│12.5│ 12.2│12.9│ - │ 1200│18.4│16.9│16.3│ 15.9│16.8│ 150 - │ │ │ │ │ │ │ - Uniflow │ 125│14.6│13.7│13.4│ 13.4│13.3│ 150 - │ 600│15.0│14.3│13.7│ 13.5│14.0│ - │ │ │ │ │ │ │ - Steam turbines, condensing, │ │ │ │ │ │ │ 125 - Allis-Chalmers │ 300│ │ 24│ 17│ 160│16.5│ - │ 2000│ │31.9│26.3│ 23.8│23.0│ 175 - │ │ │ │ │ │ │ - Steam turbines, condensing, │ │ │ │ │ │ │ 125 - Westinghouse │ 300│ │13.7│12.8│ 12.2│12.6│ - │ 2000│ │18.2│16.9│ 16.2│16.8│ 175 - │ │ │ │ │ │ │ - Steam turbines, high pressure, │ │ │ │ │ │ │ - non-con., 12″ to 36″ wheel, │4 to 8│ │ │ │ │ │ - 1000 to 3600 R.P.M. │stages│ │ │ │ 28 5│ │ - │ │ │ │ │116.5│ │ - │ │ │ │ │ │ │ - Ditto. Condensing, 26–inch │ │ │ │ │ 17 3│ │ - │ │ │ │ │112.0│ │ - │ │ │ │ │ │ │ - ───────────────────────────────┴──────┴────┴────┴────┴─────┴────┴────── - -The steam consumption per indicated horse-power, better known as the -water rate of the engine, for various types of engines at full and at -part load is shown in Fig. 64. The steam consumption of other types at -full load is shown in Table 27. The indicated horse-power (I.H.P.) of a -steam engine is the product of the mean effective pressure (M.E.P.), the -area of the steam pistons, the length of the stroke, and the number of -strokes per unit of time. A common form of this expression is, - - I.H.P = _PLAN_⁄33,000, - - in which _P_ = the M.E.P. in pounds per square inch; - - _L_ = the length of the stroke in inches; - - _A_ = the sum of the areas of the pistons in square inches; - - _N_ = the number of revolutions per minute. - -The I.H.P. multiplied by the mechanical efficiency of the machine will -give the brake or water horse-power, that is, the horse-power delivered -by the machine. The product of the M.E.P., the sum of the areas of the -steam pistons and the mechanical efficiency of the machine, should equal -the product of the total head of water pumped against expressed in -pounds per square inch and the sum of the areas of the water pistons or -plungers. The M.E.P. is determined from indicator cards taken from the -steam cylinders during operation. These cards show the steam pressure on -the head and crank ends of each cylinder at all points during the -stroke. - - -=81. Steam Turbines.=—Among the advantages in the use of steam turbines -as compared with reciprocating steam engines for driving centrifugal -pumps are their simplicity of operation, the small floor space needed, -their freedom from vibration requiring a relatively light foundation, -and their ability to operate successfully and economically either -condensing or non-condensing under varying steam pressure. They can be -operated with steam at atmospheric or low pressure, thus taking the -exhaust from other engines. The greatest economy of operation for the -turbine alone will be obtained by operating with high pressure, -superheated steam and with a vacuum of 28 inches. In large units the -economy of operation of steam turbines is equal to that of the best type -of reciprocating engines. In order to develop the highest economy -turbines are operated at speeds from about 3,600 to 10,000 r.p.m. or -greater, the smaller turbines operating at the higher speeds. As these -speeds are usually too great for the operation of centrifugal pumps for -lifting sewage, reduction gears must be introduced between the turbine -and the pump. Although the best form of spiral-cut reduction gears may -obtain efficiencies of 95 to 98 per cent, or even higher, their use, -particularly in small units, is an undesirable feature of the steam -turbine for driving pumps. - -The steam consumption of DeLaval turbines of different powers, and the -steam consumption of a 450 horse-power DeLaval turbine at different -loads are shown in Fig. 64. Some steam consumptions of other turbines -are recorded in Table 27. It is to be noted that the steam consumption -of the 450 horse-power turbine at part loads is not markedly greater -than that at full loads. This is an advantage of steam turbines as -compared with reciprocating engines. The steam consumption of any -turbine is dependent on the conditions of operation and is lower the -higher the vacuum into which the exhaust takes place. - -[Illustration: - - FIG. 65.—The DeLaval Trade Mark, Illustrating the Principle of the - DeLaval Steam Turbine. - - Courtesy, DeLaval Steam Turbine Co. -] - -There are two types of turbines in general use, the single stage or -impulse machines, and the compound or reaction type. The DeLaval is a -well-known make of the single stage or impulse type. The principle of -its operation is indicated in Fig. 65, which is the trade mark of the -DeLaval Steam Turbine Co. The energy of the steam is transmitted to the -wheel due to the high velocity of the steam impinging against the vanes. -In the compound or reaction type of machine the steam expands from one -stage to the next imparting its energy to the wheel by virtue of its -expansion in the passages of the turbine. For this reason the -single-stage or impulse type is operated at higher speeds than the -compound or reaction machines. - - -=82. Steam Boilers.=—Among the important points to be considered in the -selection of a steam boiler for a sewage pumping station are: the -necessary power; the quality of the feed water; the available floor -space; the steam pressure to be carried; and the quality and character -of the fuel. Tubular boilers of the type shown in Fig. 66, are lower in -first cost than other types of boilers. They are not ordinarily built in -units larger than 250 to 300 horse-power and where more power is desired -a number of units must be used. They are objectionable because of the -relatively large floor space required, and because of their relatively -poor economy of operation. The efficiencies of water-tube boilers of -different types are given in Table 28. Large power units of the -water-tube type, as shown in Fig. 67, although more expensive in first -cost, require less floor space. Almost any desired steam pressure can be -obtained from either type but water-tube boilers are more commonly used -for high pressures. The grate or stoker can be arranged to burn almost -any kind of fuel under either water-tube or fire-tube boilers. The use -of poor quality of water in water-tube boilers is undesirable as the -tubes are more likely to become clogged than the larger passages of the -fire-tube boilers. If necessary, a feed-water purification plant should -be installed, as it is usually cheaper to take the impurities out of the -water than to take the scale out of the boiler. - -[Illustration: - - FIG. 66.—Horizontal Fire-tube Boiler. -] - -[Illustration: - - FIG. 67.—Babcock and Wilcox Water-tube Boiler. -] - -Not less than two boiler units should be used in any power station, -regardless of the demands for power, and if the feed water is bad, three -or even four units should be provided, as two units may be down at any -time. An appreciable factor of safety is provided by the ability of a -boiler to be operated at 30 to 50 per cent overload, if sufficient draft -is available, but with resulting reduction in the economy of operation. -The number of units provided should be such that the maximum load on the -pumping station can be carried with at least one in every 6 units or -less, out of service for repairs or other cause. - - TABLE 28 - - EFFICIENCIES OF STEAM BOILERS - - From Marks’ Mechanical Engineer’s Handbook - ────────┬───────────┬──────────┬──────┬────────┬──────┬──────┬────────── - Type │Horse-power│ Furnace │ │ │ │Evap. │ - │ │ │ │ │ │ from │ - │ │ │ │ │ │and at│ - │ │ │ │ │B.T.U.│ 212° │ Combined - │ │ │ Sq. │Per Cent│ per │ per │Efficiency - │ │ │ Ft. │of Rated│ Lb. │ Lb. │of Boiler - │ │ │Grate │Capacity│ Dry │ Dry │ and - │ │ │ Area │D’v’l’d │ Coal │ Coal │ Furnace - ────────┼───────────┼──────────┼──────┼────────┼──────┼──────┼────────── - Babcock │ 300│Hand-fired│ │ │ │ │ - & │ │ │ │ │ │ │ - Wilcox│ │ │ 84│ 118.7│11,912│ 8.81│ 71.8 - Babcock │ 640│Hand-fired│ │ │ │ │ - & │ │ │ │ │ │ │ - Wilcox│ │ │ 118│ 121.5│14,602│ 10.83│ 72.0 - Stirling│ 1128│B. & W. │ │ │ │ │ - │ │ chain │ │ │ │ │ - │ │ grate │ 187│ 198.3│12,130│ 9.51│ 76.1 - Rust │ 335│Hand-fired│ 68│ 210.5│13,202│ 9.42│ 68.9 - Heine │ 400│Green │ │ │ │ │ - │ │ chain │ │ │ │ │ - │ │ grate │ 83.5│ 123.8│11,608│ 8.79│ 73.5 - Maximum efficiency recorded │ │ │ │ │ 83 - ───────────────────────────────┴──────┴────────┴──────┴──────┴────────── - -The steam delivered by a boiler is the basis of the measurement of its -capacity or power. A boiler horse-power is the delivery of 33,320 B.T.U. -per hour. It is approximately equal to the raising of 30 pounds of water -per hour from a temperature of 100° Fahrenheit, to steam at a pressure -of 70 pounds per square inch, or to 34 pounds of water per hour changed -to steam from and at 212° Fahrenheit, at atmospheric pressure. The -horse-power of a boiler is sometimes approximated by the area of its -grate or heating surface. Such a method of measuring has a low degree of -accuracy on account of the variations in the quality of the fuel, and -the rate of combustion. For example, the rate of combustion under a -locomotive boiler is high and there is less than ⅒th of a square foot of -grate area and about 4.5 square feet of heating surface per boiler -horse-power. The Scotch Marine type of boiler used on steam ships, has -slightly more grate area and slightly less heating surface than the -locomotive type of boiler, because the rate of combustion is lower. -Stationary water-tube boilers may have 2 to 3 times as much grate area -and heating surface per horse-power as is found in locomotive boilers. -If a poor type of fuel is to be used the area of the grate should be -increased about inversely as the heat content of the fuel. The -approximate heat content of various types of fuels is shown in Table 29. - - TABLE 29 - - APPROXIMATE HEAT VALUE OF FUELS - - ─────────────────────────────────────┬────────────────┬──────────────── - Fuel │ │Pounds of Water - │ │Evaporated from - │ │ and at 212° F. - │ │ All heat - │B.T.U. per Pound│ utilized - ─────────────────────────────────────┼────────────────┼──────────────── - Anthracite │ 13,500│ 14.0 - Semi-bituminous, Pennsylvania │ 15,000│ 15.5 - Semi-bituminous, best, West Virginia │ 15,000│ 15.8 - Bituminous, best, Pennsylvania │ 14,450│ 15.0 - Bituminous, poor, Illinois │ 10,500│ 10.9 - Lignite, best, Utah │ 11,000│ 11.4 - Lignite, poor, Oregon │ 8,500│ 8.8 - Wood, best oak │ 9,300│ 9.6 - Wood, poor ash │ 8,500│ 8.8 - ─────────────────────────────────────┴────────────────┴──────────────── - - -=83. Air Ejectors.=—The Ansonia compressed-air sewage ejector is shown -in Fig. 68. In its operation, sewage enters the reservoir through the -inlet pipe at the right, the air displaced being expelled slowly through -the air valve marked B. The rising sewage lifts the float which actuates -the balanced piston valve in the pipe above the reservoir when the -reservoir fills. The lifting of the valve admits compressed air to the -reservoir. The air pressure closes valve A and the inlet valve at the -right, and ejects the sewage through the discharge pipe at the left. As -the float drops with the descending sewage it shuts off the air supply -and opens the air exhaust through the small pipe at the top center. -Sewage is prevented from flowing back into the reservoir by the check -valve in the discharge pipe. Other ejectors operating on a similar -principle are the Ellis, the Pacific, the Priestmann and the Shone. - - -=84. Electric Motors.=—The most common form of alternating current -electric motor used for driving sewage pumps where continuous operation -and steady loads are met is the squirrel-cage polyphase induction motor. -These motors operate at a nearly constant speed which should be selected -to develop the maximum efficiency of the pump and motor set. While Fig. -59 shows the best efficiency under varying heads to be obtained with -variable speed, the advantages of cost, attention, and availability make -the use of a constant speed motor common.[47] This type of motor is -undesirable where stopping and starting are frequent because it has a -relatively small starting torque and it requires a large starting -current. Such motors can be constructed in small sizes for high starting -torques by increasing the resistance of the rotor, but at the expense of -the efficiency of operation. - -[Illustration: - - FIG. 68.—Ansonia Compressed-Air Sewage Ejector. -] - -Alternating current motors are more generally used than direct-current -motors because of the greater economy of transmission of alternating -current, but where direct current is available constant speed shunt -wound motors should be adopted. - -In the selection of a motor to drive a centrifugal pump it is important -that the motor have not only the requisite power, but that its speed -will develop the maximum efficiency from the pump and motor combined. If -the pump and motor operate on the same shaft the speed of the two -machines must be the same. If the two are belt connected, the size of -the pulleys may be selected so as to give the required speed. If the -motor is to be connected to a power pump an adequate automatic pressure -relief valve should be provided on the discharge pipe from the pump, to -prevent the overloading of the motor or bursting of the pump in case of -a sudden stoppage in the pipe. The motor must be selected to suit the -conditions of voltage, cycle, and phase on the line. Transformers are -available to step the voltage up or down to practically any value. -Rotary converters are used to change direct to alternating current or -vice versa. - - -=85. Internal Combustion Engines.=—Internal combustion engines are used -for driving pumps. Units are available in size from fractions of 1 -horse-power to 2,000 horse-power or more, although the use of the larger -sizes is exceptional. These engines are not commonly used for sewage -pumping but when used they are ordinarily belt connected to a -centrifugal pump, or to an electric generator which in turn drives -electric motors which operate centrifugal pumps. This type of engine is -more commonly adapted to small loads, although not entirely confined to -this field, as they serve admirably as emergency units to supplement an -electrically equipped pumping station. The fuel efficiency of internal -combustion engines is higher than for steam engines as is indicated in -Table 30, but the fuel is more expensive. - -The four-cycle gas engine shown in Fig. 69 is the type most commonly -used. Its horse-power is the product of: the mean effective pressure, -the length of the stroke, the area of the piston, and the number of -explosions per second divided by 550. The M.E.P. is dependent on the -character of the fuel used and the compression of the gas before -ignition. Producer gas will furnish mean effective pressures between 60 -and 70 pounds per square inch, natural gas and gasoline, 85 to 90 pounds -per square inch, and alcohol from 95 to 110 pounds per square inch. - - TABLE 30 - - COMPARATIVE FUEL COSTS FOR PRIME MOVERS - - ───────────────────────────────────────┬───────────────┬─────────────── - Type of Engine │ Quantity of │Cost of Fuel in - │ Fuel per H.P. │ Cents per - │ Hour │ Horse-power - │ │ Hour - ───────────────────────────────────────┼───────────────┼─────────────── - Reciprocating steam engines, simple, │ 21 to 8 lb. │ 4.2 to 1.6 - non-condensing, 25 to 200 H.P. │ coal │ - Triple condensing, 2000 to 10,000 │2.3 to 1.9 lb. │ 0.46 to 0.37 - H.P. │ coal │ - ───────────────────────────────────────┼───────────────┼─────────────── - Steam turbines, high pressure, │ │ - non-condensing, │ │ - 200 to 500 K.W. │6.5 to 4.2 lb. │ 1.3 to 0.86 - │ coal │ - 500 to 3000 K.W. │2.6 to 1.9 lb. │ 0.52 to 0.37 - │ coal │ - Condensing 5000 to 20,000 K.W. │1.8 to 1.43 lb.│ 0.36 to 0.28 - │ coal │ - ───────────────────────────────────────┼───────────────┼─────────────── - Gas engines │ │ - Natural gas, 50 to 200 H.P. │ 19 to 11 cu. │ - │ ft. │ - Producer gas, 50 to 200 H.P. │ 2 to 1.5 cu. │ - │ ft. │ - Illuminating gas, 10 to 75 H.P. │ 26 to 19 cu. │ 2.1 to 1.5 - │ ft. │ - Gasoline, 10 to 75 H.P. │ 1.5 to 0.8 │ 5.6 to 3.0 - │ pints │ - ───────────────────────────────────────┼───────────────┼─────────────── - Oil engines, 100 to 500 H.P. │1.1 to 0.75 lb.│ - │ oil │ - ───────────────────────────────────────┴───────────────┴─────────────── - NOTE.—Coal assumed at $4.00 per ton, illuminating gas at 80 cents per - thousand cubic feet, and gasoline at 30 cents per gallon. - -[Illustration: - - FIG. 69.—Bessemer Oil Engine. Twin Cylinder, Valve Side. -] - -The Diesel Engine is the most efficient of internal combustion engines. -The original aim of the inventor, Dr. Rudolph Diesel, was to avoid the -explosive effect of the ordinary internal combustion engine by injecting -a fuel into air so highly compressed that its heat would ignite the -fuel, causing slow combustion of the fuel thus utilizing its energy to a -greater extent. The fuel and air were to be so proportioned as to -require no cooling. Although the ideal condition has not been attained, -the heat efficiency of Diesel engines is high. They will consume from -0.3 to 0.5 of a pound of oil (containing 18,000 B.T.U. per pound) per -brake horse-power hour, giving an effective heat efficiency of 25 to 30 -per cent. Although not now in extensive use in the United States it is -probable that this engine will be more generally adopted for conditions -suitable for internal combustion engines. - - -=86. Selection of Pumping Machinery.=—Centrifugal pumps are particularly -adapted to the lifting of sewage because of their large passages, and -their lack of valves. The low lifts, nearly constant head, and the -possibility of equalizing the load by means of reservoirs are -particularly suited to efficient operation of centrifugal pumps. They -require less floor space than reciprocating pumps of the same capacity, -and because of their freedom from vibration they do not demand so heavy -a foundation. The discharge from the pump is continuous thus relieving -the piping from vibration. In case of emergency the discharge valve can -be shut off without shutting down the pump, an important point in “fool -proof” operation. - -Volute pumps are better adapted to pumping sewage as their passages are -more free and they are better suited to the low lifts met. Gritty and -solid matter will cause wear on the diffusion vanes of turbine pumps in -spite of the most careful design. Although turbine pumps can possibly be -built with higher efficiency than volute pumps, their efficiency at part -load falls rapidly and the fluctuations of sewage flow are sufficient to -affect the economy of operation. Turbine pumps are more expensive and -heavier than volute pumps on account of the increased size necessitated -by the diffusion vanes. - -Multi-stage pumps are used for high lifts and are seldom if ever -required in sewage pumping. As ordinarily manufactured, each stage is -good for an additional 40 to 100 pounds pressure, but wide variations in -the limiting pressures between stages are to be found. - -Reciprocating plunger pumps are sometimes used for sewage pumping where -the character of the sewage is such that the valves will not be clogged -nor parts of the pump corroded. These pumps are seldom used in small -installations or for low lifts. They are not adapted to automatic or -long distance control as are electrically driven centrifugal pumps. The -use of reciprocating pumps for sewage pumping is practically restricted -to very large pumping stations with capacities in the neighborhood of -50,000,000 gallons per day or more. Steam-driven pumps are the most -common of the reciprocating type, but power pumps are sometimes used in -special cases for small installations and may be driven by either a -steam or gas engine or an electric motor. - -Compressed air ejectors, as described in Art. 83 are used for lifting -sewage and other drainage from the basement of buildings below the sewer -level. - -Centrifugal pumps electrically driven are, as a rule, the most -satisfactory for sewage pumping. Electric drive lends itself to control -by automatic devices, which are particularly convenient in small pumping -stations. The control can be arranged so that the pump is operated only -at full load and high efficiency, and when not operating no power is -being consumed, as is not the case with a steam pump where steam -pressure must be maintained at all times. The electric driven pump is -thrown into operation by a float controlled switch which is closed when -the reservoir fills, and opens when the pump has emptied the reservoir. -The choice between steam and electric power for large pumping stations -is a matter of relative reliability and economy. - -The selection of the proper type of pump, whether reciprocating or -otherwise, requires some experience in the consideration of the factors -involved. Fig. 70 is of some assistance. In discussing this figure, -Chester states: - - “Fig. 70 attempts to represent graphically, the writer’s ideas - under general conditions, of the machines that should be selected - for certain capacities for both principal engine and alternate and - the station duty they may be expected to produce, but you must - realize that this intends the principal engine doing at least 90 - per cent of the work and that the head, the cost of coal, the load - factor, the cost of real estate ... the boiler pressure, and the - space available, and finally ... the funds available, are factors - which may shift both the horizontal and curved lines. In the field - of low service pumps of 10,000,000 capacity or over, the - centrifugal pump reigns supreme, and for constant low heads of - 20,000,000 capacity or over the turbine driven centrifugal usurps - the field.” - -A reciprocating pump of any type would have to be specially built for -pumping sewage not carefully screened or otherwise treated, as the -valves, ordinarily used in such pumps for lifting water, would clog. The -vertical triple-expansion pumping engine with special valves and for -large installations, and the centrifugal pump for large or small -installations are the only suitable types for pumping sewage. With steam -turbine or electric drive the centrifugal has the field to itself. - -[Illustration: - - FIG. 70.—Expectancy Curves for Pumping Engines Working against a - Pressure of 100 Pounds per Square Inch. - - J. N. Chester, Journal Am. Water Works Ass’n, Vol. 3, 1916, p. 493. -] - - -=87. Costs of Pumping Machinery.=—The cost of pumping machinery can not -be stated accurately as the many factors involved vary with the -fluctuations in the prices of raw materials, transportation, labor, etc. -The actual purchase price of machinery can be found accurately only from -the seller. The costs given in this chapter are useful principally for -comparative purposes and for exercise in the making of estimates. The -costs of complete pumping stations are shown in Table 31.[48] These -figures represent costs in 1911. - - TABLE 31 - - COSTS OF COMPLETE PUMPING STATIONS - - These costs include the best type of triple-expansion engines, - high-pressure boilers, brick or inexpensive stone building with slate - roof, chimney and intake. Cost of land is not included. - ─────────────────┬─────────────────┬─────────────────┬───────────────── - Discharge │ Horse-power per │ │ - Pressure, Lbs. │ Million Gals. │Cost, Dollars per│Cost, Dollars per - per Sq. In. │ Pumped │ Horse-power │ Million Gallons - ─────────────────┼─────────────────┼─────────────────┼───────────────── - 30│ 12│ 562│ 6,750 - 40│ 16│ 438│ 7,000 - 50│ 20│ 362│ 7,250 - 60│ 24│ 312│ 7,500 - 70│ 28│ 277│ 7,750 - 80│ 32│ 250│ 8,000 - 90│ 36│ 229│ 8,250 - 100│ 40│ 213│ 8,500 - 110│ 44│ 200│ 8,750 - 120│ 48│ 187│ 9,000 - 130│ 52│ 192│ 10,000 - │ │ │ - ─────────────────┴─────────────────┴─────────────────┴───────────────── - - -=88. Cost Comparisons of Different Designs.=—In the design of a pumping -station and its equipment the relative costs of different designs should -be compared, and the least expensive design selected, due consideration -being given to serviceability, reliability, and other factors without -definite financial value. In comparing the costs of different types of -machinery, all items in connection with the pumping station should be -considered. For example, the cost of an electrically driven centrifugal -pump and equipment may be less than the total cost of a steam driven -reciprocating pump and equipment because of the saving in the cost of -boilers, boiler house, etc., but a comparison of the capitalized cost of -the two might show in favor of the reciprocating steam pump because of -the lower cost of operation. - -The total cost of a plant, or any portion thereof, may be considered as -made up of three parts: (1) The first cost, (2) operation and -maintenance and, (3) renewal. The total cost S can be expressed as - - _S_ = _C_ + _O_⁄_r_ + _R_, - - in which _C_ = the first cost; - - _O_ = the annual expenditure for operation and maintenance; - - _R_ = the amount set aside to cover renewal; - - _r_ = the rate of interest. - -_S_ is called the capitalized cost of a plant. The annual payment -necessary to perpetuate a plant is - - _A_ = _Sr_ = _Cr_ + _O_ + _Rr_. - -The value of _R_ is useful when expressed in terms of the life of the -plant or machine and the current rate of interest. It is sometimes -called the depreciation factor or capitalized depreciation. If it is -borne in mind that _R_ is the amount to be set aside at compound -interest for the life of the plant, at the end of which time the accrued -interest should be sufficient to renew the plant, it is evident that - - _R_(1 + _R_)^n − _R_ = _C_ - - or _R_ = _C_⁄((1+_r_)^n − 1) - -in which _n_ is the period of usefulness, or life of the plant, -expressed in years, no allowance being made for scrap value. - -A comparison of the annual expense of three different plants is shown in -Table 32. It is evident from this comparison that the machinery with the -least first cost is not always the least expensive when all items are -considered. - -A sinking fund is a sum of money to which additions are made annually -for the purpose of renewing a plant at the expiration of its period of -usefulness. The annual payment into the sinking fund is equivalent to -the term _Rr_ in the expression for annual cost, or in terms of _C_, -_r_, and _n_, the annual payment is - - _Cr_⁄((1 + _r_)^n − 1). - -It is the same as the capitalized depreciation multiplied by the rate of -interest. The expression _r_⁄((1 + _r_)^n − 1) is sometimes called the -rate of depreciation. - -The present worth of a machine is the difference between its first cost -and the present value of the sinking fund. If _m_ represents the present -age of a plant in years, then the present worth is - - _P_ = _C_(1 – ((1 + _r_)^n − 1)⁄((1 + _r_)^m − 1)). - - TABLE 32 - - COMPARISON OF COSTS OF THREE DIFFERENT PUMPING STATIONS. NOMINAL - CAPACITY THIRTY MILLION GALLONS PER DAY RAISED THIRTY FEET - - ────────────────┬────────────────────────────────── - Equipment │ Plant A - ────────────────┼────────────────────────────────── - │One Acre of Land. Brick Building, - │ Steel Trussed Roof, Slate - │ Covered. Cross Compound - │ Condensing Horizontal Pumping - │ Engine - ────────────────┼───────┬──────────┬───────┬─────── - │Annual │ Years of │Sinking│ Total - │Payment│Usefulness│ Fund │ - │ on │ │Payment│ - │ First │ │ │ - │ Cost │ │ │ - ────────────────┼───────┼──────────┼───────┼─────── - Land │ 100│ │ 0│ 100 - Permanent │ 1188│ 50│ 1080│ 2,260 - Structures[49]│ │ │ │ - Pumps and │ 440│ 15│ 435│ 875 - Machinery │ │ │ │ - Boilers │ 280│ 10│ 446│ 726 - Labor │ │ │ │ 14,000 - Fuel │ │ │ │ 5,500 - Repairs, etc. │ │ │ │ 480 - ────────────────┼───────┼──────────┼───────┼─────── - Total │ │ │ │ 23,941 - ────────────────┴───────┴──────────┴───────┴─────── - - ────────────────┬────────────────────────────────── - Equipment │ Plant B - ────────────────┼────────────────────────────────── - │One Acre of Land. Brick Building. - │ Steel Trussed Roof, Slate - │ Covered. Compound Condensing Low - │ Duty Horizontal Pumping Engine - │ - ────────────────┼───────┬──────────┬───────┬─────── - │Annual │ Years of │Sinking│ Total - │Payment│Usefulness│ Fund │ - │ on │ │Payment│ - │ First │ │ │ - │ Cost │ │ │ - ────────────────┼───────┼──────────┼───────┼─────── - Land │ 100│ │ 0│ 100 - Permanent │ 1180│ 50│ 1080│ 2,260 - Structures[49]│ │ │ │ - Pumps and │ 390│ 15│ 395│ 785 - Machinery │ │ │ │ - Boilers │ 252│ 10│ 400│ 652 - Labor │ │ │ │ 14,000 - Fuel │ │ │ │ 7,200 - Repairs, etc. │ │ │ │ 400 - ────────────────┼───────┼──────────┼───────┼─────── - Total │ │ │ │ 25,497 - ────────────────┴───────┴──────────┴───────┴─────── - - ────────────────┬────────────────────────────────── - Equipment │ Plant C - ────────────────┼────────────────────────────────── - │One Acre of Land. Frame Building, - │ Shingle Roof. Compound Duplex - │ Non-Condensing Pumping Engine. - │ - │ - ────────────────┼───────┬──────────┬───────┬─────── - │Annual │ Years of │Sinking│ Total - │Payment│Usefulness│ Fund │ - │ on │ │Payment│ - │ First │ │ │ - │ Cost │ │ │ - ────────────────┼───────┼──────────┼───────┼─────── - Land │ 100│ │ 0│ 100 - Permanent │ 810│ 50│ 775│ 1,585 - Structures[49]│ │ │ │ - Pumps and │ 360│ 15│ 352│ 712 - Machinery │ │ │ │ - Boilers │ 308│ 10│ 490│ 798 - Labor │ │ │ │ 14,000 - Fuel │ │ │ │ 8,200 - Repairs, etc. │ │ │ │ 550 - ────────────────┼───────┼──────────┼───────┼─────── - Total │ │ │ │ 25,945 - ────────────────┴───────┴──────────┴───────┴─────── - -Where straight-line depreciation is spoken of it is assumed that the -worth of a machine depreciates an equal part of its first cost each -year. For example, if the life of a plant is assumed to be 20 years, -straight-line depreciation will assume that the plant loses 1/20 of its -original value annually. The present worth of a plant under this -assumption would be the product of its first cost and the ratio between -its remaining life and its total life. This method of estimating -depreciation and worth is frequently used, particularly for short-lived -plants and for simplicity in bookkeeping, but it is less logical than -the method given above. - - -=89. Number and Capacity of Pumping Units.=—In order to select the -number and capacity of pumping units for the best economy, a comparison -of the costs of different combinations of units should be made and the -most economical combination determined by trial. The principles outlined -in the preceding articles should be observed in making these -comparisons. In a steam pumping station, when the number of units -operating is less than the average daily maximum for the period, steam -must nevertheless be kept on a sufficient number of boilers to operate -the maximum number of pumps. This, and corresponding standby losses must -not be overlooked, as they may show that a smaller number of larger -units is ultimately more economical. - - TABLE 33 - - SUMMARY OF FLUCTUATIONS OF SEWAGE FLOW AT A PROPOSED PUMPING STATION - - ─────────────────┬─────────────────┬─────────────────┬───────────────── - Number of Days │Flow in Thousand │ │ - Loads Occurred in│ Gallons per │ │ - One Year │ Minute │ Lift in Feet │ Horse-power - ─────────────────┼─────────────────┼─────────────────┼───────────────── - 1│ 293│ 6.0│ 450 - 8│ 163│ 8.6│ 354 - 15│ 119│ 10.0│ 300 - 18│ 106│ 10.6│ 284 - 23│ 88│ 11.2│ 249 - 31│ 69│ 12.2│ 211 - 32│ 65│ 12.4│ 204 - 45│ 51│ 13.4│ 173 - 41│ 50│ 13.5│ 169 - 30│ 45│ 13.8│ 158 - 28│ 44│ 13.9│ 154 - 23│ 40│ 14.2│ 143 - 21│ 38│ 14.4│ 137 - 18│ 35│ 14.6│ 129 - 12│ 29│ 15.0│ 111 - 8│ 24│ 15.6│ 95 - 5│ 20│ 16.0│ 79 - 3│ 16│ 16.5│ 65 - 2│ 14│ 16.8│ 58 - 1│ 6.5│ 18.0│ 29 - ─────────────────┴─────────────────┴─────────────────┴───────────────── - Total horse-power days for one year, 102,000. - Average load in horse-power, 280. - - TABLE 34 - -POSSIBLE COMBINATIONS OF FIVE PUMPING UNITS TO CARE FOR THE LOADS SHOWN - IN TABLE 33[50] - - ──────────────────────────────────┬─────────────── - 40 Horse-power │ Load - Type 1[51] │ - ────────┬──────┬───────────┬──────┼───────┬─────── - Per Cent│Pounds│ Load in │Pounds│Number │ Total - of Rated│Steam │Horse-power│Steam,│of Days│ Load - Capacity│ per │ │Units │Load is│Carried - │ H.P. │ │10,000│Carried│ on - │ Hour │ │Pounds│in Year│ these - │ │ │ │ │Days in - │ │ │ │ │ H.P. - ────────┼──────┼───────────┼──────┼───────┼─────── - 151│ 45│ 60.4│ 6.5│ 1│ 681 - 120│ 44│ 48│ 40.5│ 8│ 542 - 102│ 45│ 40.8│ 66.1│ 15│ 458 - 96│ 45│ 38.4│ 74.8│ 18│ 434 - 98│ 45│ 39.2│ 97.5│ 23│ 381 - │ │ │ │ 31│ 322 - │ │ │ │ 32│ 312 - │ │ │ │ 45│ 264 - │ │ │ │ 41│ 258 - 101│ 45│ 40.4│ 131│ 30│ 242 - 98│ 45│ 39.2│ 119│ 28│ 235 - │ │ │ │ 23│ 218 - │ │ │ │ 21│ 210 - │ │ │ │ 18│ 198 - │ │ │ │ 12│ 170 - 104│ 45│ 41.6│ 20.9│ 8│ 145 - │ │ │ │ 5│ 121 - │ │ │ │ 3│ 100 - 99│ 45│ 39.6│ 8.5│ 2│ 89 - 113│ 44│ 45.2│ 4.8│ 1│ 45 - │ │ │ ————│ │ - Sub-total │ 596.6│ │ - Grand total in pounds, 65,700,000 - ────────────────────────────────────────────────── - - ──────────────────────────────────┬─────────────── - 50 Horse-power │ Load - Type 1[51] │ - ────────┬──────┬───────────┬──────┼───────┬─────── - Per Cent│Pounds│ Load in │Pounds│Number │ Total - of Rated│Steam │Horse-power│Steam,│of Days│ Load - Capacity│ per │ │Units │Load is│Carried - │ H.P. │ │10,000│Carried│ on - │ Hour │ │Pounds│in Year│ these - │ │ │ │ │Days in - │ │ │ │ │ H.P. - ────────┼──────┼───────────┼──────┼───────┼─────── - 151│ 45│ 75.5│ 8.2│ 1│ 681 - 120│ 44│ 60.0│ 50.7│ 8│ 542 - 102│ 45│ 51.0│ 82.7│ 15│ 458 - 90│ 45│ 48.0│ 93.5│ 18│ 434 - 98│ 45│ 49.0│ 122.0│ 23│ 381 - 104│ 45│ 52.0│ 174.5│ 31│ 322 - 101│ 45│ 50.5│ 174.8│ 32│ 312 - │ │ │ │ 45│ 264 - 103│ 45│ 51.5│ 228│ 41│ 258 - │ │ │ │ 30│ 242 - │ │ │ │ 28│ 235 - │ │ │ │ 23│ 218 - │ │ │ │ 21│ 210 - │ │ │ │ 18│ 198 - │ │ │ │ 12│ 170 - │ │ │ │ 8│ 145 - 109│ 44│ 54.5│ 28.8│ 5│ 121 - │ │ │ │ 3│ 100 - 99│ 45│ 49.5│ 10.7│ 2│ 89 - │ │ │ │ 1│ 45 - │ │ │ ————│ │ - │ 973.9│ │ - - ────────────────────────────────────────────────── - - ──────────────────────────────────┬─────────────── - 60 Horse-power │ Load - Type 1[51] │ - ────────┬──────┬───────────┬──────┼───────┬─────── - Per Cent│Pounds│ Load in │Pounds│Number │ Total - of Rated│Steam │Horse-power│Steam,│of Days│ Load - Capacity│ per │ │Units │Load is│Carried - │ H.P. │ │10,000│Carried│ on - │ Hour │ │Pounds│in Year│ these - │ │ │ │ │Days in - │ │ │ │ │ H.P. - ────────┼──────┼───────────┼──────┼───────┼─────── - 151│ 45│ 90.6│ 9.8│ 1│ 681 - 120│ 44│ 72.0│ 60.8│ 8│ 542 - 102│ 45│ 61.2│ 99.2│ 15│ 458 - 96│ 45│ 57.6│ 112│ 18│ 434 - │ │ │ │ 23│ 381 - 104│ 45│ 62.4│ 209.0│ 31│ 322 - 101│ 45│ 60.6│ 210│ 32│ 312 - 102│ 45│ 61.2│ 325│ 45│ 264 - │ │ │ │ 41│ 258 - │ │ │ │ 30│ 242 - │ │ │ │ 28│ 235 - │ │ │ │ 23│ 218 - │ │ │ │ 21│ 210 - │ │ │ │ 18│ 198 - 106│ 45│ 63.6│ 137│ 12│ 170 - │ │ │ │ 8│ 145 - 109│ 44│ 65.4│ 34.5│ 5│ 121 - │ │ │ │ 3│ 100 - │ │ │ │ 2│ 89 - │ │ │ │ 1│ 45 - │ │ │ ————│ │ - │1197.3│ │ - - ────────────────────────────────────────────────── - - ──────────────────────────────────┬─────────────── - 100 Horse-power │ Load - Type 4[51] │ - ────────┬──────┬───────────┬──────┼───────┬─────── - Per Cent│Pounds│ Load in │Pounds│Number │ Total - of Rated│Steam │Horse-power│Steam,│of Days│ Load - Capacity│ per │ │Units │Load is│Carried - │ H.P. │ │10,000│Carried│ on - │ Hour │ │Pounds│in Year│ these - │ │ │ │ │Days in - │ │ │ │ │ H.P. - ────────┼──────┼───────────┼──────┼───────┼─────── - 151│ 28│ 151│ 10.2│ 1│ 681 - 120│ 25│ 120│ 57.5│ 8│ 542 - 102│ 25│ 102│ 62.5│ 15│ 458 - 96│ 25│ 96│ 103.8│ 18│ 434 - 98│ 25│ 98│ 135.1│ 23│ 381 - │ │ │ │ 31│ 322 - │ │ │ │ 32│ 312 - │ │ │ │ 45│ 264 - │ │ │ │ 41│ 258 - │ │ │ │ 30│ 242 - │ │ │ │ 28│ 235 - │ │ │ │ 23│ 218 - │ │ │ │ 21│ 210 - │ │ │ │ 18│ 198 - 106│ 25│ 106│ 76.5│ 12│ 170 - 104│ 25│ 104│ 29.1│ 8│ 145 - │ │ │ │ 5│ 121 - 100│ 25│ 100│ 32.4│ 3│ 100 - │ │ │ │ 2│ 89 - │ │ │ │ 1│ 45 - │ │ │ ————│ │ - │ 507.1│ │ - - ────────────────────────────────────────────────── - - ──────────────────────────────────┬─────────────── - 200 Horse-power │ Load - Type 5[51] │ - ────────┬──────┬───────────┬──────┼───────┬─────── - Per Cent│Pounds│ Load in │Pounds│Number │ Total - of Rated│Steam │Horse-power│Steam,│of Days│ Load - Capacity│ per │ │Units │Load is│Carried - │ H.P. │ │10,000│Carried│ on - │ Hour │ │Pounds│in Year│ these - │ │ │ │ │Days in - │ │ │ │ │ H.P. - ────────┼──────┼───────────┼──────┼───────┼─────── - 151│ 23│ 302│ 16.7│ 1│ 681 - 120│ 20│ 240│ 92.0│ 8│ 542 - 102│ 20│ 204│ 147│ 15│ 458 - 96│ 20│ 192│ 166│ 18│ 434 - 98│ 20│ 196│ 216│ 23│ 381 - 104│ 20│ 208│ 309.5│ 31│ 322 - 101│ 20│ 202│ 310│ 32│ 312 - 102│ 20│ 204│ 481│ 45│ 264 - 103│ 20│ 206│ 405│ 41│ 258 - 101│ 20│ 202│ 291│ 30│ 242 - 98│ 20│ 196│ 264│ 28│ 235 - 109│ 20│ 218│ 241│ 23│ 218 - 105│ 20│ 210│ 212│ 21│ 210 - 99│ 20│ 198│ 171│ 18│ 198 - │ │ │ │ 12│ 170 - │ │ │ │ 8│ 145 - │ │ │ │ 5│ 121 - │ │ │ │ 3│ 100 - │ │ │ │ 2│ 89 - │ │ │ │ 1│ 45 - │ │ │ ————│ │ - │3322.2│ │ - - ────────────────────────────────────────────────── - - TABLE 35 - - FINANCIAL COMPARISON OF PUMPING EQUIPMENTS - - The loads to be cared for are shown in Table 34. An emergency unit is - supplied to bring the overload capacity of the plant, less the largest - unit, equal to the maximum load on the plant. No unit will be - overloaded more than fifty per cent of its rated capacity. - - ───────────┬───────────┬───────────┬───────────┬───────────┬─────────── - Number of │ │ │ │ │ - Units │ │ │ │ │ - Exclusive │ │ │ │ │ - of │ │ │ │ │ - Emergency │ │ │ │ │ - Unit │ 5 │ 4 │ 3 │ 2 │ 1 - ───────────┼───────────┼───────────┼───────────┼───────────┼─────────── - Capacity │ 40 h.p.,│ │ │ │ - and Type of│ Type 1│ │ │ │ - Units │ 50 h.p.,│ 50 h.p.,│ │ │ - │ Type 1│ Type 1│ │ │ - │ 60 h.p.,│ 100 h.p.,│ 50 h.p.,│ │ - │ Type 1│ Type 4│ Type 1│ │ - │ 100 h.p.,│ 125 h.p.,│ 150 h.p.,│ 200 h.p.,│ - │ Type 4│ Type 4│ Type 5│ Type 5│ - │ 200 h.p.,│ 175 h.p.,│ 250 h.p.,│ 250 h.p.,│ 450 h.p., - │ Type 5│ Type 5│ Type 6│ Type 6│ Type 7 - ───────────┼───────────┼───────────┼───────────┼───────────┼─────────── - Emergency │ │ │ │ │ - Unit, │ │ │ │ │ - Capacity │ 200 h.p.,│ 175 h.p.,│ 250 h.p.,│ 250 h.p.,│ 450 h.p., - and Type │ Type 5│ Type 5│ Type 6│ Type 6│ Type 7 - ───────────┼───────────┼───────────┼───────────┼───────────┼─────────── - Annual │ │ │ │ │ - payments,│ │ │ │ │ - Dollars │ │ │ │ │ - First │ │ │ │ │ - cost of│ │ │ │ │ - pumps │ 1,560│ 1,660│ 1,480│ 1,440│ 1,500 - Renewal │ │ │ │ │ - of │ │ │ │ │ - pumps │ 1,340│ 1,430│ 1,270│ 1,240│ 1,290 - First │ │ │ │ │ - cost, │ │ │ │ │ - boilers│ 1,024│ 1,089│ 1,125│ 1,115│ 1,410 - Renewal, │ │ │ │ │ - boilers│ 800│ 935│ 966│ 958│ 1,210 - Fuel │ 13,140│ 11,860│ 10,490│ 9,420│ 9,400 - Repairs, │ │ │ │ │ - oil, │ │ │ │ │ - etc. │ 2,000│ 1,800│ 1,500│ 1,300│ 1,200 - Labor │ 35,000│ 31,500│ 29,500│ 27,000│ 27,000 - Emergency│ │ │ │ │ - unit. │ │ │ │ │ - First │ │ │ │ │ - cost │ 640│ 560│ 800│ 800│ 1,500 - Emergency│ │ │ │ │ - unit. │ │ │ │ │ - Renewal│ 550│ 480│ 690│ 690│ 1,290 - ───────────┼───────────┼───────────┼───────────┼───────────┼─────────── - Total │ 56,134│ 51,314│ 47,821│ 43,963│ 45,800 - ───────────┴───────────┴───────────┴───────────┴───────────┴─────────── - - Type 1. Simple duplex, non-condensing, horizontal. - - Type 4. Compound condensing low duty horizontal. - - Type 5. Low duty, triple, condensing, horizontal. - - Type 6. Cross compound, condensing, horizontal. - - Type 7. High duty, triple, condensing, vertical. - -For example, the sewage flow expected at a proposed pumping station is -shown in Table 33. The steps involved in the selection of the number and -capacity of pumping units to care for these quantities are as follows: -(1) Determine the rated capacity of the equipment to be provided. In -this case the capacity will be taken as 450 horse-power, which is the -maximum load to be placed on the pumps. (2) Select any number of units -of such different types and capacities as are available for comparison, -and arrange them in different combinations so that each unit will -operate as nearly as possible at its rated capacity. The work involved -in such a study for 5 units is shown in Table 34. The weight of steam -consumed per indicated horse-power hour corresponding to the per cent of -the rated capacity at which the unit is operating is read from Fig. 64 -or other data. (3) Repeat this step for other numbers and types of -units. (4) Prepare a table showing the annual costs of combinations of -different numbers and types of units as shown for this example in Table -35. The figures in Table 35 show that the least expensive of the -combinations of the units studied is one 200 horse-power unit, and one -250 horse-power unit, with a 250 horse-power unit in reserve. It is to -be noted that a reserve unit has been provided in each combination, the -capacity of which is equal to that of the largest unit of the -combination. - - - - - CHAPTER VIII - MATERIALS FOR SEWERS - - -=90. Materials.=—The materials most commonly used for the manufacture of -sewer pipe are vitrified clay and concrete. Cast iron, steel, and wood -are also used, but only under special conditions. For pipes built in the -trench, concrete, concrete blocks, brick, and vitrified clay blocks are -used. Concrete is being used to-day more than bricks or blocks because -it is cheaper. A decade or more ago all large sewers were built of -bricks. Vitrified clay and concrete are used for manufactured pipe 42 -inches and less in diameter. Concrete is used almost exclusively for -larger sizes of pipe, particularly for pipe constructed in place, -although a brick invert lining is advisable when high velocities of flow -are expected. - -The character of the external load, the velocity of flow and the quality -of sewage are important factors in determining the material to be used -in the construction of sewers. Reinforced concrete should be used for -large sewers near the surface subjected to heavy moving loads. A high -velocity of flow with erosive suspended matter demand a brick wearing -surface on the invert. Many engineers consider concrete less suitable -than vitrified clay or brick for conveying septic sewage or acid -industrial wastes, as concrete deteriorates more rapidly under such -conditions. Concrete should be used on soft yielding foundations, -whereas a hard compact earth, which can be cut to the form of the sewer, -is suitable to the use of brick or concrete. - -Cast-iron pipe with lead joints is used for sewers flowing under -pressure, or where movements of the soil are to be expected. If the -sewage is not flowing under pressure, cement joints are sometimes used -in the cast-iron pipe. Movements of the soil are to be expected on side -hills, under railroad tracks, etc. Steel pipe is used on long outfalls -or under other conditions where external loads are light and the cost is -less than for other materials. Because of the thin plates used and the -liability to corrosion steel is not frequently used. It should never be -deeply buried nor externally loaded because of its weakness in resisting -such forces. Like wood pipe, its lightness is favorable to use on -bridges, but the greater heat conductivity of steel than wood -necessitates protection against freezing in exposed positions. Wood is -preferable only where the economy of its use is pronounced and the pipe -is running full at all times. It is desirable that the wood pipe should -be always submerged as the life of alternately wet and dry wood is -short. - -Corrugated galvanized iron and unglazed tile have been used for sewers, -but usually only in emergencies or as a makeshift. Corrugated iron is -not suitable on account of its roughness and liability to corrosion, and -unglazed tile because of its lack of strength. - -[Illustration: - - FIG. 71.—Diagrammatic Section through Clay-pipe Press. -] - - -=91. Vitrified Clay Pipe.=—In general the physical and chemical -qualities of clays before burning are not sufficient to cause their -condemnation or approval by the engineer, as their behavior in the -furnace is quite individual and depends greatly on the manner in which -they are fired. The engineer is interested in the result and writes his -specifications accordingly. - -In the manufacture of clay pipe, the clay as excavated is taken to a -mill and ground while dry, to as fine a condition as possible. It is -then sent to storage bins from which it is taken for wet grinding and -tempering. In this process the clay is mixed with water to the proper -degree of plasticity. A variation of 1 to 1½ per cent in the moisture -content will mean failure. Too wet a mixture will not have sufficient -strength to maintain its shape in the kiln. Too dry a mixture will show -laminations as it is pressed through the discs. - -A press used in the manufacture of clay pipe is shown in cross-section -in Fig. 71. With the piston heads in the steam and mud cylinders at -their extreme upward positions, the mud cylinder is filled with clay of -the proper consistency. Steam is then turned into the steam cylinder -under pressure and the clay is squeezed into the space between the inner -and outer shells of the die and mandrel to form the hub of the pipe. The -pressure on the clay may be from 250 to 600 pounds per square inch. When -clay appears at the holes, marked _hh_ at the bottom of the mud -cylinder, the bottom plate and the center portion of the die are removed -and the remainder or straight portion of the pipe is formed by squeezing -the clay between the mandrel and the outer wall of the die. A completely -formed pipe can be seen issuing from the press in Fig. 72. Any sized -pipe that is desired can be formed from the same press by changing the -size of the dies and mandrel. - -[Illustration: - - FIG. 72.—Clay-pipe Press. - - Courtesy, Blackmer and Post Manufacturing Co. -] - -Curved pipes are made in two ways—by bending directly as they issue from -the press, or by shaping by hand in plaster of paris molds. Junctions -are made by cutting the branch pipe to the shape of the outside of the -main pipe, fastening the branch in place with soft clay and then cutting -out the wall of the main pipe the size of the branch. Special fittings -are usually made by hand in plaster molds. - -After being pressed into shape the pipes are taken to a steam-heated -drying room where a constant temperature is maintained in order to -prevent cracking of the pipes. They remain in the drying room from 3 to -10 days until dry, when they are taken to the kilns. If taken to the -kilns when moist blisters will be produced. - -The dried pipes are piled carefully in the kiln so that heat and weight -may be as evenly distributed as possible, and the fire is then started -in the kiln. The process of burning can be roughly divided into five -stages: - -1st. Water smoking, which lasts about 72 hours during which the -temperature is raised gradually to 350 degrees Fahrenheit. - -2nd. Heating, during which the temperature is raised to 800 degrees -Fahrenheit in 24 hours. - -3rd. Oxidation, during which the temperature is raised to 1,400 degrees -Fahrenheit in 84 hours. - -4th. Vitrification, in which the temperature is raised to 2,100 degrees -Fahrenheit in 48 hours, and finally, - -5th. Glazing, during which the temperature is unchanged but salt (NaCl) -is thrown in and allowed to burn. - -Oxidation must be complete before vitrification is started as otherwise -blisters will be raised due to imprisoned carbon dioxide. The important -points in vitrification are to make the required temperature within a -reasonable time and to maintain a uniform distribution of heat -throughout the kiln. When vitrification is complete as shown by a glassy -fracture of a broken sample taken from the kiln, glazing is accomplished -by throwing a shovelful of salt on the hottest part of the fire. About -five to six applications of salt from two to three hours apart may be -needed. The kiln is then allowed to cool and the manufacture of the pipe -is complete. The completeness of vitrification is indicated by the -amount of water that the finished pipe will absorb. Completely vitrified -pipe will absorb no moisture. Soft-burned pipe may absorb as much as 15 -per cent moisture. - -Vitrified clay blocks are made of the same material and in the same -manner as vitrified clay pipe. - -The following data on vitrified pipe have been abstracted from the -specifications for vitrified pipe adopted by the American Society for -Testing Materials. - -Pipes shall be subject to rejection on account of the following: - - (_a_) Variation in any dimension exceeding the permissible - variations given in Table 36. - - (_b_) Fracture or cracks passing through the shell or hub, except - that a single crack at either end of a pipe not exceeding 2 inches - in length or a single fracture in the hub not exceeding 3 inches - in width nor 2 inches in length will not be deemed cause for - rejection unless these defects exist in more than 5 per cent of - the entire shipment or delivery. - - (_c_) Blisters or where the glazing is broken or which exceed 3 - inches in diameter, or which project more than ⅛ inch above the - surface. - - (_d_) Laminations which indicate extended voids in the pipe - material. - - (_e_) Fire cracks or hair cracks sufficient to impair the - strength, durability or serviceability of the pipe. - - (_f_) Variations of more than ⅛ inch per linear foot in alignment - of a pipe intended to be straight. - - (_g_) Glaze which does not fully cover and protect all parts of - the shell and ends except those exempted in Sect. 31. Also glaze - which is not equal to best salt glaze. - - (_h_) Failure to give a clear ringing sound when placed on end and - dry tapped with a light hammer. - - (_i_) Insecure attachment of branches or spurs. - - - _Workmanship and Finish_ - - (29) Pipes shall be substantially free from fractures, large or - deep cracks and blisters, laminations and surface roughness. - - (31) The glaze shall consist of a continuous layer of bright or - semi-bright glass substantially free from coarse blisters and - pimples.... Not more than 10 per cent of the inner surface of any - pipe barrel shall be bare of glaze except the hub, where it may be - entirely absent. Glazing will not be required on the outer surface - of the barrel at the spigot end for a distance from the end equal - to ⅔ the specified depth of the socket for the corresponding size - of pipe. Where glazing is required there shall be absence of any - well defined network of crazing lines or hair cracks. - - (32) The ends of the pipe shall be square with their longitudinal - axis. - - (33) Special shapes shall have a plain spigot end and a hub end - corresponding in all respects with the dimensions specified for - pipes of the corresponding internal diameter. - - TABLE 36 - - PROPERTIES OF CLAY SEWER PIPE - - Abstracts from Tentative Specifications of the American Society for - Testing Materials - - ─────────┬─────────┬───────────┬───────┬────────┬──────┬──────┬───────── - Internal │ Minimum │ Maximum │Laying │Diameter│Depth │Taper │ Minimum - Diameter,│Crushing │Absorption,│length,│ of │ of │ of │Thickness - Inches │Strength,│ Per Cent │ Feet │ Inside │Socket│Socket│ of - │ Pounds │ │ │ of │Inches│ │ Barrel. - │ per │ │ │Socket, │ │ │ Inches - │ Linear │ │ │ Inches │ │ │ - │ Foot. │ │ │ │ │ │ - │See Note │ │ │ │ │ │ - │ 2 │ │ │ │ │ │ - ─────────┼─────────┼───────────┼───────┼────────┼──────┼──────┼───────── - │ │ │ │ │ │ │ - │ │ │ │ │ │ │ - │ │ │ │ │ │ │ - │ │ │ │ │ │ │ - │ │ │ │ │ │ │ - ─────────┼─────────┼───────────┼───────┼────────┼──────┼──────┼───────── - │ │ │ │ │ │ │ - │ │ │ │ │ │ │ - ─────────┼─────────┼───────────┼───────┼────────┼──────┼──────┼───────── - 6 │ 1430 │ 5 │2, 2½, │ 8¼ │ 2 │1 : 20│ ⅝ - │ │ │ 3 │ │ │ │ - 8 │ 1430 │ 5 │2, 2½, │ 10¾ │ 2¼ │1 : 20│ ¾ - │ │ │ 3 │ │ │ │ - 10 │ 1570 │ 5 │2, 2½, │ 13 │ 2½ │1 : 20│ ⅞ - │ │ │ 3 │ │ │ │ - 12 │ 1710 │ 5 │2, 2½, │ 15¼ │ 2½ │1 : 20│ 1 - │ │ │ 3 │ │ │ │ - 15 │ 1960 │ 5 │2, 2½, │ 18¾ │ 2½ │1 : 20│ 1¼ - │ │ │ 3 │ │ │ │ - 18 │ 2200 │ 5 │2, 2½, │ 22¼ │ 3 │1 : 20│ 1½ - │ │ │ 3 │ │ │ │ - 21 │ 2590 │ 5 │2, 2½, │ 26 │ 3 │1 : 20│ 1¾ - │ │ │ 3 │ │ │ │ - 24 │ 3070 │ 5 │2, 2½, │ 29½ │ 3 │1 : 20│ 2 - │ │ │ 3 │ │ │ │ - 27 │ 3370 │ 5 │ 3 │ 33¼ │ 3½ │1 : 20│ 2¼ - 30 │ 3690 │ 5 │ 3 │ 37 │ 3½ │1 : 20│ 2½ - 33 │ 3930 │ 5 │ 3 │ 40¼ │ 4 │1 : 20│ 2⅝ - 36 │ 4400 │ 5 │ 3 │ 44 │ 4 │1 : 20│ 2¾ - 39 │ 4710 │ 5 │ 3 │ 47¼ │ 4 │1 : 20│ 2⅞ - 42 │ 5030 │ 5 │ 3 │ 51 │ 4 │1 : 20│ 3 - ─────────┴─────────┴───────────┴───────┴────────┴──────┴──────┴───────── - - ─────────┬────────────────────────────────────────────────┬──────── - Internal │ Permissible Variations │ Number - Diameter,│ │ of - Inches │ │Scorings - │ │ on - │ │ Spigot - │ │ and - │ │Socket ⅛ - │ │ Inch - │ │ Deep - ─────────┼───────┬─────────────┬────────┬───────┬─────────┼──────── - │Length,│ Internal │ Length │ Depth │Thickness│ - │ Inches│ Diameter, │ of Two │ of │ of │ - │ (-), │ Inches │Opposite│Socket,│ Barrel, │ - │ per │ │ Sides, │Inches │ Inches │ - │ Foot │ │ Inches │ (-) │ (-) │ - ─────────┼───────┼──────┬──────┼────────┼───────┼─────────┼──────── - │ │Spigot│Socket│ │ │ │ - │ │ (±) │ (±) │ │ │ │ - ─────────┼───────┼──────┼──────┼────────┼───────┼─────────┼──────── - 6 │ ¼ │ 3/16 │ ¼ │ ⅛ │ ¼ │ 1/16 │ 2 - │ │ │ │ │ │ │ - 8 │ ¼ │ ¼ │ 5/16 │ ⅛ │ ¼ │ 1/16 │ 2 - │ │ │ │ │ │ │ - 10 │ ¼ │ ¼ │ 5/16 │ ⅛ │ ¼ │ 1/16 │ 2 - │ │ │ │ │ │ │ - 12 │ ¼ │ 5/16 │ ⅜ │ ⅛ │ ¼ │ 1/16 │ 2 - │ │ │ │ │ │ │ - 15 │ ¼ │ 5/16 │ ⅜ │ ⅛ │ ¼ │ 3/32 │ 3 - │ │ │ │ │ │ │ - 18 │ ¼ │ ⅜ │ 7/16 │ 3/16 │ ¼ │ 3/32 │ 3 - │ │ │ │ │ │ │ - 21 │ ¼ │ 7/16 │ ½ │ 3/16 │ ¼ │ ⅛ │ 3 - │ │ │ │ │ │ │ - 24 │ ⅜ │ ½ │ 9/16 │ ¼ │ ¼ │ ⅛ │ 4 - │ │ │ │ │ │ │ - 27 │ ⅜ │ ⅝ │11/16 │ ¼ │ ¼ │ ⅛ │ 4 - 30 │ ⅜ │ ⅝ │11/16 │ ¼ │ ¼ │ ⅛ │ 4 - 33 │ ⅜ │ ¾ │13/16 │ ¼ │ ¼ │ 3/16 │ 5 - 36 │ ⅜ │ ¾ │13/16 │ ⅜ │ ¼ │ 3/16 │ 5 - 39 │ ⅜ │ ¾ │13/16 │ ⅜ │ ¼ │ 3/16 │ 5 - 42 │ ⅜ │ ¾ │13/16 │ ⅜ │ ¼ │ 3/16 │ 5 - ─────────┴───────┴──────┴──────┴────────┴───────┴─────────┴──────── - - NOTE 1. For methods of making tests see Proc. Am. Soc. for Testing - Materials. - - NOTE 2. Concentrated load at end of vertical diameter. - - (_a_) Slants shall have their spigot ends cut at an angle of - approximately 45 degrees with the longitudinal axis. - - (_b_) Curves shall be at angles of 90, 45, 22½, and 11¼ degrees as - required. They shall conform substantially to the curvature - specified. - - (_c_) ... All branches shall terminate in sockets. - -[Illustration: - - FIG. 73.—Standard Clay Pipe Specials. - - Courtesy, Blackmer and Post Manufacturing Co. -] - -In Fig. 73 are shown the various forms of vitrified pipe and specials -which are ordinarily available on the market. - -The life of vitrified clay sewers and some observations on the results -of the inspection of the sewers in Manhattan are discussed in Chapter -XII. The strength of vitrified sewer pipes is shown in Table 37. - - TABLE 37 - - STRENGTH OF SEWER PIPE - - Strength in pounds per linear foot to carry loads from ditch filling - material such as ordinary sand and thoroughly wet clay, with the under - side of the pipe bedded 60° to 90° by ordinary good methods. From Proc. - Am. Society for Testing Materials, Vol. 20, 1920, page 604. - ────────┬────────────────────────────────────────────────────────────── - Height │ - of Fill │ - Above │ - Top of │ - Pipe, │ - Feet │ Breadth of the Ditch a Little Below the Top of the Pipe - ────────┼───────────┬───────────┬───────────┬────────────┬───────────── - │ 1 Foot │ 2 Feet │ 3 Feet │ 4 Feet │ 5 Feet - ────────┼───────────┴───────────┴───────────┴────────────┴───────────── - │ Ditch Filling Material - ────────┼─────┬─────┬─────┬─────┬─────┬─────┬─────┬──────┬──────┬────── - │sand │clay │sand │clay │sand │clay │sand │ clay │ sand │ clay - ────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼──────┼──────┼────── - 2│ 265│ 280│ 615│ 635│ 970│ 990│ 1330│ 1,350│ 1,690│ 1,710 - 4│ 400│ 450│ 1055│ 1125│ 1745│ 1825│ 2455│ 2,535│ 3,165│ 3,250 - 6│ 470│ 545│ 1370│ 1500│ 2370│ 2525│ 3405│ 3,575│ 4,460│ 4,740 - 8│ 505│ 605│ 1600│ 1790│ 2875│ 3115│ 4215│ 4,495│ 5,595│ 5,890 - 10│ 525│ 640│ 1765│ 2015│ 3275│ 3610│ 4900│ 5,295│ 6,590│ 7,020 - 12│ 535│ 660│ 1880│ 2185│ 3600│ 4030│ 5485│ 6,000│ 7,460│ 8,035 - 14│ 540│ 675│ 1965│ 2320│ 3855│ 4380│ 5975│ 6,620│ 8,225│ 8,950 - 16│ 545│ 680│ 2025│ 2425│ 4065│ 4675│ 6395│ 7,165│ 8,890│ 9,775 - 18│ 545│ 685│ 2070│ 2505│ 4230│ 4920│ 6750│ 7,630│ 9,480│10,520 - 20│ 545│ 690│ 2100│ 2565│ 4365│ 5130│ 7050│ 8,060│ 9,995│11,190 - 22│ 545│ 690│ 2125│ 2610│ 4470│ 5305│ 7305│ 8,425│10,445│11,795 - 24│ 545│ 690│ 2140│ 2645│ 4560│ 5445│ 7525│ 8,750│10,840│12,340 - 26│ 545│ 690│ 2150│ 2675│ 4630│ 5575│ 7705│ 9,035│11,185│12,830 - 28│ 545│ 690│ 2160│ 2695│ 4685│ 5680│ 7860│ 9,280│11,490│13,270 - 30│ 545│ 690│ 2165│ 2715│ 4725│ 5765│ 7990│ 9,500│11,755│13,670 - Very │ │ │ │ │ │ │ │ │ │ - great │ 545│ 690│ 2180│ 2770│ 4910│ 6230│ 8725│11,075│13,635│17,305 - ────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴──────┴──────┴────── - - -=92. Cement and Concrete Pipe.=—Although there is no general recognition -of a difference between cement and concrete pipe, there is a tendency to -term manufactured pipe of small diameter cement pipe, and large pipes or -pipes constructed in place, concrete pipe. Cement, unlike clay, is used -in the manufacture of pipe in the field or by more or less unskilled -operators in “one man” plants. Great care should be used in the -selection of cement, aggregate, and reinforcement for precast cement -pipe since the shocks to which it is subjected in transit are more -liable to rupture it than the heavier but steadier loads imposed on it -in the trench. - -The United States Government, various scientific and engineering -societies, and other interested organizations have collaborated in the -preparation of specifications for cement and cement tests. These -specifications can be found in Trans. Am. Soc. Civil Engineers, Vol. 82, -1918, p. 166, and in other publications. - -The following abstracts have been taken from the proposed tentative -specifications for Concrete Aggregates, of the Am. Society for Testing -Materials, issued June 21, 1921: - - 1. Fine aggregate shall consist of sand, stone screenings, or - other inert materials with similar characteristics, or a - combination thereof, having clean, hard, strong, durable uncoated - grains, free from injurious amounts of dust, lumps, soft or flaky - particles, shale, alkali, organic matter, loam or other - deleterious substances. - - 2. Fine aggregates shall preferably be graded from fine to coarse, - with the coarser particles predominating, within the following - limits: - - Passing No. 4 sieve 100 per cent - Passing No. 50 sieve, not more than 50 per cent - Weight removed by elutriation test, not more than 3 per cent - - Sieves shall conform to the U. S. Bureau of Standards - specifications for sieves. - - 3. The fine aggregate shall be tested in combination with the - coarse aggregate and the cement with which it is to be used and in - the proportions, including water, in which they are to be used on - the work, in accordance with the requirements specified in Section - 6.... - - 7. Coarse aggregate shall consist of crushed stone, gravel or - other approved inert materials with similar characteristics, or a - combination thereof, having clean, hard, strong, durable, uncoated - pieces free from injurious amounts of soft, friable, thin, - elongated or laminated pieces, alkali, organic or other - deleterious matter. - - * * * * * - - The following Table indicates desirable gradings, in percentages, - for coarse aggregate for certain maximum sizes. - - GRADINGS OF COARSE AGGREGATES - - ─────────┬─────────────────────────────────────────┬─────────────────── - Maximum │ Circular Openings, Inches │ Passing Screen - Size of │ │ Having Circular - Aggregate│ │Openings ¼ Inch in - Inches │ │diameter, not more - │ │ than - ─────────┼───┬───┬───┬─────┬─────┬─────┬─────┬─────┼─────────────────── - │ 3 │2½ │ 2 │ 1½ │ 1¼ │ 1 │ ¾ │ ½ │ - ─────────┼───┼───┼───┼─────┼─────┼─────┼─────┼─────┼─────────────────── - 3 │100│ │ │40–75│ │ │ │ │ 15 per cent - 2½ │ │100│ │ │40–75│ │ │ │ 15 per cent - 2 │ │ │100│ │ │40–75│ │ │ 15 per cent - 1½ │ │ │ │ 100 │ │ │40–75│ │ 15 per cent - 1¼ │ │ │ │ │ 100 │ │ │35–70│ 15 per cent - 1 │ │ │ │ │ │ 100 │ │40–75│ 15 per cent - ¾ │ │ │ │ │ │ │ 100 │ │ 15 per cent - ─────────┴───┴───┴───┴─────┴─────┴─────┴─────┴─────┴─────────────────── - -The manufacture of small size cement pipe requires relatively more skill -than equipment. As a result great care must be observed in the -inspection of cement pipe and in the enforcement of specifications. For -large size concrete pipe and reinforced concrete pipe the difficulty of -holding the pipe together during transportation and lowering into the -trench aid in insuring a good product. - -Cement pipe is made by ramming a mixture of cement, sand, and water into -a cylindrical mold and allowing it to stand until set. The mold is then -removed and the pipe stands for a further period of time to become -cured. The selection and proportion of materials, the amount of water, -the method of ramming, the period of setting, the length of time of -curing, and the control of moisture and temperature during this period -are of great importance in the resulting product. E. S. Hanson[52] -states that the most conservative engineers recommend a mixture of one -sack of cement to 2½ cubic feet of aggregate measured as loosely thrown -into the measuring box. In making up the aggregate, clean gravel or -broken stone up to ¼ inch in size is used. The American Concrete -Institute recommends that 100 per cent pass a ½-inch screen, 70 per cent -a ¼-inch screen, 50 per cent a No. 10, 40 per cent a No. 20, 30 per cent -a No. 30, and 20 per cent a No. 40. The materials should be carefully -graded by experiment and not guessed at, as the behavior of all -aggregates is not the same. Too coarse an aggregate is difficult to -handle in manufacturing. It causes loss of pipe when the jacket or mold -is removed and results in rough pipe, stone pockets, and pin holes -through which water spurts when pressure tests are applied. Too fine an -aggregate causes loss of strength and with ordinary mixtures tends to -produce a pipe which will show seepage under internal pressure tests. -The amount of water in the mixture will vary, from 15 to 20 per cent. -The mixture should appear dry but should ball in the hand under some -pressure. - -[Illustration: - - FIG. 74.—Details of 24–Inch Concrete Pipe Form. -] - -The mixture can be rammed into the molds by hand or machine. A -machine-made pipe is preferable as it produces a more even and stronger -product. There are two types of machines for this purpose. One type -consists of a number of tamping feet which deliver about 200 blows to -the minute with a pressure of about 800 pounds per square inch of area -exposed. In the other type a revolving core is drawn through the pipe, -packing and polishing the concrete as it is pulled through, with special -provision for packing the bell of the pipe. The tamping machines can -make 1,500 feet of small size pipe to 300 feet of 24–inch pipe in a day. -Machines of the second type can make 750 feet of 8–inch to 200 feet of -30–inch pipe in 30–inch lengths in 9 hours. The inside and outside forms -for a 24–inch pipe are shown in Fig. 74 as used with the tamping -machines. The forms are swabbed with oil before being filled in order to -facilitate their removal. In making a Y-branch or other special, a hole -is cut in the pipe or mold the size of the joining pipe which is then -set in place and the joint wiped smooth with cement. - - TABLE 38 - - PROPERTIES OF CEMENT CONCRETE SEWER PIPE - - 1917 Specifications of American Society for Testing Materials, with - Subsequent Revisions - - ─────────┬───────┬────────┬───────┬───────┬──────┬───────── - │Laying │Diameter│Normal │ Depth │Taper │ Minimum - │Length,│ at │Annular│ of │ of │Thickness - │ Feet │ Inside │Space, │Socket,│Socket│ of - │ │ of │Inches │Inches │ │ Barrel, - │ │Socket, │ │ │ │ Inches - │ │ Inches │ │ │ │ - Internal │ │ │ │ │ │ - Diameter,│ │ │ │ │ │ - Inches │ │ │ │ │ │ - ─────────┼───────┼────────┼───────┼───────┼──────┼───────── - │ │ │ │ │ │ - │ │ │ │ │ │ - │ │ │ │ │ │ - │ │ │ │ │ │ - │ │ │ │ │ │ - ─────────┼───────┼────────┼───────┼───────┼──────┼───────── - │ │ │ │ │ │ - │ │ │ │ │ │ - ─────────┼───────┼────────┼───────┼───────┼──────┼───────── - │2, 2½, │ 8¼ │ ½ │ 2 │1 : 20│ ⅝ - 6 │ 3 │ │ │ │ │ - │2, 2½, │ 11 │ ⅝ │ 2¼ │1 : 20│ ¾ - 8 │ 3 │ │ │ │ │ - │2, 2½, │ 13¼ │ ⅝ │ 2½ │1 : 20│ ⅞ - 10 │ 3 │ │ │ │ │ - │2, 2½, │ 15⅝ │ ⅝ │ 2½ │1 : 20│ 1 - 12 │ 3 │ │ │ │ │ - │2, 2½, │ 19¼ │ ⅝ │ 2½ │1 : 20│ 1¼ - 15 │ 3 │ │ │ │ │ - │2, 2½, │ 22¾ │ ⅝ │ 2¾ │1 : 20│ 1½ - 18 │ 3 │ │ │ │ │ - │2, 2½, │ 26½ │ ¾ │ 2¾ │1 : 20│ 1¾ - 21 │ 3 │ │ │ │ │ - │2, 2½, │ 30¼ │ ¾ │ 3 │1 : 20│ 2⅛ - 24 │ 3 │ │ │ │ │ - 27 │ 3 │ 34 │ ⅞ │ 3¼ │1 : 20│ 2¼ - 30 │ 3 │ 38 │ 1 │ 3½ │1 : 20│ 2½ - 33 │ 3 │ 41½ │ 1 │ 4 │1 : 20│ 2¾ - 36 │ 3 │ 45½ │ 1¼ │ 4 │1 : 20│ 3 - 39 │ 3 │ 49 │ 1¼ │ 4 │1 : 20│ 3¼ - 42 │ 3 │ 53 │ 1½ │ 4 │1 : 20│ 3½ - ─────────┴───────┴────────┴───────┴───────┴──────┴───────── - - ─────────┬──────────────────────────────────────┬─────────┬─────────── - │ Limits of Permissible Variations │ Minimum │ Maximum - │ │Crushing │Absorption, - │ │Strength,│ Per Cent - │ │ Pounds │ - │ │ per │ - │ │ Linear │ - Internal │ │ Foot at │ - Diameter,│ │ End of │ - Inches │ │Diameter │ - ─────────┼───────┬─────────────┬──────┬─────────┼─────────┼─────────── - │Length,│ Internal │Depth │Thickness│ │ - │ Inch │ Diameter, │of Hub│of Barrel│ │ - │ per │ Inches │ (-) │ (-) │ │ - │ Foot │ │Inches│ Inches │ │ - │ (-) │ │ │ │ │ - ─────────┼───────┼──────┬──────┼──────┼─────────┼─────────┼─────────── - │ │Spigot│Socket│ │ │ │ - │ │ (±) │ (±) │ │ │ │ - ─────────┼───────┼──────┼──────┼──────┼─────────┼─────────┼─────────── - │ ¼ │ 3/16 │ 3/16 │ ¼ │ 1/16 │ 1430 │ 8 - 6 │ │ │ │ │ │ │ - │ ¼ │ ¼ │ ¼ │ ¼ │ 1/16 │ 1430 │ 8 - 8 │ │ │ │ │ │ │ - │ ¼ │ ¼ │ ¼ │ ¼ │ 1/16 │ 1570 │ 8 - 10 │ │ │ │ │ │ │ - │ ¼ │ ¼ │ ¼ │ ¼ │ 1/16 │ 1910 │ 8 - 12 │ │ │ │ │ │ │ - │ ¼ │ ¼ │ ¼ │ ¼ │ 3/32 │ 1960 │ 8 - 15 │ │ │ │ │ │ │ - │ ¼ │ ¼ │ ¼ │ ¼ │ 3/32 │ 2200 │ 8 - 18 │ │ │ │ │ │ │ - │ ¼ │ 5/16 │ 5/16 │ ¼ │ ⅛ │ 2590 │ 8 - 21 │ │ │ │ │ │ │ - │ ⅜ │ 5/16 │ 5/16 │ ¼ │ ⅛ │ 3070 │ 8 - 24 │ │ │ │ │ │ │ - 27 │ ⅜ │ 5/16 │ ⅜ │ ¼ │ ⅛ │ 3370 │ 8 - 30 │ ⅜ │ ⅜ │ ⅜ │ ¼ │ ⅛ │ 3690 │ 8 - 33 │ ⅜ │ ⅜ │ ⅜ │ ¼ │ 3/16 │ 3930 │ 8 - 36 │ ⅜ │ ½ │ ½ │ ¼ │ 3/16 │ 4400 │ 8 - 39 │ ⅜ │ ½ │ ½ │ ¼ │ 3/16 │ 4710 │ 8 - 42 │ ⅜ │ ½ │ ½ │ ¼ │ 3/16 │ 5030 │ 8 - ─────────┴───────┴──────┴──────┴──────┴─────────┴─────────┴─────────── - -After the removal of the mold the pipe may be cured by the water or the -steam process. Hanson states: - - By the former the pipe are simply set on the floor of the plant - and as soon as they are sufficiently strong so that they can be - sprinkled with water without falling down; sprinkling is commenced - and continued at such intervals for 6 or 7 days that the pipe will - be moist at all times. This is a slower process than steam curing. - It is also less uniform and less subject to control than where the - product is cured by steam. - -In the steam process the pipe is exposed to low-pressure steam with -plenty of moisture in a closed receptacle for 24 hours, or until -hardened. It has been found by tests that pipes sprinkled for 28 days -are as strong as steam-cured pipes. - -The dimensions of cement concrete sewer pipe as recommended by the Am. -Society for Testing Materials are shown in Table 38. - -The following has been abstracted from the description of the -manufacture of one form of concrete pipe by G. C. Bartram.[53] All pipe -are manufactured in 4–foot lengths near the site at which they are to be -installed because of their great weight, for example, 36–inch pipe -weighs one ton. The plant for the manufacture of the pipe consists of -cast-iron bottom and top rings for each size to be used on the job, and -inside and outside steel casings. There are three bases for each steel -casing as the pipes stand on the bases for 72 hours and the steel casing -remains on for only 24 hours after the concrete has been poured. The -pipes are then lifted off the bases and stored for aging. The pipes are -cast with the spigot end up. - -The concrete is ordinarily mixed in the proportions of 1 : 2 : 4. The -materials are placed in the mixer in the following order: first, the -stone, then the sand, then the cement, and finally the water. Sufficient -water is added to make the concrete flow freely. In cold weather or for -a hurry-up job the molds are covered with canvas and are steamed for 2 -or 3 hours immediately after the concrete is poured. The molds are then -removed but the pipe should be steamed before use. Otherwise they are -allowed to stand 72 hours, as explained above. In cold weather the steam -is used to prevent freezing and not to hasten the completion of the -pipe. - -[Illustration: - - FIG. 75.—Triangle Mesh Reinforced Concrete Pipe. - - As made by the Am. Concrete Pipe and Pile Co., Chicago. -] - -[Illustration: - - FIG. 76.—Methods of Joining and Reinforcing Concrete Pipe. -] - -One layer or ring of reinforcement is used for sizes from 24 to 48 -inches and two layers or rings for larger pipe. A type of reinforcement -sometimes used is the American Steel and Wire Company’s Triangular Mesh, -an illustration of which is shown in Fig. 75. The wire mesh is cut to -fit and is placed in a slot in the cast-iron base. The slot is then -filled with sand so that the concrete cannot enter, thus leaving a -portion of the reinforcement exposed. The inside reinforcement extends -through and out of the spigot of the completed pipe. In the trench the -two reinforcements overlap in the key-shaped space left on the inside of -the pipe by the design of the bell and spigot. This space is shown in -Fig. 76 A. When the pipe is placed in the trench the key-shaped space is -plastered with mortar and a piece is knocked out of the bell to receive -the grout with which the joint is closed. A spring steel band is then -put on the outside of the joint and grout poured into the hole at the -top. The band is removed as soon as the joint materials have set. - -The rules for the reinforcement of concrete pipe recommended in Volume -XV, 1919, of the Transactions of the Concrete Institute are as follows: - - No reinforcement is approved for pipe between 30 and 60 inches in - diameter or in rock or hard soils. For pipe 36 inches in diameter - or less the minimum thickness of shell shall be 5 inches. For - 60–inch pipe the minimum thickness shall be 7 inches with - intermediate sizes in proportion. Reinforcement for circular pipe - shall consist of one or two rings of circular wire fabric or rods - of the areas shown in Table 39. All sewers near the surface and - subject to vibration should be reinforced. For sewers 6 feet or - less in diameter the reinforcement should consist of at least ½ of - 1 per cent of the area of the concrete. It should be placed near - the inside at the crown and near the outside at the haunches. If - large horizontal pressures are expected the pipe should be - reinforced for these reverse stresses, which involves placing the - reinforcement near the outside at the crown and near the inside at - the haunches. The minimum thickness of the walls of sewers greater - than 6 feet in diameter with flat bottom and arch, with or without - side walls, should be 8 inches. - - TABLE 39 - - REINFORCEMENT FOR CIRCULAR CONCRETE SEWER PIPE - - (See Vol. XV, Proceedings Am. Concrete Institute) - ─────────────────┬─────────────────┬─────────────────┬───────────────── - Diameter in │Minimum Thickness│ Number of Rings │ Cross Sectional - Inches │ of Shell in │ │Area of Each Ring - │ Inches │ │ - ─────────────────┼─────────────────┼─────────────────┼───────────────── - 24 │3 │1 │.058 - 27 │3 │1 │.068 - 30 │3½ │1 │.080 - 33 │4 │1 │.107 - 36 │4 │1 │.146 - 39 │4 │1 │.146 - 42 │4½ │1 │.153 - 48 │5 │2 │.107 - 54 │5½ │2 │.123 - 60 │6 │2 │.146 - 66 │6½ │2 │.168 - 72 │7 │2 │.180 - 84 │8 │2 │.208 - 96 │9 │2 │.245 - ─────────────────┴─────────────────┴─────────────────┴───────────────── - -Three methods for the reinforcement of concrete sewers are shown in Fig. -76 B. - - -=93. Proportioning of Concrete.=—In the proportioning of concrete -questions of strength, of permeability, and of workability[54] may need -consideration. All of these qualities are affected by the amount of -cement, the nature and gradation and relative proportions of the fine -and the coarse aggregate, and the amount of mixing water used. - -Other things being equal the strength varies with the amount of cement -put into the concrete. For the same amount of cement and the same -consistency of the mixture, the strength increases with increased -density of concrete (that is, with decreased voids), and the effort -should be made so to proportion the fine and coarse aggregates as to -produce the densest concrete (least voids) with the aggregates -available. For the same consistency, the strength then will vary with -the ratio of the amount of cement to the amount of the voids. - -So far as the mixing water is concerned, the greatest strength in the -concrete will be attained at a rather dry mix; that which produces the -least volume of concrete. The addition of more water results in a -concrete of less strength; 40 per cent more water may give a concrete of -less than half the normal strength. The reduction in strength is then -very marked for the wetter mixes, and the water content used is a -feature of considerable importance in the design of concrete mixtures. - -Permeability is affected by the same elements as strength, but the size -and discontinuity of the pores have a greater influence. - -Workability is an important quality; in some respects it will have to be -obtained at the expense of strength. Increasing the amount of mixing -water increases the workability of the mixtures, with a resulting -decrease in strength which may have to be accepted or else overcome by -increasing the cement in the mix. - -An excess of water is often used unnecessarily through ignorance of the -injurious results. A high proportion of coarse aggregate, up to a -certain limit, will give concrete of high strength, but the mixture will -be harsh-working and not easy to place. Lower proportions of coarse -aggregate will give greater workability and better uniformity of -product, the latter being an important matter. It is apparent that the -degree of workability of the mixture needed will depend upon the nature -of the construction—for a pavement where the concrete will receive -substantial tamping or working the water content may be much less than -that which may need to be used in placing concrete around reinforcement -in narrow members, or where little tamping or spading can be done. The -nature of the work will affect the standard of consistency to be -specified. - -The proportioning of the concrete should then be dependent upon the -needs of the structure and the manner of placing the concrete. The -proportions selected should be carefully adhered to and especially -should care be taken to see that the right quantity of mixing water is -used. - -The materials are commonly measured volumetrically (by bulk). Because of -the variations which are introduced by volumetric measurement of the -materials by the presence of varying degrees of moisture, measurements -by weight would be more accurate, but these would also be affected by -differences in the specific gravity of the materials. The methods of -measuring, the allowance for moisture, as well as the proportions of the -materials, should be specified. - -The methods for proportioning concrete are: - - (1) Arbitrarily selected proportions. - - (2) Proportions based on minimum voids. - - (3) Proportions based on trial mixtures. - - (4) Proportions based on a sieve analysis curve. - - (5) Proportions based on the surface area of the aggregates. - - (6) Proportions based on the water-cement ratio and the fineness - modulus. - - (7) Proportions based on mortar-voids and cement-voids ratio. - -Arbitrarily selected proportions are in quite general use; they are -intended to apply to the materials most commonly used in the vicinity of -the work. The most common practice is to use twice as great a volume of -coarse aggregate as fine aggregate, as for instance 1 part cement, 2 -parts fine aggregate, and 4 parts coarse aggregate. Decreasing the ratio -of coarse aggregate to fine aggregate may give a more easily worked mix -or require relatively less water for a given workability, and in some -cases it will be proper to increase this ratio and thus secure an -increase of strength. Judgment and experience with given materials may -warrant changes from a stated ratio. The proportions are now frequently -given as one part cement to a certain number of parts of the mixed -aggregate, leaving the proportions of the fine to coarse to be -determined otherwise, since small variations in the relation of these -will not greatly affect the strength. Proportions in common use are:[55] - - Mortar for - Laying brick and stone masonry from 1 : 0 to 1 : 3 - Filling joints in sewer pipe 1 : 0 to 1 : 2 - Surfaces, floors, sidewalks, pavements 1 : 0 to 1 : 2 - Waterproof linings 1 : 0 to 1 : 2 - Cement, bricks, and blocks 1 : 2½ to 1 : 4 - Concrete for - Gravity retaining walls, heavy - foundations, structures needing mass - more than strength from 1 : 3 : 6 to 1 : 4 : 8 - Retaining walls, piers, sewers, - pavements, foundations, and work - requiring strength. (Compressive - strength in 28 days, 1,500 to 2,000 - pounds per square inch) from 1 : 2 : 4 to 1 : 3 : 6 - Floors, beams, pavements, reinforced - concrete, arch bridges, low-pressure - tanks. (Compressive strength in 28 - days, 2,000 to 3,000 pounds per - square inch) from 1 : 1½ : 3 to 1 : 2½ : 4½ - Reinforced concrete columns, conduit - pipe, impervious concrete. - (Compressive strength in 28 days, - 3,000 to 4,000 pounds per square - inch) from 1 : 1 : 2 to 1 : 1½ : 3 - -The usual method of proportioning based on minimum voids is to assume -that the particles of fine aggregate should fill the voids in the coarse -aggregate and that the particles of the cement will fill the voids in -the fine aggregate. About 5 to 10 per cent additional fine aggregate is -generally added to push the particles of the coarse aggregate apart and -thus give a more easily worked concrete and one freer from void spaces. -This method is inaccurate, principally because of the effect of the -moisture on the volume of the voids, and because the effect on the -volume by the addition of water is unknown. - -Trial mixtures may be made by carefully weighing each of the ingredients -and then combining them to give a workable concrete. Using a given -amount of cement, the proportion of ingredients, of the same total -weight, which will give the least volume and therefore the densest -concrete is adopted. When making the comparison the consistency of the -mixes must be maintained constant. - -Proportioning may be based on an ideal sieve analysis curve of the mixed -cement and aggregates. The sieve analysis of the aggregates is made by -screening a predetermined weight of the sample through a series of 5 to -8 sieves graded in size from slightly below the size of the largest -particle to slightly above the smallest particle of the aggregate. The -analysis is then expressed in the form of a curve. The ideal curve, -according to Fuller,[56] is shown in Fig. 77. - -[Illustration: - - FIG. 77.—Gravel Analysis. - - The dotted line indicates the ideal combination of the coarse and fine - portions. The heavy full line indicates the combination attained. -] - -The method of proportioning concrete by surface areas is based on the -theory that the strength of a concrete depends on the amount of cement -used in proportion to the surface area of the aggregates.[57] - -The proportioning of concrete on the basis of a water-cement ratio and a -fineness modulus was introduced by Prof. D. A. Abrams.[58] It is based -on the theory that with fixed conditions of aggregate, moisture, etc., -the ratio of water to cement determines the strength of the concrete. - -A method of proportioning concrete by determining experimentally the -voids in mortars made up with a given amount of sand and definite -proportions of cement, and then calculating the voids in the concrete -made up by adding a definite amount of coarse aggregate to the mixture, -has been developed.[59] The method is based on the theory that the -strength of the concrete is a known function of the ratio of the volume -of cement to the volume of the voids in the concrete. The effect of -varying the proportion of the ingredients, including an increase in the -amount of mixing water beyond that required to give the densest mixture, -may be found by the method, and a comparison may be made of results -obtainable with different classes of fine and coarse aggregates. - -Arbitrarily selected proportions, proportions based on voids, and -proportions based on trial mixtures are usually satisfactory for small -jobs where the amount of materials involved is not large. Where the -saving in materials will permit, more accurate methods should be used. -The methods can be studied more fully by reference to the original -articles quoted in the footnotes, or to the following texts: - - Materials of Construction, Johnson, 5th Edition, 1918. - Materials of Engineering, H. F. Moore, 2d Edition, 1920. - Masonry Construction, I. O. Baker, 10th Edition, 1912. - Concrete Engineer’s Handbook, Hool and Johnson, 1918. - Concrete, Plain and Reinforced, Taylor and Thompson, 1916. - - -=94. Waterproofing Concrete.=—The waterproofing of concrete is most -satisfactorily done by making dense mixtures. In practice such -substances as hydrated lime, clay, alum and soap, and proprietary -compounds such as Ceresit, Medusa, etc., are frequently mixed with the -concrete under the theory that these very fine substances will fill any -remaining voids and render the concrete impervious. The specifications -of the Joint Committee issued on June 4, 1921, are much briefer and -contain less detailed instruction than those issued earlier.[60] The -earlier instructions follow. - - Many expedients have been resorted to for making concrete - impervious to water. Experience shows, however, that when mortar - or concrete is proportioned to obtain the greatest practicable - density and is mixed to the proper consistency, the resulting - mortar or concrete is impervious under moderate pressure. - - On the other hand concrete of dry consistency is more or less - pervious to water, and, though compounds of various kinds have - been mixed with the concrete or applied as a wash to the surface, - in an effort to offset this defect, these expedients have - generally been disappointing, for the reason that many of these - compounds have at best but temporary value, and in time lose their - power of imparting impermeability to the concrete. - - In the case of subways, long retaining walls, and reservoirs, - provided the concrete itself is impervious, cracks may be so - reduced, by horizontal and vertical reinforcement properly - proportioned and located, that they will be too minute to permit - leakage, or will be closed by infiltration of silt. - - Asphaltic or coal tar preparations applied either as a mastic or - as a coating on felt cloth or fabric, are used for waterproofing, - and should be proof against injury by liquids or gases. - - For retaining and similar walls in direct contact with the earth, - the application of one or two coatings of hot coal tar pitch, - following a painting with a thin wash of coal tar dissolved in - benzol, to the thoroughly dried surface of concrete is an - efficient method of preventing the penetration of moisture from - the earth. - -Tar paper and asphaltic compounds are not often used in sewer work as -absolute imperviousness is seldom necessary. - - -=95. Mixing and Placing Concrete.=—Careful workmanship is desirable in -the mixing and placing of concrete in sewers since water-tight -construction is desired. Because of the difficulty of inspecting -concrete in wet, dark and crowded excavations, and the careless habits -of workmen experienced in concrete sewer construction, the highest class -of concrete work cannot be expected. The situation is met by designing -thick walls as shown in the sections illustrated in Fig. 22 and 23. - -In the report of the Joint Committee on Concrete and Reinforced Concrete -in Transactions of the American Society of Civil Engineers for 1917, on -page 1101 the recommendation is made concerning the mixing and placing -of concrete as follows:[61] - - The mixing of concrete should be thorough and should continue - until the mass is uniform in color and is homogeneous. As the - maximum density and greatest strength of a given mixture depends - largely on thorough and complete mixing, it is essential that this - part of the work should receive special attention and care. - - Inasmuch as it is difficult to determine by visual inspection - whether the concrete is uniformly mixed, especially where - aggregates having the color of cement are used, it is essential - that the mixing should occupy a definite period of time. The - minimum time will depend on whether the mixing is done by machine - or hand. - - (_a_) Measuring Ingredients: Methods of measurement of the various - ingredients should be used which will secure at all times separate - and uniform measurements of cement, fine aggregate, coarse - aggregate and water. - - (_b_) Machine Mixing: The mixing should be done in a batch machine - mixer of a type which will insure the uniform distribution of the - materials throughout the mass, and should continue for the minimum - time of 1½ minutes after all the ingredients are assembled in the - mixer. For mixers of 2 or more cubic yards capacity, the minimum - time of mixing should be 2 minutes. Since the strength of the - concrete is dependent on thorough mixing, a longer time than this - minimum is preferable. It is desirable to have the mixer equipped - with an attachment for automatically locking the discharging - device so as to prevent the emptying of the mixer until all the - materials have been mixed together for the minimum time required - after they are assembled in the mixer. Means should be provided to - prevent aggregates being added after the mixing has commenced. The - mixer should also be equipped with water storage, and an automatic - measuring device which can be locked if desired. It is also - desirable to equip the mixer with a device recording the - revolutions of the drum. The number of revolutions should be so - regulated as to give at the periphery of the drum a uniform speed. - About 200 feet per minute seems to be the best speed in the - present state of the art. - - (_c_) Hand Mixing: Hand mixing should be done on a water-tight - platform and especial precautions taken after the water has been - added, to turn all the ingredients together at least 6 times, and - until the mass is homogeneous in appearance and color. - - (_d_) Consistency: The materials should be mixed wet enough to - produce a concrete of such a consistency as will flow sluggishly - into the forms and about the metal reinforcement when used, and - which at the same time can be conveyed from the mixer to the forms - without separation of the coarse aggregate from the mortar. The - quantity of water is of the greatest importance in securing - concrete of maximum strength and density; too much water is as - objectionable as too little. - - (_e_) Retempering: The remixing of concrete and mortar that has - partly reset should not be permitted. - - - _Placing Concrete_ - - (_a_) Methods: Concrete after the completion of the mixing should - be conveyed rapidly to the place of final deposit; under no - circumstances should concrete be used that has partly set. - - Concrete should be deposited in such a manner as will permit the - most thorough compacting such as can be obtained by working with a - straight shovel or slicing tool kept moving up and down until all - the ingredients are in their proper place. Special care should be - exercised to prevent the formation of laitance; where laitance has - formed it should be removed, since it lacks strength and prevents - a proper bond in the concrete. - - Care should be taken that the forms are substantial and thoroughly - wetted (except in freezing weather) or oiled, and that the space - to be occupied by the concrete is free from all debris. When the - placing of concrete is suspended, all necessary grooves for - joining future work should be made before the concrete has set. - - When work is resumed concrete previously placed should be - roughened, cleansed of foreign material and laitance, thoroughly - wetted and then slushed with a mortar consisting of one part - Portland cement and not more than 2 parts of fine aggregate. - - The surfaces of concrete exposed to premature drying should be - kept covered and wet for at least 7 days. - - Where concrete is conveyed by spouting, the plant should be of - such a size and design as to insure a practically continuous - stream in the spout. The angle of the spout with the horizontal - should be such as to allow the concrete to flow without separation - of the ingredients; in general an angle of about 27 degrees or 1 - vertical to 2 horizontal is good practice. The spout should be - thoroughly flushed with water before and after each run. The - delivery from the spout should be as close as possible from the - point of deposit. Where the discharge must be intermittent, a - hopper should be provided at the bottom. Spouting through a - vertical pipe is satisfactory when the flow is continuous; when it - is checked and discontinuous it is highly objectionable unless the - flow is checked by baffle plates. - - (_b_) Freezing Weather: Concrete should not be mixed or deposited - at a freezing temperature, unless special precautions are taken to - prevent the use of materials covered with ice crystals or - containing frost, and to prevent the concrete from freezing before - it has set and sufficiently hardened. - - As the coarse aggregate forms the greater portion of the concrete, - it is particularly important that this material be warmed to well - above the freezing point. - - The enclosing of a structure and the warming of a space inside the - enclosure is recommended, but the use of salt to lower the - freezing point is not recommended. - - (_c_) Rubble Concrete: Where the concrete is to be deposited in - massive work, its value may be improved and its cost materially - reduced by the use of clean stones saturated with water, - thoroughly embedded in and completely surrounded by concrete. - - (_d_) Under Water: In placing concrete under water, it is - essential to maintain still water at the place of deposit. With - careful inspection the use of tremies, properly designed and - operated, is a satisfactory method of placing concrete through - water. The concrete should be mixed very wet (more so than is - ordinarily permissible) so that it will flow readily through the - tremie and into place with practically a level surface. - - The coarse aggregate should be smaller than ordinarily used and - never more than one inch in diameter. The use of gravel - facilitates the mixing and assists the flow. The mouth of the - tremie should be buried in the concrete so that it is at all times - entirely sealed and the surrounding water prevented from forcing - itself into the tremie. The concrete will then discharge without - coming in contact with the water. The tremie should be suspended - so that it can be lowered quickly when it is necessary either to - choke off or to prevent too rapid flow. The lateral flow - preferably should not be over 15 feet. - - The flow should be continuous in order to produce a monolithic - mass and to prevent the formation of laitance in the interior. - - In case the flow is interrupted it is important that all laitance - be removed before proceeding with the work. - - In large structures it may be necessary to divide the mass of - concrete into several small compartments or units to permit the - continuous filling of each one. With proper care it is possible in - this manner to obtain as good results under water as in the air. - - A less desirable method is the use of the drop bottom bucket. - Where this method is used the bottom of the bucket should be - released when in contact with the surface of the place of deposit. - -Concrete sewers should be constructed in longitudinal sections in a -continuous operation without interruption for the entire invert, side -walls, or arch. In pouring the concrete it should be kept level in the -forms and should rise evenly on each side of the sewer. All rough places -in the concrete should be finished smooth by brushing with a grout of -neat cement and water and honeycombs should be filled with neat cement -or a one-to-one mortar. - - -=96. Sewer Brick.=—The quality of brick used in sewers is seldom -specified with the minute care that is taken in the specifications for -concrete, iron, and certain other materials of construction, as inferior -materials in brick are more easily detected. The specifications of the -Baltimore Sewerage Commission for sewer brick are: - - Sewer brick shall be whole, new bricks of the best quality, of - uniform standard size, with straight and parallel edges and square - corners: they shall be of compact texture, burned hard and - entirely through, free from injurious cracks and flaws, tough and - strong, and shall have a clear ring when struck together. The - sides, ends and faces of all bricks shall be plane surfaces at - right angles and parallel to each other. Bricks of any one make - shall not vary more than 1/16th of an inch in thickness, nor more - than 1⅛th of an inch in width or length, from the average of the - samples submitted for approval. - - The truest bricks shall be used in the face of the masonry and the - exposed surfaces shall be true and smooth planes. - - All bricks delivered for use shall be culled by the Contractor - when required. No brick thrown out in the culling shall be used in - any work done under any contract of the Sewerage Commission, - except that the best of the culls may be used in manholes, above - the level of the top of the sewer, if permitted by the Engineer. - - The average amount of water absorbed by the bricks, after being - thoroughly dried and then immersed for 24 hours, shall not exceed - 6 per cent. All bricks shall be uniform in quality and percentage - of absorption. - - Whenever vitrified bricks are required in the invert of the sewer, - they shall be smooth, hard, tough, and of such durability as will - fit them for this use. They shall be of standard size, well and - uniformly burned, thoroughly vitrified throughout, and free from - warps, cracks, and other defects. The surfaces and edges shall be - true and straight and the corners sharp and square. They shall be - in every respect satisfactory to the Engineer, and in all respects - equal to the sample in the office of the Engineer. - -The remaining paragraphs of the specifications deal with the manner in -which samples shall be submitted and the necessity for conformity -between the samples submitted and the bricks used. - -A common size of brick in use for sewers is 2¼ × 4 × 8¼ inches, but the -variations in size are many. The bricks in use on any one job should be -as near the same size as possible as the extra mortar filling necessary -to make up for small brick detracts from the strength of the sewer. -Small brick are undesirable as the cost of laying small and large bricks -is the same, but the thickness of the finished sewer is less. Sewer -brick should not absorb more than 10 to 20 per cent moisture by volume, -in 24 hours; except the special paving brick used to prevent erosion at -the invert which should absorb less than 5 per cent moisture. - - -=97. Vitrified Sewer Block.=—Blocks and bricks are manufactured in a -manner similar to the manufacture of vitrified sewer pipe described in -Art. 91. J. M. Egan describes two types of sewer blocks[62] as follows: - - There are on the market two designs of blocks, one being a - single-ring block and the other a double-ring block. The former - has a ship-lap joint on the ends and a tongue-and-groove joint on - the sides. In the double block the laps and joints are made in the - construction of the sewer and the blocks are placed one on top of - the other as in a two ring brick sewer. The blocks are hollow - longitudinally with web braces. They are made for sewers from 30 - inches to 108 inches in diameter and weigh from 40 to 120 pounds. - They are 18 inches to 24 inches long, 9 to 15 inches wide, and 5 - to 10 inches thick. Short lengths are made for convenience in - construction and for use on sharp curves. Special blocks are made - for connections and junctions. - -A special block is also made for inverts, which has occasionally been -used with brick sewers to avoid the difficulty of constructing with -brick at this point. Such blocks are objectionable, as they leave a line -of weakness along the longitudinal joint so formed. They are not used -frequently in present day practice. - -Vitrified blocks are generally cheaper than bricks, but they do not make -so strong a structure. In some cases it is possible to lay vitrified -block without the expense of high-priced bricklayers, thus saving on the -cost of the sewer and obtaining a conduit with a smoother interior -finish. - - -=98. Cast Iron, Steel, and Wood.=—Cast iron, steel, and wood pipe belong -more to the field of waterworks than of sewerage, as they are not -extensively used in the construction of sewers. There are, however, some -special conditions under which these materials may be serviceable. - -The iron used in cast-iron pipe for sewers, and in castings for manhole -covers, inlet frames, etc., is seldom carefully or definitely specified. -The standard specifications of the American Water Works Association with -regard to the quality of iron for water pipe are: - - All pipe and special castings shall be made of cast iron of good - quality and of such character as shall make the metal of the - castings strong, tough, and of even grain and soft enough to - satisfactorily admit of drilling and cutting. The metal shall be - made without the admixture of cinder iron or other inferior metal, - and shall be remelted in a cupola or air furnace. - -The specifications of the Sanitary District of Chicago for the quality -of iron to be used in manhole covers, etc., are given on page 101. - -Although sewer pipes are not ordinarily subjected to internal pressure, -cast-iron pipe for sewers should be as heavy or heavier than water pipe -to resist the corrosive action of the sewage and the external stresses -that are to be imposed upon it. The sizes and details of standard -cast-iron pipe used for both water works and sewerage can be found in -specification of the American and New England Water Works Associations. - -The quality of steel used for reinforcing concrete should be carefully -specified because of the possibility of the substitution of inferior -material. The specifications for “Billet Steel Concrete Reinforcement -Bars,” of the American Society for Testing Materials[63] are the -standard for engineering practice, or the following specifications may -be used: - - All reinforcement shall be free from excessive rust, scale, paint, - or coatings of any character which will tend to destroy the bond. - The bars shall be rolled from new billets. No rerolled material - will be accepted. All reinforcement bars shall develop an ultimate - tensile strength of not less than 70,000 pounds per square inch. - The test specimen shall bend cold around a pin, whose diameter is - two times the thickness of the bar, 180 degrees without cracking - on the outside portion. The reinforcing bars shall in all respects - fulfill the requirements of the standard specifications of the - American Society for Testing Materials for Billet Steel Concrete - Reinforcing Bars serial designation A 15–14. - -The steel used in pipe should be a soft, open-hearth steel with an -ultimate tensile strength of 60,000 pounds per square inch, an elastic -limit of 30,000 pounds per square inch, an elongation in 8 inches before -fracture between 22 and 25 per cent, and a reduction in area before -fracture of 50 per cent. The working strength of the steel is taken at -16,000 to 20,000 pounds per square inch in tension, 10,000 to 12,000 -pounds per square inch in shear, and 20,000 to 24,000 pounds per square -inch in bearing. A liberal allowance should be made for corrosion. The -standard specifications for Open-Hearth Boiler Plate and Rivet Steel of -the American Society for Testing Materials, Aug. 16, 1919, include -“flange steel,” which is suitable for the manufacture of plates, and -extra soft steel which is suitable for rivets. - -Steel pipe should be coated both inside and out to protect it against -corrosion. The various proprietary coatings are mainly coal tar pitches, -or mixtures of coal tar pitch and asphalt. A coal tar pitch is a -distillate of coal tar from which the naphtha has been removed and to -which about one per cent of heavy linseed oil has been added. The -coating is applied to the pipe at a temperature of about 300 degrees -Fahrenheit, by dipping hot pipe in the heated coating material. The pipe -should be carefully cleaned and all rust and scale removed before it is -dipped. In some cases the steel is pickled before dipping. This consists -in rolling the cold plates to a short radius to loosen the scale, -heating them to about 125 degrees, and dipping them in a warm 5 per cent -acid solution for about 3 minutes, and finally rinsing in a weakly basic -wash water. - -The woods commonly used for the manufacture of wood pipe are spruce, -Oregon fir, Douglas fir, and California redwood. Wood pipe lines have -been constructed of other kinds of lumber but only in more or less -unusual conditions. The following has been abstracted from the -specifications for California redwood given by J. F. Partridge.[64] - - The staves shall be of clear, air-dried, California redwood, - seasoned at least one year in the open air, and shall be free from - knots (except small knots appearing on one face only), sap, dry - rot, wind shakes, pitch, pitch seams, pitch pockets, or other - defects which would materially impair their strength or - durability. The sides of the staves shall be milled to conform to - the inside and outside radii of the pipe; and the edges shall be - beveled to true radial planes. The staves shall be milled from - stock sizes of lumber, the net finished thickness of the stave, - for the various diameters of pipe, shall be as given in Table 40. - The ends shall be cut square and slotted to receive the metallic - tongues which form the butt joints. The slots shall appear in the - same position on each stave, and shall be cut to make a tight fit - with the tongues in all directions. The staves shall have an - average length of at least 15 ft. 6 in. and not more than one per - cent shall have a length of less than 9 ft. 6 in. Staves shorter - than 8 ft. will not be accepted. - - The bands shall be spaced on the pipe with a factor of safety of - at least four, and shall consist of round, mild steel rods, - connected with malleable iron shoes. Either open-hearth or - Bessemer steel may be used.... The ultimate strength shall be from - 55,000 to 65,000 lb. per sq. in. - -The original reference should be consulted for complete details and for -specifications for various kinds of wood and classes of pipe. The -discussion following the specifications is of value. - -Machine-made wood pipe is superior to stave pipe put together in the -field. It is seldom manufactured in sizes large enough for use in -sewers, which results in the almost exclusive use of field constructed -stave pipe. The steel bands used to hold the staves together should be -coated similarly to steel plates. All lumber, except California redwood -should receive a preservative coating of creosote[65] or other material. -One of the best methods of preserving the wood is to keep it submerged -and to maintain the pipe under internal pressure. - - TABLE 40 - - DETAILS OF DESIGN FOR CONTINUOUS STAVE WOOD PIPE - - CLASSES A, B, AND C - - (By J. F. Partridge, Trans. A. S. C. E., Vol. 82, page 461) - ───────────┬───────────┬───────────┬───────────┬───────────┬─────────── - │ Stave │Stock Size │ Size of │ Top Width │Spacing of - │Thickness, │of Lumber, │ Band, │of Staves, │ Bands for - Diameter, │ Standard, │ Inches │ Inches │ Standard, │ 100 Feet - Inches │ Inches │ │ │ Inches │ Head - ───────────┼───────────┼───────────┼───────────┼───────────┼─────────── - 12│ 1⅜ │ 2 × 4 │ ⅜ │ 3.56 │ 6.38 - 18│ 1–7/16 │ 2 × 4 │ 7/16 │ 3.66 │ 5.76 - 24│ 1–7/16 │ 2 × 4 │ 7/16 │ 3.70 │ 4.34 - 30│ 1½ │ 2 × 6 │ ½ │ 5.48 │ 4.53 - 36│ 1–9/16 │ 2 × 6 │ ½ │ 5.62 │ 3.77 - 42│ 1⅝ │ 2 × 6 │ ½ │ 5.51 │ 3.23 - │ 1⅝ │ 2 × 6 │ ½ or ⅝ │ 5.60 │ 2.84 or - 48│ │ │ │ │ 4.41 - 60│ 2½ │ 3 × 6 │ ⅝ │ 5.56 │ 3.54 - │ 3½ │ 4 × 6 │ ⅝ or ¾ │ 5.69 │ 2.95 or - 72│ │ │ │ │ 4.24 - 84│ 3½ │ 4 × 6 │ ¾ │ 5.65 │ 3.63 - 120│ 3⅝ │ 4 × 6 │ ¾ │ 5.68 │ 2.54 - │ 3⅝ │ 4 × 6 │ ¾ or ⅞ │ 5.64 │ 2.12 or - 144│ │ │ │ │ 2.89 - ───────────┴───────────┴───────────┴───────────┴───────────┴─────────── - - - - - CHAPTER IX - DESIGN OF THE SEWER RING - - -=99. Stresses in Buried Pipe.=—The stresses which sewer pipe should be -designed to resist are: internal bursting pressure, for sewers flowing -under pressure; stresses due to handling, for precast pipe; temperature -stresses; and external loads. The latter is by far the most important -and frequently is the only stress considered in design. - -The thickness of a pipe to resist internal stress should be - - (_PR_)⁄_f__{_t_}, - - in which _P_ = the intensity of internal pressure; - - _R_ = the radius of the inside of the pipe, and - - _f__{_t_} = the unit-strength of the material in tension - -The derivation of this expression is simple. The stresses due to -handling cannot be computed and are cared for by a thickness of material -dictated by experience. These thicknesses are given for vitrified clay -and cement pipe in the specifications in the preceding chapter. -Temperature stresses are not allowed for in the design of the pipe ring, -but allowance must be made for them in long rigid pipe lines exposed to -wide variations in temperature. Such a condition seldom exists in -sewerage works. - -The external forces are ordinarily the controlling features in the -design of sewer rings. The simplest problems arise in the design of a -circular pipe. If the external loading is uniform about the -circumference of the pipe the internal stresses will all be compression. -Almost all other forms of loading will cause bending moments resulting -in tension and compression in different parts of the pipe. The maximum -bending is caused by two concentrated loads diametrically opposed. As -such a condition is extreme it is not cared for in ordinary design, but -a loading between this condition and perfect distribution is assumed, as -explained in Art. 103. - - -=100. Design of Steel Pipe.=—The stresses which may occur in steel sewer -pipes are commonly caused by the internal or bursting pressure of the -contained liquid. Occasionally a steel pipe may be used as a bridge or -as a stressed member of a bridge, but steel pipes should not be used to -withstand compression normal to the axis. In order to avoid such -stresses the bursting tensile stresses should exceed the external -compressive stresses. Such a condition in design requires that buried -pipes shall never be emptied, a condition that cannot always be -fulfilled. Precaution should be taken, by the installation of proper -valves, to prevent the emptying of the pipe at so rapid a rate that a -vacuum is created resulting in the collapse of the pipe. - -Steel pipes are ordinarily made of plates curved to the proper diameter, -the edges being held together by rivets. The design of the pipe consists -in the determination of the thickness of the plate and the design of the -riveted joint. The longitudinal joint and the thickness of the plate are -first designed. The design of the joint consists in determining the -diameter and pitch of the rivets and the thickness of the plate so that -the full strength of the uncut metal shall be developed as nearly as -possible under bearing, tearing, and shearing. This is done by making -the efficiency of the joint the same under all stresses. The efficiency -of the joint is the ratio of the strength of the joint under any kind of -stress to the strength in tension of the unpunched plate. Properties of -riveted joints are given in Table 41. - -The diameter of the rivet holes should be computed as 1/16 of an inch -larger than the diameter of the rivets. Rivets and plates should be -designed for the nearest or next largest commercial size, and a generous -allowance for corrosion should be made in determining the thickness of -the plate. The distance from the edge of the plate to the side of the -rivet should not be less than 1½ times the diameter of the rivet. The -unit-strengths of the metal are given in the preceding chapter. - -The transverse joint must be designed empirically as the stresses in it -are indeterminate. The common form of joint for pipes less than 48 -inches in diameter is a single-riveted lap joint, and for larger pipes -or for pipes exposed to unusual stresses, a double riveted lap joint is -used. The same size rivets are used as in the longitudinal joint. The -maximum permissible distance between rivets should be used in the -transverse joint. - - TABLE 41 - - PROPERTIES OF RIVETED JOINTS - - (Chicago Bridge and Iron Works) - ──────────────────────┬─────────┬────────┬────────┬──────────┬───────── - Type of Joint │Thickness│Diameter│ Pitch, │Efficiency│Thickness - │ Plate, │ of │ Inches │of Joint, │ Butt - │ Inch │ Rivet, │ │ Per Cent │ Plate, - │ │ Inch │ │ │ Inches - ──────────────────────┼─────────┼────────┼────────┼──────────┼───────── - Single-riveted lap │ ¼ │ ⅝ │ 1.88 │ 49 │ - │ ¼ │ ¾ │ 2.25 │ 50 │ - │ 5/16 │ ⅞ │ 2.63 │ 50 │ - ──────────────────────┼─────────┼────────┼────────┼──────────┼───────── - Double riveted lap │ ¼ │ ⅝ │ 2.50 │ 70 │ - │ 5/16 │ ¾ │ 3.00 │ 71 │ - │ ⅜ │ ⅞ │ 3.40 │ 71 │ - ──────────────────────┼─────────┼────────┼────────┼──────────┼───────── - Triple riveted lap │ ¼ │ ½ │ 2.39 │ 74 │ - │ 5/16 │ ⅝ │ 2.96 │ 74 │ - │ ⅜ │ ¾ │ 3.53 │ 75 │ - │ 7/16 │ ⅞ │ 4.09 │ 76 │ - ──────────────────────┼─────────┼────────┼────────┼──────────┼───────── - Quadruple riveted lap │ ⅜ │ ⅝ │ 3.20 │ 77 │ - │ 7/16 │ ¾ │ 3.90 │ 78 │ - ──────────────────────┼─────────┼────────┼────────┼──────────┼───────── - Double riveted butt │ ½ │ ⅞ │ 3.62 │ 72 │ ⅜ - │ 9/16 │ ⅞ │ 3.62 │ 72 │ ⅜ - │ ⅝ │ ⅞ │ 3.62 │ 72 │ ⅜ - │ 11/16 │ ⅞ │ 3.62 │ 72 │ 7/16 - │ ¾ │ 1 │ 4.12 │ 73 │ 7/16 - │ ⅞ │ 1 │ 3.82 │ 71 │ ½ - │ 1 │ 1 │ 3.48 │ 68 │ 9/16 - ──────────────────────┼─────────┼────────┼────────┼──────────┼───────── - Triple riveted butt │ ⅝ │ ⅞ │ 4.94 │ 80 │ ½ - │ ¾ │ 1 │ 5.62 │ 80 │ 9/16 - │ ⅞ │ 1 │ 5.16 │ 78 │ 9/16 - │ 1 │ 1 │ 4.66 │ 76 │ 9/16 - ──────────────────────┼─────────┼────────┼────────┼──────────┼───────── - Quadruple riveted butt│ ¾ │ 1 │ 7.13 │ 84 │ ¾ - │ ⅞ │ 1 │ 6.51 │ 83 │ 11/16 - │ 1 │ 1 │ 5.84 │ 81 │ ⅝ - ──────────────────────┴─────────┴────────┴────────┴──────────┴───────── - -Pipes used as compression members of a bridge are stiffened by riveting -standard rolled steel sections longitudinally on the pipe. - -[Illustration: - - FIG. 78.—Lock Bar Pipe. -] - -Lock Bar Pipe is a steel pipe with a special form of joint made by the -East Jersey Pipe Corporation. It is arranged as shown in Fig. 78 and has -the advantage of developing the full strength of the plate. It is -equivalent to a joint with 100 per cent efficiency, which permits the -use of thinner plates. - - -=101. Design of Wood Stave Pipe.=—In the design of wood stave pipe[66] -the entire bursting pressure is taken up by steel bands wrapped around -the outside of wood staves which make up the shell of the pipe. The pipe -is not designed to resist external loads except those which may be -overcome by the internal pressure in the pipe. The thickness of the -staves is fixed by experience. The sizes of staves and bands recommended -by J. F. Partridge[67] are given in Table 40. The size of the steel -bands can be determined from the expression; - - _S_ = _Cr_(_R_ + _t_) - - in which _S_ = the total stress in the band; - - _R_ = the radius of the inside of the pipe; - - _t_ = the thickness of the stave; - - _r_ = the area of bearing per unit length of the band on the - wood. For circular bands it is assumed as the radius - of the band; - - _C_ = the crushing strength of wood, usually taken at 650 - pounds per sq. in. - -The preceding expression can be derived easily by the application of the -laws of mechanics, and from it the expression for the distance between -bands follows logically. It is, - - _p_ = _S_⁄(_PR_ + _kt_) - - in which _S_ = the strength of the band; - - _p_ = the distance between bands; - - _P_ = the intensity of bursting pressure in the pipe; - - _R_ = the radius of the inside of the pipe; - - _t_ = the thickness of the staves; - - _k_ = the swelling strength of wood, usually taken at 100 - pounds per sq. in. - -[Illustration: - - FIG. 79.—Shoe for Wood Stave Pipe. -] - -Transverse joints between staves are closed by inserting metal strips -between them, or by shaping the edges irregularly so that they fit -closely together with an irregular joint. Transverse joints between all -staves at any one point are avoided by splitting the joints between -staves. Longitudinal joints between staves are usually made smooth and -are closed by steel bands which are drawn tight about the pipe by -inserting the ends in coupling shoes as shown in Fig. 79. - -[Illustration: - - FIG. 80.—_B_ in Formula _W_ = _CwB_^2 -] - - -=102. External Loads on Buried Pipe.=—Prof. Anston Marston and H. C. -Anderson published[68] the results of a series of experiments on the -loads on buried pipes which are of extreme value in the design of sewer -pipe. The load on the pipe is given by the empirical expression _W_ = -_CwB_^2, in which _w_ is the weight of the backfilling material in -pounds per cubic foot, _B_ is the width of the trench in feet at the -elevation of the end of a radius making an angle of 45 degrees upwards -with the horizontal diameter of the pipe as illustrated in Fig. 80, and -_C_ is a coefficient dependent on the character of the backfill and the -ratio of the width to the depth of the trench. Values of _C_ are given -in Table 42. The weights of various classes of backfilling are given in -Table 43. - - TABLE 42 - - APPROXIMATE SAFE WORKING VALUES OF _C_ IN THE EXPRESSION _W_ = _CwB_^2 - - From Bulletin No. 31 of the Engineering Experiment Station, Iowa State - College of Agriculture. - ──────────────┬──────────────────────────────────────────────────────── - Ratio of Depth│ Approximate Values of _C_ - to Width │ - ──────────────┼──────────────┬─────────────┬─────────────┬───────────── - │Damp Top Soil │Saturated Top│ Damp Yellow │ Saturated - │ and Dry and │ Soil │ Clay │ Yellow Clay - │ Wet Sand │ │ │ - ──────────────┼──────────────┼─────────────┼─────────────┼───────────── - 0.5 │ 0.46 │ 0.47 │ 0.47 │ 0.48 - 1.0 │ 0.35 │ 0.86 │ 0.88 │ 0.90 - 1.6 │ 1.16 │ 1.21 │ 1.25 │ 1.27 - 3.0 │ 1.47 │ 1.51 │ 1.56 │ 1.62 - 2.6 │ 1.70 │ 1.77 │ 1.83 │ 1.91 - 3.0 │ 1.90 │ 1.99 │ 2.08 │ 2.19 - 3.6 │ 2.08 │ 2.18 │ 2.28 │ 2.43 - 4.0 │ 2.22 │ 2.35 │ 2.47 │ 2.65 - 4.6 │ 2.34 │ 2.49 │ 2.63 │ 2.85 - 6.0 │ 2.45 │ 2.61 │ 2.78 │ 3.02 - 6.5 │ 2.54 │ 2.72 │ 2.90 │ 3.18 - 6.0 │ 2.61 │ 2.81 │ 3.01 │ 3.32 - 6.6 │ 2.68 │ 2.89 │ 3.11 │ 3.44 - 7.0 │ 2.73 │ 2.95 │ 3.19 │ 3.55 - 7.5 │ 2.78 │ 3.01 │ 3.27 │ 3.66 - 8.0 │ 2.82 │ 3.06 │ 3.33 │ 3.74 - 8.5 │ 2.85 │ 3.10 │ 3.39 │ 3.82 - 9.0 │ 2.88 │ 3.14 │ 3.44 │ 3.89 - 9.5 │ 2.90 │ 3.18 │ 3.48 │ 3.96 - 10.0 │ 2.92 │ 3.20 │ 3.52 │ 4.01 - 11.0 │ 2.95 │ 3.25 │ 3.58 │ 4.11 - 12.0 │ 2.97 │ 3.28 │ 3.63 │ 4.19 - 13.0 │ 2.99 │ 3.31 │ 3.67 │ 4.25 - 14.0 │ 3.00 │ 3.33 │ 3.70 │ 4.30 - 15.0 │ 3.01 │ 3.34 │ 3.72 │ 4.34 - ∞ │ 3.03 │ 3.38 │ 3.79 │ 4.50 - ──────────────┴──────────────┴─────────────┴─────────────┴───────────── - - TABLE 43 - - APPROXIMATE WEIGHTS OF DITCH FILLING MATERIAL TO BE USED IN THE - EXPRESSION _W_ = _CwB_^2[69] - - ───────────────────────────────────┬─────────────────────────────────── - Ditch Filling │ Pounds per Cubic Foot - ───────────────────────────────────┼─────────────────────────────────── - Partly compacted top soil (damp) │ 90 - Saturated top soil │ 110 - Partly compacted damp yellow clay │ 100 - Saturated yellow clay │ 130 - Dry sand │ 100 - Wet sand │ 120 - ───────────────────────────────────┴─────────────────────────────────── - -Where surface loads are to be carried on the sewer trench the proper -proportion of the load to be carried by the sewer is determined by the -expression _L__{_p_} = _CL_, in which _L__{_p_} is the equivalent -backfill load per unit length of the trench, _L_ is the surface load per -unit length of the trench, and _C_ is a coefficient in which allowance -is made for the character of the backfilling, the ratio of depth to -width of trench, and the character of the load, whether long or short. A -long load is a load extending along the length of the trench such as a -pile of building material. A short load is one extending across the -trench and for only a short distance along it, such as that caused by a -street car or road roller crossing the trench. Values of _C_ are given -in Table 44 for long loads, and in Table 45 for short loads. Values of -long and short loads occasionally met in practice are given in Tables 46 -and 47 respectively. - - TABLE 44 - - RATIO OF LOAD ON PIPE TO LONG LOAD ON TRENCH[70] - - ──────────────┬──────────────┬──────────────┬──────────────┬────────────── - Ratio of Depth│Sand and Damp │Saturated Top │ Damp Yellow │ Saturated - to Width │ Top Soil │ Soil │ Clay │ Yellow Clay - ──────────────┼──────────────┼──────────────┼──────────────┼────────────── - 0.0│ 1.00│ 1.00│ 1.00│ 1.00 - 0.5│ 0.85│ 0.86│ 0.88│ 0.89 - 1.0│ 0.72│ 0.75│ 0.77│ 0.80 - 1.5│ 0.61│ 0.64│ 0.67│ 0.72 - 2.0│ 0.52│ 0.53│ 0.59│ 0.64 - 2.5│ 0.44│ 0.48│ 0.52│ 0.57 - 3.0│ 0.37│ 0.41│ 0.45│ 0.51 - 4.0│ 0.27│ 0.31│ 0.35│ 0.41 - 5.0│ 0.19│ 0.23│ 0.27│ 0.33 - 6.0│ 0.14│ 0.17│ 0.20│ 0.26 - 8.0│ 0.07│ 0.09│ 0.12│ 0.17 - 10.0│ 0.04│ 0.05│ 0.07│ 0.11 - ──────────────┴──────────────┴──────────────┴──────────────┴────────────── - - For example, let it be desired to determine the load on a 72–inch - concrete sewer with a 9–inch shell under the following conditions: - depth of backfill over the top of the pipe, 15 feet; character of - backfill, saturated yellow clay; superimposed load, pile of - building brick 6 feet high. The ratio of the depth of backfill to - the width of the trench is 15 ÷ 9 or 1.67. The coefficient in the - expression _CwB_^2 is 1.39, from Table 42. The weight of saturated - yellow clay is 130 pounds per cubic foot, from Table 43. Therefore - the load per foot length of the sewer due to the backfill is: - - _W_ = _CwB_^2 = 1.39 × 130 × 81 = 14,600 pounds. - - TABLE 45 - - RATIO OF LOAD ON PIPE TO SHORT LOAD ON TRENCH[71] - - ───────┬───────────────┬───────────────┬───────────────┬─────────────── - Ratio │ │ │ │ - of │ │ │ │ - Height │ │ │ │ - to │ │ │ │ - Width │ │ │ │ - of │ Sand and Damp │ Saturated Top │ Damp Yellow │ Saturated - Trench │ Top Soil │ Soil │ Clay │ Yellow Clay - ───────┼───────────────┴───────────────┴───────────────┴─────────────── - │ Length of Load Equal to - ───────┼───────┬───────┬───────┬───────┬───────┬───────┬───────┬─────── - │ Width │⅒ Width│ Width │⅒ Width│ Width │⅒ Width│ Width │⅒ Width - │ of │ of │ of │ of │ of │ of │ of │ of - │Trench │Trench │Trench │Trench │Trench │Trench │Trench │Trench - ───────┼───────┼───────┼───────┼───────┼───────┼───────┼───────┼─────── - 0.0│ 1.00│ 1.00│ 1.00│ 1.00│ 1.00│ 1.00│ 1.00│ 1.00 - 0.5│ 0.77│ 0.12│ 0.78│ 0.13│ 0.79│ 0.13│ 0.81│ 0.13 - 1.0│ 0.59│ 0.02│ 0.61│ 0.02│ 0.63│ 0.02│ 0.66│ 0.02 - 1.5│ 0.46│ │ 0.48│ │ 0.51│ │ 0.54│ - 2.0│ 0.35│ │ 0.38│ │ 0.40│ │ 0.44│ - 2.5│ 0.27│ │ 0.29│ │ 0.32│ │ 0.35│ - 3.0│ 0.21│ │ 0.23│ │ 0.25│ │ 0.29│ - 4.0│ 0 12│ │ 0.12│ │ 0.16│ │ 0.19│ - 5.0│ 0.07│ │ 0.09│ │ 0.10│ │ 0.13│ - 6.0│ 0.04│ │ 0.05│ │ 0.06│ │ 0.08│ - 8.0│ 0.02│ │ 0.02│ │ 0.03│ │ 0.04│ - 10.0│ 0.01│ │ 0.01│ │ 0.01│ │ 0.02│ - ───────┴───────┴───────┴───────┴───────┴───────┴───────┴───────┴─────── - - TABLE 46 - - WEIGHTS OR COMMON BUILDING MATERIAL WHEN PILED FOR STORAGE. POUNDS PER - CUBIC FOOT - - ────────────────────────────────────────┬────────────────────────────── - Brick │ 120 - Cement │ 90 - Sand │ 90 - Broken stone │ 150 - Lumber │ 35 - Granite paving │ 160 - Coal │ 50 - Pig iron │ 400 - ────────────────────────────────────────┴────────────────────────────── - - The pressure of the pile of brick per square foot of trench area - is, from Table 46, 120 × 6 = 720 pounds per square foot. The value - of _C_ from Table 44, is about 0.70. Therefore _L_{p}_ is 0.7 × 9 - × 720 = 4536 pounds. The equivalent depth of backfill weighing 130 - pounds per cubic foot is (4536)⁄130 × 9 = 3.88 foot. The total - equivalent depth of backfill is therefore 3.88 + 15 = 18.88 feet. - The ratio of depth to width is 18.88⁄9 = 2.98. The coefficient _C_ - in the expression _W_ = _CwB_^2 is 2.17. The total load per foot - length of sewer is therefore _W_ = 2.17 × 130 × 81 = 22,800 - pounds. - - TABLE 47 - - WEIGHTS OF SHORT LOADS ON SEWER TRENCHES - - (Adapted from Specifications of the American Bridge Company for - Bridges) - ──────────────────────────────┬──────────────────────────────────────── - Street railways, heavy │A load of 24 tons on 2 axles on 10 foot - │ centers. - Street railways, light │A load of 18 tons on 2 axles on 10 foot - │ centers. - For city streets, heavy │A load of 24 tons on 2 axles 10 feet - traffic │ apart and 5 foot gage. - For city streets, moderate │A load of 12 tons on 2 axles 10 feet - traffic │ apart and 5 foot gage. - For city streets, light │A load of 6 tons on 2 axles 10 feet - traffic or country roads │ apart and 5 foot gage. - │ - Road rollers │Total weight 30,000 pounds. Weight on - │ front wheel, 12,000 pounds, and on - │ each of two rear wheels, 9,000 pounds. - │ Width of front wheel, 4 feet and of - │ each of two rear wheels 20 inches. - │ Distance between front and rear axles - │ 11 feet. Gage of rear wheels, 5 feet, - │ c. to c. - ──────────────────────────────┴──────────────────────────────────────── - - -=103. Stresses in Circular Ring=—In Fig. 81_a_ the loads shown indicate -the distribution ordinarily assumed in sewer design, the forces being -uniformly distributed across the diameter. To find the bending moment in -the pipe caused by this loading, let _ab_ in Fig. 81_b_ represent a -section of a pipe loaded with equally distributed horizontal and -vertical forces. Then the vertical component on a strip of differential -length _ds_ is _wds_ cos Θ and the horizontal component is _wds_ sin Θ -and resolving, the resultant normal to the surface is _wds_, in which -_w_ is the intensity per unit length of the horizontal and vertical -forces and Θ is the angle which the tangent to _ds_ makes with the -horizontal. Thus the loading of the nature shown in Fig. 81_b_ is -equivalent to a loading of equally distributed normal forces which give -no moment in the ring. - -[Illustration: - - FIG. 81.—Distribution of Stresses on Buried Pipe. -] - -Considering a ring subjected to vertical forces only, the moments will -be as shown in Fig. 81_c_ and if loaded with horizontal forces only, the -moments will be as shown in Fig. 81_d_. Because of the symmetry of the -figure, moment (1) equals moment (4) but is opposite in direction and -moment (2) equals moment (3) but is opposite in direction. When the -horizontal and vertical forces are combined on the same ring as in Fig. -81_b_ these moments cancel each other as has been proven. Therefore -moment (1) equals moment (2) and moment (3) equals moment (4). Then in -Fig. 81_e_, _M_{a}_ = _M_{b}_. Now ∑_M_ = _O_ for conditions of -equilibrium, therefore _M_{a}_ + _M_{b}_ + (_W_⁄2)(_d_⁄4) = _O_ and -solving _M_{a}_ = (_Wd_)⁄16. This moment occurs at the ends of the -horizontal and vertical diameters and causes tension on the inside of -the pipe at the top and on the outside at the ends of the horizontal -diameter. There will also be compression at each end of the horizontal -diameter equal to one-half of the total load on the pipe. If the -material of the pipe is homogeneous, the maximum fiber stress _f_ can be -found through the expression _f_ = (_My_)⁄_I_ ± _P_⁄_A_ in which _M_ is -the bending moment, _y_ is the distance from the neutral axis to the -extreme fiber of a cross-section of the shell of the pipe of unit -length, _I_ is the moment of inertia of this cross-section about its -neutral axis, _P_ is one-half the total load on the pipe, and _A_ is the -area of the cross-section. For reinforced concrete, the standard -formulas should be used with this expression for _M_. The stresses in a -circular ring subjected to other distributions of loads are shown in -Table 48. An exhaustive study of the stresses in circular rings was -published by Prof. A. N. Talbot in Bulletin No. 22 of the Engineering -Experiment Station at the University of Illinois, 1908. - - TABLE 48 - - MAXIMUM STRESS IN FLEXIBLE RINGS DUE TO DIFFERENT LOADINGS - - (From Marston) - ──────────────────┬───────────────┬───────────────┬─────────── - Symmetrical │Moment at Crown│ Moment at End │Compressive - Vertical Loadings │ of Sewer │ of Horizontal │ Thrust at - │ │ Diameter │ Crown - │ │ │ - │ │ │ - ────────────┬─────┼───────────────┼───────────────┼─────────── - Character │Width│ │ │ - ────────────┼─────┼───────────────┼───────────────┼─────────── - Concentrated│ 0°│+ .318_R__W_/12│- .182_R__W_/12│ 0.000 - Uniform │ 60°│+ .207_R__W_/12│- .168_R__W_/12│ 0.000 - Uniform │ 90°│+ .169_R__W_/12│- .154_R__W_/12│ 0.000 - Uniform │ 180°│+ .125_R__W_/12│- .125_R__W_/12│ 0.000 - ────────────┴─────┴───────────────┴───────────────┴─────────── - - ──────────────────┬────────────┬───────────┬────────── - Symmetrical │Compressive │ Shear at │ Shear at - Vertical Loadings │ Thrust at │ Crown │ End of - │ End of │ │Horizontal - │ Horizontal │ │ Diameter - │ Diameter │ │ - ────────────┬─────┼────────────┼───────────┼────────── - Character │Width│ │ │ - ────────────┼─────┼────────────┼───────────┼────────── - Concentrated│ 0°│+ .500_W_/12│0.500_W_/12│ 0.000 - Uniform │ 60°│+ .500_W_/12│0.000_W_/12│ 0.000 - Uniform │ 90°│+ .500_W_/12│0.000_W_/12│ 0.000 - Uniform │ 180°│+ .500_W_/12│0.000_W_/12│ 0.000 - ────────────┴─────┴────────────┴───────────┴────────── - - _R_ = the radius of the pipe, _W_ = total weight of ditch filling and - superimposed load plus ⅝ of the weight of the pipe itself (usually - neglected), expressed in pounds per foot length of pipe. Moments are - inch-pounds per inch length of pipe. Shears and thrusts are in pounds - per inch length of pipe. - - -=104. Analysis of Sewer Arches.=—The preceding method for the -determination of the stresses in a sewer ring has referred only to a -circular pipe uniformly loaded. Other methods must be used if the pipe -is not circular or the load is not uniformly distributed. The simplest -method, is the static or so-called vouissoir method. In this method the -arch is assumed to be fixed at both ends, presumably at the springing -line or line of intersection between the inside face of the arch and the -abutment, and it is so designed that the resultant of all the forces -acting on any section shall lie within the middle third of that section. - -[Illustration: - - FIG. 82.—Voussoir Arch Analysis. -] - -[Illustration: - - FIG. 83.—Force Polygon for Voussoir Arch Analysis. -] - -To design an unreinforced sewer arch by the vouissoir method, a desired -arch is drawn to scale in apparently good proportions for the loadings -anticipated. The arch is then divided into any number of sections of -equal or approximately equal length called vouissoirs, and the line of -action of the resultant load, including the weight of the vouissoir is -drawn above each vouissoir as shown in Fig. 82. The forces are assumed -to act as shown in the figure. In symmetrically loaded sewer arches -there is no vertical reaction at the crown. The resultant _R_ is assumed -to act at the lower middle third of the skewback, which is the inclined -joint between the arch and the abutment. The upper horizontal force _H_ -is assumed to act at the upper middle third of the middle or crown -section. The magnitude of _H_ is computed by equating the sum of the -moments of all forces about the point of application of _R_ at the -skewback to zero, and solving. The force polygon is then drawn as shown -in Fig. 83, and the equilibrium polygon is completed in Fig. 82 with its -rays parallel to the corresponding strings drawn from the end of _H_ as -origin in Fig. 83. If the equilibrium polygon line, called the -resistance line, lies wholly within the middle third of each vouissoir, -the arch is satisfactory to support the assumed load without -reinforcement. If any portion of the resistance line lies outside of the -middle third, an attempt should be made to find a resistance line which -lies wholly within the middle third. The true resistance line is that -which deviates the least from the neutral axis of the arch. To -approximate more nearly the true resistance line find two points at -which the resistance line already drawn deviates the most from the -neutral axis of the arch. Select points _M_ and _N_ on these joints, _M_ -being nearer the crown than _N_. Then let _W_{1}_ and _W_{2}_ be the sum -of all the loads between the crown and _M_ and _N_ respectively, _y_ -represent the vertical distance from the crown to _N_, and _y′_ -represent the vertical distance between _M_ and _N_, and _x_{1}_ and -_x_{2}_ represent the horizontal distance from _W_{1}_ and _W_{2}_ to -_M_ and _N_ respectively. Then the horizontal thrust, _H_, and _a_, the -distance from the crown to the point of application of _H_, are, - - _H_ = ((_W_{2}x_{2}_ − _W_{1}x_{1})_)⁄_y′_, - - _a_ = _y_ − (_W_{2}x_{2}_)⁄_H_.[72] - -A resistance line should be drawn with this new horizontal thrust. If no -resistance line can be found lying wholly within the middle third, new -sections should be designed until a resistance line can be drawn lying -wholly within the middle third—unless the arch is to be reinforced. A -number of satisfactory arches should be designed and the easiest one to -build should be selected. This method is limited in its application to -sewer arches with rigid side walls and it cannot be extended to include -the invert. Although an approximate method it is accurate within less -than 10 per cent of the true stresses and is usually quite close. - -[Illustration: - - FIG. 84.—Method for Dividing Arch into Proportion _I_⁄_S_. -] - -The elastic method for the design of arches locates the true line of -resistance without approximations and is more accurate though not so -simple to apply as the static or vouissoir method. In this method a -desired form of arch is drawn as in the static method and subdivided -into vouissoirs so that the distance _S_ along the neutral axis between -joints is such that the ratio _I_⁄_S_ shall be the same for all -vouissoirs. _I_ is the average of the moments of inertia of the surfaces -of the two limiting joints about the neutral axis. If the thickness of -the arch is constant the distance between joints will be the same. The -method for dividing the arch into sections such that the ratio _I_⁄_S_ -shall be a constant[73] is as follows: divide the half arch axis into -any number of equal parts; measure the radial depth at each point of -division; lay off the length of the arch axis to scale on a straight -line; divide this line into the same number of equal parts as the half -arch, as shown in Fig. 84; at each point erect a perpendicular equal in -length by scale to the moment of inertia at the corresponding point on -the arch section; draw a smooth curve through the tops of these lines; -draw a line _ab_ at any slope from the center of the original straight -line to the curve, and then a line _bc_ back to the straight line to -form an isosceles triangle _abc_; continue forming these triangles in a -similar manner thus dividing the original straight line in the required -ratio. The distance between joints is represented by the bases of the -triangles. By construction the altitude of the triangle represents the -average moment of inertia between the two limiting joints. The base of -each isosceles triangle is _S_, and _I_⁄_S_ = ½ tan α in which α is the -base angle of all the isosceles triangles. - -[Illustration: - - FIG. 85.—Elastic Arch Analysis. -] - -The following steps in the procedure are taken from the second edition -of the American Civil Engineers Pocket Book, p. 634: - - In Fig. 85 let the middle points of the joints be marked 1, 2, 3, - etc. and the coordinates _x_ and _y_ from the crown be found for - each by computation or measurement. For a load _W_ placed at one - of these points, let _z_ denote the distance from it, toward the - nearest skewback, to another middle point. Let ∑_zx_ be the sum of - the products of all the values of _z_ by the corresponding _x_, - and ∑_zy_ be the sum of all the products of _z_ by the - corresponding _y_; that is, each _z_ in the last two summations is - multiplied by the _x_ or _y_ of the point back of _W_ which - corresponds to _z_. - - For a single load _W_ on the left semi-arch of Fig. 85 the - following formulas are deduced from the elastic theory, _n_ being - the number of parts into which the semi-arch is divided. - - Horizontal thrust, _H_ = (_W_⁄2)(_n_∑_zy_ − ∑_y_·∑_z_)⁄(_n_∑_y_^2 - − (∑_y_)^2) (1) - - Moment at Crown, _M__{0} = (½_W_∑_z_ − _H_∑_y_)⁄_n_ (2) - - Shear at Crown, _V__{0} = (½_W_∑_zx_)⁄∑_x_^2 (3) - - For symmetrical loading such as _W_ on the left and _W_ on the - right the horizontal thrust and crown moment due to both loads are - double those found by the above formulas, while the crown shear - _V__{0} is zero. For several loads unsymmetrically placed the - formulas are to be applied to each in succession and the results - added algebraically, the value of _V__{0} being taken as negative - for the left semi-arch and positive for the right semi-arch. - - For any joint whose middle point is at a distance _x_ from the - crown - - _M_ = _M__{0} + _Hy_ + _V__{0}_x_ − ∑_Wz_, - - _V_ = _V__{0} − ∑_W_, - - where ∑_W_ is the sum of all the loads between the joint and the - crown and ∑_Wz_ is the sum of the moments of those loads with - respect to the middle of the joint. The components of the - resultant thrust normal and parallel to the joints are, - - _N_ = _H_ cos θ − _V_ sin θ, - - _F_ = _H_ sin θ + _V_ cos θ, - - in which θ is the angle which the plane of the joint makes with - the vertical. - - The distances from the neutral axis to the resistance line are, - - at the crown, _e__{0} = _M__{0}⁄_H_, - - at the joint, _e_ = _M_⁄_N_. - -The resistance line should be located as in the vouissoir method and if -not within the middle third a new design should be studied. - - -=105. Reinforced Concrete Sewer Design.=—The method to be followed in -the design of reinforced concrete arches is similar except that the -moment of inertia should include both the concrete and the steel, that -is, - - _I_ = _I_{c}_ + _nI_{s}_, - -in which _I_ is the moment of inertia to be employed, _I_{c}_ is the -moment of inertia of the concrete, _I_{s}_ is the moment of inertia of -the steel, and _n_ is the ratio of their moduli of elasticity, generally -taken as 15. All of the moments of inertia are referred to the neutral -axis of the beam. The reinforcement called for in precast circular pipes -is given in Table 39. Sewers cast in place are ordinarily designed to -avoid reinforcement, except where the depth of cover is small and the -sewer may be subjected to superimposed loads. - -Concrete sewers are sometimes reinforced longitudinally, with expansion -joints from 30 to 50 feet apart. This reinforcement is to reduce the -size of expansion and contraction cracks by distributing them over the -length of a section. The pipe is divided into sections to concentrate -motion due to expansion or contraction at definite points where it can -be cared for. - -The amount of longitudinal reinforcement to be used is a matter of -judgment. It varies in practice from 0.1 to 0.4 per cent of the area of -the section. Since the coefficients of expansion of concrete and of -steel are nearly the same, movements of the structure are as important -as the stresses due to changes in temperature. - -Because of the uncertain and difficult conditions under which concrete -sewers are frequently constructed it is advisable to specify the best -grade of concrete and not to stress the concrete over 450 pounds per -square inch in compression, with no allowable stress in tension. The -concrete covering of reinforcing steel should be thicker than is -ordinarily used for concrete building design, because of the possibility -of poor concrete allowing the sewage to gain access to the steel, -resulting in more rapid deterioration than would be caused by exposure -to the atmosphere. A minimum covering of about 2 inches is advisable, -except in very thin sections not in contact with the sewage. A minimum -thickness of concrete of about 9 inches is frequently used in design, -although crown thicknesses of 4½ inches have been used with success. -Greater thicknesses should be used near the surface, particularly in -locations subjected to heavy or moving loads. - -Brick linings are often provided for the invert where moderately high -velocities of about 10 feet per second when flowing full are to be -expected. For velocities in the neighborhood of 20 feet per second the -invert should be lined with the best quality vitrified brick. Although -concrete may erode no faster than brick under the same conditions, brick -linings are more easily replaced and at a smaller expense. - - - - - CHAPTER X - CONTRACTS AND SPECIFICATIONS - - -=106. Importance of the Subject.=—Sewers may be constructed by day labor -or by contract. Under the day labor plan a city official or commission -is charged with the purchase of material, the hiring and firing of -employees, and the management of the work. Under the contract system a -private individual or company contracts to supply all the material and -labor necessary for the completion of the work. - -Under the day labor plan all persons engaged are “working for the City.” -There is not the same sense of individual responsibility, the same -incentive to economize, the same feeling of loyalty that is inspired by -work under the personality of a contractor. Under either the day labor -or contract plan unscrupulous politics are likely to enter into the -relations of the employees of the city and the city officials or between -the contractor and the city officials. Neither the day labor nor the -contract plan offer a sure cure for unscrupulous political misdealings. -Under the contract plan the contractor is led to keep his bid as low as -possible, realizing the competition of other bidders, and during -construction he will obtain greater efficiency from his labor because of -their realization of the different conditions under which they are -working. In some states and cities it is illegal for the municipality to -do sewer construction except under the contract method. - -The contract method is therefore used in the majority of cases, and it -is to the interest of the engineer that he be acquainted with the -essentials of contracts and specifications necessary for the proper -prosecution of sewer construction. - - -=107. Scope of Subject.=—The making of a contract is one of the most -common episodes of every day life. The contract may be an informal -verbal agreement to meet at a certain place at a certain time, or it may -be a formal document hedged about by confusing legal phraseology and -bearing varieties of penalties and dire consequences in the event of its -breach. The purpose of this chapter is to explain only those general -features of an engineering contract which have particular bearing upon -sewerage construction. Only the most essential points can be touched in -the limited space available to this subject, it being presumed that the -engineer is previously grounded in the principles of business law.[74] - - -=108. Types of Contracts.=—Contracts are known as lump sum, cost-plus, -unit-price, and by other titles indicating the method of payment. - -A lump sum contract is one in which a stated amount is fixed upon, -before the execution of the contract, to be paid for all the work to be -done and materials to be furnished under the contract. Such an -arrangement is not advisable for a sewer contract, as the cautious -contractor will bid high enough to protect himself in the event of any -probable emergency. The principal must therefore pay whether the -emergency or unforeseen difficulty is met or not. The advantage of this -type of payment is that the principal knows exactly the cost of the work -to him before construction is commenced. - -Cost-plus contracts are those in which the cost of the work to the -contractor is to be paid by the principal, plus, (_a_) a fixed sum of -money, (_b_) a percentage of the cost of the work, (_c_) a percentage of -the cost of the work but with a fixed limit, (_d_) a percentage of the -difference between the cost of the work and some fixed sum, or other -variations of this principle. Such contracts have the advantage that the -principal assumes all the risk in construction and therefore pays for -only those contingencies which actually arise. Except for the last named -form, they have the disadvantage that there is little or no incentive -for the contractor to keep the cost of the work down. They are most -successful where the contractor can be selected by the principal, but -where it is necessary to let contracts to the lowest bidder, the -“cost-plus” contract is not easily managed. In most states a -municipality cannot make a cost-plus contract. - -A unit-price contract is one in which the amount to be paid is fixed in -proportion to the amount of work done or materials supplied. This type -of contract is the most suitable for sewer construction for a -municipality where the contract must be let to the lowest bidder. The -contractor is protected in the event of many unforeseen emergencies and -the principal is protected against a raise in bids to cover such -emergencies and against increase in the cost of the work in order to -increase the profits under a “cost-plus” contract. - -It is sometimes desirable for the principal to furnish a portion of the -materials, the bidders being notified beforehand that this material will -be furnished. In this manner the quality of material is assured, -contractors with the necessary skill but small capital may be attracted -to bid, and uncertainties in the procuring of materials is eliminated. - - -=109. The Agreement.=—A contract is an agreement between two or more -interested parties to do a certain thing. A contract for the -construction of a sewer is an agreement between a municipality or -individual desiring sewerage facilities and a company or individual -engaged in the construction of sewers. The latter promises to construct -a sewer in return for which the former promises to pay a certain amount -of money. - -The various portions of the agreement which are bound together as the -complete contract are: I. The Advertisement, II. Information and -Instructions for Bidders, III. Proposal, IV. General Specifications, V. -Technical Specifications, VI. Special Specifications, VII. Contract, -VIII. Bond, and IX. Contract Drawings. These should be fastened together -in pamphlet form and constitute the complete instrument called the -contract. No binding contract and specifications can be drawn upon -logical deductions alone as legal precedent and tried methods must be -followed to insure success. To draw up an original contract requires the -combined knowledge of an engineer and a lawyer. The engineer of to-day -writes his specifications by copying copiously from specifications used -on work which has been completed successfully. In order that selections -may be made with judgment and discrimination some examples have been -selected from existing published specifications and contracts. - - -=110. The Advertisement.=—This should contain: (1) A heading indicating -the type of work, (2) A statement as to when, where and how bids will be -received and opened, (3) A brief description of the character and amount -of work to be done, (4) The method of payment, (5) The conditions under -which further information can be obtained, (6) A statement as to the -amount of money which must be deposited with the bid, and (7) Any other -pertinent facts concerning the work.[75] An example of an advertisement -follows; - - Sewer Construction - - Construction Turkey Creek Sewer - - Kansas City, Missouri. - - Bids for the construction of the Turkey Creek Sewer, two sewage - pumping stations to be used in connection therewith, and certain - laterals and extensions of existing sewers thereto, for Kansas - City, Missouri, will be received up to 2 p.m. August 19, 1919, at - the office of the Board of Public Works, City Hall, Kansas City, - Missouri. - - The main sewer will be about one and one-fifth miles long, and the - laterals and extensions about three and one-half miles: the main - sewer will be constructed of reinforced concrete, the laterals and - extensions will consist of concrete, segment blocks, and clay - pipe. - - This work is estimated to cost from $1,500,000 to $1,750,000. - Payment for the work will be made in four year special tax bills, - bearing 7 per cent interest, payable one-fourth each year. Time - 600 working days, barring strikes, bad weather, etc. - - Bidders are required to deposit $15,000 in cash or a certified - check with bid, to insure signing of contract when let. Same to be - returned on execution of the contract or rejection of bid. - - Complete plans and specifications for the work may be had and all - information obtained by seeing or writing to A. D. Ludlow, - Engineer of Sewers, City Hall, Kansas City, Missouri. Twenty-five - ($25.00) Dollars will be required to be deposited for a set of the - plans, but $20.00 thereof will be refunded upon return of the - plans in good condition. - - BOARD OF PUBLIC WORKS, - - Kansas City, Missouri, - - by F. E. McCabe, Secretary. - -There are usually legal restrictions which require that the -advertisement be inserted a certain number of times in specified -newspapers or other advertising mediums before the opening of bids. If -the contract is of sufficient size to attract outside contractors, the -advertisement should be inserted in engineering and contracting journals -of wide circulation. Although the advertisement appears separately from -the other portions of the contract, a copy is usually bound in as the -first page of the pamphlet containing the contract and specifications -and is made an integral part thereof. - - -=111. Information and Instructions for Bidders.=—This is somewhat on the -order of an introduction to the pamphlet in which the specifications, -contract, and contract drawings are published. As examples of the type -of information and instructions given to prospective bidders the -abstracts below have been taken from the “Contract, Specifications, -Bond, and Proposal for the North Shore Sanitary Intercepting Sewer” by -the Sanitary District of Chicago. The information and instructions to -bidders can be divided into the following sections: 1st. Examination of -Site, 2nd. Character and Quantity of Work, 3rd. Qualification for -Bidding, 4th. Instructions for Making out Proposal, 5th. Certified -Check, and 6th. Rejection of Bids. - - REQUIREMENTS FOR BIDDING AND INSTRUCTIONS TO BIDDERS - - Bidders are required to submit their bids upon the following express - conditions: - - Bidders must carefully examine the entire sites of the work - and the adjacent premises, and the various means of approach - to the sites, and shall make all necessary investigations to - inform themselves thoroughly as to the facilities for - delivering and handling materials at the sites and to inform - themselves thoroughly as to all the difficulties that may be - involved in the complete execution of all work under the - attached contract in accordance with the specifications hereto - attached. - - Bidders are also required to examine all maps, plans, and data - mentioned in the specifications, contract or proposal as being - on file in the office of the Chief Engineer, for examination - by bidders. No plea of ignorance of conditions that exist or - that may hereafter exist or of conditions or difficulties that - may be encountered in the execution of the work under this - contract, as the result of a failure to make the necessary - examinations and investigations, will be accepted as an excuse - for any failure or omission on the part of the Contractor to - fulfill in every detail all of the requirements of said - contract, specifications and plans, or will be accepted as a - basis for any claims whatsoever for extra compensation. Upon - application all information in the possession of the Chief - Engineer will be shown to bidders, but the correctness of such - information will not be guaranteed by the Sanitary District. - - The following schedule of quantities, although stated with as - much accuracy as is possible in advance, is approximate only, - and is assumed solely for the purpose of comparing bids. - -Then follows an itemized schedule of the quantity of work to be done -after which comes the following: - - Bidders must determine for themselves the quantities of work that - will be required, by such means as they may prefer, and shall - assume all risks as to variations in the quantities of the - different classes of work actually furnished under the contract. - Bidders shall not at any time after the submission of this - proposal, dispute or complain of the aforesaid schedules of - quantities or assert that there was any misunderstanding in regard - to the amount or the character of the work to be done, and shall - not make any claims for damages or for loss of profits because of - a difference between the quantities of the various classes of work - assumed for comparison of bids and the quantities of work actually - performed. - - Proposals that contain any omissions, erasures, or alterations, - conditions or items not called for in the contract and plans - attached hereto, or that contain irregularities of any kind, will - be rejected as informal. - - Bids manifestly unbalanced will not be considered in awarding the - contract.[76] - - No bid will be accepted unless the party making it shall furnish - evidence satisfactory to the Board of Trustees of the Sanitary - District of Chicago of his experience and familiarity with work of - the character specified and of his financial ability to - successfully and properly prosecute the proposed work to - completion within the specified time. - - Each bid shall be accompanied by a certified check, or cash, to - the amount of ten (10) per cent of the total amount of said bid - figured on the quantities given herewith, the lowest alternative - total being allowed. Said amounts deposited with bids, shall be - held until all of the bids have been canvassed and the contract - awarded and signed. The return of said check or cash to the bidder - to whom the contract for said work is awarded will be conditioned - upon his appearing and executing a contract for the work so - awarded and giving bond satisfactory to said Board of Trustees, - for the fulfillment of each contract in the amount of fifty (50) - per cent of the amount of each contract. - - The said Board of Trustees reserves the right to reject any or all - bids. - - Accompanying the contract form are plans which, together with the - specifications, show the work on which said tenders are to be - made. - - The proposal must not be detached herefrom or from the contract by - any bidder when submitting a bid. - - -=112. Proposal.=—The proposal is a blank printed form on which the -bidder is required to enter the prices for which he proposes to do the -work. The proposal blank is necessary in order that the bids may be -sufficiently uniform for proper comparison. Sewers are often paid for, -particularly for small sizes, per foot of completed sewer as measured -along the center line of the pipe parallel to the surface of the ground -with the exterior length of manholes and other structures deducted. -Sometimes, under other conditions, a different rate is allowed for each -additional two feet of depth of sewer, and special structures, such as -manholes, catch-basins, flush-tanks, etc., are paid for at a unit price -according to the depth. Water connections to flush-tanks are paid for -per foot of length of service pipe laid. In especially large or -difficult work, materials are paid for at a unit-price, for example, per -cubic yard of excavation, per cubic yard of concrete, per thousand feet -board measure of lumber, etc. - -The following example is taken from the contract for the North Shore -Intercepting Sewer previously quoted, to indicate the type of Proposal -used: - - - PROPOSAL - -FOR THE CONSTRUCTION OF THE NORTH SHORE INTERCEPTING SEWER - - To the Honorable, the President and the Board of Trustees of the - Sanitary District of Chicago: - - Gentlemen:__The undersigned hereby certi____ that ____ ha____ - examined the specifications and form of contract and the - accompanying plans for the construction of the North Shore - Intercepting sewer, and ha____ also examined the premises at and - adjacent to the sites of the proposed work, as herein described, - and the means of approach to the said sites. - - The undersigned ha____ also examined the foregoing “Requirements - for Bidding and Instructions to Bidders” and propose ____ to do - all the work called for in said specifications and contract, and - shown on said plans, and to furnish all materials, tools, labor - and all appliances and appurtenances necessary to the full - completion of said work at the rates and prices for said work as - follows, to_wit: - - (1_a_) For six (6) by nine (9) foot concrete sewer, complete in - place, as specified, the sum of ____ Dollars and ____ cents ($ - ____ ) per linear foot. - - (6_a_) For manholes, concrete, complete in place, as specified the - sum of ____ Dollars and ____ cents ($ ____ ) each. - - The following plans showing the work to be performed in accordance - with the attached specifications, have been examined by the - undersigned in preparing the foregoing proposal, to-wit: ____ ____ - In accordance with the requirements set forth in the attached - Information and Instructions for Bidders, there is deposited - herewith the sum of ____ ____ Dollars and ____ cents ($ ____ ) - which under the terms therein mentioned entitle ____ to bid on - said work, the said sum to be refunded to ____ ____ upon the - faithful performance of all conditions set forth in the - Information and Instructions for Bidders. - - Name ____ - Address ____ - -Blanks are provided for each item. No place is left at the end for a -summary. The proposal ends with an acknowledgment that the contract has -been examined completely and all preliminary directions therein have -been complied with. A blank is prepared for inserting the amount of the -required certified check, and finally for the signature of the bidders. - - -=113. General Specifications.=—The specifications, both general and -technical, are occasionally incorporated in the contract form, but more -frequently they are printed separately and are bound in the pamphlet -preceding the contract. The general specifications relate to the -conditions under which all work must be performed and are as applicable -to the construction of a pumping station as to the smallest lateral, -unless otherwise specified. It is not possible to include a complete set -of General Specifications in the limited space of this text, but the -more important specifications will be emphasized by examples taken from -specifications in use.[77] - -The subjects covered in General Specifications are: - - (1) Definitions of doubtful terms. - - (2) The Engineer to settle disputes. - - (3) Duties of the Engineer. - - (4) Duties of the Contractor. - - (5) Hours and days of work. - - (6) No work to be done in the absence of an inspector. - - (7) Contractor to be represented at all times. - - (8) Time of commencing and completing the work. - - (9) Liquidated damages for delay in completion. - - (10) The City may change the plans. - - (11) The City may increase the amount of the work. - - (12) Inspection and its conduct. - - (13) The Contractor to be acquainted with laws relating to the work. - - (14) Contractor responsible for damages to persons or property. - - (15) City to be protected against patent claims. - - (16) Abandonment of contract and its remedy. - - (17) Estimates of work done and moneys due. - - (18) Payments for extra work. - - (19) Character of workmen to be employed. - - (20) City may reserve a sum for repairs during stipulated term after - completion. - - (21) City may use money due Contractor to pay claims for labor or - materials used on the work and not paid for by the Contractor. - - (22) The Contractor shall have no claim for damages on account of delay - or unforeseen difficulties. - - (23) The Contractor may not assign nor sublet the contract without the - City’s consent. - - (24) Cleaning up after completion. - - (25) The Contractor’s relations to other contractors. - - (26) The portions composing the contract. - -The following examples cover the subjects named in the preceding titles: - - 1. Definitions. The word Engineer whenever not qualified shall - mean the Chief Engineer of the Commission, acting either directly - or through his properly authorized agents, such agents acting - severally within the scope of the particular duties entrusted to - them. - -This article may include words that may be in dispute or ambiguous such -as: Board of Trustees, Elevation, City, Contractor, Rock, Earth, etc., -etc. - - 2. Disputes. To prevent disputes and litigations, the Engineer - shall in all cases determine the amount, quality, and - acceptability of the work which is to be paid for under the - contract; shall decide all questions in relation to said work and - the performance thereof, and shall in all cases decide every - question which may arise relative to the fulfillment of the - contract on the part of the Contractor. His determination, - decision and estimate shall be final and conclusive, and in case - any question shall arise between the parties touching the - contract, such determination, decision, and estimate shall be a - condition precedent to the right of the Contractor to receive any - moneys under the contract. - - 3. Duties of the Engineer. The Engineer shall make all necessary - explanations as to the meaning and intentions of the - specifications and shall give all orders and directions, either - contemplated therein or thereby, or in every case in which a - difficulty or unforeseen condition shall arise in the performance - of the work. Should there be any discrepancies in or between, or - should any misunderstanding arise as to the import of anything - contained in the plans and specifications, the decision of the - Engineer shall be final and binding. Any errors or omissions in - plans and specifications may be corrected by the Engineer, when - such corrections are necessary for the proper fulfillment of their - intentions as construed by him. - - 4. Duties of the Contractor. The Contractor shall do all the work - and furnish all the labor, materials, tools and appliances - necessary or proper for performing and completing the work - required by the contract, in the manner called for by the - specifications, and within the contract time. He shall complete - the entire work at the prices agreed upon and fixed therefor to - the satisfaction of the Commission and its Chief Engineer and in - accordance with the specifications, the drawings, and such - detailed drawings as may be furnished from time to time, together - with such extra work as may be required for the performance of - which written orders may be given and received as hereinafter - provided. - - The Contractor shall place sufficient lights on or near the work - and keep them burning from twilight to sunrise; shall erect - suitable railings, fences or other protections about all open - trenches, and provide all watchmen on the work, by day or night, - that may be necessary for the public safety. The Contractor shall, - upon notice from the Engineer that he has not satisfactorily - complied with the foregoing requirements, immediately take such - methods and provide such means and labor to comply therewith as - the Engineer may direct, but the Contractor shall not be relieved - of this obligation under the contract by any such notice or - directions given by the Engineer, or by neglect, failure, or - refusal on the part of the Engineer to give such notice and - directions. - - The Contractor shall furnish such stakes and the necessary labor - for driving them as may be required by the Engineer. He shall - maintain the stakes when set, with reasonable diligence, and - stakes misplaced due to the carelessness of the Contractor or his - workmen shall be reset under the direction of the Engineer, at the - Contractor’s expense. - - 5. Night, Sunday, and Holiday Work:[78] No night, Sunday, nor - holiday work requiring the presence of an engineer or inspector - will be permitted except in case of emergency, and then only to - such an extent as is absolutely necessary and with the written - permission of the Engineer; provided that this clause shall not - operate in the case of a gang organized for regular and continuous - night, Sunday, or holiday work. - - 6. Absence of Engineer or Inspector. Any work done without lines, - levels, and instructions having been given by the Engineer or - without the supervision of an assistant or inspector, will not be - estimated or paid for except when such work is authorized by the - Engineer in writing. Work so done may be ordered removed and - replaced at the Contractor’s sole cost and expense. - - 7. Absence of Contractor. During the absence of the Contractor he - shall at all times have a duly authorized representative on the - work. The Contractor shall give written notice to the Commission - of the name and address of said representative and shall state - where and how such representative can be reached, at any and all - hours, whether by day or night. - - Whenever the Contractor or his representative is not present at - any place on the work where it may be necessary to give orders or - directions, such orders or directions will be given by the - Engineer and they shall be received and promptly obeyed by the - superintendent or foreman who may have immediate charge of the - particular work in relation to which the order may be given. - - 8. Commencing Work. The Contractor agrees to begin the work - covered by this contract within —— days of the execution of the - contract and to prosecute the same with all due diligence and to - entirely complete the work within —— days. - - It is understood and agreed that time is of the essence of this - contract, and that a failure on the part of the Contractor to - complete the work herein specified within the time specified will - result in great loss and damage to said Sanitary District and that - on account of the peculiar nature of such loss it is difficult, if - not impossible, to accurately ascertain and definitely determine - the amount thereof. - - 9. Liquidated Damages. It is therefore covenanted and agreed that - in case the said Contractor shall fail or neglect to complete the - work herein specified on or before the date hereinbefore fixed for - completion, the said Contractor shall and will pay the said - Sanitary District the sum of —— Dollars for each and every day the - Contractor shall be in default in the time of completion of this - contract. - - Said sum of —— Dollars per day is hereby agreed upon, fixed and - determined by the parties hereto as the liquidated damages which - said Sanitary District will suffer by reason of such defaults, and - not by way of a penalty. - - 10. Changes in Plans. The Board reserves the right to change the - alignment, grade, form, length, dimensions or materials of the - sewers or any of their appurtenances, whenever any condition or - obstructions are met that render such changes desirable or - necessary. In case the alterations thus ordered make the work less - expensive to the Contractor a proper deduction shall be made from - the contract prices and the Contractor shall have no claim on this - account for damages or for anticipated profits on the work that - may be dispensed with. In case such alterations make the work more - expensive, a proper addition shall be made to the contract prices. - Any deduction or addition as aforesaid shall be determined and - fixed by the Engineer. - - 11. Extensions and Additions. In the event that any material - alterations or additions are made as herein specified which in the - opinion of the Engineer will require additional time for execution - of all the work under this contract, then, in that case the time - of completion of the work shall be extended by such a period or - periods of time as may be fixed by said Engineer and his decision - shall be final and binding upon both parties hereto, provided that - in such case the Contractor, within four (4) days after being - notified in writing of such alterations and additions, shall - request in writing an extension of time, but the provisions of - this paragraph shall not otherwise alter the provisions of this - contract with reference to _liquidated damages_, and the said - Contractor shall not be entitled to any damages or compensation - from the said Sanitary District on account of such additional time - required for the execution of the work. - - 12. Inspection. All materials of whatsoever kind to be used in the - work shall be subject to the inspection and approval of the - Engineer and shall be subject to constant inspection before - acceptance. Any imperfect work that may be discovered before its - final acceptance shall be corrected immediately, and any - unsatisfactory materials used in the work or delivered at the site - shall be rejected and removed on the requirement of the Engineer. - The inspection of any work shall not relieve the Contractor of any - of his obligations to perform proper and satisfactory work as - herein specified, and all work which, during the progress and - before the final acceptance, may become damaged from any cause, - shall be removed and replaced by good and satisfactory work - without extra charge therefor. The Engineer and his assistants - shall have at all times free access to every part of the work and - to all points where material to be used in the work is - manufactured, procured or stored and shall be allowed to examine - any material furnished for use in the work under this contract. - - All inspection of any and all material furnished for use in work - to be performed under this contract shall be made at the site of - the work after the delivery of the material, provided, that, if - requested by the Contractor the Engineer may at his option - perform, or have performed, inspection of materials at points - other than the site of the work. In any such case the Contractor - shall pay the Sanitary District the extra cost of such inspection, - including the necessary expenses of the inspector for the extra - time expended in performing any such inspection at said other - points. - - 13. Legal Requirements. The Contractor shall keep himself fully - informed of all existing and future national and state laws and - local ordinances and regulations in any manner affecting those - engaged or employed in the work, or the materials used in the - work, or of all such orders and degrees of bodies or tribunals - having any jurisdiction or authority over the same, and shall - protect and indemnify the party of the first part against any - claim or liability arising from or based on the violation of such - law, ordinance, regulation, order or decree, whether by himself or - his employees. - - 14. Damages. If any damage shall be done by the Contractor or by - any person or persons in his employ to the owner or occupants of - any land or to any real or personal property adjoining, or in the - vicinity of the work herein contracted to be done or to the - property of a neighboring contractor the Engineer shall have the - right to estimate the amount of said damage and to cause the - Sanitary District to pay the same to the said owner, occupant, or - contractor, and the amount so paid shall be deducted from the - money due said Contractor under this contract. Said Contractor - covenants and agrees to pay all damages for any personal injury - sustained by any person growing out of any act or doing of himself - or his employees that is in the nature of a legal liability, and - he hereby agrees to indemnify and save the Sanitary District - harmless against all suits or actions of every name and - description brought against said Sanitary District, for or on - account of any such injuries, or such damages received or - sustained by any person or persons; and the said Contractor - further agrees that so much of the money due to him under this - contract, as shall be considered necessary by the Board of - Trustees of said Sanitary District, may be retained by the - Sanitary District until such suit or claim for damages shall have - been settled, and evidence to that effect shall have been - furnished to the satisfaction of said Board of Trustees. - - 15. Patents. It is further agreed that the Contractor shall - indemnify, keep and save harmless said Sanitary District from all - liabilities, judgments, costs, damages and expenses which may in - any wise come against said Sanitary District, or which may be the - result of an infringement of any patent by reason of the use of - any materials, machinery, devices, apparatus, or process furnished - or used in the performance of this contract, or by reason of the - use of designs furnished by the Contractor and accepted by the - Sanitary District, and in the event of any claim or suit or action - at law or in equity of any kind whatsoever being made or brought - against said Sanitary District, then the Sanitary District shall - have the right to retain a sufficient amount of money in the same - manner and upon the conditions as hereinafter specified. - - 16. Abandonment of Contract. If the work to be done under the - contract shall be abandoned by the Contractor, or if at any time - the Engineer shall be of the opinion, and shall so certify, in - writing, to the Commission, that the performance of the contract - is unnecessarily or unreasonably delayed, or that the Contractor - is willfully violating any of the conditions of the - specifications, or is executing the same in bad faith, or not in - accordance with the terms thereof, or if the work be not fully - completed within the time named in the contract for its - completion, the Commission may notify the Contractor to - discontinue all work thereunder, or any part thereof, by a written - notice served upon the Contractor, as herein provided; and - thereupon the Contractor shall discontinue the work, or such part - thereof, and the Commission shall thereupon have the power to - contract for the completion of said work in the manner prescribed - by law, or to procure and furnish all necessary materials, - animals, machinery, tools and appliances, and to place such and so - many persons as it may deem advisable to work at and complete the - work described in the specifications, or such part thereof, and to - charge the entire cost and expense thereof to the Contractor. And - for such completion of the work or any part thereof, the - Commission may for itself or its contractors, take possession of - and use or cause to be used any or all such materials, animals, - machinery, tools and implements of every description as may be - found on the line of the said work. The cost and expense so - charged shall be deducted from, and paid by the City out of such - moneys as may be due or may become due to the Contractor, under - and by virtue of the contract. In case such expense shall exceed - the amount which would have been payable under the contract, if - the same had been completed by the Contractor, he shall pay the - amount of such excess to the City. When any particular part of the - work is being carried on by the Commission, by contract or - otherwise, under the provisions of this clause of the contract, - the Contractor shall continue the remainder of the work in - conformity with the terms of his contract, and in such manner as - in no wise to hinder or interfere with the persons or workmen - employed by the Commission by contract or otherwise as above - provided, to do any part of the work or to complete the same under - the provisions hereof. - - 17. Estimates. The Engineer shall from time to time as the work - progresses, on or about the last day of each month, make in - writing an estimate, such as he shall believe to be just and fair, - of the amount and value of the work done and the materials - incorporated into the work by the Contractor under the - specifications, provided however that no such estimate shall be - required to be made when, in the judgment of the Engineer the - total value of the work done and the materials incorporated into - the work since the last preceding estimate is less than —— - dollars. Such estimates shall not be required to be made by strict - measurements, but they may be approximate only. - - The Contractor shall not be entitled to demand from the Commission - as a right, a detailed statement of the measurements or quantities - entering into the several items of the monthly estimates, but he - will be given such opportunities and facilities to verify the - estimates as may be deemed reasonable by the Commission. - - When in the opinion of the Engineer, the Contractor shall have - completely performed the contract on his part, the Engineer shall - make a final estimate, based on actual measurements, of the whole - amount of the work under and according to the terms of the - contract, and shall certify to the Commission in writing, the - amount of the final estimate at the completion of the work. After - the completion of the work the City shall pay to the Contractor - the amount remaining after deducting from the total amount or - value of the work, as stated in the final estimate, all such sums - as have theretofore been paid to the Contractor under any of the - provisions of the contract, except such sums as may have been paid - for extra work, and also any sum or all sums of money which by the - terms thereof the City is or may be authorized to reserve or - retain; provided that nothing therein contained shall affect the - right of the City, hereby reserved, to reject the whole or any - portion of the aforesaid work, should the said certificate be - found or known to be inconsistent with the terms of the contract - or otherwise improperly given. All monthly estimates upon which - partial payments have been made, being merely estimates, shall be - subject to correction in the final estimate, which final estimate - may be made without notice thereof to the Contractor, or of the - measurements upon which it is based. - - 18. Extra Work. The Contractor shall do any work not herein - otherwise provided for, when and as ordered in writing by the - Engineer or his agents specially authorized thereto in writing, - and shall when requested by the Engineer so to do, furnish - itemized statements of the cost of the work ordered and give the - Engineer access to accounts, bills, vouchers, etc. relating - thereto. If the Contractor claims compensation for extra work not - ordered as aforesaid, or for any damages sustained, he shall - within one week after the beginning of any such work or the - sustaining of any such damage, make a written statement of the - nature of the work performed or the damage sustained, to the - Engineer, and shall, on or before the fifteenth day of the month - succeeding that in which any such extra work shall have been done - or any such damage shall have been sustained, file with the - Engineer an itemized statement of the details and amount of any - such work or damage; and unless such statement shall be made as so - required, his claim for compensation shall be forfeited and he - shall not be entitled to payment on account of any such work or - damage. - - For all such extra work the Contractor shall receive the - reasonable cost of said work, plus fifteen (15) per cent of said - cost. - - 19. Competent Employees. The Contractor shall employ only - competent skillful men to do the work; and whenever the Engineer - shall notify the Contractor, in writing, that any man employed on - the work is, in his opinion unsatisfactory, such man shall be - discharged from the work and shall not again be employed on it, - except with the consent of the Engineer. - - 20. Money Retained. Upon the completion of the work and its - acceptance by the City, the City shall reserve and retain five (5) - per cent of the total value of the work done under the contract as - shown by the final estimate, over and above any and all other - reservations which the city by the terms thereof is entitled or - required to retain and shall hold the said five (5) per cent for a - period of nine (9) months from and after the date of completion - and acceptance, and the City shall be authorized to apply such - part of said five (5) per cent so retained to any and all costs of - repairs and renewals as may become necessary during such period of - nine (9) months, due to improper work done or materials furnished - by the Contractor, if the Contractor shall fail to make such - repairs or renewals within twenty-four (24) hours after receiving - notice from the City so to do. - - Upon the expiration of said nine (9) months from and after the - completion and acceptance of the work, the City shall pay to the - Contractor the said five (5) per cent hereby retained, less such - sums as may have been retained hereunder. - - 21. Unpaid Claims against Contractor. The Contractor shall furnish - the City with satisfactory evidence that all persons who have done - work or furnished materials under the contract, and have given - written notices to the City, before and within ten (10) days after - the final completion and acceptance of the whole work under the - contract, that any balance for such work or materials is due and - unpaid, have been fully paid or satisfactorily secured. And in - case such evidence is not furnished as aforesaid, such amount as - may be necessary to meet the claims of the persons aforesaid shall - be fully discharged or such notices withdrawn. - - 22. Delays and Difficulties. The Contractor shall not be entitled - to any claims for damages on account of postponement or delay in - the work occasioned by forces beyond the control of the City, nor - for postponement or delay in the work where ten (10) days written - notice has been given the Contractor of such postponement or - delay, nor where unforeseen difficulties are encountered in the - prosecution of the work. In the event of a postponement or delay - ordered in writing by the City the time of completion of the - contract shall be extended a number of days equal to the number of - days that the work has been postponed or delayed. - - 23. Assignment of Contract. The Contractor shall not assign by - power of attorney or otherwise, nor sublet the work or any part - thereof, without the previous written consent of the party of the - first part, and shall not either legally nor equitably assign any - of the moneys payable under this agreement or his claim thereto - unless by and with the consent of the party of the first part. - - 24. Cleaning Up. On or before the completion of the work, the - Contractor shall, without charge therefor, tear down and remove - all buildings and other structures built by him, shall remove all - rubbish of all kinds from any grounds which he has occupied, and - shall leave the line of the work in a clean and neat condition. - - 25. Access to Work and Other Contractors. The Commission and its - engineers, agents and employees may at any time and for any - purpose enter upon the work and the premises used by the - Contractor, and the Contractor shall provide proper and safe - facilities therefor. Other contractors of the Commission may also - when so authorized by the Engineer, enter upon the work and the - premises used by the Contractor for all the purposes which may be - required by their contracts. Any differences or conflicts which - may arise between this Contractor and other contractors of the - Commission in regard to their work shall be adjusted and - determined by the Engineer. - - 26. The Contract. It is understood and agreed by the City and the - Contractor that the terms of this contract are embodied and - included in the Advertisement, Information and Instructions to - Bidders, Proposal, Specifications of every nature, the Bond and - the contract drawings hereto attached. - -These few articles have been given as examples of some of the essential -subjects to be treated in general specifications. It is to be understood -that these examples do not represent a complete set of general -specifications and items have been omitted the absence of which in a -complete contract might be injurious to the successful completion of the -work. - - -=114. Technical Specifications.=—These ordinarily follow the general -specifications and have to do with the quality of materials, the manner -of putting them together, and the method of doing the work. The subject -headings in the Technical Specifications on the Baltimore Sewerage -Commission are: - - Excavation - Tunneling - Rock Excavation - Sheeting - Sheet Piling - Sheeting and Bracing - Piles - Blasting - Pumping and Drainage - Foundations - Refilling - Repaving - Underdrains - Buildings - Inlets and Catch-Basins - Cement - Mortar - Concrete - Brick - Masonry - Reinforced Concrete - Vitrified Pipe - Concrete and Brick Sewers - Vitrified Pipe Sewers and Drains - Manholes - Iron Castings - House Connections - Obstructions - Fences - Flush-Tanks - -Each of these subjects is treated in the appropriate section of this -book. - -An important part of each section of the technical specifications is the -clause providing for the method of payment for the work specified. This -is usually the last clause in the section. For example, the last clause -in the Baltimore Specifications relating to Rock Excavation, is: - - “Payment will be made for the number of cubic yards of rock - measured and allowed as above specified at the price of four - dollars and fifty cents ($4.50) per cu. yd., measured in place. - Payment for rock excavation will be made in addition to the prices - bid for excavation.” - - -=115. Special Specifications.=—These have to do with problems, methods -of construction, or materials peculiar to certain contracts or certain -portions of the work. It frequently occurs that the construction of -sewerage works will be let out under a number of contracts, or bids will -be called for on different alternatives to which the entire -Advertisement, Information and Instructions for Bidders, Proposal, and -General Specifications are applicable. The special specifications will -apply only to the contract in question, e.g., in some work done under -the direction of the author, the sewer on one contract came within -twelve inches of the surface of a highway. The special specification -relating to this piece of construction, was: - - “Where crossing under the Chicago Road the pipe sewer shall be - embedded in concrete as shown on the contract drawings. The - concrete for this purpose shall be mixed in the proportions of one - (1) part cement, three (3) parts fine aggregate, and six (6) parts - coarse aggregate. Payment for the concrete so used will be made at - the unit price stated in the accompanying Proposal.” - -In order to avoid confusion the special specifications are either -incorporated directly in the Contract form, or follow the Technical -Specifications and are grouped according to the contracts to which they -apply. - - -=116. The Contract.=—The contract is a brief instrument which includes a -simple statement of the obligations of each party involved. The -following is an example of a form in successful use: - - - CONTRACT - - This agreement made and entered into this ____ day of ____ in the - year one thousand nine hundred and ____ by and between the City of - ____ by its duly constituted or elected authorities herein acting - for the City of ____ without personal liability to themselves, - party of the first part, hereinafter designated as the City, and - ____ party of the second part hereinafter designated as the - Contractor. - - WITNESSETH, that the parties to these presents each in - consideration of the undertakings, promises and agreements on the - part of the other herein contained, have undertaken, promised and - agreed, and do hereby undertake, promise and agree, the party of - the first part for itself, its successors and assigns, and the - part ____ of the second part for ____ and ____ heirs, executors, - administrators and assigns as follows, to-wit: - - Art. I. To be bounden by all the articles of the General, - Technical, and Special Specifications applicable, and by the terms - of the Advertisement, Information and Instructions for Bidders, - Proposal and Contract Drawings hereto attached, and which are - understood and acknowledged to be an integral part of this - contract. - - Art. II. The work to be completed under this contract is ____ - - Art. III. The City shall pay and the Contractor shall receive as - full compensation for everything furnished and done by the - Contractor under this contract, including all work required but - not specifically mentioned in the following items, and also for - all loss or damage arising from the nature of the work aforesaid, - or from the action of the elements, or from any unforeseen - obstruction or difficulty encountered in the prosecution of the - work and for well and faithfully completing the work as herein - provided, as follows: - -Then follows a copy of the Proposal with the prices bid. The contract -closes with the final clause: - - In witness whereof the said City of ____, party of the first part - have hereunto set their hands and seals, and the Contractor has - also hereunto set his hand and seal and the party of the first - part and the Contractor have executed this agreement in duplicate, - one part to remain with the party of the first part and one to be - delivered to the Contractor this ____ day of ____ in the year one - thousand nine hundred and ____ - - City of ____ - ____ - ____ - - Contractor ____ - ____ - ____ - - -=117. The Bond.=—The bond called for in the Information and Instructions -for Bidders is bound in the pamphlet following the Contract. No uniform -practice is followed in the amount of the bond required. It varies from -50 to 100 per cent of the contract price and may be stated as a lump sum -before the contract price is known. There is a possibility that the -Contractor may fail before he has commenced work and the City may be -unable to procure another contractor to take up the work. The City -should then be protected by a 100 per cent bond. Such a contingency is -remote. The Contractor seldom fails until work is well under way, and -other contractors are usually available, although the failure of one -contractor tends to increase the bids of other contractors for the same -work. In fixing the amount of the bond the judgment of the Engineer is -called into play in order that the amount may be as low as possible in -fairness to the Contractor, and high enough to protect the interests to -the City. By reducing the amount of the bond the expense to the City is -also reduced as the City ultimately must pay its cost. - -Upon the acceptance of the bond and the execution of the Contract, the -Engineer’s duties take him out of the designing office and into the -construction field. - - - - - CHAPTER XI - CONSTRUCTION - - -=118. Elements.=—The principal elements in construction are: labor, -materials, tools, and transportation. The lack of or inadequateness of -any one of these detracts from the effectiveness of the others. The -engineer should assure himself of the completeness of his plans or those -of the contractor on each of these points. The disposition of labor and -the handling of materials to obtain the largest amount of good with the -least expenditure of money and effort are problems which must be solved -by the engineer or the contractor during construction. - - - WORK OF THE ENGINEER - - -=119. Duties.=—The duties of the engineer during construction consist in -giving lines and grades; inspecting materials; interpreting the -contract, specifications and drawings; making decisions when unexpected -conditions are encountered; making estimates of work done; collecting -cost data; making progress reports; keeping records; and in guarding the -interests of the City. - - -=120. Inspection.=—In the inspection of workmanship and materials, the -engineer is assisted by a corps of inspectors and assistants who act -under his direction. The duties of the inspector are to be present at -all times that work is in progress and to act for the engineer in -enforcing the terms of the contract, the details of the drawings, and -the tests applicable to the workmanship and materials that he is -delegated to inspect. He should have a copy of the contract, or that -portion of it which pertains to his work, available at all times. He -should examine all materials as they are delivered on the job and see -that rejected materials are removed at once. An ordinary recourse of -some foremen will be to place rejected material to one side until a -brief absence of the inspector will present the opportunity for the use -of the rejected material. The methods to be followed in the inspection -of materials and workmanship should be such as to discover discrepancies -between the specifications and the materials delivered or the work done. -Other duties of the inspector are: to record the location of house -connections or to drive a stake over them for subsequent location by the -engineer; to see that plugs are put in the branches left for future -house connections; to inspect the workmanship in the making of joints in -pipe sewers; to protect the line and grade stakes from displacement; to -check the size, depth, and grade of sewers and elevations of special -structures, etc. - -Dishonest and unscrupulous workmen have many tricks to get by the -inspector. These tricks are best learned by experience as no academic -list can impress them properly on the memory. The position of the -inspector is not always enviable. He must hold the respect of the -workmen, of the contractor, and of the engineer. To do this he must not -be unreasonable or arbitrary in his decisions, but when a decision is -once made he must be firm in following up its enforcement. He must be -careful not to give directions whose fulfillment he cannot enforce, nor -for which he cannot give adequate reason to his superiors. His integrity -must never be questioned. He must not allow himself to become under -obligations to the contractor by the acceptance of favors he cannot -return except at the expense of his employer, yet at the same time he -must not appear priggish by the refusal of all favors or social -invitations. In brief he must be friendly without being intimate, -independent without being aloof, and firm without being arbitrary. - -The engineer must support his inspectors in their decisions or discharge -them if he cannot. - - -=121. Interpretation of Contract.=—In interpreting the contract, -specifications and drawings, the engineer is supposedly an impartial -arbiter between the interests of the city and the contractor. His -decisions, as to the meaning of the contract, must be founded on his -engineering judgment, and should aim to produce the best results without -demanding more from the contractor than, in his honest opinion, it is -the intention of the contract to demand. However conscientiously he may -attempt to remain impartial, and in spite of the honesty of the -contractor, his position, as an employee of the city will almost -invariably cause him to favor the city in his decisions on close points. -The experienced contractor knows this and fixes his bid accordingly, the -personality of the engineer sometimes acting as an important factor in -the amount of the bid. The situation arises through the character of the -contract, and not through a lack of moral integrity on the part of -anyone concerned. - - -=122. Unexpected Situations.=—When unexpected or uncertain conditions -are encountered in construction the engineer should visit the spot at -once and should advise or direct, according to the terms of the -contract, the procedure to be followed. Such conditions may be the -encountering of other pipes, quicksand, rock, etc. Each case is a -problem in itself. Water, gas, telephone and electric wire conduits can -be moved above or below the sewer being constructed with comparative -ease. Other sewers, if smaller, may be permitted to flow temporarily -across the line of the sewer under construction and finally discharge -into the completed sewer, or one sewer must be made to pass under the -other, either as an inverted siphon or by changing the grade of one of -the sewers. Rock, or other material for which a special rate of payment -is allowed, must be measured as soon as uncovered in order to avoid -delaying the work or losing the record of the amount removed. When -quicksand is met special precautions must be taken to safeguard the -sewer foundation and to insure that the sewer will remain in place until -after the backfilling is completed. These precautions are described in -Art. 135. - - -=123. Cost Data and Estimates.=—Cost account keeping and the making of -monthly or other estimates are closely connected. Cost accounts are of -value in estimating the amount of work done to date, and in making -preliminary estimates of the cost of similar work. Although the engineer -is not always required to keep such accounts, they are usually of -sufficient value to pay for the labor of keeping them. Under some -contracts the contractor’s accounts are open to examination by the -engineer. Usually, however, he must depend on reports from the -inspectors for information concerning the man-hours required on -different pieces of work, and on his own measurements of materials used -and his knowledge of their unit costs, in order to make up an estimate -of total cost. - -The measurement of a completed structure and a summary of the materials -used in its construction may act as a check on the use of proper -materials as called for in the contract. For example, if it is known -that 2,000 bricks are required for the construction of a manhole and if -only 15,000 have been used in the construction of ten manholes, it is -probable that some or all of the manholes have been skimped. Similar -conditions may show in the proportions of concrete, backfilling in -tunnels, sheeting to be left in place, etc. - -The statement of a few principles of cost accounting, and the -illustration of a few blanks in use should be sufficiently suggestive to -lead a resourceful engineer in the right direction.[79] Costs should be -divided into four general classifications: labor, materials, equipment, -and overhead. Labor should be subdivided under its several different -classifications arranged in accordance with rates of pay. The number of -laborers under each classification and the amount of work done per day -should be recorded. Fig. 86 is an example of a form which may be used -for such a purpose. - -[Illustration: - - FIG. 86.—Foreman’s Daily Payroll Report. - - From Engineering and Contracting, 1907. -] - -Materials may be recorded as they are delivered on the job, as they are -used, or in both cases. Measurements are usually easier to make at the -time of delivery, but records made at the time materials are used are -more serviceable. For example, 100 barrels of cement may be delivered on -a job in November, 50 of them are used before the job freezes up and the -other 50 are held over until spring. It would be misleading to charge -100 barrels used in November. Fig. 87 is a form in use for an -inspector’s report on materials. The total cost must be made up in the -office from these records and a knowledge of unit costs. - -[Illustration: - - FIG. 87.—Foreman’s Daily Material Report. - - From Engineering and Contracting, 1907. -] - -Equipment consists of tools, animals, machinery, and apparatus used in -construction. Only equipment that is actually used should be charged to -the job and a credit should be made at the completion of the job for the -fair value of the equipment remaining after the completion of the work. - -Overhead charges include the expense of the office force, -superintendence, and miscellaneous items such as insurance, rent, -transportation, etc., which cannot be charged to any particular portion -of the work but are equally applicable to all portions. It happens -frequently that many jobs are handled in the same main office. The -division of overhead becomes more difficult and is frequently arranged -on an arbitrary basis, e.g., each job may be charged the proportion of -overhead that its contract price bears to the total contract prices -being performed under that office. This rule may be modified when it -becomes evident that some job is taking distinctly more than its share -of the overhead. - -Estimates of work done in any period can be made with the above data in -hand by subtracting the total costs of the work up to the beginning of -the period from the total costs up to the end of the period. Fig. 88 -shows a sample blank from the final estimate sheets used at Scarsdale, -N. Y. - - -=124. Progress Reports.=[80]—These are kept by the engineer in order -that he may see that the work is progressing as called for in the -contract, and any portion which is lagging behind without reason may be -pushed. Such reports are most useful when the information is expressed -graphically, as the eye quickly catches points where the work is falling -behind schedule. - - -=125. Records.=—The contract drawings are supposed to show exactly where -and how construction is to be done. Due to unexpected contingencies -changes occur, of which a record should be made and preserved. These -records may be kept in a form similar to the contract drawings, or if -the changes are not extensive, they can be recorded on the original -contract drawings. The location of house and other connections should be -recorded in a separate note book available for immediate consultation. -The engineer should keep a diary of the work in which are recorded -events of ordinary routine as well as those of special interest and -importance. This diary should be illustrated by photographs showing the -condition of the streets before and after construction, methods of -construction, accidents, etc. Such accounts are of great value in -defending subsequent litigation and their existence sometimes prevents -litigation. A contractor may wait a year or so after the completion of a -piece of work until the engineer and other city officials have broken -their connection with the city. Suit is then brought against the city -and unless good records are available the administration may be forced -to buy the claimant off or may elect to enter court, only to be beaten. - -[Illustration: - - FIG. 88.—Samples of Cost Record Forms. - - From Engineering and Contracting, 1909. -] - - - Excavation - - -=126. Specifications.=—The following abstracts have been taken from the -specifications on Excavation by the Baltimore Sewerage Commission as -illustrative of good practice. In conducting the work the contractor -shall: - - ... remove all paving, or grub and clear the surface over the - trench, whenever it may be necessary and shall remove all surface - materials of whatever nature or kind. He shall properly classify - the materials removed, separating them as required by the - Engineer; and shall properly store, guard, and preserve such as - may be required for future use in backfilling, surfacing, repaving - or otherwise. All macadam material removed shall be separated and - graded into such sizes as the Engineer may direct and materials of - different sizes shall be kept separate from each other and from - any and all other materials. - - All the curb, gutter, and flag-stones and all paving material - which may be removed, together with all rock, earth and sand taken - from the trenches shall be stored in such parts of the carriageway - or such other suitable place, and in such manner as the Engineer - may approve. The Contractor shall be responsible for the loss of - or damage to curb, gutter and flag-stones and to paving material - because of careless removal or wasteful storage, disposal, or use - of the same. - - ... When so directed by the Engineer the bottom of the trench - shall be excavated to the exact form of the lower half of the - sewer or of the foundation under the sewer. - - The bottom width of the trench for a brick or concrete sewer shall - be ... not less in any case than the overall width of the sewer, - as shown on the plans. In case the trench is sheeted this minimum - width will be measured between the interior faces of the sheeting - as driven, but in no case shall bracing, stringers, or waling - strips be left within any portion of the masonry of the sewer - except by permission of the Engineer; and such braces, stringers - and waling strips shall not, in any case, be allowed to remain - within the neat lines of the masonry as shown on the plans. In - case that the distance between faces of the sheeting is less than - that called for by the width of the sewer to be laid in the - trench, the Engineer may direct the sheeting to be drawn and - redriven, or otherwise changed and altered; or he may direct that - the sewer be reinforced in such manner and to such an extent as he - may deem necessary without compensation to the Contractor, even - though such narrower trench was not caused by negligence or other - fault on the part of the Contractor. - - Trenches for vitrified pipe shall be at all points at least six - inches wider in the clear on each side than the greatest external - width of the sewer, measured over the hubs of the pipe.... Bell - holes shall be excavated in the bottoms of trenches for vitrified - pipe sewers wherever necessary. - - Not more than three hundred feet of trench shall be opened at any - one time or place in advance of the completed building of the - sewer, unless by written permission of the Engineer and for a - distance therein specified.... - - The excavation of the trench shall be fully completed at least - twenty feet in advance of the construction of the invert, unless - otherwise ordered. - - During the progress of construction the Contractor will be - required to preserve from obstruction all fire hydrants and the - carriageway on each side of the line of the work. - - The streets, cross-walks, and sidewalks shall be kept clean, - clear, and free for the passage of carts, wagons, carriages and - street or steam railway cars, or pedestrians, unless otherwise - authorized by special permission in writing from the Engineer. In - all cases a straight and continuous passageway on the sidewalks - and over the cross walks of not less than three feet in width - shall be preserved free from all obstruction. - - Where any cross walk is cut by the trench it shall be temporarily - replaced by a timber bridge at least three feet wide, with side - railings, at the Contractor’s expense. The placing of planks - across the trench without proper means of connection or - fastenings, or pipe or other material, or the using of any other - makeshift in place of properly constructed bridges, will not be - permitted. - -This is equally applicable to certain wagon bridges to be fixed upon by -the Engineer, on the basis of traffic requirements. - - In streets that are important thoroughfares or in narrow streets - the material excavated from the first one hundred feet of any - opening or from such additional length as may be required, shall - upon the order of the Engineer, be removed by the Contractor, as - soon as excavated. The material subsequently excavated shall be - used to refill the trench where the sewer has been built. - -The preceding specifications are applicable to open-trench excavation. -Rigid restrictions are placed about tunneling because of the greater -difficulty of doing good work, the greater danger to life and property -and the possibility of later surface subsidence if the backfilling is -done improperly. A common clause in specifications is: - - All excavations for sewers and their appurtenances shall be made - in open trenches unless written permission to excavate in tunnel - shall be given by the Engineer. - - -=127. Hand Excavation.=—Earth excavation by pick and shovel is the -simplest and most primitive mode of excavation. Only small jobs are -handled in this manner in order to save the investment necessary in -machines or the expense of hiring and moving one to the work. The tools -used in the hand excavation of trenches are: picks, pickaxes, -long-handled and short-handled pointed shovels, square-edged long- and -short-handled shovels, scoop shovels, axes, crowbars, rock drills, -mauls, sledges, etc. The excavating gangs are divided up into units of -20 to 50 men under one foreman or straw boss, and among the men may be a -few higher priced laborers who set the pace for the others. Each laborer -on excavation should be provided with a shovel, the style being -dependent on the character of the material being excavated and the depth -of the trench. In stiff material and deep trenches requiring the lifting -of the material in the shovel, long-handled pointed shovels should be -used. In loose sandy material loaded directly into buckets -short-handled, square pointed shovels are satisfactory. Picks are used -in cemented gravels or where hard obstructions prevent cutting down with -the edge of the shovel. Very stiff but not hard material can be cut out -in chunks with a pickaxe and thrown from the trench or into a bucket -with a scoop shovel. Scoop shovels are also useful in wet running -quicksand. The number of picks, axes, crowbars, and other tools must be -proportioned according to the material being excavated. Under the worst -conditions of excavation in a hard cemented gravel it may be necessary -to provide each man with a pick as well as a shovel, whereas in sand -only a shovel is necessary. Two or three crowbars, axes, a length of -chain, two or three screw jacks, etc., are provided per gang in case of -an unexpected encounter with an obstruction in the trench, such as a -boulder, a tree stump, a length of pipe, etc. - -In laying out the work the foreman marks the outlines of the trench on -the ground by means of a scratch made with a pick, chalk marks, tape, or -other devices. These marks are measured from offset or center stakes set -by the engineer. Center stakes are less conducive to error but are more -likely to be disturbed before use than are offset stakes, but careless -foremen make more errors with offset than with center stakes. The -inspector should assist or be present at the laying out of the trench. -After the trench has been laid out each laborer should be given a -certain specific portion of it to dig and this portion is marked out on -the ground. In this way a check can be kept upon the performance of each -laborer and the knowledge of this fact tends to a uniformly better -performance. The amount of work that can be performed by one man with a -pick and shovel is as shown in Table 49. Some men may exceed these -rates, many will not attain them. The allotted task must be gaged on the -character of the ground in order that the tasks may be equal and a -spirit of competition fostered. The hard worker will set the pace for -the lazy man. Some contractors have adopted the expedient of dismissing -laborers for the day as soon as the allotted task is done. - - TABLE 49 - - AMOUNT OF MATERIAL MOVED BY ONE MAN WITH A PICK AND SHOVEL - - (From H. P. Gillette) - ────────────────────────────────────────┬────────────────────────────── - Material │ Cubic Yard per hour - ────────────────────────────────────────┼────────────────────────────── - Hardpan │ 0.33 - Common earth │ 0.8 to 1.2 - Stiff clay │ 0.85 - Clay │ 1.00 - Sand │ 1.25 - Sandy soil │ 0.8 to 1.2 - Clayey earth │ 1.3 - Sandy soil (frozen) │ 0.75 - ────────────────────────────────────────┴────────────────────────────── - -The opening of the trench may be facilitated by breaking ground with a -plow. In hard ground or on paved roads it may be necessary to cut -through the surface crust with a hammer and drill, although in some -cases a plow can be used successfully. Frozen ground can be thawed by -building fires along the line of the trench, or greater economy may be -achieved by placing steam pipes along the surface with perforations -about every 18 inches and either boxing them on the top and sides or -burying them in the frozen earth with a covering of sand. Another -arrangement is to blow steam into a line of bottomless boxes in which -each box is about 8 feet long. Holes are left in the top of the boxes -into which the pipe is shoved, and after its withdrawal the holes are -covered. Blasting of frozen earth is sometimes successful but cannot be -resorted to in built up districts where it is unsafe unless properly -controlled. Once the frost crust is broken through it can be attacked -from below and frequently broken down by undermining. - -A laborer cannot dig and raise the earth much more than to the height of -his head, and preferably not quite so high, without tiring quickly. -After the trench has passed a depth of 4 feet he cannot throw the earth -clear of the trench. An additional laborer is needed then at the surface -to throw the earth back. He should shovel the earth from a board -platform placed at the edge of the trench as a protection to the bank. -When the trench passes the 6–foot depth a staging is put in about 4 feet -from the top on which the lowest laborer piles his materials. It is then -passed up to the surface by a second laborer on the staging, and a third -laborer on the surface throws the material back clear of the trench. -Stagings are put in about every 5 or 6 feet for the full depth of the -trench. - -When the trench has come within half the diameter of the pipe of the -final grade, if the material is sufficiently firm, the remainder of the -trench should be cut to conform to the shape of the lower half of the -outside of the pipe, with proper enlargements for each bell. - - -=128. Machine Excavation.=—On work of moderately large magnitude -excavation by machine is cheaper than by pick and shovel alone. In -comparing the cost of excavation by the two methods all items such as -sheeting, pipe laying, backfilling, etc., should be included, since -these items will be affected by the method of excavation. The cost of -setting up and reshipping the machine must be included as this is -frequently the item on which the use of the machine depends. Because of -the cost of setting up and shipping, which must be distributed over the -total number of yards excavated, the cost per cubic yard of excavating -by machine varies with the number of cubic yards excavated. The point of -economy in the use of a machine is reached when the cost by hand and by -machine are equal. For all work of greater magnitude, excavation by -machine will prove cheaper.[81] Items favoring the use of machinery -which may cause its adoption for small jobs are: its greater speed, -reliability, ease in handling, economy in sheeting, economy in labor, -and small amount of space needed making it useful in crowded streets. -Continuous bucket machines, drag lines, and occasionally steam shovels -are not adapted to conditions where rocks, pipes and other underground -obstacles are frequently met. - -The following problem is an example of the work necessary in making a -comparison of the relative economy of machine and hand excavation: - - It is assumed that a man can excavate 15 feet of trench 30 inches - wide and 8 feet deep in 10 hours. He receives 55 cents per hour - for his work. A machine costing $10,000 has a life of 6 years. It - can be kept busy 150 days in the year. When operating it costs - $1.25 per hour for the operator, fuel and repairs. It will - excavate 800 linear feet of 30 inch trench to a depth of 8 feet in - 10 hours. It is assumed that capital is worth 10 per cent on such - a venture and that the sinking fund will draw 10 per cent. If the - cost of moving and setting up the machine is $1,800, how many - cubic yards of excavation must there be to make excavation by - machine economical? Costs of sheeting, pumping, etc., are assumed - to be the same for machine or hand work. - - _Solution._—For hand work the man excavated 1.11 cubic yard per - hour at 55 cents. The relative cost of hand excavation is then 50 - cents per cubic yard. - - The cost of machine work will be divided into: interest on first - cost; operation and repairs; and sinking fund for renewal. The - interest on the first cost of $10,000 at 10 per cent is $1,000 per - year. The machine works 1,500 hours in the year. Therefore the - cost per hour is $0.67. - - The sinking fund payment, as found from sinking fund tables or the - accumulation of $10,000 in. 6 years, is $1,300 per year or per - hour for 1,500 hours is $0.87. - - The cost of operation per hour is given as $1.25. - - The total cost per hour is therefore $2.79. - - The machine excavated 59.3 cubic yards per hour which makes the - cost, exclusive of moving, equal to $0.47 per cubic yard. In order - to equalize the cost of machine and hand excavation the cost of - moving the machine must be divided among a sufficient number of - cubic yards so that the cost per cubic yard shall be 3 cents. The - cost of moving is given as $1,800. This amount divided among - 60,000 cubic yards equals 3 cents per cubic yard. Therefore the - job must provide at least 60,000 cubic yards of excavation in - order that the use of the machine shall be justifiable from the - viewpoint of economy alone. - - -=129. Types of Machines.=—Machines particularly adapted to the -excavation of sewer and water pipe trenches are of four types: (1) -continuous bucket excavators; (2) overhead cableway or track excavators; -(3) steam shovels; and (4) boom and bucket excavators. Other types of -excavating machinery can be used for sewer trenches under special -conditions. Machines are ordinarily limited to a minimum width of trench -of 22 inches. Between widths of 22 inches and 36 inches the limit of -depth for the first class of machines is about 25 feet. For other types -of machines there is no definite limit, though the economical depth for -open cut work seldom exceeds 40 feet. - - -=130. Continuous Bucket Excavators.=—Continuous bucket excavators are of -the types shown in Figs. 89 and 90. The buckets which do the digging and -raising of the earth may be supported on a wheel as in Fig. 89 or on an -endless chain as in Fig. 90. The support of the wheel or endless chain -can be raised or lowered at the will of the operator so as to keep the -trench as close to grade as can be done by hand work. In some machines -the shape of the buckets can be made such as to cut the bottom of the -trench, in suitable material, to the shape of the sewer invert. In -operation, the buckets are at the rear of the machine and revolve so -that at the lowest point in their path they are traveling forward. The -excavated material is dropped on to a continuous belt which throws it on -the ground clear of the trench, into dump wagons, or on to another -continuous belt running parallel with the trench to the backfiller, by -means of which the excavated material is thrown directly into the -backfill without rehandling. The body of the machine supporting the -engine travels on wheels ahead of the excavation and is kept in line by -means of the pivoted front axle. When obstacles are encountered the -excavating wheel or chain is raised to pass over the obstacle, and -allowed to dig itself in on the other side. - -[Illustration: - - FIG. 89.—Buckeye Wheel Excavator. - - Courtesy, Buckeye Traction Ditcher Co. -] - -[Illustration: - - FIG. 90.—Buckeye Endless-chain Excavator. - - Courtesy, Buckeye Traction Ditcher Co. -] - -[Illustration: - - FIG. 91.—Movable Sheeting Fastened to Traction Ditcher. - - From Eng. News-Record, Vol. 82, 1919, p. 740. -] - -Wheel excavators are not adapted to the excavation of sewer trenches -over 3 to 4 feet in width and 6 to 8 feet in depth. The endless-chain -excavators are suitable for depths of 25 feet with widths from 22 to 72 -inches, and due to the arrangement permitting buckets to be moved -sideways they will cut trenches of different widths with the same size -buckets. This is an advantage where there are to be irregularities in -the width of the trench such as for manholes or changes in size of pipe. -With excavating machines pipe can be laid within 3 feet of the moving -buckets and the trench backfilled immediately, thus making an -appreciable saving in the amount of sheeting. In the construction of -trenches for drain tile at Garden Prairie, Illinois, the sheeting was -built in the form of a box or shield fastened to the rear of the machine -and pulled along after it as is shown in Fig. 91. - -The performance of this type of excavating machine under suitable -conditions is large. A remarkable record was made by Ryan and Co. in -Chicago,[82] with an excavating machine. 1338 feet of 32–inch trench -were excavated to an average depth of 8½ feet in 7 hours, or an average -of 160 cubic yards per hour. More could have been accomplished if it had -not been for delays in supplies. Another crew at Greeley, Colorado,[83] -with a Buckeye endless-chain ditcher weighing 17 tons and costing $5200, -averaged 232 cubic yards per day for 300 days, and the cost was 10.7 -cents per cubic yard. A 15–ton Austin excavator can be expected to -remove 300 to 500 cubic yards per day. - -The cost of operation of the machines is made up of items listed in -Table 50. The figures given are merely suggestive. - - TABLE 50 - - COST OF OPERATING DITCHING MACHINE - - ─────────────────────────────────────────────────────────┬──────┬────── - │ Per │ - │ Day │Total - ─────────────────────────────────────────────────────────┼──────┼────── - Labor: │ │ - 1 Operator at $150 per month │ $6.00│ - 1 Assistant Operator at $120 per month │ 4.00│ - 4 laborers at 4.00 per day │ 16.00│ - │——————│ - │ │$26.00 - │ │ - Fuel: │ │ - 20 Gallons of gasoline at 28 cents │ 5.60│ 5.60 - │ │ - Miscellaneous: │ │ - Oil, waste, etc. │ 1.20│ - Repairs and maintenance │ 10.00│ - Interest, 6 per cent on $10,000 for 150 days │ 4.00│ - Depreciation, 200 working days per year and an 8 year │ │ - life │ 11.11│ 26.31 - │——————│—————— - Total cost per day │ │$57.91 - ─────────────────────────────────────────────────────────┴──────┴────── - - TABLE 51 - - COMPARISON OF COST OF HAND EXCAVATION AND MACHINE EXCAVATION WITH - CONTINUOUS-BUCKET EXCAVATOR - - ───────────────────────────┬───────┬───────────────────────────┬─────── - Hand Work │ Per │ Machine Work │ Per - │ Day, │ │ Day, - │Dollars│ │Dollars - ───────────────────────────┼───────┼───────────────────────────┼─────── - Foreman │ 4.00│Engineer │ 4.00 - Timberman │ 3.00│Fireman │ 2.50 - Helper │ 2.50│Coal │ 5.00 - 4 Laborers at $2.00 │ 80.00│Team │ 4.00 - │ │Foreman │ 4.00 - │ │Pipe layer │ 3.00 - │ │Helper │ 2.50 - │ │2 Teams backfilling │ 8.00 - │ │2 Helpers │ 4.00 - │ │Interest, depreciation and │ - │ │ repairs │ 10.00 - │ ——————│ │ —————— - Total │ 95.00│ Total │ 54.50 - ───────────────────────────┴───────┴───────────────────────────┴─────── - -In making a comparison of the cost of hand and machine excavation the -figures given in Table 51 are from “Excavating Machinery” by McDaniel, -who quotes the cost of machine excavation from the manufacturers of the -Parsons machine issued as the result of several years’ experience with -their excavator. In the comparison the hand crew is assumed to dig 315 -linear feet of trench 28 inches wide by 12 feet deep in a day of 10 -hours. This assumes that each man will excavate 7 cubic yards per day. -The machine is assumed to excavate 250 feet of the same trench. The -comparison indicates that an excavator will work at about 50 per cent of -the cost of hand excavation, if the cost of moving the machine is not -included. - -[Illustration: - - FIG. 92.—Carson Excavating Machine on Trench Excavation in South - Milwaukee. - - Courtesy, Mr. C. F. Henning. -] - - -=131. Cableway and Trestle Excavators.=—Cableway and trestle excavators -are most suitable for deep trenches and crowded conditions. They should -not be used for trenches much less than 8 feet in depth. They differ -from the continuous bucket excavators in that the actual dislodgment of -the material is done by pick and shovel, the excavated material being -thrown by hand into the buckets of the machine. A machine of the Carson -type is shown in Fig. 92. The machine consists of a series of -demountable frames held together by cross braces and struts to form a -semirigid structure. An I beam or channel extending the length of the -machine is hung closely below the top of the struts. The lower flange of -this beam serves as a track for the carriages which carry the buckets. -All the carriages are attached to each other and to an endless cable -leading to a drum on the engine. This cable serves to move the buckets -along the trench. The buckets are attached to another cable which is -wound around another drum on the engine and serves to lower or raise all -the buckets at the same time. In operation there are always at least two -buckets for each carriage, one in the trench being filled and the other -on the machine being dumped. There should be a surplus of buckets to -replace those needing repairs. - -The machines may be from 200 to 350 feet in length, and the number of -buckets which can be lifted at one time varies from one to a dozen or -more. On trenches over 5 to 6 feet in width a double line of buckets is -sometimes used. The entire machine rests on rollers and straddles the -trench. It is moved along the trench by its own power, either by gearing -or chains attached to the wheels, or by a cable attached to a dead-man -ahead. - -The Potter trench machine differs from the Carson in that only 2 buckets -are used at a time and these are carried on a car which travels on a -track on top of the trestle. The movement of the buckets and the car are -controlled by 2 dump men who ride on the car and who can raise or lower -the buckets independently. - -The organization needed to operate these machines is: a lockman who -locks and unlocks the buckets on the cable, a dumper, as many shovelers -as there are buckets on the machine, and an engineman who is usually his -own fireman. From 50 to 400 cubic yards of material can be excavated in -a day with one of these machines, dependent on the character of the -material and the depth of the trench. H. P. Gillette in his Handbook of -Cost Data reports that about 190 cubic yards were excavated per day with -a Potter machine. The machine was 370 feet long. Six ¾-yard buckets were -used, 4 in the trench and 2 on the carrier. The trench was 10½ feet wide -and 18 feet deep in wet sand and soft blue clay. The organization -consisted of an engineman, a fireman, 2 dumpmen on the carrier, and from -17 to 21 excavating laborers depending on the kind and the amount of the -excavation. In general the capacity of such machines is limited by the -amount of material which can be shoveled into them by hand. - - -=132. Tower Cableways.=—These are essentially of the same class as the -trestle cableway machines. They differ in that the carriage supporting -the buckets travels on a cable suspended between 2 towers instead of on -a track supported on a trestle. As a rule only one bucket is handled in -the machine at a time. They are used in sewer work only in exceptional -cases as the towers must be taken down and re-erected each time that -there is an advance in the trench greater than the distance between the -towers. - - -=133. Steam Shovels.=—The use of steam shovels for the excavation of -sewer trenches is becoming more prevalent because of their growing -dependability and durability as compared with other machines, their -adaptability for small trenches, and the relatively large number of -widely different uses to which they can be put. In excavating a trench -the shovel straddles the trench and runs on tractors, wheels, or rollers -on either side of it. The shovel cuts the trench ahead of it. As a -result it is difficult to set sheeting and bracing close to the end of -the trench while the shovel is operating. Steam shovels are therefore -not suitable for excavation in unstable material, unless the sheeting is -driven ahead of the excavation. It is only in the softest ground that -ordinary wood sheeting can be driven ahead of the excavation. Steel -sheet piling is more suitable for such use. Fig. 93[84] shows a shovel -at work on a trench in Evanston, Illinois. - -Shovels are equipped with extra long dipper handles to adapt them to -trench excavation. The dipper handle in the picture is longer than the -standard for this type of machine. The method of supporting the shovel -can be seen in the picture under the machine and the method of bracing -and of finishing the trench by hand work are also shown. The excavated -material is taken out in the shovel and dropped on the bank or into -wagons. - -The limiting depth to which trenches can be excavated by steam shovels -is about 20 to 25 feet, where the trench is too narrow for the shovel to -enter. Wider trenches are cut in steps of about 15 feet, the shovel -working in the trench for additional depths. Shovels are now made to cut -trenches as narrow as a man can enter to lay pipe. The greatest width -that can be cut from one position of the shovel is from 15 to 40 feet, -dependent on the size of the shovel. Occasionally a combination of a -drag line and a steam shovel can be used, as on the construction of the -Calumet sewer in Chicago. On this work the first step was cut by a steam -shovel. It was followed by a drag line resting on the step thus -prepared, and excavating the remaining distance to grade. The depth of -the trench in this work averaged about 25 to 30 feet. - -[Illustration: - - FIG. 93.—Steam Shovel at Work on Sewer Trench for North Shore - Intercepting Sewer, Evanston, Illinois. -] - -Steam shovels are rated according to their tonnage and the capacity of -the dipper in cubic yards. Both are necessary as the size of the dipper -is varied for the same weight of machine, dependent on the character of -the material being excavated. For rock the dipper is made smaller than -for sand. Gillette in his Hand Book of Cost Data gives the coal and -water consumption of steam shovels as shown in Table 52. The performance -of steam shovels is recorded in Table 53. The conditions of the work -have a marked effect on the output of the shovel. A shovel in a thorough -cut, i.e., in a trench just wide enough for the shovel to turn 180 -degrees but too narrow to run cars or wagons along side of it, will -perform less than one-half of the work that it can perform in a side -cut, i.e., where the cars can be run along side the shovel which turns -less than 90 degrees. - - TABLE 52 - - COAL AND WATER CONSUMPTION BY STEAM SHOVELS - - (From Handbook of Cost Data, by H. P. Gillette) - ───────────────────────────────────┬─────┬─────┬─────┬─────┬─────┬───── - Weight in tons │ 35 │ 45 │ 55 │ 65 │ 75 │ 90 - Dipper, cubic yards │ 1¼ │ 1½ │ 1¾ │ 2 │ 2½ │ 3 - Coal, tons per 10 hour day │ ¾ │ 1 │ 1¼ │ 1½ │ 2 │ 2¼ - Water, gallons per 10 hour day │1500 │2000 │2500 │3000 │4000 │4500 - ───────────────────────────────────┴─────┴─────┴─────┴─────┴─────┴───── - - TABLE 53 - - PERFORMANCE BY STEAM SHOVELS - - ──────┬──────┬──────┬───────┬───────────┬──────┬──────────────┬──────── - Weight│Dipper│Depth │ Width │ 10–Hour │ Cost │ Authority │Remarks - in │Cubic │ of │of Cut │Performance│ in │ │ - Tons │Yards │ Cut, │ │ │Cents,│ │ - │ │ Feet │ │ │ per │ │ - │ │ │ │ │Cubic │ │ - │ │ │ │ │ Yard │ │ - ──────┼──────┼──────┼───────┼───────────┼──────┼──────────────┼──────── - 25 │ 1 │ 9 │36 in. │ 85 │ 22.6 │R. T. Dana │ 1 - │ │ │ │ │ │ Eng. Rec., │ - │ │ │ │ │ │ 69:581 │ - 25 │ 1 │ 8 │35 in. │ 96 │ 23.5 │ do. │ 2 - 70 │ 2 │ 26 │16 ft. │ 569 │ 6.7 │ do. │ 3 - 30 │ 1 │15–18 │60 in. │ 300 │ │A. B. McDaniel│ 4 - │ │ │ │ │ │ Excavating │ - │ │ │ │ │ │ Machinery │ - 15 │ ⅝ │ 14 │134 ft.│ 400 │ │Eng. Cont’r, │ 5 - │ │ │ │ │ │ 8–25–09 │ - │ 8 │ 36 │ Very │16 yd. cars│ │Marion Steam │ 6 - │ │ │ wide │ │ │ Shovel Co. │ - 55 │ │ │ │ 296 │ │H. P. │ 7 - │ │ │ │ │ │ Gillette’s │ - │ │ │ │ │ │ Cost Data │ - 65 │ 2¼ │ │ │ 280 │ │ do. │ - │ │ │Greater│ 700 │ 30.6 │G. C. D. │ 8 - │ │ │than 78│ │ │ Lenth, Eng. │ - │ │ │ in. │ │ │ News-Record,│ - │ │ │ │ │ │ 85:22 │ - ──────┴──────┴──────┴───────┴───────────┴──────┴──────────────┴──────── - - Remarks: - - 1. One runner at $5.00, one fireman at $2.31, two laborers - at $1.70 each, supplies at $4.50, and interest and - depreciation on 200 days per year, $4.00. Total per - day, $19.21. Material, clay and gravel. - - 2. Average of 11 jobs with the same shovel. - - 3. Cost per day, one runner at $5.00, one crane-man at $3.60, - one fireman at $2.00, 7 roller men at $1.50 each, supplies - $9.00 and interest and depreciation on $9000 at 200 days - per year $8.00. Total, $38.10. - - 4. Hard clay. - - 5. Stiff clay for the basement of a building in Chicago. - - 6. Stripping ore. This is a maximum record. The average was - about three hundred and twenty 16 cubic yard cars per day. - - 7. Blasted mica-schist. - - 8. General average. - - -=134. Drag Line and Bucket Excavators.=—A drag line excavator is shown -in Fig. 94. The back of the bucket is attached to a drum on the engine -by means of a cable passing over the wheel in the end of the long boom. -The front of the bucket is attached by another cable directly to another -drum on the engine. In operation the bucket is raised by its rear end -and dropped out to the extremity of the boom. It is then dragged over -the ground towards the machine, digging itself in at the same time. When -filled the bucket is raised by tightening up on the two cables, swung to -one side by means of the movable boom, and dumped. - -[Illustration: - - FIG. 94.—Drag Line at Work on Trench for Drain Tile. -] - -Drag line excavators will perform as much work as steam shovels under -favorable conditions. They are less expensive in first cost and -operation, and are equally reliable but they are not adapted to the more -difficult situations where steam shovels can be used to advantage. Drag -lines are suitable only for relatively wide trenches in material -requiring no bracing, and in a locality where relatively long stretches -of trench can be opened at one time. - -The bucket excavator differs from the drag line in that the bucket can -be lifted vertically only and the types of buckets used in the two types -of machine are different. The bucket may be self filling of the -orange-peel or clam-shell type, or a cylindrical container which must be -filled by hand. A drag line can be easily converted into a boom and -bucket excavator. Boom and bucket excavators are well adapted to use in -deep, closely braced trenches and shafts. - - -=135. Excavation in Quicksand.=[85]—A sand or other granular material in -which there is sufficient upward flow of ground water to lift it, is -known as quicksand. Its most important property, from the viewpoint of -sewer construction, is its inability to support any weight unless the -sand is so confined as to prevent flowing of the sand, or unless the -water is removed from the sand. - -Excavation in quicksand is troublesome and expensive and is frequently -dangerous. The material will flow sluggishly as a liquid, it cannot be -pumped easily, and its excavation causes the sides of the trench to fall -in or the bottom to rise. The foundations of nearby structures may be -undermined, causing collapse and serious damage. These conditions may -arise even after the backfilling has been placed unless proper care has -been taken. The greatest safeguard against such dangers is not only to -exercise care in the backfilling to see that it is compactly tamped and -placed, but to leave all sheeting in position after the completion of -the work. - -The ordinary method of combating quicksand and in conducting work in wet -trenches is to drive water-tight sheeting 2 or 3 feet below the bottom -of the trench, and to dewater the sand by pumping. When dry it can be -excavated relatively easily. A more primitive but equally successful -method is to throw straw, brickbats, ashes, or other filling material -into the trench in order to hold the excavation once made, or this may -supplement the attempts at pumping, or the wet sand may be bailed out in -buckets. Successful excavation in quicksand requires experience, -resourcefulness. and a careful watch for unexpected developments. The -well points described in Art. 142 are used for dewatering quicksand. - - -=136. Pumping and Drainage.=—Ground water is to be expected in nearly -all sewer construction and provision should be made for its care. Where -geological conditions are well known or where previous excavations have -been made and it is known that no ground water exists it may be safe to -make no provision for encountering ground water. Where ground water is -to be expected the amount must remain uncertain within certain rather -wide limits until actually encountered. - -In order to avoid the necessity for pumping, or working in wet trenches -it is sometimes possible to build the sewer from the low end upwards and -to drain the trench into the new sewer. The wettest trenches are the -most difficult to drain in this manner as the material is usually soft -and the water so laden with sediment as to threaten the clogging of the -sewer. It is undesirable to run water through the pipes until the cement -in the joints has set. This necessitates damming up the trench for a -period which may be so long as to flood the trench or delay the progress -of the work. If it is not possible to drain the trench through the sewer -already constructed the amount of water to be pumped can be reduced by -the use of tight sheeting. - -[Illustration: - - FIG. 95. Improvised Trench Pump. -] - -Pumps for dewatering trenches must be proof against injury by sand, mud, -and other solids in the water. For this purpose pumps with wide passages -and without valves or packed joints are desirable. The types of pumps -used are: simple flap valve pumps improvised on the job, diaphragm -pumps, jet pumps, steam vacuum pumps, centrifugal pumps, and -reciprocating pumps. All are of the simplest of their type and little -attention is paid to the economy of operation because of the temporary -nature of their service. - - -=137. Trench Pump.=—A simple pump which can be improvised on the job is -shown in section in Fig. 95. Its capacity is about 20 gallons per minute -but its operation is backaching work. It is inexpensive, quickly put -together and may be a help in an emergency. It is to be noted that the -passages are large and straight, that there are no packed joints, and -that the velocity of flow is so small that it is not liable to clogging -by picking up small objects. - -[Illustration: - - FIG. 96.—Diaphragm Pump - - Courtesy, Edson Manufacturing Co. -] - - -=138. Diaphragm Pump.=—The type of pump shown in Fig. 96 is the most -common in use for draining small quantities of water from excavations. -It is known as the diaphragm pump from the large rubber diaphragm on -which the operation depends. The pump is made of a short cast-iron -cylinder, divided by the rubber diaphragm or disk to the center of which -the handle is connected. The valve is shown at the center of the disk. -As the diaphragm is lifted the valve remains closed, creating a partial -vacuum in the suction pipe and at the same time discharging the water -which passed through the valve on the previous down stroke. When the -valve is lowered the foot valve on the suction pipe closes, holding the -water in place, and the valve in the pump opens allowing the water to -flow out on top of the disk to be discharged on the next up stroke. -Table 54 shows the capacities of some diaphragm pumps as rated by the -manufacturers. The smaller sizes are the more frequently used and are -equipped with a 3–inch suction hose with strainer and foot valve. They -are not adapted to suction lifts over 10 to 12 feet. Where greater lifts -are necessary one pump may discharge into a tub in which the foot valve -of a higher pump is submerged. - - TABLE 54 - - CAPACITIES OF DIAPHRAGM PUMPS - - ─────────────────┬─────────────────┬─────────────────┬───────────────── - Diameter of │ Diameter of │Length of Stroke │ Capacity per - Cylinder, Inches │ Suction, Inches │ in Inches │ Stroke, Gallons - ─────────────────┼─────────────────┼─────────────────┼───────────────── - 6│ 3│ 4│ 0.49 - 8½│ 4│ 6│ 1.47 - 9[86]│ 2½│ │ 0.75 - 12½[86]│ 3│ │ 1.25 - │ Power driven by 1 horse-power │ - 12½[86]│ engine │ 0.58[87] - ─────────────────┴───────────────────────────────────┴───────────────── - -[Illustration: - - FIG. 97.—McGowan Steam Jet Pump. - - Courtesy, The John H. McGowan Co. -] - - -=139. Jet Pump.=—The simplicity of the parts of the jet pump is shown in -Fig. 97. It has a distinct advantage over pumps containing valves and -moving parts in that there are no obstructions offered to the passage of -solids as well as liquids through the pump. It is not economical in the -use of steam, however. It operates by means of a steam jet entering a -pipe at high velocity through a nozzle. This action causes a vacuum -which will lift water from 6 to 10 feet. The lower the suction lift, -however, the greater the efficiency of the work. The sizes and -capacities of jet pumps as manufactured by the J. H. McGowan Co. are -shown in Table 55. - - TABLE 55 - - CAPACITIES OF JET PUMPS - - (J. H. McGowan Co.) - ──────────────┬─────────────┬─────────────┬─────────────┬────────────── - Size of Pump │ │ │ Capacity, │ Approximate - and Suction │ Discharge │ Steam Pipe, │ Gallons per │ Horse-power - Pipe, Inches │Pipe, Inches │ Inches │ Minute │ Required - ──────────────┼─────────────┼─────────────┼─────────────┼────────────── - ¾│ ½│ ⅜│ 8│ 2 - 1│ ¾│ ½│ 15│ 3 - 1¼│ 1│ ½│ 20│ 4 - 1½│ 1¼│ ¾│ 30│ 6 - 2│ 1½│ ¾│ 40│ 8 - 2½│ 2│ 1│ 50│ 10 - 3│ 2½│ 1│ 60│ 15 - 4│ 3½│ 1¼│ 85│ 25 - ──────────────┴─────────────┴─────────────┴─────────────┴────────────── - - -=140. Steam Vacuum Pumps.=—This type of pump depends on the condensation -of steam in a closed chamber to create a vacuum which lifts water into -the chamber previously occupied by the steam and from which the water is -ejected by the admission of more steam. The best known pumps of this -type are the Pulsometer, manufactured by the Pulsometer Steam Pump Co., -the Emerson, manufactured by the Emerson Pump and Valve Co., and the Nye -Pump, manufactured by the Nye Steam Pump and Machinery Co. - -[Illustration: - - FIG. 98.—Pulsometer Steam Vacuum Pump. -] - -A section of a Pulsometer is shown in Fig. 98. It consists of two -bottle-shaped chambers _A_ and _B_ with their necks communicating at the -top and each opening into the outlet chamber _O_ through a check valve. -Steam is admitted at the top and enters chamber _A_ or _B_ according to -the position of the steam valve _C_ as shown. This steam valve is a ball -which is free to roll either to the right or left and forms a -steam-tight joint with whichever seat it rests upon. In normal operation -chamber _A_ would be filled with water as the steam enters the cylinder. -At the same time a check valve at the top opens to admit a small -quantity of air which forms a cushion insulating the steam from the -water, reduces the condensation of the steam, and serves as a cushion -for the incoming water on the opposite stroke. The pressure of the steam -depresses the surface of the water without agitation and forces the -water through the check valve _F_ into the discharge chamber _O_. When -the water falls to the level of the discharge chamber the even surface -is broken up and the intimate contact of the steam and water condenses -the former instantaneously. This forms a vacuum in chamber _A_ which, -assisted by a slight upward pressure in chamber _B_ caused by the -incoming water, immediately pulls the ball _C_ over to the other seat -and directs the steam into chamber _B_. The vacuum in chamber _A_ now -draws up a new charge of water through the suction pipe into the -chamber. - -[Illustration: - - FIG. 99.—Emerson Steam Vacuum Pump. -] - -A section of the Emerson pump is shown in Fig. 99. The pump consists of -two vertical cylinders _B_ and _C_. Each chamber has a suction valve _L_ -at the bottom, opening upward from a common chamber from which the -discharge pipe _U_ extends. On the top of each chamber is a baffle plate -_G_ which operates to distribute the steam evenly to the two chambers -and to prevent it from agitating the surface of the water in the -chambers. A condenser nozzle _F_ is connected with the bottom of the -opposite chamber by a pipe into which a check valve opens upward. As the -pressure in the chamber alternates water will be injected through _F_ -into the opposite chamber and condense the steam therein, promptly -forming a vacuum. An air valve _P_ admits a small quantity of air while -the chamber is filling with water, the air acting as an insulating -cushion as in the Pulsometer. Valve _O_, just above the top connection -_S_ is used to regulate the amount of steam that enters the pump. The -top connection _S_ has two ports, one leading to each chamber. An -oscillating valve enclosed in it admits the steam through these ports to -the two chambers alternately. This valve is driven by a small -three-cylinder engine, the crank shaft of which extends into the top -connection in the center of the bearing on which the valve oscillates. A -positive geared connection is made between the valve and the engine and -so arranged that the engine will run faster than the valve. - -The action of these pumps consists of alternately filling and emptying -the two chambers. They will continue operation without attention or -lubrication so long as the steam is turned on. In view of the simplicity -of their operation and make-up, their ability to handle liquids heavily -charged with solids, and their reasonable steam consumption these pumps -are widely used for pumping water in construction work. They have an -added advantage that no foundation or setting is required for them as -they can be hung by a chain from any available support. - -These pumps are manufactured in sizes varying from 25 to 2500 gallons -per minute at a 25–foot head, and with a steam consumption of about 150 -pounds per horse-power hour. They reduce about 4 per cent in capacity -for each 10 feet of additional lift. They will operate satisfactorily -between heads of 5 to 150 feet, with a suction lift not to exceed 15 -feet. Lower suction lifts are desirable and the best operation is -obtained when the pump is partly submerged. The steam pressure should be -balanced against the total head. It varies from 50 to 75 pounds for -lifts up to 50 feet, and increases proportionally for higher lifts. The -dryer the steam the lower the necessary boiler pressure. - - -=141. Centrifugal and Reciprocating Pumps.=—The details of these pumps, -their adaptability to various conditions, and their capacities are given -in Chapter VII. The centrifugal is better adapted to trench pumping as -it is not so affected by water containing sand and grit, but for clear -water, high suction lifts and fairly permanent installations, -reciprocating pumps can be used with satisfaction. - - -=142. Well Points.=—In dewatering quicksand a method frequently attended -with success is to drive a number of well points into the sand and -connect them all to a single pump. Figure 100 shows a well point system -used on sewer work in Indiana. The well points are 3 feet apart and are -connected to a 2½-inch header which in turn is connected to six Nye -pumps, each with a capacity of 200 gallons per minute for a lift of 50 -feet. The number and size of well points and pumps to use will depend on -conditions as met on the job. On a piece of work in Atlantic City[88] -the equipment consisted of two complete outfits each comprising one -hundred 1½ inch by 36–inch No. 60 well points, one hundred 6–foot -lengths of rubber hose, about 600 feet of suction main, one hundred -valved T connections, and a 7 × 8–inch Gould Triplex Pump with a -capacity of 200 gallons per minute, belted to a 7½ horse-power motor. - -[Illustration: - - FIG. 100.—Well Points Pumped by Nye Steam Vacuum Pump. -] - - -=143. Rock Excavation.=—A common definition of rock used in -specifications is: whenever the word Rock is used as the name of an -excavated material it shall mean the ledge material removed or to be -removed properly by channeling, wedging, barring, or blasting; boulders -having a volume of 9 (this volume may be varied) cubic feet or more, and -any excavated masonry. No soft disintegrated rock which can be removed -with a pick, nor loose shale, nor previously blasted material, nor -material which may have fallen into the trench will be measured or -allowed as rock. - -Channeling consists in cutting long narrow channels in the rock to free -the sides of large blocks of stone. The block is then loosened by -driving in wedges or it is pried loose with bars. It is a method used -more frequently in quarrying than in trench excavation where it is not -necessary to preserve the stone intact. In blasting, a hole is drilled -in the rock, and is loaded with an explosive which when fired shatters -the rock and loosens it from its position. - -[Illustration: - - FIG. 101.—Plug and Feathers for Splitting Rock. -] - -In drilling rock by hand the drill is manipulated by one man who holds -it and turns it in the hole with one hand while striking it with a -hammer weighing about 4 pounds held in the other hand, or one man may -hold and turn the drill while one or two others strike it with heavier -hammers. In churn drilling a heavy drill is raised and dropped in the -hole, the force of the blow developing from the weight of the falling -drill. Hand drills are steel bars of a length suitable for the depth of -the hole, with the cutting edge widened and sharpened to an angle as -sharp as can be used without breaking. The drill bar is usually about -⅛th of an inch smaller than the diameter of the face of the drill. - -Wedges used are called plugs and feathers. They are shown in Fig. 101 -which shows also the method of their use. The feathers are wedges with -one round and one flat face on which the flat faces of the plug slide. - - -=144. Power Drilling.=—In power drilling the drill is driven by a -reciprocating machine which either strikes and turns the drill in the -hole, or lifts and turns it as in churn drilling, or the drill may be -driven by a rotary machine which is revolved by compressed air, steam, -or electricity. There are many different types of machines suitable for -drilling in the different classes of material encountered and for -utilizing the various forms of power available. - -A jack hammer drill is shown in Fig. 102. In its lightest form the drill -weighs about 20 pounds and is capable of drilling ⅞-inch holes to a -depth of 4 feet. Heavier machines are available for drilling larger and -deeper holes. The same machine can be adapted to the use of steam or -compressed air. When in use the point of the drill is placed against the -rock and a pressure on the handle opens a valve admitting air or steam. -The piston is caused to reciprocate in the cylinder, striking the head -of the drill at each stroke. The drill is revolved in the hole by hand -or by a mechanism in the machine. A hollow drill can be used by means of -which the operator admits air or steam to the hole, thus blowing it out -and keeping it clean. These machines have the advantage of small size, -portability and simplicity. They can be easily and quickly set up and -the drills can be changed rapidly. Their undesirable features are the -vibration transmitted to the operator and the dust raised in the trench. - -[Illustration: - - FIG. 102.—Jack Hammer Rock Drill. -] - -[Illustration: - - FIG. 103.—Tripod Drill. -] - -A type of drill heavier and larger than the jack hammer drill is shown -in Fig. 103. It requires some form of support such as a tripod, or in -tunnel work it can be braced against the roof or sides. Some data on -steam and air drills are given in Table 56. The effect of the length of -the transmission pipe, temperature of the outside air, pressure at the -boiler or compressor, etc., will have a marked effect on the amount of -steam or air to be delivered to the drill. Compressed air is affected -more than steam by these outside factors, but it has an advantage in -that as it loses in pressure it increases in volume so that the loss of -power is not so marked. Gillette states: - - We may assume that a cubic foot of steam will do practically the - same work in a drill as a cubic foot of compressed air at the same - pressure, because neither the steam nor the air acts expansively - to any great extent in a drill cylinder, due to the late cut-off. - This being so ... one pound of steam is equivalent to nearly 30 - cubic feet of free air ... all at the same pressure of 75 pounds - per square inch. If a drill consumes at the rate of 100 cubic feet - of free air per minute ... it would therefore consume 240 pounds - of steam (at 75 pounds pressure) per hour.... Where not more than - three or four drills are to be operated, probably no power can - equal compressed air generated by gasoline. It will require 12 - horse-power to compress air for each drill, hence 1½ gallons of - gasoline will be required per hour per drill while actually - drilling. - - TABLE 56 - - DATA ON ROCK DRILLS - - (From H. P. Gillette) - ───────────────────────────────────┬─────┬─────┬─────┬─────┬─────┬───── - Diameter of cylinder in inches │ 2¼│ 2½│ 2¾│ 3⅛│ 3¼│ 3⅜ - Length of stroke in inches │ 5│ 6│ 6½│ 6⅝│ 6⅝│ 7¼ - Length of drill from end of crank │ │ │ │ │ │ - to end of piston │ 36│ 43│ 50│ 50│ 50│ 52 - Depth of hole drilled without │ │ │ │ │ │ - change of bit, inches │ 15│ 20│ 24│ 24│ 24│ 24 - Diameter of supply inlet. Standard │ │ │ │ │ │ - pipe, inches │ ¾│ ¾│ ¾│ 1│ 1│ 1¼ - Approximate strokes per minute with│ │ │ │ │ │ - 60 pound pressure at the drill │ 500│ 450│ 375│ 350│ 325│ 300 - Depth of vertical hole each machine│ │ │ │ │ │ - will drill easily, feet │ 6│ 8│ 10│ 14│ 16│ 20 - Diameter of holes drilled, inches │ ¾ to 1½ as desired - Diameter of octagon steel, inches │ ¾ to│ ⅞ to│ 1 to│1⅛ to│1⅛ to│1¼ to - │ ⅞│ 1│ 1⅛│ 1¼│ 1¼│ 1⅜ - Best size of boiler to give plenty │ │ │ │ │ │ - of steam at high pressure, │ │ │ │ │ │ - horse-power │ 6│ 8│ 8│ 9│ 10│ 12 - Best size of supply pipe to carry │ │ │ │ │ │ - steam 100 to 200 feet, inches │ ¾│ ¾│ ¾│ 1│ 1│ 1¼ - Weight of drill unmounted, with │ │ │ │ │ │ - wrenches and fittings, hot boxed,│ │ │ │ │ │ - pounds │ 128│ 190│ 265│ 315│ 385│ 390 - Weight of tripod, without weights, │ │ │ │ │ │ - not boxed, pounds │ 80│ 160│ 160│ 160│ 210│ 275 - Weight of holding down weights, not│ │ │ │ │ │ - boxed, pounds │ 120│ 270│ 270│ 285│ 330│ 375 - Cubic feet of free air per minute │ │ │ │ │ │ - required to run one drill at 100 │ │ │ │ │ │ - pounds │ 92│ 104│ 126│ 146│ 154│ 160 - ───────────────────────────────────┴─────┴─────┴─────┴─────┴─────┴───── - For more than one drill, multiply the value in the above line by the - following factors: For 2 drills, 1.8; 5 by 4.1; 10 by 7.1; 15 by 9.5; - 20 by 11.7; 30 by 15.8; 40 by 21.4; 70 by 33.2. - - Since gasoline air compressors are self regulating, when the drill - is not using air very little gasoline is burned by the gasoline - engine driving the compressor. A gasoline compressor possesses - other very important economic advantages over a small steam-driven - plant. First, there is the saving in wages of firemen and second, - there is the saving in hauling and pumping of water and the - hauling of fuel. The cost of gasoline is often less than the cost - of coal for operating a small plant. - -An electric drill[89] operated on the principle of the solenoid does -away with motor, valves, pipes, vapor, freezing, and other difficulties -attendant on the use of steam or air. - -The rates of drilling in different classes of rock are shown in Table -57. Frequent changes of drills and relocation of tripods will materially -reduce the performance of a drill, for as much as 45 minutes may be lost -in making a new set up. In this the jack hammer drills show their -advantage as no time is lost in a set up. - - TABLE 57 - - RATES OF ROCK DRILLING - - Rates in Feet per Ten-hour Shift. Vertical Holes 10–20 Feet Deep. - (From Gillette) - - Hard Adirondack granite 48 - Maine and Massachusetts granite 45–50 - Mica-schist of New York City. Possible 60–70 - Mica-schist of New York City. Average 40–50 - Hard, Hudson River trap rock 40 - Soft red sand stone of Northern New Jersey 90 - Hard limestone near Rochester, N. Y 70 - Limestone of Chicago Drainage Canal 70–80 - Douglass, Indiana, syenite. Difficult set ups 36 - Canadian granite on Grand Trunk R. R 30 - Windmill point, Ontario limestone: - 3⅝-inch drills 75 - 2¾-inch drills 60 - 2¼-inch drills 37 - - -=145. Steam or Air for Power=.—The choice between steam or air is -dependent on the conditions of the work. Steam is undesirable in tunnels -on account of the heat produced. In open cut work it is at a -disadvantage because of the loss of power due to radiation from the hose -or pipe. The life of the hose is not so long as when air is used, -escaping steam causes clouds of vapor which obscure the work, and -serious burns may occur due to hot water thrown from the exhaust. It is -advantageous since leaks may be easily discovered and remedied, it -requires less machinery than air, and it is sometimes less expensive. -With compressed air, gasoline or electric motors can be used for -operating the compressors. - - TABLE 58 - - ROCK BLASTING - - (From Gillette) - ────────────────────┬────────────────────┬─────────┬─────────┬───────── - Character of │Powder Used per Hole│ │Distance │Distance - Material │ │Depth of │ Back of │ Hole to - │ │ Hole, │ Face, │ Hole, - │ │ Feet │ feet │ feet - ────────────────────┼────────────────────┼─────────┼─────────┼───────── - Limestone of Chicago│40 per cent dynamite│ │ │ - Drainage Canal │ │ 12│ 8│ 8 - Sandstone │200 pounds black │ │ │ - │ powder │ 20│ 18│ 14 - Granite │2 pounds 60 per cent│ │ │ - │ dynamite │ 12│ 1½│ 4½ to 5 - Pit mining, │ │ │ │ - Treadwell, Mine, │ │ │ │ - Alaska │ │ 12│ 2½│ 6 - ────────────────────┴────────────────────┴─────────┴─────────┴───────── - - -=146. Depth of Drill Hole.=—The depth of the hole is dependent on the -character of the work. The deepest holes can be used in open cut work -where the shattered rock is to be removed by steam shovel. The face can -be made 10 to 15 feet high. The depth of the hole in center cut tunnel -facings are from 6 to 10 or even 12 feet. In the bench the depth is -equal to the height of the bench. In narrow trenches where the rock is -to be removed by derrick or thrown into a bucket by hand, the hole -should be sufficiently deep to shatter the rock to a depth of at least 6 -inches below the finished sewer. Frequently shooting to this depth at -one shot cannot be done due to the built up condition of the -neighborhood or other local factors. The depth of the hole in trench -work should not much exceed the distance between holes. Deep holes are -usually desirable as a matter of economy in saving frequent set ups, but -the holes cannot be made much over 20 feet in depth without increasing -the friction on the drill to a prohibitive amount. - - -=147. Diameter of Drill Hole.=—The diameter of the hole should be such -as to take the desired size of explosive cartridge. The common sizes of -dynamite cartridges are from ⅞ inch to 2 inches in diameter. In -drilling, the diameter of the hole is reduced about one-eighth of an -inch at a time as the drill begins to stick. This reduction should be -allowed for, and experience is the best guide for the size of the hole -at the start. In general the softer or more faulty or seamy the rock, -the more frequent the necessary reductions in size of bit.[90] For hard -homogeneous rock the holes can be drilled 10 feet or more without -changing the size of the drill bit. - - -=148. Spacing of Drill Holes.=—The spacing of holes in open cut -excavation is commonly equal to the depth of the hole. The character of -the material being excavated has much to do with the spacing of the -holes. The spacing, diameter and depth of holes used on some jobs is -shown in Table 58. Gillette states: - - It is obviously impossible to lay down any hard and fast rule for - drill holes. In stratified rock that is friable, and in traps that - are full of natural joints and seams, it is often possible to - space the holes a distance apart somewhat greater than their - depth, and still break the rock to comparatively small sizes upon - blasting. In tough granite, gneiss, syenite, and in trap where - joints are few and far between, the holes may have to be spaced 3 - to 8 feet apart regardless of their depth for with wider spacing - the blocks thrown down will be too large to handle with ordinary - appliances. Since in shallow excavations the holes can seldom be - much further apart than one to one and one-half times their depth - we see that the cost of drilling per cubic yard increases very - rapidly the shallower the excavation. Furthermore the cost of - drilling a foot of hole is much increased where frequent shifting - of the drill tripod is necessary. - - The common practice in placing drill holes is to put down holes in - pairs, one hole on each side of the proposed trench; and if the - trench is wide one or more holes are drilled between these two - side holes[91] but in narrow trench work, such as for a 12–inch - pipe, one hole in the middle of the trench will usually prove - sufficient. - -The holes are spaced about 3 feet apart longitudinally. After the holes -have been completed they should be plugged to keep out dirt and water. - - - SHEETING AND BRACING - - -=149. Purposes and Types.=—Sheeting and bracing are used in trenching to -prevent caving of the banks and to prevent or retard the entrance of -ground water. The different methods of placing wooden sheeting are -called stay bracing, skeleton sheeting, poling boards, box sheeting, and -vertical sheeting. Steel sheeting is usually driven to secure -water-tightness and if braced the bracing is similar to the form used -for vertical wooden sheeting. - - -=150. Stay Bracing.=—This consists of boards placed vertically against -the sides of the trench and held in position by cross braces which are -wedged in place. The purpose of the board against the side of the trench -is to prevent the cross brace from sinking into the earth. The boards -should be from 1½ × 4 inches to 2 × 6 inches and 3 to 4 feet long. The -cross braces should not be less than 2 × 4 inches for the narrowest -trenches and larger sizes should be used for wider trenches. The spacing -between the cross braces is dependent on the character of the trench and -the judgment of the foreman. Stay bracing is used as a precautionary -measure in relatively shallow trenches with sides of stiff clay or other -cohesive material. It should not be used where a tendency towards caving -is pronounced. Stay bracing is dangerous in trenches where sliding has -commenced as it gives a false sense of security. The boards and cross -braces are placed in position after the trench has been excavated. - - -=151. Skeleton Sheeting.=—This consists of rangers and braces with a -piece of vertical sheeting behind each brace. A section of skeleton -sheeting is shown in Fig. 104 with the names of the different pieces -marked on them. This form of sheeting is used in uncertain soils which -apparently require only slight support, but may show a tendency to cave -with but little warning. When the warning is given vertical sheeting can -be quickly driven behind the rangers and additional braces placed if -necessary. The sizes of pieces, spacing and method of placing should be -the same as for complete vertical sheeting in order that this may be -placed if necessary. - - -=152. Poling Boards.=—These are planks placed vertically against the -sides of the trench and held in place by rangers and braces. They differ -from vertical sheeting in that the poling board is about 3 or 4 feet -long. It is placed after the trench has been excavated; not driven down -with the excavation like vertical sheeting. An arrangement of poling -boards is shown in Fig. 105. This type of support is used in material -that will stand unsupported for from 3 to 4 feet in height. Its -advantages lie in that no driving is necessary, thus saving the trench -from jarring; no sheeting is sticking above the sides of the trench to -interfere with the excavation; and only short planks are necessary. - -[Illustration: - - FIG. 104.—Skeleton Sheeting. -] - -[Illustration: - - FIG. 105.—Poling Boards. - - Showing Different Types of Cross Bracing. -] - -The method of placing poling boards is as follows: Excavate the trench -as far as the cohesion of the bank will permit. Poling boards, 1½ inch -to 2 inch planks, 6 inches or more in width, are then stood on end at -the desired intervals along each side of the trench for the length of -one ranger. The poling boards may be held in place by one or two -rangers. Two are safer than one but may not always be necessary. If one -ranger is to be used it is placed at the center of the poling board. -After the poling boards are in position the rangers are laid in the -trench and the cross braces are cut to fit. If wedges are to be used for -tightening the cross braces, the cross braces are cut about 2 inches -short. If jacks are to be used the braces are cut short enough to -accommodate the jacks when closed, or adjustable trench braces may be -used as shown in Fig. 106. The use of extension braces saves the labor -of fitting wooden braces. With everything in readiness in the trench, -the cross brace is pressed against the ranger which is thus held in -place. The wedge or jack is then tightened holding the poling boards and -cross brace in position. - -[Illustration: - - FIG. 106.—Box Sheeting. - - Showing Different Types of Cross Bracing. -] - - -=153. Box Sheeting.=—Box sheeting is composed of horizontal planks held -in position against the sides of the trench by vertical pieces supported -by braces extending across the trench. The arrangement of planks and -braces for box sheeting is shown in Fig. 106. This type of sheeting is -used in material not sufficiently cohesive to permit the use of poling -boards, and under such conditions that it is inadvisable to use vertical -sheeting which protrudes above the sides of the trench while being -driven. This sheeting is put in position as the trench is excavated. No -more of the excavation than the width of three or four planks need be -unsupported at any one time. In placing the sheeting the trench is -excavated for a depth of 12 to 24 inches. Three or four planks are then -placed against the sides of the trench and are caught in position by a -vertical brace which is in turn supported by a horizontal cross brace. - -[Illustration: - - FIG. 107.—Vertical Sheeting. -] - - -=154. Vertical Sheeting.=—This is the most complete and the strongest of -the methods for sheeting a trench. It consists of a system of rangers -and cross braces so arranged as to support a solid wall of vertical -planks against the sides of the trench. An arrangement of complete -vertical sheeting is shown in Fig. 107. This type can be made nearly -water-tight by the use of matched boards, Wakefield piling, steel -piling, etc. Wakefield piling is made up of three planks of the same -width and usually the same thickness. They are nailed together so that -the two outside planks protrude beyond the inside one on one side, and -the inside one protrudes beyond the two outside ones on the other side -as shown in Fig. 108. The protruding inside plank forms a tongue which -fits into the groove formed by the protruding outside planks of the -adjacent pile. - -[Illustration: - - FIG. 108.—Wakefield Sheet Piling. -] - -[Illustration: - - FIG. 109. Section through Malleable Steel Driving Cap. -] - -In placing vertical sheeting the trench is excavated as far as it is -safe below the surface. Blocks of the same thickness as the sheeting are -then placed against the bank at the middle and at the ends of two -rangers on opposite sides of the trench. The ranger rest against blocks, -and are held away from the sides of the trench by them. Cross braces are -next tightened into position opposite the blocks to hold the rangers in -place. After the skeleton sheeting is in place the planks forming the -vertical sheeting are put in position with a chisel edge cut on the -lower end of the plank, with the flat side against the bank. The planks -should be driven with a maul, the edge of the plank following closely -behind the excavation. In relatively dry work the driving of the plank -is facilitated by excavating beneath the edge as it is driven. The upper -end of the sheeting should be protected by a malleable steel or iron cap -to prevent brooming of the lumber. A cap is shown in Fig. 109. A sledge -hammer may be used for driving when the lumber is protected. If the -sheeting is to start at the surface and is to be driven by hand, the -first length should not exceed 4 feet unless a platform is erected for -the driver. Succeeding lengths may be longer, the driver standing on -planks supported on the cross braces in the trench. Steam hammers and -pile drivers are sometimes used for driving sheeting. - -The framework of the sheeting should be placed with a cross brace for -each end of each ranger and a cross brace for the middle of each ranger. -If the ends of two rangers rest on the same cross brace an accident -displacing one ranger will be passed on to the next and might cause a -progressive collapse of a length of trench, whereas the movement of an -independently supported ranger should have no effect on another ranger. -The cross braces should have horizontal cleats nailed on top of them as -shown in Fig. 107 to prevent the braces from being knocked out of place -by falling objects. In driving vertical sheeting a vacant place will be -left behind each cross brace corresponding to the original block placed -to hold the ranger away from the bank. This is an undesirable feature in -the use of vertical sheeting. It is ordinarily remedied by slipping in -planks the width of the slot and wedging or nailing them against the -convenient cross bracing. In extremely wet trenches, after all other -pieces of vertical sheeting are in place, the original cleat behind the -cross brace can be knocked out and a piece of sheeting slipped into this -opening and driven. Care must be taken in this event not to drive the -rangers down when driving the sheeting. If the bracing begins to drop, -it should be supported by vertical pieces between the rangers and -resting on a sill at the bottom of the trench. - -[Illustration: - - FIG. 110.—Steel Clamp for Pulling Wood Sheeting. -] - - -=155. Pulling Wood Sheeting.=—Wood sheeting is pulled after the -completion of the trench by a device shown in Fig. 110. In wet trenches -where the removal of the sheeting would permit a movement of the banks, -resulting in danger to the sewer or other structures, the sheeting -should be left in place in the trench. If sufficient saving can be made -the sheeting is cut off in the trench immediately above the danger line, -usually the ground water line. The cutting is done with an axe or by a -power driven saw devised for the purpose. - - -=156. Earth Pressures.[92]=—The various theories of earth pressure are -so conflicting in their conclusions as to be confusing. Rankine’s -theory, the most frequently used, assumes that the pressure increases -with the depth, whereas Meem’s theory[93] leads to an opposite -conclusion. The discussion following Meem’s article is very -illuminating. It indicates that no matter how good the theory, practical -experience together with the use of generous sizes and close spacing are -the best guides for bracing trenches and coffer dams. All are not -possessed with the desired practical experience and some basis on which -to commence work is essential. Another factor affecting computations of -sizes based on theory is the tendency in practice to use the same size -material for rangers and braces on any one job for all except very deep -trenches and other special cases. Occasionally where there is an -independent brace for each end of each ranger, the brace is made -thinner, but is of the same depth as the ranger. - -The application of Rankine’s theory of earth pressure to the computation -of the sizes of rangers and braces will be shown. His formula for the -active earth pressure against a retaining wall is: - - _P_ = _wh_ cosθ (cos θ − √(cos^2 θ − cos^2 φ))⁄(cos θ + √(cos^2 θ − - cos^2 φ)) - - in which _w_ = the weight of earth in pounds per cubic foot; - - _h_ = depth in feet at point at which pressure is to be - determined; - - θ = the angle of surcharge, or the angle which the surface - makes with the horizontal; - - φ = the angle of repose of the earth. Usually taken as - 33°–41′ = 1½ horizontal to 1 vertical; - - _P_ = the intensity of pressure in pounds per square foot on - a vertical plane in a direction parallel to the - surface of the ground. - -In studying the pressures for trenches the surface of the ground will be -assumed as horizontal and the formula reduces to - - _P_ = (1 − sin φ)⁄(1 + sin φ)_wh_. - - -=157. Design of Sheeting and Bracing=.—The trench shown in Fig. 111 is -assumed to be constructed in moist sand weighing 110 pounds per cubic -foot, with an angle of repose of 30 degrees. The material used for -sheeting and bracing is yellow pine. The steps taken in the design of -the sheeting and bracing for this trench are as follows: - -[Illustration: - - FIG. 111.—Diagram for the Design of Wood Sheeting. -] - -1. _Earth Pressure._—Substituting the units given in the data, in -Rankine’s formula for earth pressures, - - _P_ = 36.7_h_. - -Because the earth has been freshly cut and will not be kept open long -enough to break up the cohesiveness of the banks it is customary to -reduce the assumed pressure by dividing by 2, 3, or 4, according to the -natural cohesiveness of the material. The cohesiveness of sand is not -great, therefore the pressure will be assumed as one-half of the amount -given by the formula, or - - _p_ = 18_h_. - -2. _Thickness of Sheeting and Spacing of Rangers._—It is desirable to -use the same thickness of sheeting throughout the depth of the trench. -Computations should therefore be commenced at the bottom of the trench -where the pressures are the greatest and the thickest sheeting will be -required. It is necessary to determine by trial a spacing for the -rangers and a thickness of sheeting so that the sheeting is stressed to -its full working strength. Having determined the thickness of the -sheeting at the bottom, the remainder of the computations consists in -determining the spacing of the rangers. - -In the example the lower ranger will be assumed as 3 feet from the -bottom of the trench and the distance to the next ranger as 4 feet. - - The intensity of pressure at 22 feet 9 inches is 409.5 pounds per - square foot. - - The intensity of pressure at 26 feet 9 inches is 481.5 pounds per - square foot. - -The distribution of pressures is shown by the diagram on Fig. 111. The -maximum bending moment is slightly below the point midway between the -rangers and for a 12–inch strip is 10,500 inch-pounds. - -Assuming 3 inch sheeting the maximum fiber stress is: - - _f_ = _Mc_⁄_I_ = (10,400 × 1.5 × 12)⁄12 × 27 = 568 pounds per square - inch. - -The working strength of yellow pine as given in Table 59, is 1200 pounds -per square inch. Thinner sheeting should therefore be used. - - TABLE 59 - - WORKING UNIT STRESSES FOR TIMBER - - The most used value in the Building Codes of Baltimore, Boston, - Cincinnati, Chicago, District of Columbia, and New York City - ─────────────┬────────┬───────────┬───────────┬──────────┬──────┬────── - Wood │ │ │ │ │Shear │Shear - │ │ │ │ │ With │Across - │ │ │Compression│Transverse│Grain,│Grain, - │Tension,│Compression│ Across │ Bending, │ lb. │ lb. - │lb. sq. │With Grain,│Grain, lb. │ lb. sq. │ sq. │ sq. - │ in. │lb. sq. in.│ sq. in. │ in. │ in. │ in. - ─────────────┼────────┼───────────┼───────────┼──────────┼──────┼────── - Yellow pine │ 1200│ 1000│ 600│ 1200│ 70│ 500 - White pine │ 800│ 800│ 400│ 800│ 40│ 250 - Spruce and │ │ │ │ │ │ - Va. pine. │ 800│ 800│ 400│ 800│ 50│ 320 - Oak │ 1000│ 900│ 800│ 1000│ 100│ 600 - Hemlock │ 600│ 500│ 500│ 600│ 40│ 275 - Chestnut │ 600│ 500│ 1000│ 800│ │ 150 - Locust │ │ 1200│ 1000│ 1200│ 100│ 720 - ─────────────┴────────┴───────────┴───────────┴──────────┴──────┴────── - As published in American Civil Engineers Pocket Book. - -Assuming 2–inch sheeting, the fiber stress is 1,300 pounds per square -inch. This stress is too large. By reducing the ranger spacing slightly -the stress can be brought within the required limits. - -Assuming a ranger spacing of 3 feet 9 inches the depth to the upper -ranger is changed to 23 feet and the maximum stress in the 2–inch -sheeting becomes 1,140 pounds per square inch, a satisfactory result. -The results for the computations for the other ranger spacings are shown -in Table 60. The spacing of the rangers at the sheeting junctions is -controlled by convenience and is not computed so long as it is obviously -safe. - -3. _Size of Rangers._—The rangers will be assumed as 16 feet long with -two end cross braces and one intermediate cross brace for each ranger. -Starting as before at the bottom of the trench. - - The area of the panel below the ranger and between cross - braces is 24 square feet. - - The average intensity of pressure is 28.25 × 18 = 508.5 - pounds per square inch. - - The load transmitted to the ranger is 6,000 pounds. - - Similarly the load transmitted to the ranger from the - panel above is 6,890 pounds. - - The total distributed load on the ranger is 12,890 pounds. - -If _b_ is the vertical dimension of the ranger and _d_ is the horizontal -dimension in inches, then from the beam theory, using _f_ as 1,200 -pounds per square inch, _bd_^2 = _M_⁄200, in which _M_ is expressed in -inch-pounds. The maximum bending moment is - - (_Wl_)⁄8 = 12,200 × 8 × 12⁄8 = 155,000 inch-pounds - - Therefore, _bd_^2 = 775. - -An 8 × 10 inch beam will fulfill the conditions closely. Substituting -these dimensions in the beam formula - - _f_ = (_Mc_)⁄_I_ = (155,000 × 5 × 12)⁄8 × 1000 - -= 1,160 pounds per square inch tension in outer fiber. The results of -the computations for other rangers are shown in Table 60. - -4. _Size of Cross Braces._—The cross braces act as columns. The -dimensions of the cross braces are determined by trial in such a manner -that the vertical dimension of the brace is equal to the vertical -dimension of the ranger and the compressive stress in pounds per square -inch is computed from the expression, - - _S_ ⪙ _S__{1}(1 − _l_⁄(60_d_)),[94] - - TABLE 60 - - COMPUTATIONS FOR SHEETING AND BRACING FOR TRENCH SHOWN IN FIG. 111 - - Material is moist sand weighing 110 pounds per cubic foot, with an angle of - repose of 30°. Lumber is yellow pine, with working stress as given in Table - 59. Working stresses for columns given as _S_(1 − _l_⁄(60_d_)). - ──────────────────────────────┬─────────────────────────────────────────────── - Sheeting 2 inches × 12 Inches │ Cross Braces - ──────────┬───────────┬───────┼───────────┬──────┬──────┬──────────┬────────── - │ │Maximum│ │ │ │ │ - │ │ Fiber │ │ │ │ │ - │ │Stress,│ │ │ │ Actual │Allowable - │ Maximum │Pounds │ │ │ │Intensity,│Intensity, - │ Bending │ per │ │Total │ │Pounds per│Pounds per - │ Moment, │Square │ Depth and │Load, │Size, │ Square │ Square - Depth │Inch-Pounds│ Inch │Description│Pounds│Inches│ Inch │ Inch - ──────────┼───────────┼───────┼───────────┼──────┼──────┼──────────┼────────── - │ │ │end at 26′│ │ │ │ - 23′–26.75′│ 9100│ 1140│ 9″│ 6,445│ 4 × 8│ 202│ 784 - │ │ │int. at 26′│ │ │ │ - 19′–23′│ 8800│ 1100│ 9″│12,890│ 4 × 8│ 403│ 784 - │ │ │end at 23′│ │ │ │ - 13′–17.5′│ 8550│ 1070│ 0″│ 6,393│ 4 × 8│ 200│ 784 - │ │ │int. at 23′│ │ │ │ - 8′–13′│ 7160│ 900│ 0″│12,785│ 4 × 8│ 400│ 784 - │ │ │end at 19′│ │ │ │ - 0′–6′│ 3000│ 375│ 0″│ 3,930│ 4 × 8│ 123│ 784 - │ │ │int. at 19′│ │ │ │ - │ │ │ 0″│ 7,860│ 4 × 8│ 240│ 784 - │ │ │end at 17′│ │ │ │ - │ │ │ 6″│ 3,566│ 4 × 8│ 112│ 684 - │ │ │int. at 17′│ │ │ │ - │ │ │ 6″│ 7,132│ 4 × 8│ 224│ 684 - │ │ │end at 13′│ │ │ │ - │ │ │ 0″│ 4,385│ 4 × 8│ 137│ 684 - │ │ │int. at 13′│ │ │ │ - │ │ │ 0″│ 8,770│ 4 × 8│ 274│ 684 - │ │ │end at 8′│ │ │ │ - │ │ │ 0″│ 2,270│ 4 × 6│ 96│ 687 - │ │ │int. at 8′│ │ │ │ - │ │ │ 0″│ 4,540│ 4 × 6│ 189│ 667 - │ │ │end at 6′│ │ │ │ - │ │ │ 0″│ 1,344│ 4 × 6│ 60│ 584 - │ │ │int. at 6′│ │ │ │ - │ │ │ 0″│ 2,687│ 4 × 6│ 112│ 584 - │ │ │end at 0′│ │ │ │ - │ │ │ 0″│ 432│ 4 × 6│ 18│ 584 - │ │ │int. at 0′│ │ │ │ - │ │ │ 0″│ 863│ 4 × 6│ 36│ 584 - ──────────┴───────────┴───────┴───────────┴──────┴──────┴──────────┴────────── - - Rangers - ──────┬──────┬─────────┬──────┬────────────────────┬──────┬───────────┬─────── - │ Area │ │ │ │ │ │ - │ of │Intensity│ │ │ │ │ - │Panel │ of │ │ │ │ │Maximum - │Below │Pressure,│ │ │ │ Maximum │Stress - │ this │ Pounds │Total │ │ │ Bending │Pounds - │Depth,│ per │ Load │ │ │ Moment in │ per - │Square│ Square │ in │Load Transmitted to │Size, │ Thousand │Square - Depth │ Feet │ Inch │Pounds│the Ranger from the │Inches│Inch-Pounds│ Inch - ──────┼──────┼─────────┼──────┼──────┬──────┬──────┼──────┼───────────┼─────── - │ │ │ │Panel │Panel │ Both │ │ │ - │ │ │ │Below │Above │Panels│ │ │ - ──────┼──────┼─────────┼──────┼──────┼──────┼──────┼──────┼───────────┼─────── - 26′ 9″│ 24│ 508.5│12,200│ 6000│ 6890│12,890│8 × 10│ 155│ 1160 - 23′ 0″│ 30│ 448│13,440│ 6545│ 6240│12,785│8 × 10│ 153│ 1150 - 19′ 0″│ 32│ 378│12,100│ 5860│ 2000│ 7,860│8 × 10│ 94.3│ 708 - 17′ 6″│ 12│ 328.5│ 3,942│ 1942│ 5190│ 7,132│8 × 10│ 85.6│ 636 - 13′ 0″│ 36│ 274.5│ 9,880│ 4690│ 4080│ 8,770│8 × 10│ 105│ 790 - 8′ 0″│ 40│ 189│ 7,560│ 3480│ 1060│ 4,540│6 × 8│ 54.4│ 850 - 6′ 0″│ 16│ 126│ 2,020│ 960│ 1727│ 2,687│6 × 8│ 32.2│ 503 - 0′ 0″│ 48│ 54│ 2,590│ 863│ 0│ 863│6 × 8│ 10.4│ 161 - ──────┴──────┴─────────┴──────┴──────┴──────┴──────┴──────┴───────────┴─────── - - in which _S_ = permissible crushing across the grain in a column whose - length is greater than 15 diameters; - - _S__{1} = unit working compressive strength of wood; - - _l_ = length of the column; - - _d_ = smallest dimension of the column; - - _l_ and _d_ are in the same units. - -The lower intermediate cross brace supports a length of 8 feet of the -lower ranger on which the load has been found to be 12,890 pounds. The -load on the end cross brace for the same ranger is one-half of this or -6,445 pounds. The length of each brace is 4 feet 4 inches. From Table -59, _S__{1} is 1,000 pounds per square inch. From the column formula, -_S_ is 784 pounds per square inch. - -A 4 × 8 inch cross brace is the smallest that is feasible. This is -stressed only 12,890 pounds or 403 pounds per square inch, which is well -within the permissible limits. The results of the other computations for -cross braces are shown in Table 60. - - -=158. Steel Sheet Piling.=—This is coming into more general use with the -increased cost of lumber and better acquaintance with its superiority -over wood under many conditions. Although its first cost is higher than -that of wood, the fact that with proper care it can be used almost an -indefinite number of times renders it economical to contractors who may -have an opportunity to make repeated use of it. The life of good yellow -pine sheeting with the best of care may be as much as three or four -seasons. With no particular care it will be destroyed at the first -using. Fig. 112 shows various sections of steel piling used for trench -sheeting. These forms are practically water-tight and aid materially in -maintaining dry trenches. The piling can be made water tight by slipping -a piece of soft wood between the steel sections when they are being -driven, or by pouring in between the piles some dry material which will -swell when wet. The piling is generally driven by a steam hammer and is -pulled by attaching a ring through a bolt hole in the pile, or by -grasping the pile with a clutch that tightens its grasp as the pull -increases. An inverted steam hammer attached to the pile is sometimes -used in pulling it. The impulses of the hammer together with a steady -pull on the cable serve to drag out the most stubborn piece of piling. - -[Illustration: - - FIG. 112.—Sections of Lackawanna Steel Sheet Piling. -] - - - LINE AND GRADE - - -=159. Locating the Trench.=—In order to locate a trench a line of stakes -should be driven at about 50–foot intervals along the center line of the -proposed sewer before excavation is commenced. Reference stakes or -reference points to this line are located at some fixed offset or easily -described point, or the stakes marking the center line of the trench may -be driven at some constant offset distance one side of the trench, in -order to avoid danger of loss or disturbance of the stakes. Grade or cut -is seldom marked on the line of preliminary stakes, although the -approximate cut may be indicated. - -For hand excavation the foreman lays out the trench from these stakes. -In machine work the operator guides the machine so as to follow the line -of the stakes. - - -=160. Final Line and Grade.=—After the excavation of the trench has -proceeded to within a foot or two of the final depth, the grade and line -are transferred to markers supported over the center of the trench. The -markers are horizontal boards spanning the trench and held in position -either by nails driven into stakes at the side of the trench, by nails -driven into the sheeting, or by weights holding the boards on the -ground. Two stakes driven in the ground at the side of the trench as -shown in Fig. 113 are the common method of support. If the banks are too -weak to stand under the jarring of the driving of the stakes, or -pavement or other causes prevent their use the horizontal cross piece -may be weighted down by bricks or a bank of earth. The cross pieces are -located about every 25 feet along the trench and at any convenient -distance above the surface of the ground. The nearer the ground the -stronger the support but the greater the interference with work in the -trench. The center line of the sewer is marked on the cross pieces after -they are set, and vertical struts are nailed on them with one edge of -the strut straight, vertical, and on the center line as shown in Fig. 1. -The corresponding edge should be used on all struts in order to avoid -confusion. The edge is placed in a vertical position by means of a plumb -bob or carpenter’s level. - -[Illustration: - - FIG. 113.—Methods for the Support of the Grade Line. -] - -The cut to the invert of the sewer is recorded to an even number of feet -where practicable by driving a nail in the upright strut so that the top -edge of the nail is at the desired elevation above the sewer, or the -upright is nailed with its top at the proper number of feet above the -sewer invert. The cut is marked on the upright in feet, tenths, and -hundredths from the recorded point to the elevation of the invert. - -The inspector should watch these grade markers with care by sighting -back along them to see that they are in line and have not moved. In -quicksand or caving material the marks may move during the setting of -the pipes and the levelman should be on the job constantly. - -When excavation is being done by machine the depth of the excavation is -controlled by the operator who maintains a sighting rod on the machine -in line with the grade marks on the uprights. - -[Illustration: - - FIG. 114.—Diagram Showing the Use of the Grade Rod for Fixing the - Elevation of a Sewer. -] - - -=161. Transferring Grade and Line to the Pipe.=—In transferring grade -and line to the sewer a light strong string is stretched tightly from -nail to nail on the uprights marking the line and grade. A rod with a -right angle projection at the lower end, as shown in Fig. 114, is marked -with chalk or a notch at such a distance from the end that when the mark -is held on the grade cord the lower portion of the rod which projects -into the pipe will rest on the invert. The pipe is placed in line by -hanging a plumb bob so that the plumb bob string touches the grade and -center line cord. These marks are taken only as frequently as may be -necessary to keep the sewer in line. An experienced workman can maintain -the line by eye for considerable distances. Measurements should never be -taken to the top of the pipe in order to determine position and grade as -the variations in the diameter of the pipe may cause appreciable errors. - -The position and elevation of the forms for brick, concrete, and unit -block sewers are located by reference to the grade line, or they may be -placed under the immediate direction of the survey party, or by -specially located stakes. For large sewers requiring deep and wide -excavation the grade and line stakes are driven in the bottom of the -trench about a foot above the finished grade. This requires the constant -presence of an engineer who is usually available on work of such -magnitude. - - -=162. Line and Grade in Tunnel.=—In tunnels, line and grade are given by -nails driven in the roof, the progress of excavation or the shield being -followed by eye and the forms set by direct measurement to the nails. - - - - - TUNNELING - - -=163. Depth.=—The depth at which it becomes economical to tunnel depends -mainly upon the character of the material to be excavated and on the -surface conditions. In soft dry material with unobstructed working space -at the surface, open cut may be desirable to depths as great as 35 or 40 -feet. Tunnels are cut in rock at depths of 15 feet or less. In some very -wet and running quicksand encountered in the construction of sewers for -the Sanitary District of Chicago it was found economical to tunnel at -depths of 20 feet and less. Crowded conditions on the surface, expensive -pavements, or extensive underground structures near the surface may make -it advantageous to tunnel at shallower depths than would otherwise be -economical. Winter is the best season for tunneling as the workmen are -protected from the elements and labor is more plentiful. - - -=164. Shafts.=—In sinking a shaft in soft material, the excavation is -usually done by hand, the material being thrown into a bucket which is -hoisted to the surface and dumped. The size of the shaft is independent -of the size of the sewer and depends principally on the machinery which -it is necessary to lower into the tunnel. Ordinarily a shaft 6 feet in -the clear is satisfactory. A method of timbering a shaft is shown in -Fig. 115. Because of the timbering the shaft must be started -sufficiently large at the top to finish with the desired dimensions at -the bottom. This excess size is sometimes obviated by driving the -sheeting at an angle to maintain the same size of shaft from top to -bottom. - -In timbering a shaft as shown in Fig. 115 the upper frame is staked -securely in position at the surface of the ground. This frame is -composed of timbers fastened together in the form of a square with the -ends of the timbers extending about 12 inches on all sides. The -protruding ends are used to hold the frame in position. Excavation is -begun inside the frame, and sheeting is driven around the outside of it -as excavation progresses. Only two or three men can work advantageously -at one time in these small shafts. The second frame is made up of the -same size timbers, but all are cut off flush with the outside of the -square. The outside dimensions of this frame are such as to allow -sheeting to be slipped in between it and the sheeting already driven. -The frame is lowered into position and supported from the upper frame by -vertical struts nailed to it. The lower end of the sheeting already -driven is held out from the lower frame by blocks of the thickness of -the next length of sheeting. These blocks are removed as the next length -of sheeting is placed and driven. The driving of the sheeting is -facilitated by excavating beneath it as it descends. - -[Illustration: - - FIG. 115.—Section of Shaft Timbering. - - Abbot, Journal Western Society of Engineers, Vol. 22. -] - -The sizes of sheeting and timbering should be computed on the same basis -as that for trench sheeting except that for depths greater than 30 to 35 -feet Rankine’s Theory is not applicable and judgment must be relied on -for computing the sizes for deep shafts. In stiff dry material the -pressures will change very little as the depth increases. Sheeting is -needed in shaft excavation in rock only to protect the workmen from -falling fragments, but in sand, particularly in quicksand and in wet -ground, the pressures increase directly with the depth and the sheeting -should be computed accordingly. Care must be taken to prevent the -formation of cavities behind the sheeting, to fill them if formed, and -to see that all pieces of the sheeting and bracing have a firm bearing. -It is difficult to prevent the collapse of the shaft once the movement -of earth against the sheeting has commenced. - -Shafts are also sunk in soft ground by constructing a concrete or metal -shell resting on a cutting shoe on the surface. The material inside is -dug out and the shell sinks of its own or added weight. The first -section of the shell may be from 5 to 10 feet long. As this section -sinks other sections are added. This is called the caisson method. It is -advantageous in wet ground and when the shafts are to be left as a -permanent manhole. If a permanent shaft is to be left in an excavation -being braced with wood, the permanent lining should follow within 20 to -30 feet of the shaft excavation. This is done to avoid the difficulty of -maintaining a great length of temporary wood shaft with the danger of -collapse, or of blocks or other objects falling on the workers below. - -The distance between shafts is controlled by the depth and size of the -tunnel, surface conditions, and the character of the material being -tunneled. Except where surface conditions are crowded the shallower the -cover to the tunnel the more frequent the shafts. The advantage of -frequent shafts lies in the possibility of removing excavated material -from the tunnel promptly, and in making ventilation of the tunnel -easier. The saving made by the construction of numerous shafts must be -balanced against the extra cost of the shafts. For the shallowest -tunnels the shafts are seldom placed closer than every 500 feet. - - -=165. Timbering.=—After the shaft has been excavated to the proper grade -the tunnel is struck out either by cutting through the wooden sheeting -or by removing portions of the caisson lining. Practically all tunnels -except those in solid rock must be framed to some extent. Some of the -types of frames used in tunnel construction are shown in Fig. 116. -Different combinations of these may be used in different classes of -materials. In solid rock which remains firm on exposure no timbering is -necessary. Where the roof only need be supported and the sides are -strong enough to be used for support, a timber “hitch” or frame -supported on the sides of the tunnel may be used. This is suitable for -loose rock roofs with solid rock sides. Timbering such as is shown in -the lower left hand corner of Fig. 116 becomes necessary in extremely -soft, wet, or swelling material, where the bottom and sides as well as -the roof tend to push in. The remaining frame in Fig. 116 shows a form -frequently used and lying between the two extremes indicated. In wet -tunnels a channel may be cut in the bottom below the sill for drainage -purposes as shown in this form. The needle beam method of timbering is -also shown in Fig. 116. This method of timbering is used mainly near the -heading because of the speed and ease with which it can be installed, -but it is undesirable because of the space occupied. - -The distance between frames is dependent on the size of the tunnel and -the character of the material. It is seldom greater than 6 feet and the -frames are sometimes placed touching each other. The size of the -timbering is a matter of experience and is generally determined by the -judgment of the responsible person in charge of the construction as the -result of observation during the progress of the work. - -The sheeting between frames is called poling boards, or spiling or -lagging according as it is sharpened and driven ahead of the excavation -or placed after the excavation has progressed. The horizontal strips -placed between the frames to keep them apart are called wales. - -[Illustration: - - FIG. 116.—Types of Frames and Timbering for Tunnels. -] - -In cutting out from the shaft in soft materials requiring support, where -the width of the tunnel is the same or smaller than that of the shaft, a -frame with a maximum width four thicknesses of sheeting less than the -width of the tunnel is set up against the lining of the shaft. The -vertical side pieces of the tunnel frame rest on the bottom frame of the -shaft as a sill and are securely wedged into position. As the lining of -the shaft at the top is cut away the top poling boards of the tunnel are -slipped in between the cap of the first tunnel frame and the shaft frame -immediately above it. The poling boards are driven with an upward pitch -so that there may be room to slip the second length of boards between -the next tunnel frame and the first length of boards. The placing of the -side sheeting follows in a similar manner. Excavation is then started -and the poling boards driven to keep pace with it. The next frame is -placed in position and the previous sheeting or boards wedged out a -sufficient distance to allow the advance lining to be slipped in when -the wedges are removed. Waling pieces are nailed firmly between the -frames to hold them in position. The various phases in the driving of a -12–foot sewer tunnel in Seattle are shown in Fig. 117. - -[Illustration: - - FIG. 117.—Stages of Sewer Tunneling. - - Eng. Record, Vol. 69, 1914, p. 195. -] - -In soft or running material it may be necessary to protect the face of -the tunnel by horizontal boards, called breast boards, wedged back to -the last frame placed. The excavation is performed by removing one board -at a time, excavating behind it and then replacing it in the advance -position. The advance is made from the top downwards. This represents -the method pursued in the most difficult material where wooden sheeting -without a shield is used. The timbering during the advance may be -modified in any manner that the character of the material will permit. -The timbering may lag behind the excavation a distance of two or more -frames, or it may be omitted altogether. Heavier timbering may be -necessary in soft, slipping or shattered rock. - -[Illustration: - - FIG. 118.—Shield for Driving Milwaukee Sewer Tunnel. - - Eng. News-Record, Vol. 80, 1918, p. 669. -] - - -=166. Shields.=—Shields are used in tunneling in soft wet material and -are particularly suitable for work under air pressure. They are used in -rock tunnels where water is anticipated or air pressure is used. The -shields often save the expense and difficulty of timbering as the -masonry of the sewer follows closely behind the shield. Fig. 118 shows -the arrangement for a shield for tunneling in soft material in the -construction of the Milwaukee sewers. The shield has an exterior -diameter of 9 feet 4 inches and an overall length of 9 feet 8⅛ inches. -The cutting edge section is 20 inches long. The shell is made of one -inch plate to the back of the jack chambers and one-half inch plate in -the tail. The shield is driven by ten 60–ton hydraulic jacks. The jacks -are shown in position in the figure. These jacks rest against the -finished tunnel lining and serve to consolidate it at the same time that -they push the shield into the material to be excavated. The face of the -tunnel is cut with a pick and shovel while the jacks are removed one at -a time and a new ring of lining is put in place. The lining may be -temporary timbering to receive the thrust of the jacks, but it is -usually desirable that the permanent lining follow immediately behind -the shield. Since the shield is larger than the outside of the lining -the space left by its passage should be grouted immediately after it has -passed. - - -=167. Tunnel Machines.=—Tunnel machines have been used successfully on -sewer tunnels in soft materials, but not in rock.[95] The machines are -of different types, but in general consist of a revolving cutting head, -equipped with knives, and driven by an electric motor. The bearing on -which the shaft for the cutting head rests is supported against the -sides of the tunnel. The muck is carried away by means of a conveyor and -dumped into muck cars without rehandling. Rapid progress can be made -with these machines in suitable conditions. - -[Illustration: - - FIG. 119.—Method of Drilling and Loading Rock Tunnel Face. - - Courtesy, Aetna Power Co. -] - - -=168. Rock Tunnels.=—Tunnels in rock are advanced by drilling into the -face as shown in diagrammatic form in Fig. 119. The holes near the -center are driven in at an angle towards the center and to depths from 6 -to 15 feet. The harder the rock the greater the angle with the tunnel. -This is called the center cut. Other holes are driven near the outer -edge of the tunnel and parallel to its axis. When fired, the wedge of -rock between the center cut holes is thrown back into the tunnel and a -delayed explosion then throws the sides into the hole thus made. A final -delay thrusting shot throws the muck so formed away from the face of the -tunnel. For tunnels up to 6 or 8 feet in height the entire bore is cut -out in this fashion. For larger tunnels, the upper portion called the -heading, is taken out in this way, and the remainder, called the bench, -is taken out by drilling and blowing holes normal to the axis of the -tunnel. The amount of powder necessary in the bench holes is much less -than that required in the heading. - - -=169. Ventilation.=—No tunnel more than 50 feet long should be built -without ventilation. A fair amount of air for ordinary conditions is 75 -cubic feet of free air per minute per person in the tunnel, and double -this amount for each animal. Where explosive gases are met, or under -conditions where the tunnel is hot, five or six times as much air may be -needed in order to cool the tunnel or to dilute the gases. In order that -the air may be fresh and cool at the face of the tunnel where work is -going on it should be conducted to the tunnel face in a pipe and blown -out into the tunnel. Immediately following a blast at the face the -current should be reversed so as to draw the poisonous gases out of the -tunnel through the duct. The high pressure air line leading to the -drills should be opened at the same time to create a current towards the -face in order to accelerate the clearing of the air at the heading. The -capacity of the air machines should be sufficient to exhaust four times -the volume of the gases created by the explosion, in 15 minutes. This -will ordinarily call for a capacity of about 4,000 cubic feet of free -air per minute. If the same blower is to be used for exhausting the -gases as for ventilation while work is going on, it should have a high -overload capacity to care for this situation. The air line should be -arranged to allow for reversal of flow. - -The diameter of the air pipe should be determined by a study of the -saving of the cost and operation of the air equipment compared to the -increased cost of a larger pipe line. Other factors affecting the size -of the pipe line to be used are: the available space in the tunnel, the -temporary character of the installation, the use of the exhaust from -high-pressure air machines for the purpose of ventilation, etc. -Cast-iron, spiral-riveted galvanized sheet iron, and canvas pipes have -been used for conducting low-pressure ventilating air. - -Ventilation in tunnels working under air pressure is supplied from the -compressors, and the air is delivered near the face of the heading, -except that being used in the locks. In tunnels using air drills, the -air for the drills is conducted through a separate pipe as it is not -economical to compress the ventilating air to the pressure necessary to -operate the drills. - - -=170. Compressed Air.=—Compressed air is used in tunnel work to prevent -the entrance of water into the tunnel and to keep the work dry. The -pressure of air used is closely that of the pressure of the ground water -but in a large tunnel or a tunnel with a weak roof the pressure may be -somewhat lower on account of the danger of blowing through the roof. It -is evident that the water pressure cannot be balanced at the top and the -bottom of the tunnel. To balance it at the bottom makes a blow out near -the top more probable. To balance the pressure at the top may leave the -bottom wet. Judgment and care must be exercised during construction and -if the pressure is balanced at or near the bottom the roof must be -carefully guarded by grouting and puddling with clay, or the surface, -particularly if under water, may be covered with a clay bank. If the -cavities in the tunnel lining are large, sawdust can be mixed with the -grout to advantage, the mixture being pumped through holes in the roof -by hand or power operated force pumps. “Blows” must be carefully guarded -against as they endanger the lives of the workmen and threaten the loss -of the tunnel. The pressure and volume of air supplied for some large -subaqueous tunnels is shown in Table 61. - -Labor under compressed air is arduous and dangerous with the best of -safeguards.[96] Pressure more than about 43 pounds per square inch -cannot be used and at this high pressure men cannot work more than four -hours at a time. Little or no distress is noted at pressures less than -15 pounds. - - TABLE 61 - - VOLUME AND PRESSURE OF COMPRESSED AIR IN TUNNELS - - (American Civil Engineers Pocket Book) - ──────────┬────────┬───────┬─────────┬─────────┬─────────────────────── - Tunnel │ │ │ Maximum │ Average │ Conditions and Cubic - │Maximum │ │ Air │ Air │ Feet of Free Air per - │Distance│ │Pressure,│Pressure,│ Minute - │ High │ │ Pounds │ Pounds │ - │Water to│Minimum│ per │ per │ - │Invert, │ Cover │ Square │ Square │ - │ Feet │in Feet│ Inch │ Inch │ - ──────────┼────────┼───────┼─────────┼─────────┼─────────────────────── - City and │ │ │ │ │In water bearing-sand. - South │ │ │ │ │ 1660 cubic feet per - London │ │ │ │ │ minute per face. When - │ │ │ │ │ grouted 1000 to 1300 - │ │ │ │ │ cubic feet per minute - │ 34│ 42│ 15│ │ per face - ──────────┼────────┼───────┼─────────┼─────────┼─────────────────────── - Blackwall │ │ │ │ │10,000 cubic feet per - │ │ │ │ │ minute per face in - │ │ │ │ │ open ballast for some - │ 80│ 5│ 37│ 35│ time - ──────────┼────────┼───────┼─────────┼─────────┼─────────────────────── - Baker St. │ │ │ │ │In gravel, 3300 cubic - and │ │ │ │ │ feet of air per - Waterloo│ │ │ │ │ minute per face. - │ │ │ │ │ Parallel tunnel 1650 - │ │ │ │ │ cubic feet per min. - │ 70│ 18│ 35│ 28│ per face - ──────────┼────────┼───────┼─────────┼─────────┼─────────────────────── - Greenwich │ │ │ │ │Average 83.5 per man - │ │ │ │ │ per minute. Never - │ 70│ 30│ 28│ 20│ less than 66.7 - ──────────┼────────┼───────┼─────────┼─────────┼─────────────────────── - Battery, │ │ │ │ │In sand. Two working - East │ │ │ │ │ faces. Maximum 32,000 - River. │ │ │ │ │ - N. Y. │ 94│ 12│ 42│ 26│ - ──────────┼────────┼───────┼─────────┼─────────┼─────────────────────── - East │ │ │ │ │Maximum for one face - River, │ │ │ │ │ 25,000 cubic feet per - N. Y., │ │ │ │ │ minute for 24 hours. - Penn. │ │ │ │ │ Capacity of plant for - R.R. │ │ │ │ │ 8 faces, 80,400 cubic - │ 93│ 8│ 42│ 27│ feet per minute - ──────────┼────────┼───────┼─────────┼─────────┼─────────────────────── - North │ │ │ │ │Maximum in gravel - River, │ │ │ │ │ 10,000 cubic feet per - N. Y., │ │ │ │ │ man per hour. - Penn. │ │ │ │ │ Generally ranged - R.R. │ 98│ 20│ 37│ 26│ between 1500 and 5000 - ──────────┴────────┴───────┴─────────┴─────────┴─────────────────────── - -Entrance and exit to the tunnel are gained through air locks. These are -sheet iron cylinders concreted into the lining of the tunnel or shaft. -Air-tight iron doors are provided at both ends, which open inwards -towards the tunnel. On entering the lock from the outside the door to -the tunnel is found tightly closed. The outside door is then closed by -hand, the air valve is opened and air is admitted to the lock until the -pressure on the lock side of the tunnel door equalizes that on the -tunnel side and the tunnel door is swung open by hand. When the lock is -open to the tunnel the pressure in the tunnel keeps the outside door -closed. In order to leave the tunnel the process is reversed. Materials -are passed through the lock by the lock tender or tenders who pass -through the lock with the material if the pressure is low, or who -manipulate the air outside of the lock if the pressure is high. If -pressures of 30 to 40 pounds are being used, two or even three locks may -be necessary. - - - EXPLOSIVES AND BLASTING[97] - - -=171. Requirements.=—The desirable features in an explosive to be used -in trenching and tunneling in rock are: (1) stability in make up so as -not to deteriorate in strength or to become dangerous during storage, -(2) imperviousness to ordinary variations in temperature and moisture, -(3) insensibility to ordinary shocks received in transportation and -handling, (4) not too difficult of detonation, (5) convenient form for -transportation and loading and for making up charges of different -weights, (6) the non-formation of poisonous gases when fired, (7) -imperviousness to water and usefulness in wet holes, (8) power without -bulk, etc. - - -=172. Types of Explosives.=—Explosives which fill some or all these -requirements can be divided into two classes, deflagrating and -detonating. A deflagration is an explosion transmitted progressively -from grain to grain. A detonation is a sudden disruption caused by -synchronous vibrations of a wave-like character. The deflagrating -explosives are represented by gun-powders and contractors’ powders. They -must be carefully tamped in the hole to develop their full power and -they must be ignited by a fuse or flame. They are valueless in water or -moist holes. These powders are used mainly for loosening frozen earth, -soft sandstone, cemented gravels and similar materials where a thrusting -action rather than a disruption is desired. The detonating explosives -are most commonly represented by the dynamites. These are exploded by a -shock usually caused by another explosive which has been ignited by a -fuse or electric spark, and which is known as the “detonator.” -Detonating explosives are more powerful than deflagrating explosives and -are used in all but the softest materials. - -_Gunpowder._—This is a mechanical mixture of sulphur, charcoal, and -saltpeter generally in the proportions of 10 parts sulphur, 15 parts -charcoal, and 75 parts saltpeter (sodium nitrate). It weighs about 62½ -pounds per cubic foot and produces about 280 times its own volume in gas -at a pressure of 4.68 tons per square inch at a temperature of 32 -degrees F., which amounts to a pressure of approximately 38 tons per -square inch at the temperature of explosion of 4,000 degrees F. - -_Blasting Powder._—This is a mixture of 19 parts sulphur, 15 parts -charcoal, and 66 parts saltpeter. These powders are made in different -size angular polished grains, from the size of a pin head to sizes just -passing a ⅜ to ½ inch hole. The larger the grains the slower the action -of the powder. - -_Nitro-Substitution Compounds._—These compounds are formed by the action -of nitric acid on hydrocarbons. Triton, T.N.T., or trinitrotoluene, made -famous during the war, is an example of these compounds. It is made by -the successive nitration of toluene, a coal tar derivative. It melts at -80 degrees C., is very stable, and is of great explosive strength. It is -manufactured in a convenient form, being compressed into blocks about 2 -inches square by about 4 inches long with a specific gravity of about -1.5. The blocks are usually copper plated to protect the T.N.T. from -moisture. The more dense it is the less its sensitiveness. It is also -put up in crystalline form in cartridges like dynamite, in which -condition it is practically equal to 40 per cent dynamite. It can be cut -with a knife, pounded with a hammer, and will burn freely and slowly in -small quantities in the open air without exploding. It is suitable for -all but the hardest rocks. It creates poisonous gases on detonation -which are quickly dissipated in the open air but which render it -unsuitable for use in tunnel work. - -_Nitro-glycerine._—This is formed by the action of nitric and sulphuric -acids on animal compounds such as gelatine or glycerine. Nitro-glycerine -is a yellowish, oily, highly unstable explosive liquid with a specific -gravity of about 1.6. It will burn quietly when ignited in the open air. -It will freeze at 41 degrees F., and will explode at 388 degrees F., or -on concussion at a lower temperature. It develops about 1,500 times its -volume in gas, which due to the heat of combustion is increased to about -10,000 times its volume. It is a very dangerous explosive to handle, and -is unsuitable for use in the liquid form. - -_Blasting Gelatine._—This is made by soaking guncotton in -nitro-glycerine. Gelatine dynamite is a combination of blasting gelatine -and an absorbent. Forcite is a gelatine dynamite in which the blasting -gelatine, forming 50 per cent of the compound, contains 90 per cent -nitro-glycerine and 2 per cent guncotton; and the absorbent, forming the -other 50 per cent of the compound, contains 76 per cent of sodium -nitrate, 3 per cent sulphur, 20 per cent of wood tar, and 1 per cent of -wood pulp. - -Blasting gelatine is packed in a jelly-like mass in metal lined wooden -boxes. It is less sensitive than straight dynamite and is one of the -most powerful explosives known. It can be made up to equal 100 per cent -dynamite. It is suitable for use in the hardest rocks and for subaqueous -work as it is not affected by moisture. It is suitable for use in -tunnels as the amount of carbon monoxide, peroxide of nitrogen, hydrogen -sulphide and other dangerous gases is comparatively low when fully -detonated. Gelatine dynamite[98] is sold as 30 per cent to 70 per cent -dynamite, the actual percentage of nitro-glycerine being less than the -nominal quantity given. - -_Dynamite._—The dynamites are made by soaking nitro-glycerine in some -absorbent. If the absorbent is some neutral substance such as infusorial -earth the combination is known as a true dynamite. The false or active -dynamites are those in which the absorbent is also an explosive -compound. The false dynamites form the best known contractors’ -explosives. Among the materials mixed with the nitro-glycerine are: -magnesium carbonate, sulphur, wood meal, wood pulp, wood fiber, wood -tar, nut galls, kieselguhr, sawdust, resin, pitch, sugar, charcoal, and -guncotton. The strength of dynamites is noted by the per cent of -nitro-glycerine and nitro substitutes contained. Dualin and Hercules -powder both contain 40 per cent nitro-glycerine. Dualin contains 30 per -cent sawdust and 30 per cent potassium nitrate, but the Hercules powder, -which is stronger, contains 16 per cent sugar, 3 per cent potassium -chlorate, 31 per cent potassium nitrate, and 10 per cent magnesium -carbonate. - -Dynamite is the most common explosive used on construction work. It is -supplied in cylindrical sticks wrapped in paper, the diameter of the -sticks varying between ⅞ and 2 inches. They are about 8 inches long. -Forty per cent dynamite is the common strength found on the market. It -is suitable for ordinary work in all but very hard rocks or very soft -material. Direct contact with water separates the nitro-glycerine from -the base and is dangerous when the explosive is used in wet places -unless it is fired immediately after the hole is loaded. It freezes at -about 42 degrees F., or at even higher temperatures and in the frozen -state it is highly dangerous, requiring powerful detonators for firing, -but exploding spontaneously from a slight jar, or the breaking of the -stick. Special low-freezing dynamites are made that will not freeze -above 35 degrees F. - -_Ammonia Compounds._—Ammonia dynamite is a combination of -nitro-glycerine, ammonium nitrate and such other ingredients as sodium -nitrate, calcium carbonate and combustible material. This form of -explosive is advantageous for underground work because, like gelatine -dynamite, its explosion does not create large quantities of poisonous -gases. It has a low freezing point and is relatively low in cost. It is -seriously affected by moisture, however, and can not be used in wet -places. Ammonium nitrate explosives which do not contain nitro-glycerine -include 70 per cent to 95 per cent ammonium nitrate and some combustible -material. Ammonal is a special type of this class formed by a mixture of -ammonium nitrate, aluminum, and triton. All of these explosives are -deliquescent, insensitive to shock, and are cheaper than the dynamites. - - -=173. Permissible Explosives.=—As specified by the United States Bureau -of Mines explosives whose rapidity, detonation, and temperature of -explosion will not ignite explosive mixtures of pit gases and air are -known as permissible explosives. They include nitrate explosives, -ammonia dynamite, and others. - -Gunpowder, triton, picric acid, blasting gelatine, dynamite, guncotton, -etc., are not classed as permissible explosives. - - -=174. Strength.=—The relative weights for equal strength of various -explosives are given in Table 62. - - TABLE 62 - - RELATIVE WEIGHTS OF EXPLOSIVES WITH THE SAME STRENGTH AS A UNIT WEIGHT - OF 40 PER CENT DYNAMITE - - ───────────────────────────────────────────────────────┬─────────────── - Explosive │Relative Weight - ───────────────────────────────────────────────────────┼─────────────── - Picric acid │ 0.86 - Gun powder (well tamped) │ 3.10 - Straight dynamite, 15% │ 1.45 - Straight dynamite, 20 │ 1.33 - Straight dynamite, 25 │ 1.28 - Straight dynamite, 30 │ 1.18 - Straight dynamite, 35 │ 1.07 - Straight dynamite, 40 │ 1.00 - Straight dynamite, 45 │ 0.93 - Straight dynamite, 50 │ 0.86 - Straight dynamite, 55 │ 0.83 - Straight dynamite, 60 │ 0.78 - │ - Low-freezing dynamites are the same as straight │ - dynamites │ - Smokeless powder, well tamped │ 0.74 - │ - Triton │ 0.86 - Blasting gelatine │ 0.43 - Gelatine dynamite, 30% │ 1.28 - Gelatine dynamite, 35 │ 1.21 - Gelatine dynamite, 40 │ 1.14 - Gelatine dynamite, 50 │ 1.04 - Gelatine dynamite, 55 │ 0.97 - Gelatine dynamite, 60 │ 0.90 - Gelatine dynamite, 70 │ 0.83 - │ - Ammonia dynamites are the same as gelatine dynamites. │ - Chlorates (sprengle) Rack-a-rock │ 1.33 - Guncotton │ 0.72 - ───────────────────────────────────────────────────────┴─────────────── - - -=175. Fuses and Detonators.=—The explosion of gunpowder and other -deflagrating explosives is caused by the direct application of a flame -led to the charge by a powder fuse, or they may be fired by a blasting -cap which is itself exploded by the heat from a fuse or an electric -spark. The powder fuse is a cord made up of a train of powder securely -wrapped in a number of thicknesses of woven cotton or linen threads and -usually made waterproof. Ordinary fuse burns at about 2 feet per minute -but there may be wide variations from this rate due to the quality of -the fuse, moisture, temperature, or pressure. Moisture tends to retard -the rate, pressure to increase it. Instantaneous fuse will burn at about -120 feet per second. It is distinguished from the ordinary safety fuse -both by eye and touch due to the rough red braid with which it is -covered. It is used in firing a number of charges simultaneously. Powder -fuses are lighted by the application of a flame or smoldering torch to -the freshly cut or opened end exposing the powder grains. Cordeau -Bickford is lead tubing filled with triton, in which the flame travels -at about 17,000 feet per second. This is also used for igniting charges -simultaneously. - -The detonation of an explosive is caused by the shock or heat of the -explosion of a more sensitive substance which has been exploded by a -powder fuse or electric spark. The common method of detonating explosive -charges is by the firing of a blasting cap. These caps are copper -cylinders, closed at one end, about 1½ inches long and ¼ to ⅜ of an inch -in diameter, or larger. They contain a mixture of about 85 per cent -fulminate of mercury and 15 per cent potassium chlorate held in place by -a wad of shellac, collodion, or paper. The strength of detonators is -based on the weight of fulminate of mercury and is designated as shown -in Table 63. - - TABLE 63 - - STRENGTH OF BLASTING CAPS - - ────────────────────────────────────────┬────────────────────────────── - Blasting Cap, Commercial Grade │ Grains Fulminate of Mercury - ────────────────────────────────────────┼────────────────────────────── - 3X or Triple │ 8.3 - 4X or Quadruple │ 10.0 - 5X or Quintuple │ 12.3 - 6X or Sextuple │ 15.4 - 7X or Number 20 │ 23.1 - 8X or Number 30 │ 30.9 - Single strength │ 12.3 - Double strength │ 15.4 - Triple strength │ 23.1 - Quadruple strength │ 30.9 - ────────────────────────────────────────┴────────────────────────────── - -The force of the explosion is markedly affected by the strength of the -caps, the effect being greater for low-grade powders. For 40 per cent -dynamite the explosion caused by a 5X cap is 15 per cent stronger than -that caused by a 3X cap. For 60 per cent dynamite the difference is only -6 per cent. The deterioration of the caps will reduce the strength of an -explosion noticeably. With straight dynamite, 3X caps are generally -used, but with gelatine dynamite 6X or heavier caps must be used. Caps -may be tested by exploding them in a confined space and noting the -report and the effect on the shell. A full strength cap will tear the -shell into minute pieces, while a deteriorated cap will merely tear it -into three or four large pieces. An ordinary blasting cap is shown in -Fig. 120 together with other equipment for blasting. - -Firing by electricity is generally safer and more satisfactory than by -the use of ordinary caps and powder fuses. The explosion is more certain -and its exact time is under the control of the operator. Fig. 121 shows -a section through an electric blasting cap or detonator, commonly called -an electric fuse. Delayed action electric detonators are made by -inserting a slow-burning substance between the platinum bridge and the -detonating substance. The time of delay is controlled by the depth of -the slow-burning substance. Delayed action detonators are useful in -tunnel work where it is desired to explode the charge in three or four -stages in order that the debris from one charge may be out of the way of -the following, and that the forces of the explosions may not serve to -nullify each other. - -[Illustration: - - FIG. 120.—Blasting Supplies. - - Courtesy, Aetna Powder Co. -] - - -=176. Care in Handling.=—Some of the don’ts in the handling of -explosives recommended by the U. S. Army Engineer Field Manual are: in -the use of nitro-glycerine explosives of all kinds— - - (_a_) Don’t store detonators with explosives. Detonators should be - kept by themselves. - - (_b_) Don’t open packages of explosives in a store house. - - (_c_) Don’t open packages of explosives with a nail puller, pick - or chisel. Packages should be opened with a hard wood wedge and - mallet, outside of the magazine and at some distance from it. - - (_d_) Don’t store explosives in a hot or damp place. All - explosives spoil rapidly if so stored. - - (_e_) Don’t store explosives containing nitro-glycerine so that - the cartridges stand on end. The nitro-glycerine is more likely to - leak from the cartridges when they stand on end than it is when - they lie on their sides. - - (_f_) Don’t use explosives that are frozen or partly frozen. The - charge may not explode completely and serious accidents may - result. If the explosion is not complete the full strength of the - charge is not exerted and larger quantities of harmful gases are - given off. - -[Illustration: - - FIG. 121.—Electric Fuse. - - Full size. -] - - (_g_) Don’t thaw frozen explosives in front of an open fire, nor - in a stove, nor over a lamp, nor near a boiler, nor near steam - pipes, nor by placing cartridges in hot water. Use a commercial or - improvised thawer. - - (_h_) Don’t put hot water or steam pipes in a magazine for thawing - purposes. - - (_i_) Don’t carry detonators and explosives in the same package. - Detonators are extremely sensitive to heat, friction, or blows of - any kind. - - (_j_) Don’t handle detonators or explosives near an open flame. - - (_k_) Don’t expose detonators or explosives to direct sunlight for - any length of time. Such exposure may increase the danger in their - use. - - (_l_) Don’t open a package of explosives until ready to use the - explosive, then use it promptly. - - (_m_) Don’t handle explosives carelessly. They are all sensitive - to blows, friction, and fire. - - (_n_) Don’t crimp a detonator (blasting cap) around a fuse with - the teeth. Use a cap crimper, which is supplied for this purpose. - - (_o_) Don’t economize by using a short length of fuse. - - (_p_) Don’t return to a charge for at least one-half hour after a - miss fire. Hang fires are likely to happen. - - (_q_) Don’t attempt to draw nor to dig out the charge in case of a - miss fire. - -Some of the positive rules in connection with the handling of explosives -are: build the magazine on an earth foundation remote from any other -structures, protect it with earth embankments that will direct the force -of the explosion upwards, and build it of materials that will supply as -few missiles as possible. Hollow tile brick, double-walled galvanized -iron filled with sand, and similar constructions are satisfactory. The -magazine may be heated by steam or hot-water pipes so located that -explosives cannot come in contact with them, or by a cluster of -incandescent bulbs, but if the explosives become frozen they must not be -thawed out by turning on the steam or hot water. If powder or -nitro-glycerine is dropped on the floor the magazine should be emptied, -washed out with a hose and spots of nitro-glycerine scrubbed with a -brush and a mixture of ½ gallon of wood alcohol, ½ gallon of water and 2 -pounds of sodium sulphide. Frozen explosives may be thawed by spreading -out on special shelves in a warm thaw house—not in the magazine proper, -by burying in a manure pile so that the explosive may not become -moistened, or more commonly by heating slowly in a water bath. This is a -dry kettle in which the explosives are placed and covered. The kettle is -then put in another containing water which is heated gently to about 120 -degrees F. It should not be boiled. - -In case of a miss fire, instead of digging out the old charge put a new -charge on top of the old and fire the two simultaneously. - - -=177. Priming, Loading, and Firing.=—Priming is the act of placing the -cap or detonator in the cartridge of explosive. The primer is either the -cap or the cap and cartridge which are to be detonated by the fuse. If a -cap and safety fuse are to be used the paper at the upper end of the -cartridge is opened, a hole is poked in the explosive with the finger or -a piece of wood, the cap and the attached fuse are pushed into the hole -and gently embedded in the explosive so that the end of the cap is -exposed sufficiently to prevent the fuse from igniting the dynamite -directly. The paper is then folded up and tied firmly around the fuse -with a piece of string. The result is shown in Fig. 122. - -[Illustration: - - FIG. 122.—Dynamite Cartridge, Safety Fuse, and Cap. -] - -In placing the fuse in the cap the end of the fuse is cut off square, -and inserted in the open end of the cap, care being taken not to spill -the loose grains of powder or to grind the fuse down on top of the cap. -When the fuse is shoved firmly into place the upper portion of the -copper cap is pressed or crimped with the cap crimpers shown in Fig. -120. - -The number of primers to be used is dependent on the size and location -of the charge, but in practically all sewer work only one primer is used -to each hole. In bulky charges the primer should be placed near the -center of the charge and the fuse so protected that it will not ignite -the charge prematurely. In drill holes the primer is put in last with -the cap end down. - -In loading a hole, it is first pumped and cleaned out. This can be done -satisfactorily with the end of a stick frayed out into a broom. -Cartridges which very nearly fill the hole are dropped in one at a time -and are pressed firmly together, with a light wooden tamping bar. They -should not be pounded. After the primer is placed, a wad of clay or -similar material is pressed gently into the hole against it and the hole -is then filled with well-tamped clay. In tunnel work tamping is not so -essential as an overcharge of powder is usually used and the time of -tamping, which is worth more than two or three sticks of dynamite, is -saved. In handling bulk explosives, such as gunpowder, they are poured -into the hole, the fuse is set in the upper portion and the remainder of -the hole is tamped with clay as for dynamite cartridges. - -[Illustration: - - FIG. 123.—Methods for Cutting Safety Fuse for Splicing. -] - -If a large number of charges are to be fired simultaneously with a -safety fuse, the length of the fuse to each charge should be made equal -or a safety fuse used to a common center and approximately equal lengths -of instantaneous fuse or Cordeau Bickford used from there to the charge. -In splicing the fuses for such connections they are cut diagonally as -shown in Fig. 123 and bound together firmly with tape. Electric -connections are particularly advantageous under such conditions as they -avoid the dangers incidental to spliced fuses and are less expensive. In -tunnel work simultaneous electric detonation is not desirable as the -holes should be fired progressively: 1st, the cuts; 2nd, the relievers; -3rd, the backs; 4th, the sides; and 5th, the lifters. Different lengths -of safety fuse, or delayed action electric fuses can be used for these -delay shots. - -In igniting a safety fuse an open flame such as that furnished by a -match or candle is the most satisfactory. For electric fuses the current -is generated by a magneto shown in Fig. 120. Pressing vigorously down on -the handle closes the circuit and generates an electric current which -heats the platinum bridges and explodes the charges. For the small -number of charges used in ordinary construction they are connected in -series so that if there is a broken connection anywhere no charge will -be exploded. If many charges are to be fired and a line circuit is to be -used, the final connection should not be made until just before the -charge is to be fired in order to obviate the danger of stray currents -firing the charge prematurely. Care should be taken to see that all -connections are good and that there are no broken wires on the line. - - -=178. Quantity of Explosive.=—The quantity of explosive to be used can -be determined satisfactorily only by experience on the job in question, -as the factors affecting the necessary quantity are so diverse. The -figures in Table 64 indicate the relative amounts needed under different -conditions. - - TABLE 64 - - QUANTITIES OF EXPLOSIVES - - ───────────┬──────┬────────┬─────────┬─────────────┬─────────┬────────── - Kind of │Drift │Feet[99]│Black[99]│Dynamite[99],│Grade of │ - Rock │ in │of Hole │ Powder, │ Pounds │Dynamite,│ Remarks - │ Feet │ │ Pounds │ │Per Cent │ - ───────────┼──────┼────────┼─────────┼─────────────┼─────────┼────────── - Limestone, │ │ │ │ │ │ - Chicago │ 12│ 0.40│ │ 0.75│ 40│Gillette - Drainage │ │ │ │ │ │ - Canal │ │ │ │ │ │ - Limestone │ │ │ │ │ │ - for │ 6│ 1.00│ │ 0.70│ 40│Gillette - crushing │ │ │ │ │ │ - Limestone │ │ │ │ │ │ - for │ 20│ │ │ 0.37│ 50│Gillette - cement │ │ │ │ │ │ - Limestone, │ │ │ │ │ │ - holes │ 15│ 0.40│ │ 0.26│ 50│Gillette - sprung │ │ │ │ │ │ - Sandstone, │ 20│ 0.10│ 1.0│ 0.10│ 40│Gillette - side cut │ │ │ │ │ │ - Sandstone, │ │ │ │ │ │ - thorough │ 20│ 0.20│ 2.0│ 0.20│ 40│Gillette - cut │ │ │ │ │ │ - Shale, soft│ 24│ 0.08│ 0.7│ 0.03│ 40│Gillette. - side cut │ │ │ │ │ │ Open cut - Shale, hard│ │ │ │ │ │ - thorough │ 24│ 0.20│ 1.5│ 0.10│ 40│Gillette - cut │ │ │ │ │ │ - Granite for│ 16│ 1.36│ │ 0.20│ 60│Gillette - rubble │ │ │ │ │ │ - Gneiss, New│ 12│ 1.33│ │ 0.60│ 40│Gillette - York City│ │ │ │ │ │ - Gneiss, New│ 14│ 0.63│ │ 0.50│ 40│Gillette - York City│ │ │ │ │ │ - Syenite, │ │ │ │ │ │ - Treadwell│ 12│ 1.70│ │ 0.67│ 40│Gillette - Mine │ │ │ │ │ │ - Magnetic │ 12½│ 0.32│ │ 0.44│ 52│Gillette - iron ore │ │ │ │ │ │ - Trap, seamy│ 14│ 0.35│ │ 0.20│ 75│Gillette - Trap, │ 17│ 1.00│ │ 0.70│ 40│Gillette - massive │ │ │ │ │ │ - │ │ │ │ │ │50% - Granite, │ │ │ │ │ │ dynamite - Grand │ 25│ 0.10│ │ 0.80│ 50│ used to - Trunk │ │ │ │ │ │ spring - │ │ │ │ │ │ holes - Clay, rock │ │ │ │ │ │ - and │Tunnel│ │ │ 1.00│ │ - Gypsum │ │ │ │ │ │ - │ │ │ │ │Grade │ - │ │ │ │ │ varied │ - │ │ │ │ │ ⅗ at │ - Hard shale │Tunnel│ │ │ 2.07│ 45%, ⅕ │ - │ │ │ │ │ at 60%,│ - │ │ │ │ │ some at│ - │ │ │ │ │ 100% │ - Hard rocky │Tunnel│ 1.60│ │ 3.57│ │ - slate │ │ │ │ │ │ - Hard rocky │Tunnel│ 1.46│ │ 3.57│ │ - slate │ │ │ │ │ │ - Mill Creek │ │ │ │ │ │Mun. - sewer, │Tunnel│ │ │ 4.00│ 60│ Eng’g. - St. Louis│ │ │ │ │ │ Vol. 52, - │ │ │ │ │ │ p. 14 - ───────────┴──────┴────────┴─────────┴─────────────┴─────────┴────────── - - - PIPE SEWERS - - -=179. The Trench Bottom.=—It is customary to dig the bottom of the -trench to conform to the shape of the lower 45 degrees to 90 degrees of -the sewer if the character of the material will allow such construction. -In soft material which will not hold its shape the sewer may be encased -in concrete or a concrete cradle may be prepared for the pipe. In rock -the trench is excavated to about 6 inches below grade and refilled with -well-tamped earth so as to form a cradle giving bearing to 60 to 90 -degrees of the pipe circumference. For large sewers to be constructed in -the trench special foundations are sometimes built. - - -=180. Laying Pipe.=—Before the pipe is lowered into the trench the -sections which are to be adjacent should be fitted together on the -surface and the relative positions marked by chalk so that the same -position can be obtained in the trench. - -Small pipes are lowered into the trench and swung into position on a -hook as shown in Fig. 124. Pipes up to 15 or 18 inches in diameter can -be handled by the pipe layer and helper in the trench without -assistance. Heavier pipes may be lowered into the trench by passing -ropes around each end of the pipe. One end of the rope is fastened at -the surface and the ropes are paid out by the men at the surface as the -pipe is lowered. If the pipes have been fitted together and marked at -the surface it is undesirable to use this method of lowering as the -position in which the pipes arrive in the bottom of the trench can not -be easily predicted. A cradle may be used for shoving the pipe into -position as is shown in Fig. 125. - -[Illustration: - - FIG. 124.—Hook for Lowering and Placing Sewer Pipe. -] - -[Illustration: - - FIG. 125.—Cradle for Placing Sewer Pipe. -] - -Pipes above 24 to 27 inches in diameter are too large to be handled from -the side of the trench. A hook as shown in Fig. 124 is placed in the -pipe so that it will be in the proper position when lowered. It is -raised by a rope passing through a block at the peak of a stiff-legged -derrick which spans the trench, or by a crane. If a derrick is used the -rope passes to a windlass on the opposite side of the trench from the -pipe. Mechanical power may be used for raising pipes too heavy to be -raised by hand. The pipe is then lowered and swung into position while -supported from the derrick. Excessive swinging is prevented by holding -back on the guide rope as the pipe is raised and lowered. - -Pipes are usually laid with the bell end up grade as it is easier to fit -the succeeding pipe into the bell so laid and to make the joint, -particularly on steep grades. The Baltimore specifications state: - - The ends of the pipe shall abut against each other in such a - manner that there shall be no shoulder or unevenness of any kind - along the inside of the bottom half of the sewer or drain. Special - care should be taken that the pipe are well bedded on a solid - foundation.... The trenches where pipe laying is in progress shall - be kept dry, and no pipe shall be laid in water or upon a wet bed - unless especially allowed in writing by the Engineer. As the pipe - are laid throughout the work they must be thoroughly cleaned and - protected from dirt and water, no water being allowed to flow in - them in any case during the construction except such as may be - permitted in writing by the Engineer. No length of pipe shall be - laid until the preceding length has been thoroughly embedded and - secured in place, so as to prevent any movement or disturbance of - the finished joint. - - The mouth of the pipe shall be provided with a board or stopper, - carefully fitted to the pipe, to prevent all earth and any other - substances from washing in. - - -=181. Joints.=—Pipes may be laid with open joints, mortar joints, cement -joints, or poured joints. Open joints are used for storm sewers in dry -ground close to the surface. Mortar and cement joints are commonly used -on all sewers except in special cases. Cement joints are more carefully -made than mortar joints and result in a greater percentage of -water-tight joints. Poured joints are used in wet trenches where it is -necessary to exclude ground water from the sewer. - -A specification used in some cities for open joints is: - - Pipes laid with open joints are to be laid with their inverts in - the same straight line and shall be firmly bedded throughout their - length on the bottom of the trench. No cement or mortar is to be - used in the joints. Not more than ⅛ inch shall be left between the - spigot end of the pipe and the shoulder of the hub of the pipe - into which it fits. The joints shall be surrounded with cheese - cloth, burlap, broken pipe, gravel or broken stone. - -The purpose of the cheese cloth, etc., is to prevent fine earth from -sifting into the pipe until the cheese cloth or other material has -rotted away, by which time the earth has become arched over the opening. - -Mortar joints are specified by Metcalf and Eddy as follows: - - Before a pipe is laid the lower part of the bell of the preceding - pipe shall be plastered on the inside with stiff mortar of equal - parts of Portland cement and sand, of sufficient thickness to - bring the inner bottoms of the abutting pipe flush and even. After - the pipe is laid the remainder of the bell shall be thoroughly - filled with similar mortar and the joint wiped inside and finished - to a smooth bevel outside. - -In some work a wood block or a stone is embedded in the mortar at the -bottom of the joint to bring the spigot in place concentric with the -next pipe. - -Cement joints are specified in the Baltimore specifications as follows: - - Cement joints shall be made with a narrow gasket of hemp or jute - and cement mortar, and special care shall be taken to secure tight - joints. The gasket shall be soaked in Portland cement grout and - then carefully inserted between the bell and the spigot, and well - calked with suitable hardwood or iron calking tools. It shall be - in one continuous piece for each joint, and of such thickness as - to bring the inverts of the two pipes smooth and even. The - remainder of the joint shall be filled with cement mortar all - around, on the bottom, top and sides, applied by hand with rubber - mittens, well pressed into the annular space and beveled off from - the outer edge of the bell to a distance of two inches therefrom, - or to an angle of 45 degrees. The inside of each joint shall be - thoroughly cleansed of all surplus mortar that may squeeze out in - making the joint; and to accomplish this some suitable scraper or - follower, or form shall be provided and always used immediately - after each joint is finished. - -Cement joints so made, form the most satisfactory joint for ordinary -conditions and are the most frequently used. They are not always -water-tight and can be penetrated by roots. Some roots are able to -penetrate holes of almost microscopic size and to form growths in the -sewer or to split the joints. - -Poured joints are made by pouring some jointing compound, while in a -fluid state, into the joint in which it hardens, thus sealing the joint. -Water-tightness in sewer lines to exclude ground water has also been -attempted by using the ordinary cement joint and surrounding the pipe -with a layer of cement or concrete. This has not always been successful -as it is difficult to obtain the proper class of workmanship in wet -sewer trenches. - -The requisite qualities of a poured jointing material are: - - (1) It should make a joint proof against the entrance of water and - roots. - - (2) It should be inexpensive. - - (3) It should have a long life. - - (4) It should not deteriorate in sewage which may be either acid - or alkaline. - - (5) It should adhere to the surface of the pipe. - - (6) It should run at a temperature below about 400° F., as too - high temperatures will crack the pipe. - - (7) It should neither melt nor soften at temperatures below 250° - F. in order to maintain the joint if hot liquids are poured into - the sewer. - - (8) It should be elastic enough to permit slight movements of the - pipes. - - (9) It should not require great skill in using as it must be - handled ordinarily by unskilled workers. - -The materials used for poured joints are: cement grout; sulphur and -sand; and asphalt or some bituminous compound made of vulcanized linseed -oil, clay, and other substances the resulting mixture having the -appearance of vulcanized rubber or coal tar. The bituminous materials -most nearly approach the ideal conditions. - -Cement grout is made up of pure cement and water mixed into a soupy -consistency. Its main advantages are its cheapness and ease in handling -in wet trenches or difficult situations. The result is no better than a -well made cement joint. There is no elasticity to the joint and a -movement of the pipe will break it. - -Sulphur and sand are inexpensive, comparatively easy to handle, and make -an absolutely water-tight and rigid joint which is stronger than the -pipe itself. It frequently results in the cracking of the pipe and is -objected to by some engineers on that account. In making the mixture, -powdered sulphur and very fine sand are mixed in equal proportions. It -is essential that the sand be fine so that it will mix well with the -sulphur and not precipitate out when the sulphur is melted. Ninety per -cent of the sand should pass a No. 100 sieve and 50 per cent should pass -a No. 200 sieve. The mixture melts at about 260° F. and does not soften -at lower temperatures. For making a joint in an 8 inch pipe about 1½ -pounds of sulphur, 1½ pounds of sand, ½ pound of jute, and 0.4 pound of -pitch are used. The pitch is used to paint the surface of the joint -while still hot in order to close up any possible cracks. - -Among the better known of the bituminous joint compounds are: “G.K.” -Compound made by the Atlas Company, Mertztown, Pa., Jointite and -Filtite, manufactured by the Pacific Flush Tank Co., Chicago and New -York, and some of the products of the Warren Brothers Co., Boston. These -compounds fill nearly all of the ideal conditions except as to cost and -ease in handling. They are somewhat expensive and if overheated or -heated too long become carbonized and brittle. In cold weather they do -not stick to the pipe well unless the pipe is heated before the joint is -poured. On some work joints have been poured under water with these -compounds, but success is doubtful without skillful handling. An -overheated compound will make steam in the joint causing explosions -which will blow the joint clean, and an underheated compound will harden -before the joint is completed. - -The materials should be heated in an iron kettle over a gasoline furnace -or other controllable fire, until they just commence to bubble and are -of the consistency of a thin sirup. Only a sufficient quantity of -material for immediate use should be prepared and it should be used -within 10 to 15 minutes after it has become properly heated. The ladle -used should be large enough to pour the entire joint without refilling. -There are other important points to be considered in pouring joints -which can be learned best by experience. - -The quantity of material necessary for making these joints, as announced -by the manufacturers, is shown in Table 65. - - TABLE 65 - - QUANTITY OF COMPOUND NEEDED FOR POURED JOINTS - - ───────────┬─────────────────────────────────────────────────────────── - Diameter of│ - Pipe, in │ Quantity of Material in Pounds per Joint - Inches │ - ───────────┼─────────────────────────────┬───────────────────────────── - │ Standard Socket │ Deep and Wide Socket - ───────────┼─────────┬─────────┬─────────┼─────────┬─────────┬───────── - │Jointite │ Filtite │ G. K. │Jointite │ Filtite │ G. K. - ───────────┼─────────┼─────────┼─────────┼─────────┼─────────┼───────── - 6│ 0.82│ 0.72│ 0.42│ 1.46│ 1.28│ 0.72 - 8│ 1.06│ 0.95│ 0.73│ 1.82│ 1.60│ 1.25 - 10│ 1.30│ 1.15│ 0.89│ 2.26│ 1.98│ 1.52 - 12│ 2.08│ 1.82│ 1.42│ 2.65│ 2.32│ 1.80 - 15│ 2.52│ 2.20│ 1.74│ 3.20│ 2.80│ 2.20 - 18│ 3.02│ 2.64│ 2.58│ 3.75│ 3.29│ 3.25 - 20│ 3.44│ 3.00│ 2.86│ 4.30│ 3.78│ 3 60 - 22│ 3.62│ 3.16│ 3.13│ 4.62│ 4.07│ 3.97 - 24│ 4.03│ 3.50│ 3.41│ 4.91│ 4.31│ 4.27 - ───────────┴─────────┴─────────┴─────────┴─────────┴─────────┴───────── - -In making a poured joint the pipes are first lined up in position. A -hemp or oakum gasket is forced into the joint to fill a space of about ¾ -of an inch. An asbestos or other non-combustible gasket such as a rubber -hose smeared with clay is forced about ½ inch into the opening between -the bell and the spigot and the compound is poured down one side of the -pipe through a hole broken in the bell, until it appears on the other -side, and the hole is filled. Occasionally the non-combustible gasket is -wrapped tightly around the spigot of the pipe and pressed or tied firmly -to the bell. In pouring cement grout joints a paper gasket is used which -is held to the bell and spigot by draw strings. Greater speed in -construction and economy in the use of materials are obtained by joining -two or three lengths of pipe on the bank and lowering them into the -trench as a unit. The pipes are set in a vertical position on the bank -with the bell end up, one length resting in the other. The joint is -calked with hemp and poured without the use of the gasket. The joint -should always be poured immediately after being calked so that the hemp -can not become water soaked. The asbestos gasket should be removed as -soon as possible after the joint is poured in order to prevent sticking -with resultant danger of breaking of the joint when attempting to pull -the gasket free. - -One man can pour about 33 eight-inch joints, and two men can complete -about 26 twelve-inch joints per hour on the bank where conditions are -more or less fixed. - - -=182. Labor and Progress.=—The labor required for the laying of pipe -sewers, exclusive of excavation, bracing and backfilling, consists of -pipe layers and helpers. For pipes 24 to 27 inches in diameter or -smaller one pipe layer and one or more helpers are necessary, dependent -on the size of the pipe and the depth of the trench. For larger pipes -two pipe layers can work economically each working on one-half of the -pipe and making half of the joint. The speed of pipe laying is -ordinarily limited by the speed of the excavation, but on a job in -Topeka, Kan.,[100] where the average day’s progress with a machine -excavator was 200 to 500 feet of trench per day, the pace was limited by -the speed of the pipe laying gang. This gang consisted of two pipe -layers in the trench and two helpers on the surface. The sizes of pipes -handled were from 8 to 27 inches. - - - BRICK AND BLOCK SEWERS - - -=183. The Invert.=—In good firm ground the excavation is cut to the -shape of the sewer and the bricks are laid directly on the ground, being -embedded in a thick layer of mortar. After the foundation has been -prepared and before the bricks are laid, two wooden templates, called -profiles, are prepared, similar to that shown in Fig. 126, to conform to -the shape of the inside and outside of the sewer. Each course of bricks -is represented by a row of nails in the profile and each nail -corresponds to a joint in the row. The two profiles are set true to line -and grade. A cord is stretched tightly between the two lowest nails on -opposite templates and a row of bricks is laid. The bricks are laid -radially and on edge with their long dimension parallel to the axis of -the sewer and with one edge just touching the string. As each one or two -or three rows are completed the guide line is moved up to the next -nails. When the bricks are laid on the ground all but large depressions -are filled in with tamped sand or mortar by the masons. Approximately -the same number of rows of bricks is kept completed on either side of -the center line. The succeeding courses follow within three to five rows -of each other, the only bond between courses being the mortar joint. -This is called row lock bond and with few exceptions has been used on -all brick sewers in the United States. As the sides of the sewer become -higher during the construction, platforms must be built for the masons. -These platforms are built of wood and rest directly on the green -brickwork. They should be designed to spread the load as much as -possible. The brickwork of the invert is continued up in this way to the -springing line. As soon as one section is completed one profile is moved -10 to 20 feet ahead along the trench according to the standard length of -sections, and set in position. The line is then strung from it to nails -driven or pushed into the cement joints of the last completed section. -Between work done on separate days the bricks are racked back in courses -to provide a satisfactory bond. - -[Illustration: - - FIG. 126.—Profile for Brick Sewers. -] - -In ground too soft to support the brickwork directly a cradle is -prepared by placing profiles in position in the sewer and nailing 2–inch -planks to these profiles, first firmly tamping earth under the planks. -The bricks are laid in this cradle in a manner similar to that explained -for sewers with a firm foundation. In still softer ground it may be -necessary to construct a concrete cradle to support the bricks. - - -=184. The Arch.=—The arch centering consists of a wooden form made up of -wooden ribs as shown in Fig. 127. The center conforms to the shape of -the inside of the arch with allowance for the thickness of the lagging. -The lagging is nailed on the ribs in straight strips parallel to the -axis of the sewer. The center is supported on triangular struts resting -against the sides and on the bottom of the sewer and is lifted into -position by wedges driven between it and the support. The centers may be -placed immediately after the completion of the invert, or a day or two -may be allowed to pass to give the invert an opportunity to set. After -the centers are fixed in place the arch brick are carried up evenly on -each side and are pounded firmly into place. The center is usually, but -not always “struck” immediately, and the arch brick are cleaned and -pointed up from the inside. The outside is covered with a layer of ¼ to -¾ of an inch of cement mortar and may be backfilled to the top of the -arch in order to maintain the moisture of the mortar during setting and -to press the bricks of the arch together firmly. The centers are -sometimes made collapsible so that they can be carried or rolled through -the finished brickwork to the advanced position. In “striking” the -centers the wedges are removed and the wings folded in. - -[Illustration: - - FIG. 127.—Centering for Brick Sewer. -] - -In tunneling, the invert of the sewer is constructed in the same fashion -as for open cut work. The arch centering is made in short sections and -the bricks are put in position by reaching in over the end of the -centering. All of the timbering of the tunnel is removed except the -poling boards or lagging against which the bricks or mortar are tightly -pressed, the boards being bricked in permanently. - - -=185. Block Sewers.=—Sewers made of unit blocks of concrete or vitrified -clay are constructed in a similar manner to brick sewers. Fig. 128 shows -the construction of a block sewer at Clinton, Iowa. In this sewer there -are two rings; an inside one of solid blocks and an outside one of -hollow blocks. Block sewers do not demand the skill in construction that -is demanded by brick sewers, as the blocks are so cast that the joints -are radial, whereas only experienced masons can lay bricks radially. - -[Illustration: - - FIG. 128.—Segmental Block Sewer at Clinton, Iowa. -] - - -=186. Organization.=—The number of men employed on a brick or block -sewer is proportioned according to the size of the sewer and the working -conditions. The number of men working on different tasks usually bears -the same ratio to the number of masons employed, regardless of the size -of the work. These proportions are shown for different jobs, in Table -66. - - TABLE 66 - - ORGANIZATIONS FOR THE CONSTRUCTION OF BRICK AND BLOCK SEWERS - - ─────────────┬──────────────┬────────┬────────┬────────┬────────┬────────── - │ │ │ │ │ 84– to │ - │General Ratio │15–foot,│66–inch │84–inch │108–inch│ 42–inch - Type of Work │ on Basis of │ 5–ring │Circular│Circular│ Sewer │Lock-Joint - │ Four Brick │ Brick, │ Brick, │ Brick, │Brick in│Tile Block - │ Layers │Chicago │ Gary │ Gary │Detroit │ - │ │ │ │ │ Tunnel │ - ─────────────┼──────────────┼────────┼────────┼────────┼────────┼────────── - Foreman │ 1│ 1│ 1│ 1│ 1│ 1 - Brick layers │ 4│ 12│ 6│ 6│ 5│ 2 - Helpers │ 2│ 11│ 3│ 3│ │ 1 - Scaffold men │ 2│ 21│ 3│ │ │ - Brick tossers│ 2│ 7│ │ 15│ │ 2 - Brick │ 2│ 2│ │ │ │ 2 - carriers │ │ │ │ │ │ - Cement mixers│ 2│ 6│ 6│ 5│ │ 1 - Cement │ 2│ 10│ │ 8│ │ - carriers │ │ │ │ │ │ - Form setters │ 1│ │ 3│ 3│ │ - Laborers │ 1│ 8│ 19│ 3│ 14│ 7 - │ Municipal │ - Source of │ Engineering, │ H. P. Gillette, Handbook of Cost Data - Information│ Vol. 54, p. │ - │ 228 │ - ─────────────┴──────────────┴────────────────────────────────────────────── - - -=187. Rate of Progress.=—In a general way it can be assumed that the -laying of 1,000 bricks will require 3⅓ hours of the time of one mason, -10 man-hours for helpers and laborers, 2 barrels of cement, 0.6 cubic -yard of sand, and about 10 feet board measure of centering. One thousand -bricks will make about 2 cubic yards of brickwork. To the costs, as -estimated on the basis of materials and labor, must be added about 15 -per cent for overhead and an additional amount for the contractor’s -profit. The number of bricks required in various size sewers is shown in -Table 67. A mason can lay more bricks per hour in a large sewer than in -a small one as there is a smaller percentage of face work, there is more -room to work, and it is easier to lay the bricks radially. The number of -bricks laid and the rate of progress on various jobs are shown in Table -68. - - TABLE 67 - - BRICK MASONRY IN CIRCULAR SEWERS. CUBIC YARDS PER LINEAR FOOT - - (From H. P. Gillette) - ─────────────────┬─────────────────┬─────────────────┬───────────────── - Diameter, │ One Ring │ Two Ring │ Three ring - Feet and Inches │ (4½ Inches) │ (9 Inches) │ (13½ Inches) - ─────────────────┼─────────────────┼─────────────────┼───────────────── - 2 0│ 0.103│ 0.240│ - 2 6│ 0.125│ 0.280│ - 3 0│ 0.147│ 0.327│ - 3 6│ 0.169│ 0.371│ - 4 0│ 0.191│ 0.415│ - 4 6│ 0.213│ 0.458│ - 5 0│ 0.234│ 0.501│ 0.802 - 5 6│ 0.256│ 0.545│ 0.867 - 6 0│ 0.278│ 0.589│ 0.933 - 6 6│ │ 0.633│ 1.000 - 7 0│ │ 0.677│ 1.063 - 7 6│ │ 0.720│ 1.128 - 8 0│ │ 0.763│ 1.193 - 8 6│ │ 0.807│ 1.260 - 9 0│ │ 0.851│ 1.325 - 9 6│ │ 0.895│ 1.390 - 10 0│ │ 0.938│ 1.456 - ─────────────────┴─────────────────┴─────────────────┴───────────────── - - - CONCRETE SEWERS - - -=188. Construction in Open Cut.=—In the construction of sewer pipe of -cement and concrete one of two methods may be employed; 1st, to -manufacture the pipe in a plant at some distance from the place of final -use, or 2nd, to manufacture the pipe in place. The methods of the -manufacture of cement and concrete pipe which are to be transported to -the place of use are treated in Chapter VIII. The process of -constructing the pipes in place is ordinarily used for pipes 48 inches -or more in diameter. For smaller sizes, brick, vitrified clay, and -precast cement pipes are usually more economical. - -The preparation of the foundation of a concrete sewer is similar to that -for a brick sewer. If the ground is suitable the trench is shaped to the -outside form of the sewer and the concrete poured directly on it. In -soft material which would give poor support to a sewer with a rounded -exterior, the bottom of the trench is cut horizontal and a concrete -cradle of poorer quality than that in the finished sewer is poured on -the soft ground, on a board platform, on piles, or on cribbing supported -on piles. - -If the invert of the sewer is so flat that the concrete will stand -without an inside form the shape of the invert is obtained by a screed -or straight-edge which is passed over the surface of the concrete and -guided on two centers, or on one center and the face of the finished -work. The construction of a flat invert sewer at Baltimore is shown in -Fig. 1. The center for the concrete is shown in the foreground. When the -concrete for the next section is poured it will be smoothed to shape by -a screed or straight-edge resting on the face of the finished concrete -and the center. The center is shaped to conform to that of the finished -concrete. It is firmly staked in position and acts as a bulkhead for the -concrete as it is poured, as well as a guide for the screed. - - TABLE 68 - - RATE OF PROGRESS ON BRICK SEWER CONSTRUCTION - - (Based on 8–hour day) - ────────┬────────┬──────┬──────┬──────┬──────── - │ │ │ │Bricks│ - Diameter│ │Number│Number│ per │ Number - of Sewer│ Shape │Rings,│Masons│Mason │Laborers - │ │Brick │ │ per │ - │ │ │ │ Day │ - ────────┼────────┼──────┼──────┼──────┼──────── - 7′ 0″│Circular│ │ │ │ - 8′ 11″│ and │ 2½ │ 6│ 4710│ 39 - │ Oval │ │ │ │ - │ │ │ │ │ - │ │ │ │ │ - 4′ 0″│Circular│ 2 │ 3│ 2500│ - │ │ │ │ │ - │ │3 arch│ │ │ - 6′ 8″│Circular│ 1 │ 18│ │ 62 - │ │invert│ │ │ - │ │ │ │ │ - │ │1 arch│ │ │ - 2′ 9″│Egg │ 2 │ 2│ │ 3 - │ │invert│ │ │ - │ │ │ │ │ - 5′ 6″│Circular│ 2 │ 6│ 4570│ 35 - 6′ 6″│Circular│ │ 4│ 4800│ - │ │ │ │ │ - │ │ │ │ │ - 2′ 9″│Circular│ 2 │ 2│ 2080│ 5 - │ │ │ │ │ - 16′ 0″│Circular│ 5 │ 8│ 5 cu.│ - │ │ │ │ yd.│ - 16′ 0″│Circular│ 5 │ 12│ │ 70–75 - 3′ 6″│Egg │ │ │ 2300│ - 9′ 6″│Circular│ │ │ 3000│ - │ │ │ │ │ - │ │ │ │ │ - 3′ 6″│Circular│blocks│ 2│ │ 13 - │ │ │ │ │ - │ │ │ │ │ - ────────┴────────┴──────┴──────┴──────┴──────── - - ────────┬────────┬────────────┬─────────┬─────────── - │ │ │ │ - Diameter│ Feet │ │ │ - of Sewer│Progress│ Location │Authority│ Remarks - │per Day │ │ │ - │ │ │ │ - ────────┼────────┼────────────┼─────────┼─────────── - 7′ 0″│ │ │ │ - 8′ 11″│ 60│Gary │Gillette │9–hour day - │ │ │ │ - │ │ │ │ - │ │ │Metcalf │General - 4′ 0″│ 36│ │ and │ average - │ │ │ Eddy │ - │ │ │ │Concrete - 6′ 8″│ │Denver │Gillette │ invert - │ │ │ │ - │ │ │Eng. │ - │ │Springfield,│ Con., │ - 2′ 9″│ │ Mass. │ Jan. │ - │ │ │ 16, │ - │ │ │ 1907 │ - 5′ 6″│ 110│Gary │Gillette │ - 6′ 6″│ │ │Gillette │Exceptional - │ │ │ │ speed - │ │ │ │Tunnel - 2′ 9″│ 13.9│Syracuse │Gillette │ 12–hour - │ │ │ │ day - 16′ 0″│ 22│Chicago │Gillette │First year - │ │ │ │ - 16′ 0″│ 35│Chicago │Gillette │Second year - 3′ 6″│ │St. Louis │Gillette │ - 9′ 6″│ 12.5│Chicago │H. R. │ - │ │ │ Abbott │ - │ │ │ │Lock joint - 3′ 6″│ 30│ │ │ and tile. - │ │ │ │ 10–hour - │ │ │ │ day - ────────┴────────┴────────────┴─────────┴─────────── - -If inside forms are to be used they are made as units in lengths of 12 -or 16 feet for wooden forms, and 5 feet for steel forms. The inside form -is supported by precast concrete blocks placed under it and which are -concreted into the sewer. It is held in position by cleats nailed to the -outside form, to the sheeting, or wedged against the outside of the -trench. In some cases, particularly where steel forms are used, the -inside form is hung by chains from braces across the trench as is shown -in Fig. 129. The form is easily brought to proper grade by adjustment of -the turnbuckles and is then wedged into position to prevent movement -either sideways or upwards during the pouring of the concrete. It may be -necessary to weight the forms down to prevent flotation. Cross bracing -in the trench which interferes with the placing of the form is removed -and the braces are placed against the form until the concrete is poured. -They are removed immediately in advance of the rising concrete. - -[Illustration: - - FIG. 129.—Blaw Standard Half Round Sewer Form, Suspended from Overhead - Support. - - Courtesy, Blaw Steel Form Co. -] - -The sewer section may be built as a monolith, in two parts, or in three -parts. In casting the sewer as a monolith the complete full round inside -form is fixed in place by concrete blocks and wires. The full round -outside form is completed as far as possible without interfering too -much with the placing and tamping of the concrete. The concrete is -poured from the top, being kept at the same height on each side of the -form, and tamped while being poured. The remaining panels of the outside -form are placed in position as the concrete rises to them. An opening is -left at the top of the outside arch forms which is of such a width that -the concrete will stand without support. The casting of sewers as a -monolith is difficult and is usually undesirable because of the -uncertainty of the quality of the work. It has the advantage, however, -of eliminating longitudinal working joints in the sewers which may allow -the entrance of water or act as a line of weakness. - -[Illustration: - - FIG. 130.—Construction Joints for Concrete Sewers. -] - -If the sewer is to be cast in two sections the invert is poured to the -springing line or higher. A triangular or rectangular timber is set in -the top of the wet concrete as shown in Fig. 130. When the concrete has -set the timber is removed and the groove thus left forms a working joint -with the arch. After the invert concrete has set, the arch centering is -placed and the arch is completed. This is the most common method for the -construction of medium-sized circular sewers. - -Large sewers with relatively flat bottoms are poured in two or three -sections. First the invert is poured without forms and is shaped with a -screed. About 6 inches of vertical wall is poured at the same time. This -acts as a support for the side-wall forms. The side walls reach to the -springing line of the arch and are poured after the invert has set. At -the third pouring the arch is completed. The sewer shown in Fig. 1 is -being poured in two steps, as the side walls are so low that they are -poured at the same time as the invert. A transverse working joint -similar to one of the types used in Fig. 130 is set between each day’s -work. - -The length of the form used and the capacity of the plant should be -adjusted so that one complete unit of invert, side wall, or arch can be -poured in one operation. The forms are left in place until the concrete -has set. Invert and side-wall forms are generally left in position for -at least two days, and in cold weather longer. The arch forms are left -in place for double this time. For example if 20 feet of invert and arch -can be poured in a day, 60 feet of invert form and 100 feet of arch form -will be required. As the forms are released they must be moved forward -through those in place. For this reason collapsible or demountable forms -are necessary and steel forms are advantageous. Wooden arch forms are -sometimes dismantled and carried forward in sections, but are preferably -designed to collapse as shown in Fig. 131, so that they can be pulled -through on rollers or a carriage. - - -=189. Construction in Tunnels.=—In tunnels the invert and side walls are -constructed in the same manner as for open cut work. The tunneling, -which acts as the outside form, is concreted permanently in place. The -concreting of a tunnel by hand is shown in Fig. 132. If the work is to -be done by hand the concrete is thrown in between the ribs of the arch -centering and behind the plates or lagging, which are set in advance of -the rising concrete. The lagging plates are 5 feet long which makes it -possible to throw the concrete in place at the arch, and to tamp it in -place from the end. A bulkhead and a well-greased joint timber are -placed in position as the concrete rises. - -[Illustration: - - FIG. 131.—Section through a Collapsible Wood Form. -] - -Pneumatic transmission of concrete is also used for filling the arch -forms as well as the side walls and invert forms. In using this method -the mixer may be placed at the surface or at the bottom of the shaft or -other convenient permanent location which may be some distance from the -form. The mixture is discharged into a pipe line through which it is -blown by air to the forms. The starting pressure of about 80 pounds per -square inch can be reduced after flow has commenced. In constructing the -St. Louis Water Works tunnel the compressor equipment for moving the -concrete had a capacity of 1,600 cubic feet per minute at a pressure of -110 pounds. The tunnel is horseshoe shaped, 8 feet in height and with -walls varying from 9 to 20 inches in thickness. The extreme travel of -the concrete was 1,100 feet in an 8 inch pipe. The amount of air -consumed at 110 pounds varied from 1.2 to 1.7 cubic feet of free air per -linear foot of pipe. By the time the batch had been discharged the -pressure had reduced to 25 to 40 pounds, depending on the length of the -pipe. It is reported that a 6–inch pipe line would probably have given -better results. - -[Illustration: - - FIG. 132.—Ogier’s Run Intercepting Storm-Water Drain, Baltimore, - Maryland. - - Placing concrete in Arch. The steel lagging of the forms is carried up - in sections as the concrete is deposited. The drain is horseshoe - shaped, and is 12 feet 3 inches high and 12 feet 3 inches wide. -] - -The end of the concrete conveying pipe is provided with a flexible joint -the simplest form of which can be made by slipping a section of pipe of -larger diameter over the end of the transmission line. The concrete is -deposited directly on the invert or into the side-wall forms and can be -blown into the arch forms for 20 to 25 feet. - - -=190. Materials for Forms.=—The materials used in forms for concrete -sewers are: wood, wood with steel lining, and steel alone. The first -cost of wood forms is lower than that of steel but their life is -relatively short. If the forms are to be used a number of times steel is -more economical. With proper care and repairs steel forms will outlast -any other material. Because of the increasing price of lumber and -improvements in steel forms, wood forms are not frequently used. A -common type of specification under which forms are used is: - - The material of the forms shall be of sufficient thickness and the - frames holding the forms shall be of sufficient strength so that - the forms shall be unyielding during the process of filling. The - face of the form next to the concrete shall be smooth. If wooden - forms are used the planking forming the lining shall invariably be - fastened to the studding in horizontal lines, the ends of these - planks shall be neatly butted against each other, and the inner - surface of the form shall be as nearly as possible perfectly - smooth, without crevices or offsets between the ends of adjacent - planks. Where forms are used a second time, they shall be freshly - jointed so as to make a perfectly smooth finish to the concrete. - All forms shall be water-tight and shall be wetted before using. - -Any material in contact with wet concrete should be oiled or greased -beforehand in order to prevent adherence to the concrete. - - -=191. Design of Forms.=—The design of forms for reinforced concrete work -requires some knowledge of the strength of materials and the theories of -beams, columns, and arches. Forms can be constructed without such -knowledge but that they will be both economical and adequate is an -improbability. The ordinary beam and column formulas are applicable to -the design of forms. The maximum bending moment for sheeting and ribs is -taken as (_wl_^2)⁄8, where _w_ is the load per unit length, and _l_ is -the length between supports. Sanford Thompson recommends that the -deflection be calculated as (_wl_^3)⁄(128_EI_), in which _E_ is the -modulus of elasticity of the material, and _I_ is the moment of inertia -of the cross-section referred to the neutral axis. The horizontal -pressure of the concrete against the forms has been expressed -empirically by E. B. Smith,[101] as - - _P_ = _H_^{0.2}_R_^{0.3} + 120_C_ − 0.3_S_ - - in which _P_ = lateral pressure in pounds per square inch; - - _R_ = rate of filling forms in feet per hour; - - _H_ = head of fill. Ordinarily taken as ½_R_, but in cold - weather or when continuously agitated it may be as - high as ¾_R_; - - _C_ = ratio, by volume, of cement to aggregate; - - _S_ = consistency in inches of slump. - -Earlier investigators have usually concluded that the pressures were -equal to those caused by a liquid weighing 144 pounds per cubic foot, -but the tests of the United States Bureau of Public Roads, from which -the above formula was devised, show the pressures to be decidedly below -this amount under certain conditions. - -[Illustration: - - FIG. 133.—Centering for Large Forms. -] - -With these units and formulas the design of the lagging becomes a matter -of substitution in, and the solution of, the equations produced.[102] -The forces acting on the ribs are indeterminate. No more satisfactory -design can be made for the ribs than to follow successful practice, or -what is seldom done, to determine the stresses in the forms by the -application of one of the theories for the solution of arch stresses. -The sizes of the lumber used in the ribs varies from 1½ × 6 inches to 2 -× 10 inches, depending on the size of the sewer. If vertical posts are -used at the ends to support the arch forms they are computed as columns -taking the full weight of the arch. If the span is so wide that radial -supports are used as shown in Fig. 133 the load at the center is assumed -as one-fourth of the weight of the arch. - - -=192. Wooden Forms.=—Norway and Southern pine, spruce, and fir are -satisfactory for form construction. White pine is satisfactory but is -generally too expensive. The hard woods are too difficult to work. The -lumber should be only partly dried as kiln-dried lumber swells too much -when it is moistened, warping the forms out of shape or crushing the -lagging at the joints. Green lumber must be kept moist constantly to -prevent warping before use and when it is used it does not swell enough -to close the cracks. The lumber should be dressed on the face next to -the concrete and at the ends. Either beveled or matched lumber may be -used for lagging. The joint made by beveled lumber shown in Fig. 134 is -cheaper but less satisfactory than a tongued and grooved joint. - -[Illustration: - - FIG. 134.—Beveled Joint for Wood Fords. -] - -[Illustration: - - FIG. 135.—Collapsible Wooden Invert Form for Concrete Sewers. -] - -[Illustration: - - FIG. 136.—Support for Arch Centering. -] - -[Illustration: - - FIG. 137.—Wooden Forms Used in Tunnel, North Shore Sewer, Sanitary - District of Chicago. - - Journal Western Society of Engineers, Vol. 22, p. 385. -] - -Types of wooden forms are shown in Figs. 135 and 136 for use in sewers -to be built as monoliths or in two portions. Fig. 137 shows the details -of a built-up wooden form used in tunnel work for a 42½ inch egg-shaped -sewer. - - -=193. Steel-lined Wooden Forms.=—Sheet metal linings are sometimes used -on wooden forms. They permit the use of cheaper undressed lumber, demand -less care in the joining of the lagging, and when in good condition give -a smooth surface to the finished concrete. Their use has frequently been -found unsatisfactory and more expensive than well-constructed wooden -forms because of the difficulty of preventing warping and crinkling of -the metal lining and in keeping the ends fastened down so that they will -not curl. Sheet steel or iron of No. 18 or 20 gage (0.05 to 0.0375 of an -inch) weighing 2 to 1½ pounds per square foot is ordinarily used for the -lining. - -[Illustration: - - FIG. 138.—Blaw Standard Full Round Telescopic Sewer Forms, Showing - Knocked-Down Sections Loaded on a Truck. - - Courtesy, Blaw Steel Form Co. -] - - -=194. Steel Forms.=—These are simple, light, durable, and easy to -handle. The engineer is seldom called upon to design these forms as the -types most frequently used are manufactured by the patentees and are -furnished to the contractor at a fixed rental per foot of form, -exclusive of freight and hauling from the point of manufacture. The -forms can be made in any shape desired, the ordinary stock shapes such -as the circular forms being the least expensive. The smaller circular -forms are adjustable within about 3 inches to different diameters so -that the same form can be used for two sizes of sewers. The same form -can be used for arch and invert in circular sewers. Fig. 138 shows the -collapsible circular forms and the manner in which they are pulled -through those still in position. Fig. 129 shows a half round steel form -swung in position by chains and turnbuckles from the trench bracing, and -Fig. 139 shows the free unobstructed working space in the interior of -some large steel forms. - -[Illustration: - - FIG. 139.—Interior of Steel Forms for Calumet Sewer, Chicago. - - Sewer is 16 feet wide. Note absence of obstructions. Courtesy, - Hydraulic Steelcraft Co. -] - - -=195. Reinforcement.=—It is essential that the reinforcement be held -firmly in place during the pouring of the concrete. A section of -reinforcement misplaced during construction may serve no useful purpose -and result in the collapse of the sewer. In sewer construction a few -longitudinal bars may be laid in order that the transverse bars may be -wired to them and held in position by notches in the centering and in -fastenings to bars protruding from the finished work. This construction -is shown in Fig. 1. The network of reinforcement is held up from the -bottom of the trench by notched boards which are removed as the concrete -reaches them, or better by stones or concrete blocks which are concreted -in. Sometimes the reinforcement is laid on top of the freshly poured -portion of the concrete the surface of which is at the proper distance -from the finished face of the work. This method has the advantage of not -requiring any special support for the reinforcement, but it is -undesirable because of the resulting irregularity in the reinforcement -spacing and position. - -In the side walls the position of the reinforcement is fixed by wires or -metal strips which are fastened to the outside forms or to stakes driven -into the ground. Wires are then fastened to the reinforcement bars and -are drawn through holes in the forms and twisted tight. When the forms -are removed the wires or strips are cut leaving a short portion -protruding from the face of the wall. The reinforcing steel from the -invert should protrude into the arch or the side walls for a distance of -about 40 diameters in order to provide good bond between the sections. -The protruding ends are used as fastenings for the new reinforcement. -The arch steel may be supported above the forms by specially designed -metal supports, by small stones or concrete blocks which are concreted -into the finished work; or by notched strips of wood which are removed -as the concrete approaches them. Strips of wood are not satisfactory -because they are sometimes carelessly left in place in the concrete -resulting in a line of weakness in the structure. Metal chairs are the -most secure supports. They are fastened to the forms and the bars are -wired to the chairs. In some instances the entire reinforcement has been -formed of one or two bars which are fastened into position as a complete -ring. This results in a better bond in the reinforcement, requires less -fastening and trouble in handling, but is in the way during the pouring -of the concrete and interferes with the handling of the forms. - - -=196. Costs of Concrete Sewers.=—Under present day conditions a general -statement of the costs of an engineering structure can not be given with -accuracy. Only the items of labor, materials, and transportation that go -to make up the cost can be estimated quantitively, and the total cost -computed by multiplying the amount of each item by its proper unit cost -obtained from the market quotations. - -A summary of some of the items that go to make up the cost of a concrete -sewer and the relative amount of these items on different jobs is given -in Tables 69 and 70. - - TABLE 69 - - DIVISION OF LABOR COSTS FOR THE CONSTRUCTION OF 96–INCH CIRCULAR - CONCRETE SEWER - - ─────────────────────────────────────────╥───────────────────────────── - Classification of Labor ║ Classification of Work - ─────────────────┬───────────┬───────────╫─────────────────┬─────────── - Task or Title │ │ Total ║ Type of Work │ - │ Number of │dollars per║ │Dollars per - │ men │ day ║ │ foot - ─────────────────┼───────────┼───────────╫─────────────────┼─────────── - Superintendent │ 1│ 6.00║Excavation │ 1.80 - Engineman │ │ ║Sheeting and │ - │ 1│ 3.50║ bracing │ 0.58 - Hoister │ │ ║Bottom plank │ - (engineman) │ 1│ 2.00║ │ 0.17 - Tag-men │ 2│ 3.30║Pulling sheeting │ 0.45 - Earth diggers │ 10│ 16.50║Backfilling │ 0.33 - On dump cars │ │ ║Making and │ - │ 2│ 3.30║ placing invert │ 1.17 - Carpenter on │ │ ║Making and │ - bracing │ 2│ 3.00║ placing arch │ 1.54 - Carpenters’ │ │ ║Laying brick in │ - helpers │ 2│ 3.30║ invert │ 0.29 - Laying bottom │ 2│ 3.30║ │ - Moving pumps, │ │ ║Bending and │ - etc. │ │ ║ placing steel │ - │ 2│ 3.30║ in arch │ 0.20 - Pulling sheeting │ 3│ 5.25║ │ - Mixing and │ │ ║Bending and │ - placing │ │ ║ placing steel │ - concrete │ 16│ 26.40║ in invert │ 0.09 - On steel forms │ │ ║Moving forms and │ - │ 3│ 5.25║ centers │ 0.62 - Water boy │ │ ║Watchmen, water │ - │ 1│ 1.00║ boy, etc. │ 0.62 - Coal and oil │ │ 5.00║ │ - │ │ —————║ │ ————— - Total │ │ 90.40║ Total │ 7.86 - ─────────────────┴───────────┴───────────╨─────────────────┴─────────── - NOTES.—Trench was 12½ feet wide and of various depths. At depth of 12 - feet the cost of excavation was $1.61 per foot. From Engineering and - Contracting, Vol. 47, p. 157. - - - BACKFILLING - - -=197. Methods.=—Careful backfilling is necessary to prevent the -displacement of the newly laid pipe and to avoid subsequent settlement -at the surface resulting in uneven street surfaces and dangers to -foundations and other structures. - -The backfilling should commence as soon as the cement in the joints or -in the sewer has obtained its initial set. Clay, sand, rock dust, or -other fine compactible material is then packed by hand under and around -the pipe and rammed with a shovel and light tamper. This method of -filling is continued up to the top of the pipe. The backfill should rise -evenly on both sides of the pipe and tamping should be continuous during -the placing of the backfill. For the next 2 feet of depth the backfill -should be placed with a shovel so as not to disturb the pipe, and should -be tamped while being placed, but no tamping should be done within 6 -inches of the crown of the sewer. The tamping should become -progressively heavier as the depth of the backfill increases. Generally -one man tamping is provided for each man shoveling. - - TABLE 70 - - DIVISION OF COSTS FOR THE CONSTRUCTION OF CONCRETE SEWERS - - Gillette’s Handbook of Cost Data. - ──────────────┬──────────────────────────────────────────────────────── - Item │ Location - ──────────────┼─────────┬────────┬──────────┬────────────────────────── - │ Fond du │ South │ │ - │ Lac │ Bend │Wilmington│ Richmond, Indiana - ──────────────┼─────────┼────────┼──────────┼────────┬────────┬──────── - Diameter in │ │ │ │ │ │ - inches │ 30 │ 66 │ 53 │ 54 │ 48 │ 42 - Shape │circular │circular│horseshoe │circular│circular│circular - Plain or │ │ │ │ │ │ - reinforced │ plain │ rein. │ rein. │ rein. │ rein. │ rein. - Cubic yards │ │ │ │ │ │ - per foot │ 0.11 │ 0.594 │ 0.37 │5″ shell│5″ shell│4″ shell - Daily │ │ │ │ │ │ - progress, │ │ │ │ │ │ - feet │ 47 │24 to 36│ │ │ │ - Cost per foot,│ │ │ │ │ │ - dollars │ 1.20 │ 4.40 │ 2.97 │ 1.35 │ 1.08 │ 0.91 - Per cent of │ │ │ │ - total cost: │ │ │ │ - Labor │39.0[103]│ 33.5 │ 33.0 │ =17.1= - Tools │ 1.5 │ 11.5 │ │ - Sand and │ │ │ │ - gravel │ 12.4 │ 15.5 │ 18.9 │ =19.3= - Lumber │ 0.9 │ │ │ - Water │ 0.7 │ 11.5 │ │ - Reinforcing │ 0.0 │ │ 14.5 │ =22.3= - Cement │ 23.0 │ 20.0 │ 27.5 │ =32.0[104]= - Frost │ │ │ │ - prevention│ 2.0 │ │ │ - Forms │ 12.5 │ 8.0 │ 6.1 │ =9.3= - Engineering │ 8.0 │ │ │ - Length of day,│ │ │ │ - hours │ 8 │ 10 │ │ - Year of │ │ │ - construction│ 1908 │ 1906 │ Pre-war conditions - ──────────────┴─────────┴────────┴───────────────────────────────────── - -Above a point 2 feet above the top of the sewer the method pursued and -the care observed in backfilling will depend on the character of the -backfilling material and the location of the sewer. If the sewer is in a -paved street the backfill is spread in layers 6 inches thick and tamped -with rammers weighing about 40 pounds with a surface of about 30 square -inches. One man tamping for each man shoveling is frequently specified. -If no pavement is to be laid but it is required that the finished -surface shall be smooth, slightly less care need be taken and only one -man tamping is specified for each two men shoveling. On paved streets a -reinforced concrete slab with a bearing of at least 12 inches on the -undisturbed sides of the trench may be designed to support the pavement -and its loads. This is of great help in preventing the unsightly -appearance and roughness due to an improperly backfilled trench. On -unpaved streets the backfill is crowned over the trench to a depth of -about 6 inches and then rolled smooth by a road roller. In open fields, -in side ditches, or in locations where obstruction to traffic or -unsightliness need not be considered, after the first 2 feet of backfill -have been placed with proper care, the remainder is scraped or thrown -into the trench by hand or machine, care being taken not to drop the -material so far as to disturb the sewer. - -If the top of the sewer, manhole, or other structure comes close to or -above the surface of the ground, an earth embankment should be built at -least 3 feet thick over and around the structure. The embankment should -have side slopes of at least 1½ on 1 and should be tamped to a smooth -and even finish. - -If sheeting is to be withdrawn from the trench it should be withdrawn -immediately ahead of the backfilling, and in trenches subject to caving -it may be pulled as the backfilling rises. - -Puddling is a process of backfilling in which the trench is filled with -water before the filling material is thrown in. It avoids the necessity -for tamping and can be used satisfactorily with materials that will -drain well and will not shrink on drying. Sand and gravel are suitable -materials for puddling, heavy clay is unsatisfactory. Puddling should -not be resorted to before the first 2 feet of backfill has been -carefully placed. More compact work can be obtained by tamping than with -puddling. - -Frozen earth, rubbish, old lumber, and similar materials should not be -used where a permanent finished surface is desired as these will -decompose or soften resulting in settlement. Rocks may be thrown in the -backfill if not dropped too far and the earth is carefully tamped around -and over them. In rock trenches fine materials such as loam, clay, sand, -etc., must be provided for the backfilling of the first portion of the -trench for 2 feet over the top of the pipe. More clay can generally be -packed in an excavation than was taken out of it, but sand and gravel -occupy more space than originally even when carefully tamped. - -Tamping machines have not come into general use. One type of machine -sometimes used consists of a gasoline engine which raises and drops a -weighted rod. The rod can be swung back and forth across the trench -while the apparatus is being pushed along. It is claimed that two men -operating the machine can do the work of six to ten men tamping by hand. -The machine delivers 50 to 60 blows per minute, with a 2 foot drop of -the 80 to 90 pound tamping head. - -Backfilling in tunnels is usually difficult because of the small space -available in which to work. Ordinarily the timbering is left in place -and concrete is thrown in from the end of the pipe between the outside -of the pipe and the tunnel walls and roof. If vitrified pipe is used in -the tunnel, the backfilling is done with selected clayey material which -is packed into place around the pipe by workmen with long tamping tools. -The backfilling should be done with care under the supervision of a -vigilant inspector in order that subsequent settlement of the surface -may be prevented. - - - - - CHAPTER XII - MAINTENANCE OF SEWERS - - -=198. Work Involved.=—The principal effort in maintaining sewers is to -keep them clean and unobstructed. A sewerage system, although buried, -cannot be forgotten as it will not care for itself, but becoming clogged -will force itself on the attention of the community. Besides the -cleaning and repairing of sewers and the making of inspections for -determining the necessity for this work, ordinances should be prepared -and enforced for the purpose of protecting the sewers from abuse. -Inspections to determine the amount of the depreciation of sewers with a -view towards possible renewal, or to determine the capacity of a sewer -in relation to the load imposed upon it are sometimes necessary. The -valuation of the sewerage system as an item in the inventory of city -property may be assigned to the engineer in charge of sewer maintenance. - -The work involved in the inspection and cleaning of sewers in New York -City for the year ending May, 1914, included the removal of 22,687 cubic -yards of material from catch-basins, and 14,826 catch-basin cleanings. -This made an average of two and one-half cleanings per catch-basin per -year, or 1½ cubic yards removed at each cleaning. The 6,432 catch-basins -were inspected 71,890 times. There were 4,112 cubic yards of material -removed from 517 miles of sewers, or about 8 cubic yards per mile. -Inspection of 194 miles of brick sewers were made, 4.4 miles were -flushed, and 27 miles were cleaned. Inspections of 198 miles of pipe -sewers were made, 80 miles were examined more closely, 37 miles were -flushed, and 91 miles were cleaned. The field organization for this work -consisted of 17 foremen, 8 assistant foremen, 29 laborers, 71 cleaners, -13 mechanics, 7 inspectors of construction, 3 inspectors of sewer -connections, 13 horses and wagons, and 28 horses and carts.[105] - - -=199. Causes of Troubles.=—The complaints most frequently received about -sewers are caused by clogging, breakage of pipes, and bad odors. Sewers -become clogged by the deposition of sand and other detritus which -results in the formation of pools in which organic matter deposits, -aggravating the clogged condition of the sewers and causing the odors -complained of. Grease is a prolific cause of trouble. It is discharged -into the sewer in hot wastes, and becoming cooled, deposits in thick -layers which may effectively block the sewer if not removed. It can be -prevented from entering the sewers by the installation of grease traps -as described in Chapter VI. The periodic cleaning of these traps is as -important as their installation. - -Tree roots are troublesome, particularly in small pipe sewers in -residential districts. Roots of the North Carolina poplar, silver leaf -poplar, willow, elm, and other trees will enter the sewer through minute -holes and may fill the sewer barrel completely if not cut away in time. -Fungus growths occasionally cause trouble in sewers by forming a network -of tendrils that catches floating objects and builds a barricade across -the sewer. Difficulties from fungus growths are not common, but constant -attention must be given to the removal of grit, grease, and roots. Tarry -deposits from gas-manufacturing plants are occasionally a cause of -trouble, as they cement the detritus already deposited into a tough and -gummy mass that clings tenaciously to the sewer. - -Broken sewers are caused by excessive superimposed loads, undermining, -and progressive deterioration. The changing character of a district may -result in a change of street grade, an increase in the weight of -traffic, or in the construction of other structures causing loads upon -the sewer for which it was not designed. The presence of corrosive acids -or gases may cause the deterioration of the material of the sewer. - - -=200. Inspection.=—The maintenance of a sewerage system is usually -placed under the direction of a sewer department. In the organization of -the work of this department no regular routine of inspection of all -sewers need be followed ordinarily. Attention should be given regularly -to those sewers that are known to give trouble, whereas the less -troublesome sewers need not be inspected more frequently than once a -year, preferably during the winter when labor is easier to obtain. - -The routine inspection of sewers too small to enter is made by an -examination at the manhole. If the water is running as freely at one -manhole as at the next manhole above, it is assumed that the sewer -between the manholes is clean and no further inspection need be given -unless there is some other reason to suspect clogging between manholes. -If the sewage is backed up in a manhole it indicates that there is an -obstruction in the sewer below. If the sewage in a manhole is flowing -sluggishly and is covered with scum it is an indication of clogging, -slow velocity and septic action in the sewer. Sludge banks on the -sloping bottom of the manhole or signs of sewage high upon the walls -indicate an occasional flooding of the sewer due to inadequate capacity -or clogging. - -[Illustration: - - FIG. 140.—Inspecting Sewers with Reflected Sunlight. -] - -If any of the signs observed indicate that the sewer is clogged, the -manhole should be entered and the sewer more carefully inspected. Such -inspection may be made with the aid of mirrors as shown in Fig. 140 or -with a periscope device as shown in Fig. 141. Sunlight is more brilliant -than the electric lamp shown in Fig. 141, but the mirror in the manhole -directs the sunlight into the eyes of the observer, dazzling him and -preventing a good view of the sides of the sewer. The observers’ eyes -can be protected against the direct rays of the electric light, which -can be projected against the sides of the pipe by proper shades and -reflectors. It is possible with this device to locate house connection, -stoppages, breaks of the pipe, and to determine fairly accurately the -condition of the sewer without discomfort to the observers. - -Sewers that are large enough to enter should be inspected by walking -through them where possible. The inspection should be conducted by -cleaning off the sewer surface in spots with a small broom, and -examining the brick wall for loose bricks, loose cement or cement lost -from the joints, open joints, broken bond, eroded invert, and such other -items as may cause trouble. An inspection in storm sewers is sometimes -of value in detecting the presence of forbidden house connections. - -[Illustration: - - FIG. 141.—Inspecting Sewers with Periscope and Electric Light. The G-K - System. -] - -Certain precautions should be taken before entering sewers or manholes. -If a distinct odor of gasoline is evident the sewer should be ventilated -as well as possible by leaving a number of manhole covers open along the -line until the odor of gasoline has disappeared. The strength of -gasoline odor above which it is unsafe to enter a sewer is a matter of -experience possessed by few. A slight odor of gasoline is evident in -many sewers and indicates no special danger. A discussion of the amount -of gasoline necessary to create explosive conditions is given in Art. -206. In making observations of the odor it should also be noted whether -air is entering or leaving the manhole. The presence of gasoline cannot -be detected at a manhole into which air is entering. - -As soon as it is considered that the odors from a sewer indicate the -absence of an explosive mixture, a lighted lantern or other open flame -should be lowered into the manhole to test the presence of oxygen. -Carbon monoxide or other asphyxiating gases may accumulate in the sewer, -and if present will extinguish the flame. If the flame burns brilliantly -the sewer is probably safe to enter, but if conditions are unknown or -uncertain, the man entering should wear a life belt attached to a rope -and tended by a man at the surface. Asphyxiating or explosive gases are -sometimes run into without warning due to their lack of odor, or the -presence of stronger odors in the sewer. Breathing masks and electric -lamps are precautions against these dangers, the masks being ready for -use only when actually needed. More deaths have occurred in sewers due -to asphyxiating gases than by explosions, as the average sewer explosion -is of insufficient violence to do great damage, although on occasion, -extremely violent explosions have occurred. During inspections of sewers -there should always be at least one man at the surface to call help in -case of accident and the inspecting party should consist of at least two -men. - -It must not be felt that entering sewers is fraught with great danger, -as it is perfectly safe to enter the average sewer. The air is not -unpleasant and no discomfort is felt, but conditions are such that -unexpected situations may arise for which the man in the sewer should be -prepared. It is therefore wise to take certain precautions. These may -indicate to the uninitiated, a greater danger than actually exists. - -The inspection of sewers should include the inspection of the -flush-tanks, control devices, grit chambers, and other appurtenances. A -common difficulty found with flush-tanks is that the tank is “drooling,” -that is to say the water is trickling out of the siphon as fast as it is -entering the tank, and the intermittency of the discharge has ceased. -If, when the tank is first inspected the water is about at the level of -the top of the bell it is probable that the siphon is drooling. A mark -should be made at the elevation of the water surface and the tank -inspected again in the course of an hour or more. If the water level is -unchanged the siphon is drooling. This may be caused by the clogging of -the snift hole or by a rag or other obstacle hanging over the siphon -which permits water to pass before the air has been exhausted, or a -misplacement of the cap over the siphon, or other difficulty which may -be recognized when the principle on which the siphon operates is -understood. Occasionally it is discovered that an over zealous water -department has shut off the service. - -Control devices, such as leaping or overflow weirs, automatic valves, -etc., may become clogged and cease to operate satisfactorily. They -should be inspected frequently, dependent upon their importance and the -frequency with which they have been found to be inoperative. An -inspection will reveal the obstacle which should be removed. Floats -should be examined for loss of buoyancy or leaks rendering them useless. -Grit and screen chambers should be examined for sludge deposits. - -Catch-basins on storm sewers are a frequent cause of trouble and need -more or less frequent cleaning. Cleanings are more important than -inspections for catch-basins for if they are operating properly they are -usually in need of cleaning after every storm of any magnitude, and a -regular schedule of cleaning should be maintained. - -A record should be kept of all inspections made. It should include an -account of the inspection, its date, the conditions found, by whom made -and the remedies taken to effect repairs. - - -=201. Repairs.=—Common repairs to sewerage systems consist in replacing -street inlets or catch-basin covers broken by traffic; raising or -lowering catch-basin or manhole heads to compensate for the sinking of -the manhole or the wear of the pavement; replacing of broken pipes, -loosened bricks or mortar which has dropped out; and other miscellaneous -repairs as the necessity may arise. Connections from private drains are -a source of trouble because either the sewer or the drain has broken due -to careless work or the settlement of the foundation or the backfill. - - -=202. Cleaning Sewers.=—Sewers too small to enter are cleaned by -thrusting rods or by dragging through them some one of the various -instruments available. The common sewer rod shown in Fig. 142 is a -hickory stick, or light metal rod, 3 or 4 feet long, on the end of which -is a coupling which cannot come undone in the sewer. Sections of the rod -are joined in the manhole and pushed down the sewer until the -obstruction is reached and dislodged. Occasionally pieces of pipe -screwed together are used with success. The end section may be fitted -with a special cutting shoe for dislodging obstructions. In extreme -cases these rods may be pushed 400 to 500 feet, but are more effective -at shorter distances. Obstructions may be dislodged by shoving a fire -hose, which is discharging water under high pressure through a small -nozzle, down the sewer toward the obstruction. The water pressure -stiffens the hose, which, together with the support from the sides of -the conduit, make it possible to push the hose in for effective work 100 -feet or more from the manhole. A strip of flexible steel about ½ inch -thick and 1½ to 2 inches wide is useful for “rodding” a short length of -crooked sewer. - -[Illustration: - - FIG. 142.—Sewer Rods -] - -Sewers are seldom so clogged that no channel whatever remains. As a -sewer becomes more and more clogged, the passage becomes smaller, -thereby increasing the velocity of flow of the sewage around the -obstruction and maintaining a passageway by erosion. This phenomenon has -been taken advantage of in the cleaning of sewers by “pills.” These -consist of a series of light hollow balls varying in size. One of the -smaller balls is put into the sewer at a manhole. When the ball strikes -an obstruction it is caught and jammed against the roof of the sewer. -The sewage is backed up and seeks an outlet around the ball, thus -clearing a channel and washing the ball along with it. The ball is -caught at the next manhole below. A net should be placed for catching -the ball and a small dam to prevent the dislodged detritus from passing -down into the next length of pipe. The feeding of the balls into the -sewer is continued, using larger and larger sizes, until the sewer is -clean. This method is particularly useful for the removal of sludge -deposits, but it is not effective against roots and grease. The balls -should be sufficiently light to float. Hollow metal balls are better -than heavier wooden ones. - -[Illustration: - - FIG. 143.—Cable and Windlass Method of Cleaning Sewers. - - The cable is held to the bottom of the sewer by bracing a 2 x 4 - upright in the sewer, with a snatch block attached. A trailer is - attached to the scoop to prevent loss of material. -] - -Plows and other scraping instruments are dragged through pipe sewers to -loosen banks of sludge and detritus and to cut roots or dislodge -obstructions. One form of plow consists of a scoop[106] similar to a -grocer’s sugar scoop, which is pushed or dragged up a sewer against the -direction of flow. As fast as the scoop is filled it is drawn back and -emptied. The method of dragging this through a sewer is indicated in -Fig. 143. At Atlantic City the crew operating the scoop comprises five -men, two are at work in each manhole and one on the surface to warn -traffic and wait on the men in the manholes. The outfit of tools is -contained in a hand-drawn tool box and includes sewer rods, metal scoops -for all sizes of sewers, picks, shovels, hatchets, chisels, lanterns, -grease and root cutters, etc., and two winches with from 400 to 600 feet -of ⅜-inch wire cable. - -[Illustration: - - FIG. 144.—Sewer Cleaning Device. - - Eng. News, Vol. 42, 1899, p. 328. -] - -[Illustration: - - FIG. 145.—Tools for Cleaning Sewers. -] - -[Illustration: - - FIG. 146.—Turbine Sewer Machine Connected to Forcing Jack. - - The forcing jack is used when windlass and cable cannot be used. - - Courtesy, The Turbine Sewer Machine Co. -] - -Another form of plow or drag consists of a set of hooks or teeth hinged -to a central bar as shown in Fig. 144. A root cutter and grease scraper -in the form of a spiral spring with sharpened edges, and other tools for -cleaning sewers are shown in Fig. 145. A turbine sewer cleaner shown in -Fig. 146 consists of a set of cutting blades which are revolved by a -hydraulic motor of about 3 horse-power under an operating pressure of -about 60 pounds per square inch. The turbine is attached to a standard -fire hose and is pushed through the sewer by utilizing the stiffness of -the hose, or by rods attached to a pushing jack as shown in the figure. -This machine was invented and patented by W. A. Stevenson in 1914. Its -performance is excellent. The blades revolve at about 600 R.P.M., -cutting roots and grease. The revolving blades and the escaping water -also serve to loosen and stir up the deposits and the forward helical -motion imparted to the water is useful in pushing the material ahead of -the machine and in scrubbing the walls of the sewer. In Milwaukee four -men with the machine cleaned 319 feet of 12–inch sewer in 16 hours, and -in Kansas City 7,801 feet of sewers were cleaned in 14 days. - -Sewers large enough to enter may be cleaned by hand. The materials to be -removed are shoveled into buckets which are carried or floated to -manholes, raised to the surface and dumped. In very large sewers -temporary tracks have been laid and small cars pushed to the manhole for -the removal of the material. Hydraulic sand ejectors may also be used -for the removal of deposits, similar to the steam ejector pump shown in -Fig. 97. The water enters the apparatus at high velocity, under a -pressure of about 60 pounds per square inch, leaps a gap in the machine -from a nozzle to a funnel-shaped guide leading to the discharge pipe. -The suction pipe of the machine leads to the chamber in which the leap -is made. In leaping this gap the water creates a vacuum that is -sufficient to remove the uncemented detritus large enough to pass -through the machine, and will lift small stones to a height of 10 to 12 -feet. Occasionally barricades of logs, tree branches, rope, leaves, and -other obstructions which have piled up against some inward projecting -portion of the sewer, must be removed by hand either by cutting with an -axe or by pulling them out. Projections from the sides of sewers are -objectionable because of their tendency to catch obstacles and form -barricades. - -Little authentic information on the cost of cleaning sewers is -available. A permanent sewer organization is maintained by many cities. -The division of their time between repairs, cleaning, and other duties -is seldom made a matter of record. From data published in Public -Works[107] it is probable that the cost varies from $3 to $15 per cubic -yard of material removed. From the information in Vol. II of “American -Sewerage Practice” by Metcalf and Eddy the combined cost of cleaning and -flushing will vary between $10 and $40 per mile; the expense of either -flushing or cleaning alone being about one-half of this. - - -=203. Flushing Sewers.=—Sewers can sometimes be cleaned or kept clean by -flushing. Flushing may be automatic and frequent, or hand flushing may -be resorted to at intervals to remove accumulated deposits. Automatic -flush-tanks, flushing manholes, a fire hose, a connection to a water -main, a temporary fixed dam, a moving dam, and other methods are used in -flushing sewers. The design, operation, and results obtained from the -use of automatic flush-tanks and flushing manholes are discussed in -Chapter VI. - -The method in use for cleaning a sewer by thrusting a fire hose down it -can also be used for flushing sewers. It is an inexpensive and fairly -satisfactory method. There is, however, some danger of displacing the -sewer pipe because of the high velocity of the water. An easier and -safer but less effective method is to allow water to enter at the -manhole and flow down the sewer by gravity. Direct connections to the -water mains are sometimes opened for the same purpose. - -Sewers are sometimes flushed by the construction of a temporary dam -across the sewer, causing the sewage to back up. When the sewer is half -to three-quarters full the dam is suddenly removed and the accumulated -sewage allowed to rush down the sewer, thus flushing it out. The dam may -be made of sand bags, boards fitted to the sewer, or a combination of -boards and bags. The expense of equipment for flushing by this method is -less than that by any other method, but the results obtained are not -always desirable. Below the dam the results compare favorably with those -obtained by other methods, but above the dam the stoppage of the flow of -the sewage may cause depositions of greater quantities of material than -have been flushed out below. A time should be chosen for the application -of this method when the sewage is comparatively weak and free from -suspended matter. The most convenient place for the construction of a -dam is at a manhole in order that the operator may be clear of the rush -of sewage when the dam is removed. - -Movable dams or scrapers are useful in cleaning sewers of a moderate -size, but are of little value in small sewers. The scraper fits loosely -against the sides of the sewer and is pushed forward by the pressure of -the sewage accumulated behind it. The iron-shod sides of the dam serve -to scrape grease and growths attached to the sewer and to stir up sand -and sludge deposited on the bottom. The high velocity of the sewage -escaping around the sides of the dam aids in cleaning and scrubbing the -sewer. - -A natural watercourse may be diverted into the sewer if topographical -conditions permit, or where sewers discharge into the sea below high -tide a gate may be closed during the flood and held closed until the -ebb. The rush of sewage on the opening of the gate serves to flush the -sewers and stir up the sludge deposited during high tide. Other methods -of flushing sewers may be used dependent on the local conditions and the -ingenuity of the engineer or foreman in charge. - -In some sewers it is not necessary to remove the clogging material from -the sewer. It is sufficient to flush and push it along until it is -picked up and carried away by higher velocities caused by steeper grades -or larger amounts of sewage. - - -=204. Cleaning Catch-basins.=[108]—Catch-basins have no reason for -existence if they are not kept clean. Their purpose is to catch -undesirable settling solids and to prevent them from entering the -sewers, on the theory that it is cheaper to clean a catch-basin than it -is to clean a sewer. If the cleaning of storm sewers below some inlet to -which no catch-basin is attached becomes burdensome, the engineer in -charge of maintenance should install an adequate catch-basin and keep it -clean. Catch-basins are cleaned by hand, suction pumps, and grab -buckets. In cleaning by hand the accumulated water and sludge are -removed by a bucket or dipper and dumped into a wagon from which the -surplus settled water is allowed to run back into the sewer. The grit at -the bottom of the catch-basin is removed by shoveling it into buckets -which are then hoisted to the surface and emptied. - -Suction pumps in use for cleaning catch-basins are of the hydraulic -eductor type. The eductor works on the principle of the steam pump shown -in Fig. 97, except that water is used instead of steam. The material -removed may be discharged into settling basins constructed in the -street, or may be discharged directly into wagons.[109] In Chicago a -special motor-driven apparatus is used. This consists of a 5–yard body -on a 5–ton truck, and a centrifugal pump driven by the truck motor. In -use, the truck, about half filled with water, drives up to the -catch-basin, the eductor pipe is lowered and water pumped from the truck -into the eductor and back into the truck again, together with the -contents of the catch-basin. The surplus water drains back into the -sewer. The Chicago Bureau of Sewers reports a truck so equipped to have -cleaned 1013 catch-basins, removing 1763 cubic yards of material, and -running 1380 miles, during the months of August, September and October, -1917. The cost, including all items of depreciation, wages, repairs, -etc., was $1,393.89. Orange-peel buckets, about 20 inches in diameter, -operated by hand or by the motor of a 3½ to 5–ton truck with a -water-tight body, are used for cleaning catch-basins in some cities. - -Catch-basins in unpaved streets and on steep sandy slopes should be -cleaned after every storm of consequence. Basins which serve to catch -only the grit from pavement washings require cleaning about two or three -times per year, and from one to three cubic yards of material are -removed at each cleaning. The cost of cleaning ordinary catch-basins by -hand may vary from $15 to $25, but with the use of eductors or -orange-peel buckets the cost is somewhat lower. In Seattle the cost of -cleaning large detritus basins by hand is said[110] to vary from $45 to -$60. With the use of eductors this cost has been reduced to one-third or -one-fifth the cost of cleaning by hand. - - -=205. Protection of Sewers.=[111]—City ordinances should be wisely drawn -and strictly enforced for the protection of sewers against abuse and -destruction. The requirements of some city ordinances are given in the -following paragraphs. - -Washington, D. C.,[112] sewer ordinances provide that: - - No person shall make or maintain any connection with any public - sewer or appurtenance thereof whereby there may be conveyed into - the same any hot, suffocating, corrosive, inflammable or explosive - liquid, gas, vapor, substance or material of any kind ... provided - that the provisions of this act shall not apply to water from - ordinary hot water boilers or residences. - -The following extracts from the ordinances of Indianapolis are typical -of those from many cities: - - 2950. No connection shall be made with any public sewer without - the written permission of the Committee on Sewers and the Sewerage - Engineer. - - 2953. No person shall be authorized to do the work of making - connections until he has furnished a satisfactory certificate that - he is qualified for the duties. He shall also file bond for not - less than $1,000 that he will indemnify the City from all loss or - damage that may result from his work and that he will do the work - in conformity to the rules and regulations established by the City - Council. - - 2955. It shall be unlawful for any person to allow premises - connected to the sewers or drains to remain without good fixtures - so attached as to allow a sufficiency of water to be applied to - keep the same unobstructed. - - 2956. No butcher’s offal or garbage, or dead animals, or - obstructions of any kind shall be thrown in any receiving basin or - sewer in penalty not greater than $100. Any person injuring, - breaking, or removing any portion of any receiving basin, manhole - cover, etc., shall be fined not more than $100. - - 2962. No person shall drain the contents of any cesspool or privy - vault into any sewer without the permission of the Common Council. - -The Cleveland ordinances are similar and contain the following in -addition: - - 1251. Rule 4. All connections with the main or branch sewers shall - be made at the regular connections or junctions built into the - same, except by special permit. - - Rule 16. No steam pipe, nor the exhaust, nor the blow off from any - steam engine shall be connected with any sewer. - -Evanston, Illinois, protects its sewers against the additions of grease -and other undesirable substances as follows: - - 1444. It is unlawful for any person to use any sewer or - appurtenance to the sewerage system in any manner contrary to the - orders of the Commissioner of Public Works. - - 1446. Wastes from any kitchen sinks, floor drains, or other - fixtures likely to contain greasy matter from hotels, certain - apartment houses, boarding houses, restaurants, butcher shops, - packing houses, lard rendering establishments, bakeries, - laundries, cleaning establishments, garages, stables, yard and - floor drains, and drains from gravel roofs shall be made through - intervening receiving basins constructed as prescribed in par. - VIII of this code. - -Receiving basins suitable for the work required in the code are -illustrated in Chapter VI. - - -=206. Explosions in Sewers.=—Disastrous explosions in sewers were first -recorded about 1886.[113] Up to about 1905 explosions were infrequent -and were considered as unavoidable accidents and so rare as to be -unworthy of study. For a decade or more after 1905 explosions occurred -with increasing violence and frequency causing destruction of property, -but by some freakish chance, but little loss of life. A violent and -destructive explosion occurred in Pittsburgh on Nov. 25, 1913,[114] and -another on March 12, 1916. The property damage amounted to $300,000 to -$500,000 on each occasion, but there was no loss of life. Two miles of -pavement were ripped up, gas, water, and other sewer pipes were broken, -buildings collapsed and the streets were flooded. The streets were -rendered unserviceable for long periods during the expensive repairs -that were necessary. In recent years the number of explosions in sewers -has been smaller, due probably to the gain in knowledge of the causes -and intelligent methods of prevention. - -The three principal causes of explosions in sewers are: gasoline vapor, -illuminating gas, and calcium carbide. It is probable that gasoline -vapor is by far the most troublesome. Explosions caused by these gases -are not so violent as those caused by dynamite or other high explosives, -as the volume of gas and the temperature generated are much less. The -violence of sewer explosions may be increased somewhat by the sudden -pressures that are put upon them. - -Gasoline finds its way into sewers from garages and cleaning -establishments. A mixture of 1½ per cent gasoline vapor and air may be -explosive. It needs only the stray spark of an electric current, a -lighted match, or a cigar thrown into the sewer to cause the explosion. -As the result of a series of experiments on 2,706 feet of 8–foot sewer, -Burrell and Boyd conclude.[115] - - One gallon of gasoline if entirely vaporized produces about 32 - cubic feet of vapor at ordinary temperature and pressure. If 1½ - per cent be adopted as the low explosive limit of mixtures of - gasoline vapor and air, 55 gallons or a barrel of gasoline would - produce enough vapor to render explosive the mixture in 1,900 feet - of 9 foot sewer provided the gasoline and the air were perfectly - mixed. Many different factors, however, govern explosibility, such - as: size of the sewer, velocity of the sewage, temperature of the - sewer, volatility and rate of inflow of the gasoline. Only under - identical conditions of tests would duplicate results be obtained. - A large amount of gasoline poured in at one time is less dangerous - than the same amount allowed to run in slowly. With a velocity of - flow of about 6½ feet per second it was evident that 55 gallons of - gasoline poured all at once into a manhole rendered the air - explosive only a few minutes (less than 10) at any particular - point. With the same amount of gasoline run in at the rate of 5 - gallons per minute, an explosive flame would have swept along the - sewer if ignited 15 minutes after the gasoline had been dumped. - With a slow velocity of flow and a submerged outlet the gasoline - vapor being heavier than air accumulated at one point and - extremely explosive conditions could result from a small amount of - gasoline. Comparatively rich explosive mixtures were found 5 hours - after the gasoline had been discharged. High-test gasoline is much - more dangerous than the naphtha used in cleaning establishments, - yet on account of the large quantity of waste naphtha the sewage - from cleaning establishments may be very dangerous. - -Illuminating gas is not so dangerous as gasoline vapor as it is lighter -than air and it is more likely to escape from the sewer than to -accumulate in it. It requires about one part of illuminating gas to -seven parts of air to produce an explosive mixture. - -Calcium carbide is dangerous because it is self igniting. The heat of -the generation of gas is sufficient to ignite the explosive mixture. The -gases are highly explosive and cause a relatively powerful explosion. -Fortunately large amounts of this material seldom reach a sewer, the gas -being generated in garage drains or traps and escaping in the -atmosphere. - -A hydrocarbon oil used by railroads in preventing the freezing of -switches, if allowed to reach the sewers, may cause explosions -therein.[116] The oil crystallizes and in this form it is soluble in -water. It will thus pass traps and on volatilization will produce -explosive mixtures. - -Methane, generated by the decomposition of organic matter, is a feebly -explosive gas occasionally found in sewers. Its presence may add to the -strength of other explosive mixtures. - -Sewer explosions may be prevented by the building of proper forms of -intercepting basins to prevent the entrance of gasoline and calcium -carbide gases, and by ventilation to dilute the explosive mixtures which -may be made up in the sewer. There are no practical means to predict -when an explosion is about to occur, and after an explosion has occurred -it is difficult to determine the cause as all evidence is usually -destroyed. - - -=207. Valuation of Sewers.=—The necessity for the valuation of a -sewerage system may arise from the legal provisions in some states -limiting the amount of outstanding bonds which may be issued by a -municipality to a certain percentage of the present worth of municipal -property. The investment in the sewerage system is usually great and -forms a large portion of the City’s tangible property. It may be -desirable also to determine the depreciation of the sewers with a view -towards their renewal. - -The most valuable work on the valuation of sewers has been done in New -York City[117] by the engineers of the Sewer Department. The committee -of engineers appointed to do the work recommended: (1) that the original -cost be made the basis of valuation, and that (2), in fixing this cost -the cost of pavement should be omitted or at most the cost of a cheap -(cobblestone) pavement should be included. Trenches previously excavated -in rock were considered as undepreciated assets. - -The present worth of sewers depends on many factors aside from the -effects of age, such as the care exercised in the original construction, -the material used, the kind and quantity of sewage carried, the care -taken in maintenance, and finally the injury caused by the careless -building of adjoining substructures. During the progress of the -inspections the examination of brick sewers, due to their accessibility, -yielded better results than the examination of pipe sewers. The routine -of the examination of the brick sewers consisted in cleaning off the -bricks with a short broom, tapping the brick with a light hammer to -determine solidity, and testing the cement joints by scraping with a -chisel. In addition, measurements of height and width were taken every -30 feet. The bricks in the invert at and below the flow line were -examined for wear. - -A study of the reports of these examinations disclosed that the -following defects were noticeable: - - 1. Cement partly out at water line. - - 2. Cement partly out above water line. - - 3. Depressed arch and sewer slightly spread. - - 4. Large open joints. - - 5. Loose brick. - - 6. Bond of brick broken. - - 7. Distorted sides, uneven bottom, joints out of line. - -[Illustration: - - FIG. 147.—Diagrams used in Estimating Depreciation of Brick Sewers Due - to Age, Manhattan Borough, New York City. - - _a._ Proportionate deterioration from various causes. - - _b._ Percentage of depreciation based on examination of sewers, use of - deterioration curve (Fig. a), and age of sewers examined. - - Eng. News, Vol. 71, p. 84. -] - -Inspection of pipe sewers from manholes, the pipe being illuminated by -floating candles, was found to be unsatisfactory. Reliance was placed on -the reports of men experienced in making connections and repairs to the -sewers. Early pipe sewers in New York were laid directly on the bottom -of the trench. Under these circumstances a small leak at a joint was -sufficient to wash the earth away and to drop the pipe, causing serious -conditions along the line. No wear or deterioration of pipe sewers were -noted, the only defects being cracking of the pipes at the center line -due to poor foundation and to defects in the pipe itself. - -[Illustration: - - FIG. 148.—Diagram Showing Rate of Depreciation of Pipe Sewers. - - Eng. News, Vol. 71, p. 86. -] - -The depreciation of brick sewers as studied in New York, is shown -graphically in Fig. 147. At zero the sewer is in good condition and at -100 it is in such a state of dilapidation as to require instant -rebuilding. Repairs are not considered economical in this condition. In -the preparation of this diagram each condition on the list above was -given a certain number of points, which when added together represented -the state of depreciation of the sewer. These sums were plotted as -ordinates and the corresponding ages of the sewer were plotted as -abscissas. The various points were taken cumulatively, and where the -bond of the brickwork was broken (given a value of 72) plus other -defects gave a total of 164 the sewer was considered as valueless and -not worth repair. The scale of 164 was later reduced to a percentage -basis as shown on the right of the figure. Fig. 148 shows a similar -diagram for the depreciation of pipe sewers. - -It was concluded that the life of a brick sewer in New York is 64 years. -Some of the sewers examined were over 200 years old. The total original -cost of 483 miles of brick, pipe and wood sewers was figured as -$23,880,000 with a present worth of $18,665,000 and an average annual -depreciation of 2.2 per cent. In figuring these amounts no account was -taken of obsolescence. The deterioration of catch-basins proceeded at -about the same rate as for brick sewers. - - - - - CHAPTER XIII - COMPOSITION AND PROPERTIES OF SEWAGE - - -=208. Physical Characteristics.=—Sewage is the spent water supply of a -community containing the wastes from domestic, industrial, or commercial -use, and such surface and ground water as may enter the sewer.[118] -Sewages are classed as: domestic sewage, industrial waste, storm water, -surface water, street wash, and ground water. Domestic sewage is the -liquid discharged from residences or institutions and contains water -closet, laundry, and kitchen wastes. It is sometimes called sanitary -sewage. Industrial sewage is the liquid waste resulting from processes -employed in industrial establishments. Storm water is that part of the -rainfall which runs over the surface of the ground during a storm and -for such a short period following a storm as the flow exceeds the normal -and ordinary run-off. Surface water is that part of the rainfall which -runs over the surface of the ground some time after a storm. Street wash -is the liquid flowing on or from the street surface. Ground water is -water standing in or flowing through the ground below its surface. - -Ordinary fresh sewage is gray in color, somewhat of the appearance of -soapy dish water. It contains particles of suspended matter which are -visible to the naked eye. If the sewage is fresh the character of some -of the suspended matter can be distinguished as: matches, bits of paper, -fecal matter, rags, etc. The amount of suspended matter in sewage is -small, so small as to have no practical effect on the specific gravity -of the liquid nor to necessitate the modification of hydraulic formulas -developed for application to the flow of water. The total suspended -matter in a normal strong domestic sewage is about 500 parts per -1,000,000. It is represented graphically in Fig. 149. The quantity of -organic or volatile suspended matter is about 200 parts per 1,000,000. -It is shown graphically in the smaller cube in Fig. 149. - -[Illustration: - - FIG. 149.—Graphical Representation of Relative Volumes of Liquids and - Solids in Sewage. -] - -The odor of fresh sewage is faint and not necessarily unpleasant. It has -a slightly pungent odor, somewhat like a damp unventilated cellar. -Occasionally the odor of gasoline, or some other predominating waste -matter may hide all other odors. Stale sewage is black and gives off -nauseating odors of hydrogen sulphide and other gases. If the sewage is -so stale as to become septic, bubbles of gas will be seen breaking the -surface and a black or gray scum may be present. Before the South Branch -of the Chicago River was cleaned up and flushed this scum became so -thick in places, particularly in that portion of the Stock Yards where -the river became known as Bubbly Creek, that it is said that weeds and -small bushes sprouted in it, and chickens and small animals ran across -its surface. - -A physical analysis of sewage should include an observation of its -appearance, and a determination of its temperature, turbidity, color, -and odor, both hot and cold. The temperature is useful in indicating -certain of the antecedents of the sewage, its effect on certain forms of -bacterial life, and its effect on the possible content of dissolved -gases. Temperatures higher than normal are indicative of the presence of -trades wastes discharged while hot into the sewers. A low temperature -may indicate the presence of ground water. If the temperature is much -over 40° C. bacterial action will be inhibited and the content of -dissolved gases will be reduced. Turbidity, color, and odor -determinations may be of value in the control of treatment devices, or -to indicate the presence of certain trades wastes, which give typical -reactions. Since all normal sewages are high in color and turbidity, the -relative amounts of these two constituents in two different sewages has -little significance regarding the relative strengths of the two sewages -or the proper method of treating them. A fresh domestic sewage should -have no highly offensive odor. The presence of certain trades wastes can -be detected sometimes in fresh sewages, and a stale sewage may sometimes -be recognized by its odor. - -Sewage is a liability to the community producing it. Although some -substances of value can be obtained from sewage[119] the cost of the -processes usually exceed the value of the substances obtained. Where it -becomes necessary to treat sewage the value of these substances may be -helpful in defraying the cost of treatment. - - -=209. Chemical Composition.=—Sewage is composed of mineral and organic -compounds which are either in solution or are suspended in water. In -making a standard chemical analysis of sewage only those chemical -radicals and elements are determined which are indicative of certain -important constituents. Neither a complete qualitative nor quantitative -analysis is made. A sewage analysis will not show, therefore, the number -of grams of sodium chloride present or any other constituent. A complete -standard sanitary chemical analysis will report the constituents as -named in the first column of Table 71. The quantities of these materials -found in average strong, medium and weak sewages are also shown in this -table. These values are not intended as fixed boundaries between sewages -of different strengths. They are presented merely as a guide to the -interpretation of sewage analyses. - -The principal objects of a chemical analysis of sewage are to determine -its strength and its state of decomposition. The influents and effluents -of a sewage treatment device are analyzed to aid in the control of the -device and to gain information concerning the effect of the treatment. -Chemical and other analyses, in connection with the desired conditions -after disposal, will indicate the extent of treatment which may be -required. The standard methods of water and sewage analysis adopted by -the American Public Health Association have been generally accepted by -sanitarians. These uniform methods make possible comparisons of the -results obtained by laboratories working according to these standards. - - - CHEMICAL ANALYSIS OF SEWAGES - - (Parts per million) - - From Report on Industrial Wastes from the Stock Yards and Packingtown, - Chicago by the Sanitary District of Chicago in 1921, page 231. - - ──────────┬──────────────────┬───────┬────────┬────────── - │ │ │ │ - │ │ │ │ - │ │ │ │ - │ │ │ │Waterbury, - │ │Boston │Columbus│ Conn., - │ Typical Analyses │1905–7 │ 1904–5 │ 1905–6 - ──────────┼──────┬──────┬────┼───────┼────────┼────────── - │Strong│Medium│Weak│ │ │ - ──────────┼──────┼──────┼────┼───────┼────────┼────────── - Nitrogen │ │ │ │ │ │ - as │ │ │ │ │ │ - Organic │ │ │ │ │ │ - Nitrogen│ 35│ 20│ 10│ 9.1│ 9.0│ 14.8 - Free │ │ │ │ │ │ - Ammonia │ 50│ 30│ 15│ 13.9│ 11.0│ 7.8 - Nitrites │ 0.10│ 0.05│ 0.0│ 0.0│ 0.09│ 0.14 - Nitrates │ 0.40│ 0.20│ 0.1│ 0.20│ 0.20│ 1.52 - Oxygen │ │ │ │ │ │ - consumed│ 75│ 50│ 30│56[120]│ 51[121]│ 46[120] - Oxygen │ │ │ │ │ │ - demand │ 300│ 200│ 100│ │ │ - Chlorine │ 175│ 100│ 15│ 2300│ 65│ 48 - Suspended │ │ │ │ │ │ - matter │ 500│ 300│ 150│ 135│ 209│ 165 - Volatile│ │ │ │ 91│ 79│ 115 - Fixed │ │ │ │ 44│ 130│ 50 - Alkalinity│ 200│ 100│ 50│ 125│ 350│ 41 - Fats │ 40│ 20│ │ │ 25│ 26 - ──────────┴──────┴──────┴────┴───────┴────────┴────────── - - ──────────┬─────────────┬──────────┬───────────┬─────────── - │ │ │ │ Chicago, - │ │ │ │ Center - │ │ │ Chicago, │ Avenue. - │Gloversville,│Worcester,│ 39th St. │Industrial. - │ N. Y. │ Mass. │Residential│Day Sewage - │ 1908–9 │ 1908 │ 1909–12 │ 1913 - ──────────┼─────────────┼──────────┼───────────┼─────────── - │ │ │ │ - ──────────┼─────────────┼──────────┼───────────┼─────────── - Nitrogen │ │ │ │ - as │ │ │ │ - Organic │ │ │ │ - Nitrogen│ 23.0│ │ 7.8│ 79 - Free │ │ │ │ - Ammonia │ 12.0│ 22.2│ 9.1│ 22 - Nitrites │ 0.38│ │ 0.10│ 0.49 - Nitrates │ 0.88│ │ 0.33│ 3.04 - Oxygen │ │ │ │ - consumed│ 95[120]│ 117│ 43│ 268 - Oxygen │ │ │ │ - demand │ │ │ │ - Chlorine │ 158│ 57│ 40│ 1100 - Suspended │ │ │ │ - matter │ 406│ 258│ 144│ 605 - Volatile│ 229│ 166│ 90│ 46 - Fixed │ 177│ 92│ 54│ 144 - Alkalinity│ 233│ │ 212│ 291 - Fats │ 48│ │ 23[122]│ 198[123] - ──────────┴─────────────┴──────────┴───────────┴─────────── - - -=210. Significance of Chemical Constituents.=—Organic nitrogen and free -ammonia taken together are an index of the organic matter in the sewage. -Organic nitrogen includes all of the nitrogen present with the exception -of that in the form of ammonia, nitrites, and nitrates. Free ammonia or -ammonia nitrogen is the result of bacterial decomposition of organic -matter. A fresh cold sewage should be relatively high in organic -nitrogen and low in free ammonia. A stale warm sewage should be -relatively high in free ammonia and low in organic nitrogen. The sum of -the two should be unchanged in the same sewage. - -Nitrites (RNO_{2}) and nitrates (RNO_{3})[124] are found in fresh -sewages only in concentrations of less than one part per million. In -well-oxidized effluents from treatment plants the concentration will -probably be much higher. Nitrates contain one more atom of oxygen than -nitrites. They represent the most stable form of nitrogenous matter in -sewage. Nitrites are not stable and are reduced to ammonias or are -oxidized to nitrates. Their presence indicates a process of change. They -are not found in large quantities in raw sewage because their formation -requires oxygen which must be absorbed from some other source than the -sewage. In an ordinary sewer or sluggishly flowing open stream this -absorption cannot take place from the atmosphere with sufficient -rapidity to supply the necessary oxygen. - -Oxygen consumed is an index of the amount of carbonaceous matter readily -oxidizable by potassium permanganate. It does not indicate the total -quantity of any particular constituent, but it is the most useful index -of carbonaceous matter. Carbonaceous matter is usually difficult of -treatment and a high oxygen consumed is indicative of a sewage difficult -to care for. The amount of oxygen consumed, as expressed in the -analysis, is dependent on the amount of oxidizable carbonaceous matter -present, the oxidizing agent used, and the time and temperature of -contact of the sewage and the oxidizing agent. It is essential therefore -that the test be conducted according to some standard method, since the -results are of value only as compared with results obtained under -similar conditions. - -Total solids (residue on evaporation) are an index of the strength of -the sewage. They are made up of organic and inorganic substances. The -inorganic substances include sand, clay, and oxides of iron and -aluminum, which are usually insoluble, and chlorides, carbonates, -sulphates and phosphates, which are usually soluble. The insoluble -inorganic substances are undesirable in sewage because of their sediment -forming properties which result in the clogging of sewers, treatment -plants, pumps, and stream beds. The soluble inorganic substances are -generally harmless and cause no nuisance, except that the presence of -sulphur may permit the formation of hydrogen sulphide, which has a -highly offensive odor. The organic substances are: carbohydrates, fats, -and soaps, which are carbonaceous and are difficult of removal by -biological processes; and the nitrogenous substances such as urea, -proteins, amines, and amino acids. The inorganic and organic substances -may be either in solution or suspension or in a colloidal condition. - -Volatile solids are used as an index of the organic matter present, as -it is assumed that the organic matter is more easily volatilized than -the inorganic matter. The amount of volatile inorganic matter present is -usually so small as to be negligible. - -Fixed solids are reported as the difference between the total and -volatile solids. They are therefore representative of the amount of -inorganic matter present. - -Suspended matter is the undissolved portion of the total solids. High -volatile suspended matter is an indication of offensive qualities in the -nature of putrefying organic matter, whereas fixed suspended matter is -indicative of inoffensive inorganic matter. It is difficult to obtain a -sample of sewage which will represent the amount of suspended matter in -the sewage, since a sample taken from near the surface will contain less -inorganic matter and grit than a sample taken near the bottom. - -Settling solids are indicative of the sludge forming properties of the -sewage and of the probable degree of success of treatment by plain -sedimentation. Volatile settling solids indicate the property of the -formation of offensive putrefying sludge banks. There is no chemical -test which will indicate the scum-forming properties of sewage. Fixed -settling solids indicate the presence of inorganic matter, probably -gritty material such as sand, clay, iron oxide, etc. - -Colloidal matter is material which is too finely divided to be removed -by filtration or sedimentation, yet is not held in solution. It can -sometimes be removed by violent agitation in the presence of a -flocculent precipitate, as in the treatment with activated sludge, or by -the flocculent precipitate alone, as in chemical precipitation, or by -the acidulation of the sewage so as to precipitate the colloids. -Colloidal matter is probably the result of the constant abrasion of -finely divided suspended matter while flowing through the sewer or other -channel. High colloidal matter may therefore indicate a stale sewage, or -the presence of a particular trades waste. Colloids are difficult of -removal. For this reason, where sewage is to be treated, turbulence in -the tributary channels should be avoided. - -Alkalinity may indicate the possibility of success of the biologic -treatment of sewage, since bacterial life flourishes better in a -slightly alkaline than in a slightly acid sewage. Within the normal -limits of the amount of alkalinity in sewage the exact amount has little -significance in sewage analyses. Sewages are normally slightly alkaline. -An abnormal alkalinity or acidity may indicate the presence of certain -trades wastes necessitating special methods of treatment. A method of -sewage treatment may be successful without changing the amount of -alkalinity in the sewage since the amount of alkalinity is not -inherently an objection. - -Chlorine, in the form of sodium chloride, is an inorganic substance -found in the urine of man and animals. The amount of chlorine above the -normal chlorine content of pure waters in the district is used as an -index of the strength of the sewage. The chlorine content may be -affected by certain trades wastes such as ice-cream factories, -meat-salting plants, etc., which will increase the amount of chlorine -materially. Since chlorine is an inorganic substance which is in -solution it is not affected by biological processes nor sedimentation. -Its diminution in a treatment plant or in a flowing stream is indicative -of dilution and the reduction of chlorine will be approximately -proportional to the amount of dilution. - -Fats have a recoverable market value when present in sufficient quantity -to be skimmed off the surface of the sewage. Ordinarily fats are an -undesirable constituent of sewage as they precipitate on and clog the -interstices in filtering material, they form objectionable scum in tanks -and streams, and they are acted on very slowly by biological processes -of sewage treatment. Although fats are carbonaceous matter they are not -indicated by the oxygen consumed test because they are not easily -oxidized. They are therefore determined in another manner; by -evaporation of the liquid and extracting the fats from the residue by -dissolving them in ether. - -Relative stability and bio-chemical oxygen demand are the most important -tests indicating the putrefying characteristics of sewage. Since -stability and putrescibility have opposite meanings the relative -stability test is sometimes called the putrescibility test. The relative -stability of a sewage is an expression for the amount of oxygen present -in terms of the amount required for complete stability. - - A relative stability of 75 signifies that the sample examined - contains a supply of available oxygen equal to 75 per cent of the - amount of oxygen which it requires in order to become perfectly - stable. The available oxygen is approximately equivalent to the - dissolved oxygen plus the available oxygen of nitrate and - nitrite.[125] - - TABLE 72 - - RELATIVE STABILITY NUMBERS - - ──────────────────────────────────┬────────────────────────────────── - Time Required for Decolorization │ - at 20° C. Days │ Relative Stability Number - ──────────────────────────────────┼────────────────────────────────── - 0.5│ 11 - 1.0│ 21 - 1.5│ 30 - 2.0│ 37 - 2.5│ 44 - 3.0│ 50 - 4.0[126]│ 60 - 5.0│ 68 - 6.0│ 75 - 7.0│ 80 - 8.0│ 84 - 9.0│ 87 - 10.0│ 90 - 11.0│ 92 - 12.0│ 94 - 13.0│ 95 - 14.0│ 96 - 16.0│ 97 - 18.0│ 98 - 20.0│ 90 - ──────────────────────────────────┴────────────────────────────────── - -The relative stability numbers, given in Table 72, are computed from the -expression, _S_ = 100(1 − 0.794_t_) in which _S_ is the stability number -and _t_ is the time in days that the sample has been incubated at 20° C. -The bio-chemical oxygen demand is more directly an index of the -consumption of available oxygen by the biological and chemical changes -which take place in the decomposition of sewage or polluted water. As -such it is a more valuable, though less easily performed test than the -test of relative stability. - -The methods for the determination of the relative stability and the -bio-chemical oxygen demand are given to show more clearly what these -tests represent. The procedure in the relative stability test is to add -0.4 c.c. of a standard solution of methylene blue to 150 c.c. of the -sample. The mixture is then allowed to stand in a completely filled and -tightly stoppered bottle at 20° C. for 20 days or until the blue fades -out due to the exhaustion of the available oxygen. There are three -methods in use for the determination of the bio-chemical oxygen -demand;[127] the relative stability method, the excess nitrate method, -and the excess oxygen method. In the relative stability method the -sample to be treated should have a relative stability of at least 50. If -it is lower than this the sample should be diluted with water containing -oxygen until the relative stability has been raised to or above this -point. The oxygen demand in parts per million is then expressed as - - _O′_ = ((1 − _P_)_O_)⁄_RP_,[128] - -in which _O′_ is the oxygen demand, _O_ is the initial oxygen in parts -per million (p.p.m.) in the diluting water or sewage, _P_ is the -proportion of sewage in the mixture expressed as a ratio, and _R_ is the -relative stability of the mixture expressed as a decimal. For the -effluents from sewage treatment plants, polluted waters, and similar -liquids, the total available oxygen expressed as the sum of the -dissolved oxygen, nitrites, and nitrates, divided by the relative -stability expressed as a decimal will give the bio-chemical oxygen -demand. The excess nitrate method requires the determination of the -total oxygen available as dissolved oxygen, nitrites, and nitrates and -the addition of a sufficient amount of oxygen in the form of sodium -nitrate to prevent the exhaustion of oxygen during a 10–day period of -incubation. At the end of the period the total available oxygen is again -determined. The difference between the original and the final oxygen -content represents the bio-chemical oxygen demand. The excess oxygen -test requires the determination of the total available oxygen as before, -and the addition of a sufficient amount of oxygen, in the form of -dissolved oxygen in the diluting water, to prevent exhaustion of the -oxygen in a 10–day period of incubation. The difference between the -original and final oxygen content represents the bio-chemical oxygen -demand. Theriault concludes as a result of his tests, that the relative -stability and excess nitrate methods are open to objections but that the -excess oxygen method yields very accurate and consistent results with as -little or less labor than is required by other methods. - -Dissolved oxygen represents what its name implies, the amount of oxygen -(_O__{2}) which is dissolved in the liquid. Normal sewage contains no -dissolved oxygen unless it is unusually fresh. It is well, if possible, -to treat a sewage before the original dissolved oxygen has been -exhausted. Normal pure surface water contains all of the oxygen which it -is capable of dissolving, as shown in Table 73. The presence of a -smaller amount of oxygen than is shown in this table indicates the -presence of organic matter in the process of oxidation, which may be in -such quantities as ultimately to reduce the oxygen content to zero. -Normal pure ground waters may be deficient in dissolved oxygen because -of the absence of available oxygen for solution. The presence of certain -oxygen-producing organisms in polluted or otherwise potable surface -waters may cause a supersaturation with oxygen however. - -The dissolved-oxygen test for polluted water is probably the most -significant of all tests. If dissolved oxygen is found in a polluted -water it means that putrefactive odors will not occur, since -putrefaction cannot begin in the presence of oxygen. It is possible for -different strata in a body of water to have different quantities of -dissolved oxygen, and putrefaction may be proceeding in the lower strata -before the oxygen is exhausted from the upper strata. The oxygen content -of a river water will indicate the ability of the river to receive -sewage without resulting in a nuisance. - - TABLE 73 - - SOLUBILITY OF OXYGEN IN WATER - - Under an atmospheric pressure of 760 mm. of mercury, the atmosphere - containing 20.9 per cent of oxygen. - ───────────────────────────────────┬─────────────────────────────────── - Temperature, degrees C │ Oxygen in parts per million - ───────────────────────────────────┼─────────────────────────────────── - 0│ 14.62 - 1│ 14.23 - 2│ 13.84 - 3│ 13.48 - 4│ 13.13 - 5│ 12.8 - 6│ 12.48 - 7│ 12.17 - 8│ 11.87 - 9│ 11.59 - 10│ 11.33 - 11│ 11.08 - 12│ 10.83 - 13│ 10.6 - 14│ 10.37 - 15│ 10.15 - 16│ 9.95 - 17│ 9.74 - 18│ 9.54 - 19│ 9.35 - 20│ 9.17 - 21│ 8.99 - 22│ 8.83 - 23│ 8.68 - 24│ 8.53 - 25│ 8.38 - 26│ 8.22 - 27│ 8.07 - 28│ 7.92 - 29│ 7.77 - 30│ 7.63 - ───────────────────────────────────┴─────────────────────────────────── - - -=211. Sewage Bacteria.=—A slight knowledge of the nature of bacteria is -necessary in order that the biological changes which occur in the -treatment of sewage may be understood. Bacteria are living organisms -which are so small that it is difficult or impossible to study them -either with the eye alone or with the aid of powerful microscopes. They -are studied by means of cultures, stains, and certain characteristic -phenomena such as the production of a gas, the production of a red -colony on litmus lactose agar, etc. Bacteria occur in three forms: -spherical, called coccus; cylindrical, called bacillus; and spiral, -called spirillum. In size they vary from the largest at about 1⁄10,000 -of an inch to sizes so small as to be invisible under the most powerful -microscope. An ordinary size is 1⁄25,000 of an inch. The cylindrical or -rod bacteria are about four times as long as they are wide. Some -bacteria possess the power of motion due to the presence of flagella or -hairs which can be moved and cause the cell to progress at a rate as -high as 18 cm. per hour, but usually the rate is very much less than -this. The composition of the bacterial cell has never been definitely -determined. - -Bacteria are unicellular plants. They possess no digestive organs and -apparently obtain their food by absorption from the surrounding media. -Reproduction is by the division of the cell into two approximately equal -portions. This reproduction may occur as frequently as once every half -hour and if unchecked would quickly mount to unimaginable numbers. The -natural cause limiting the growth of bacteria is the generation by the -bacterium of certain substances such as the amino acids, which are -injurious to cell life. The exhaustion of the food supply is not -considered as an important cause of inhibition of multiplication. The -products of growth of one species of bacteria may be helpful or harmful -to other forms. Where the products are helpful the effect is known as -symbiosis, and where harmful the effect is known as antibiosis. In -sewage the presence of both aërobic and anaërobic bacteria is usually -mutually helpful and the condition is an example of symbiosis. The -aërobes, sometimes called obligatory aërobes, are bacteria which demand -available oxygen for their growth. The anaërobes, or obligatory -anaërobes, can grow only in the absence of oxygen. There are other forms -that are known as facultative anaërobes (or aërobes) whose growth is -independent of the presence or absence of oxygen. - -Spores are formed by some bacteria when they are subjected to an -unfavorable environment such as high temperatures, the absence of food, -the absence of moisture, etc. Spores are cells in which growth and -animation are suspended but the life of the cell is carried on through -the unsuitable period, somewhat similar to the condition in a plant -seed. - - -=212. Organic Life in Sewage.=—Living organisms, both plants and -animals, exist in sewage. Bacteria are the smallest of these organisms. -Others, which can be studied easily under the microscope or can be seen -with difficulty by the naked eye but which do not require special -cultures for their study, are classed as microscopic organisms or -plankton. Organisms which are large enough to be studied without the aid -of a microscope or special cultures are classed as macroscopic. The part -taken in the biolysis of sewage by macroscopic organisms belonging to -the animal kingdom, such as birds, fish, insects, rodents, etc., which -feed upon substances in the sewage is so inconsequential as to be of no -importance. Both plants and animals are found among the macroscopic -organisms. - -Organisms in sewage may be either harmful, harmless, or beneficial. From -the viewpoint of mankind the harmful organisms are the pathogenic -bacteria. Their condition of life in sewage is not normal and in general -their existence therein is of short duration. It may be of sufficient -length, however, to permit the transmission of disease. The diseases -which can be transmitted by sewage are only those that are contracted -through the alimentary canal, such as typhoid fever, dysentery, cholera, -etc. Diseases are not commonly contracted by contact of sewage with the -skin nor by breathing the air of sewers. It is safe to work in and -around sewage so long as the sewage is kept out of the mouth, and -asphyxiating or toxic gases are avoided. - -The beneficial organisms in sewage are those on which dependence is -placed for the success of certain methods of treatment. These organisms -have not all been isolated or identified. - -The total number of bacteria in a sample of sewage has little or no -significance. In a normal sewage the number may be between 2,000,000 and -20,000,000 per c.c. and because of the extreme rapidity of -multiplication of bacteria a sample showing a count of 1,000,000 per -c.c. on the first analysis may show 4 to 5 times as many 3 or 4 hours -later. A bacterial analysis of sewage is ordinarily of little or no -value, since pathogenic organisms are practically certain to be present, -there is no interest in the harmless organisms, and the helpful -nitrifying and aërobic bacteria will not grow on ordinary laboratory -media. Occasionally the presence of certain bacteria may indicate the -presence of certain trades wastes. In general, the total bacterial -count, as sometimes reported, represents only the number of bacteria -which have grown under the conditions provided. It bears no relation to -the total number of bacteria in the sample. - -The presence of bacteria in sewage is of great importance however, as -practically all methods of treatment depend on bacterial action, and all -sewages which do not contain deleterious trades wastes, contain or will -support the necessary bacteria for their successful treatment, if -properly developed. - - -=213. Decomposition of Sewage.=—If a glass container be filled with -sewage and allowed to stand, open to the air, a black sediment will -appear after a short time, a greasy scum may rise to the surface, and -offensive odors will be given off. This condition will persist for -several weeks, after which the liquid will become clear and odorless. -The sewage has been decomposed and is now in a stable condition. The -decomposition of sewage is brought about by bacterial action the exact -nature of which is uncertain. - - It[129] is well established that many of the chemical effects - wrought by bacteria, as by other living cells, are due, not to the - direct action of the protoplasm, but to the intervention of - soluble ferments or enzymes. - -Enzymes are soluble ferments produced by the growth of the bacterial -cell. - - In[130] many cases the enzymes diffuse out from the cell and exert - their effort on the ambient substances ... in others the enzyme - action occurs within the cell and the products pass out, (for - example) ... the alcohol-producing enzymes of the yeast cell act - upon sugar within the cell, the resulting alcohol and carbon - dioxide being ejected. - -Other chemical effects may be brought about by the direct action of the -living cells, but this has never been well established. - -Metabolism is the life process of living cells by which they absorb -their food and convert it into energy and other products. It is the -metabolism of bacterial growth that in itself or by the production of -enzymes hastens the putrefactive or oxidizing stages of the organic -cycles in sewage treatment. Bacteria can assimilate only liquid food -since they have no digestive tract through which solid food can enter. -The surrounding solids are dissolved by the action of the enzymes, the -resulting solution diffusing through the chromatin or outer skin, and -being digested throughout the interior cytoplasm. - -Bacteria are sometimes classified as parasites and saprophytes. The -parasites live only on the growing cells of other plant or animal life. -The saprophytes obtain their food only from the life products of living -organisms and do not exist at the expense of the organisms themselves. -Facultative saprophytes (or parasites) may exist on either living or -dead tissue. - -The decomposition of sewage may be divided into anaërobic and aërobic -stages. These conditions are usually, but not always, distinctly -separate. The growth of certain forms of bacteria is concurrent, while -the growth of other forms is dependent on the results of the life -processes of other bacteria in the early stages of decomposition. - -When sewage is very fresh it contains some oxygen. This oxygen is -quickly exhausted so that the first important step in the decomposition -of sewage is carried on under anaërobic conditions. This is accompanied -by the creation of foul odors of organic substances, ammonia, hydrogen -sulphide, etc.; other odorless gases such as carbon dioxide, hydrogen, -and marsh gas, the latter being inflammable and explosive; and other -complicated compounds. An exception to the rule that putrefaction takes -place only in the absence of oxygen is the production of other -foul-smelling substances by the putrefactive activity of obligatory and -facultative aërobes. Hydrogen sulphide may be produced apparently in the -presence of oxygen the action which takes place not being thoroughly -understood. - -The biolysis of sewage is the term applied to the changes through which -its organic constituents pass due to the metabolism of bacterial life. -Organic matter is composed almost exclusively of the four elements: -carbon, oxygen, hydrogen, and nitrogen (COHN) and sometimes in addition -sulphur and phosphorus. The organic constituents of sewage can be -divided into the proteins, carbohydrates, and fats. The proteins are -principally constituents of animal tissue, but they are also found in -the seeds of plants. The principal distinguishing characteristic of the -proteins is the possession of between 15 and 16 per cent of nitrogen. To -this group belong the albumens and casein. The carbohydrates are organic -compounds in which the ratio of hydrogen to oxygen is the same as in -water, and the number of carbon atoms is 6 or a multiple of 6. To this -group belong the sugars, starches and celluloses. The fats are salts -formed, together with water, by the combination of the fatty acids with -the tri-acid base glycerol. The more common fats are _stearin_, -_palmatin_, _olein_, and _butyrine_. The soaps are mineral salts of the -fatty acids formed by replacing the weak base glycerol with some of the -stronger alkalies. - -The first state in the biolysis of sewage is marked by the rapid -disappearance of the available oxygen present in the water mixed with -organic matter to form sewage. In this state the urea, ammonia, and -other products of digestive or putrefactive decomposition are partially -oxidized and in this oxidation the available oxygen present is rapidly -consumed, the conditions in the sewage becoming anaërobic. The second -state is putrefaction in which the action is under anaërobic conditions. -The proteins are broken down to form urea, ammonia, the foul-smelling -mercaptans, hydrogen sulphide, etc., and fatty and aromatic acids. The -carbohydrates are broken down into their original fatty acid, water, -carbon dioxide, hydrogen, methane, and other substances. Cellulose is -also broken down but much more slowly. The fats and soaps are affected -somewhat similarly to the hydrocarbons and are broken down to form the -original acids of their make up together with carbon dioxide, hydrogen, -methane, etc. The bacterial action on fats and soaps is much slower than -on the proteins, and the active biological agents in the biolysis of the -hydrocarbons, fats, and soaps are not so closely confined to anaërobes -as in the biolysis of the proteins. The third state in the biolysis of -sewage is the oxidation or nitrification of the products of -decomposition resulting from the putrefactive state. The products of -decomposition are converted to nitrites and nitrates, which are in a -stable condition and are available for plant food. It must be understood -that the various states may be coexistent but that the conditions of the -different states predominate approximately in the order stated. In the -biolysis of sewage there is no destruction of matter. The same elements -exist in the same amount as at the start of the biolytic action. - - -=214. The Nitrogen Cycle.=—Nitrogen is an element that is found in all -organic compounds. Its presence is necessary to all plant and animal -life. The nitrogenous compounds are most readily attacked by bacterial -action in sewage treatment. The non-nitrogenous substances such as soaps -and fats, and the inorganic compounds are more slowly affected by -bacterial action alone. The element nitrogen passes through a course of -events from life to death and back to life again that is known as the -Nitrogen Cycle. It is typical of the cycles through which all of the -organic elements pass. - -Upon the death of a plant or animal, decomposition sets in accompanied -by the formation of urea which is broken down into ammonia. This is -known as the _putrefactive stage_ of the Nitrogen Cycle. The next state -is _nitrification_ in which the compounds of ammonia are oxidized to -nitrites and nitrates, and are thus prepared for plant food. In the -state of _plant life_ the nitrites and nitrates are denitrified so as to -be available as a plant or animal food. The highest state of the -Nitrogen Cycle is _animal life_, in which nitrogen is a part of the -living animal substance or is charged from protein to urea, ammonia, -etc., by the functions of life in the animal. Upon the death of this -animal organism the cycle is repeated. The Nitrogen Cycle, like the -cycle of Life and Death, is purely an ideal condition as in nature there -are many short circuits and back currents which prevent the continuous -progression of the cycle. The conception of this cycle is an aid, -however, in understanding the processes of sewage treatment. - - -=215. Plankton and Macroscopic Organisms.=—In general the part played by -these organisms in the biolysis of sewage is not sufficiently well -understood to aid in the selection of methods of sewage treatment -involving their activities. The presence in bodies of water receiving -sewage, of certain plankton which are known to exist only when -putrefaction is not imminent, indicates that the body of water into -which the discharge of sewage is occurring is not being overtaxed. The -control of sewage treatment plant effluents so as to avoid the poisoning -of fish life or the contamination of shell fish is likewise important. -The study of plankton and macroscopic life in the treatment of sewage is -an open field for research. - - -=216. Variations in the Quality of Sewage.=—The quality of sewage varies -with the hour of the day and the season of the year. Some of the causes -of these variations are: changes in the amount of diluting water due to -the inflow of storm water or flushing of the streets or sewers; -variations in domestic activities such as the suspension of -contributions of organic wastes during the night, Monday’s wash, etc.; -characteristics of different industries which discharge different kinds -of wastes according to the stage of the manufacturing process, etc. In -general night sewage is markedly weaker than day sewage in both domestic -and industrial wastes, but in specific cases the varying strength -depends entirely upon the characteristics of the district. Some analyses -are given in Table 74, which emphasize these points. - - TABLE 74 - - SEWAGE ANALYSES SHOWING HOURLY, DAILY, AND SEASONAL VARIATIONS IN - QUALITY - ────────────┬────────────┬─────┬────────┬─────────┬──────────┬───────── - Place │ Time │ │ │Suspended│ Remarks │Reference - │ Nitrogen │Total│Chlorine│ Matter │ │ - ────────────┼────────────┼─────┼────────┼─────────┼──────────┼───────── - Marion, Ohio│Mid’t-noon, │ │ │ │Industrial│ 1 - │ 5–21–06. │ 45│ 53│ 190│ │ - │Noon-mid’t │ │ │ │Domestic │ 1 - │ 5–21–06. │ 37│ 94│ 133│ │ - Westerville,│Day │ │ │ │college │ 1 - Ohio │ │ 10.2│ 76│ 118│ town │ - │Night │ 2.6│ 74│ 41│ │ 1 - Columbus, │1904–1905 │ │ │ │ │ - Ohio │ │ │ │ │ │ - │Mid’t to 2 │ │ │ │ │ 2 - │ a.m. │ 4.6│ 50│ 131│ │ - │2 a.m. to 4 │ │ │ │ │ 2 - │ a.m. │ 3.0│ 52│ 95│ │ - │4 a.m. to 6 │ │ │ │ │ 2 - │ a.m. │ 2.3│ 51│ 83│ │ - │6 a.m. to 8 │ │ │ │ │ 2 - │ a.m. │ 2.7│ 48│ 83│ │ - │8 a.m. to 10│ │ │ │ │ 2 - │ a.m. │ 16.3│ 66│ 476│ │ - │10 a.m. to │ │ │ │ │ 2 - │ noon │ 11.4│ 100│ 324│ │ - │Noon to 2 │ │ │ │ │ 2 - │ p.m. │ 11.3│ 86│ 246│ │ - │2 p.m. to 4 │ │ │ │ │ 2 - │ p.m. │ 12.3│ 78│ 246│ │ - │4 p.m. to 6 │ │ │ │ │ 2 - │ p.m. │ 22.0│ 78│ 368│ │ - │6 p.m. to 8 │ │ │ │ │ 2 - │ p.m. │ 8.2│ 71│ 209│ │ - │8 p.m. to 10│ │ │ │ │ 2 - │ p.m. │ 7.8│ 80│ 120│ │ - │10 p.m. to │ │ │ │ │ 2 - │ mid’t │ 6.2│ 56│ 117│ │ - │ │ │ │ │ │ - Center Ave.,│Mid’t to 3 │ │ │ │ │ 3 - Chicago. │ a.m. │ │ │ 123│ │ - │4 a.m. to 7 │ │ │ │ │ 3 - │ p.m. │ │ │ 316│ │ - │8 a.m. to 11│ │ │ │ │ 3 - │ p.m. │ │ │ 608│ │ - │Noon to 3 │ │ │ │ │ 3 - │ p.m. │ │ │ 785│ │ - │4 p.m. to 7 │ │ │ │ │ 3 - │ p.m. │ │ │ 717│ │ - │8 p.m. to 11│ │ │ │ │ 3 - │ p.m. │ │ │ 287│ │ - │ │ │ │ │ │ - Columbus, │Sunday │ │ │ │ │ 2 - Ohio │ │ 6.7│ 55│ 858│ │ - │Monday │ 9.1│ 66│ 1048│ │ 2 - │Tuesday │ 9.4│ 69│ 1024│ │ 2 - │Wednesday │ 9.6│ 68│ 1005│ │ 2 - │Thursday │ 9.2│ 66│ 990│ │ 2 - │Friday │ 9.2│ 67│ 1018│ │ 2 - │Saturday │ 9.3│ 67│ 1016│ │ 2 - │ │ │ │ │ │ - Baltimore, │Aug. 1 to │ │ │ │ │ 4 - 1907–1908 │ Sept. 1 │ 16.0│ │ 246│ │ - │Sept. 4 to │ │ │ │ │ 4 - │ Oct. 3 │ 19.0│ │ 190│ │ - │Oct. 6 to │ │ │ │ │ 4 - │ Nov. 4 │ 20.0│ │ 188│ │ - │Nov. 15 to │ │ │ │ │ 4 - │ Nov. 29 │ 20.0│ │ 164│ │ - │Dec. 3 to │ │ │ │ │ 4 - │ Dec. 29 │ 20.0│ │ 123│ │ - │Jan. 6 to │ │ │ │ │ 4 - │ Jan. 21 │ 19.0│ │ 127│ │ - │Feb. 2 to │ │ │ │ │ 4 - │ Feb. 26 │ 20.0│ │ 149│ │ - │Feb. 29 to │ │ │ │ │ 4 - │ Mar. 24 │ 28.0│ │ 274│ │ - │Mar. 27 to │ │ │ │ │ 4 - │ April 29 │ 25.0│ │ 165│ │ - │April 30 to │ │ │ │ │ 4 - │ May 26 │ 19.0│ │ 104│ │ - │June 8 to │ │ │ │ │ 4 - │ July 11 │ 15.0│ │ 88│ │ - │July 13 to │ │ │ │ │ 4 - │ Aug. 8 │ 9.5│ │ 124│ │ - ────────────┴────────────┴─────┴────────┴─────────┴──────────┴───────── - - References: - - 1. 1908 Report of the Ohio State Board of Health. - - 2. Report on Sewage Purification at Columbus, Ohio, by G. A. Johnson, - 1905. - - 3. Report on Industrial Wastes from the Stock Yards and Packingtown in - Chicago, by the Sanitary District of Chicago. 1921. - - 4. Report of the Baltimore Sewerage Commission, 1911. - - -=217. Sewage Disposal.=—Previous to the development of the -water-carriage method for removing human excreta and other liquid wastes -the solid matter was disposed of by burial and the liquid wastes were -allowed to seep into the ground or to run away over its surface. -Following the development of the water-carriage system, which -necessitated the development of sewers, the problem of ultimate disposal -was rendered more serious by the concentration of human excreta together -with a large volume of water. The unthinking citizen believes the -problem of sewage disposal is solved when the toilet is flushed or the -bath tub is drained. The problem may more truly be said to commence at -this point. - -It would appear that the simplest method of disposal of sewage would be -to discharge it into the nearest water course. Unfortunately the nature -of sewage is such that it may be either highly offensive to the senses -or dangerous to health or both, when discharged in this manner. Only the -most fortunate communities are favored with a body of water of -sufficient size to receive sewage without creating a nuisance. - -The problems of sewage disposal are to prevent nuisances causing offense -to sight and smell; to prevent the clogging of channels; to protect -pumping machinery; to protect public water supplies; to protect fish -life; to prevent the contamination of shell fish; to recover valuable -constituents of the sewage; to enrich and to irrigate the soil; to -safeguard bathing and boating; for other minor purposes; and in some -cases to comply with the law. Sewage may be treated to attain one or -more of these objects by methods of treatment varying as widely as the -objects to be attained. - - -=218. Methods of Sewage Treatment.=—In studying the subject of sewage -treatment it must be borne in mind that it is impossible to destroy any -of the elements present. They may be removed from the mixture only by -gasification, straining or sedimentation. Their chemical combinations -may be so changed, however, as to result in different substances than -those introduced to the treatment plant. It is with these chemical -changes that the student of sewage treatment is interested. - -The methods of sewage treatment can be classified as mechanical, -chemical and biological. These classifications are not separated by -rigid lines but may overlap in certain treatment devices or methods. -Mechanical methods of treatment are exemplified by sedimentation, and -screening. Chemical precipitation and sterilization are examples of -chemical methods. The biological methods, the most important of all, -include dilution, septicization, filtration, sewage farming, activated -sludge, etc. If for any reason it is desired to treat sewage by more -than one of these methods the procedure should follow as nearly as -possible the order of the occurrence of the phenomena in the natural -biolysis of sewage. For example, in one treatment plant the sewage would -first pass through a grit chamber where the coarse sediment would be -removed, then through a screen where the floating matter and coarse -suspended matter would be removed, then to a sedimentation basin where -some finer suspended matter might settle out, then to a digestive tank -where the solid matter deposited would be worked upon by bacterial -action and partially liquefied. Simultaneous to the liquefaction of the -deposited solid matter the liquid effluent from the digestive tank might -proceed to an aërating device to expedite oxidation, then to an aërobic -filter, and finally to disposal by dilution. - - - - - CHAPTER XIV - DISPOSAL BY DILUTION - - -=219. Definition.=—Disposal of sewage by dilution is the discharge of -raw sewage or the effluent from a treatment plant into a body of water -of sufficient size to prevent offense to the senses of sight and smell, -and to avoid danger to the public health. - - -=220. Conditions Required for Success.=—Among the desired conditions for -successful disposal by dilution are: adequate currents to prevent -sedimentation and to carry the sewage away from all habitations before -putrefaction sets in, or sufficient diluting water high in dissolved -oxygen to prevent putrefaction; a fresh or non-septic sewage; absence of -floating or rapidly settling solids, grease or oil; and absence of back -eddies or quiet pools favorable to sedimentation in the stream into -which disposal is taking place. The conditions which should be prevented -are: offensive odors due to sludge banks, the rise of septic gases, and -unsightly floating or suspended matter. In some instances the pollution -of the receiving body of water is undesirable and the sewage must be -freed from pathogenic organisms and the danger of aftergrowths minimized -before disposal. Such conditions are typified at Baltimore, where the -sewage is discharged into Back Bay, an arm of Chesapeake Bay. One of the -important industries of the state of Maryland is the cultivation of -oysters. The pollution of the Bay was therefore so objectionable that -careful treatment of the Baltimore sewage has been a necessary -preliminary to final disposal by dilution. It is unwise to draw public -water supplies, without treatment, from a stream receiving a sewage -effluent, no matter how careful or thorough the treatment of the sewage. -The treatment of the sewage is a safeguard, and lightens the load on the -water purification plant, but under no considerations can it be depended -upon to protect the community consuming the diluted effluent. - -The sewer outlet should be located well out in the current of the -stream, lake, or harbor. Deeply submerged outlets are usually better -than an outlet at the surface, as a better mixture of the sewage and -water is obtained. The discharge of sewage into a body of water of which -the surface level changes, alternately covering and exposing large areas -of the bottom is unwise, as the sludge which is deposited during -inundation will cause offensive odors when uncovered. Such conditions -must be carefully guarded against when selecting a point of disposal in -tidal estuaries because of the frequent fluctuations in level. - - -=221. Self-Purification of Running Streams.=—The self-purification of -running streams is due to dilution, sedimentation, and oxidation. The -action is physical, chemical, and biological. When putrescible organic -matter is discharged into water the offensive character of the organic -matter is minimized by dilution. If the dilution is sufficiently great, -it alone may be sufficient to prevent all nuisance. The oxidation of the -organic matter commences immediately on its discharge into the diluting -water due to the growth and activity of nitrifying and other oxidizing -organisms and to a slight degree to direct chemical reaction. So long as -there is sufficient oxygen present in the water septic conditions will -not exist and offensive odors will be absent. When the organic matter is -completely nitrified or oxidized there will be no further demand on the -oxygen content of the stream and the stream will be said to have -purified itself. At the same time that this oxidation is going on some -of the organic matter will be settling due to the action of -sedimentation. If oxidation is completed before the matter has settled -on the bottom the result will be an inoffensive silting up of the river. -If oxidation is not complete, however, the result will be offensive -putrefying sludge banks which may send their stinks up through the -superimposed layers of clean water to pollute the surrounding -atmosphere. - -The most important condition for the successful self-purification of a -stream is an initial quantity of dissolved oxygen to oxidize all of the -organic matter contributed to it, or the addition of sufficient oxygen -subsequent to the contribution of sewage to complete the oxidation. -Oxygen may be added through the dilution received from tributaries, -through aëration over falls and rapids, or by quiescent absorption from -the atmosphere. The rapidity of self-purification is dependent on the -character of the organic matter, the presence of available oxygen, the -rate of reaëration, temperature, sedimentation, and the velocity of the -current. Sluggish streams are more likely to purify themselves in a -shorter distance and rapidly flowing turbulent streams are more likely -to purify themselves in a shorter time, other conditions being equal. -Although the absorption of oxygen by a stream whose surface is broken is -more rapid than through a smooth unbroken surface, the growth of algæ, -biological activity, the effect of sunlight, and sedimentation are more -potent factors and have a greater effect in sluggish streams than the -slightly more rapid absorption of oxygen in a turbulent stream. It is -frequently more advantageous to discharge sewage into a swiftly moving -stream, however, regardless of the conditions of self-purification, as -the undesirable conditions which may result occur far from the point of -disposal and may be offensive to no one. - -The sewage from a population of about 3,000,000 persons residing in and -about Chicago is discharged into the Chicago Drainage Canal. It -ultimately reaches tide water through the Des Plaines, the Illinois, and -the Mississippi Rivers. The action occurring in these channels is one of -the best illustrations known of the self-purification of a stream. In -Table 75 are shown the results of analyses of samples taken at various -points below the mouth of the Chicago River where the diluting water -from Lake Michigan enters, to Grafton, Illinois, at the junction of the -Illinois and Mississippi Rivers about 40 miles above St. Louis. The -effect of the physical characteristics of the stream on its chemical -composition is well illustrated in this table. The rise in the chlorine -content between Lake Michigan and the entrance to the Drainage Canal is -a measure of the addition of sewage. Since the chlorine is an inorganic -substance which is not affected by biologic action, its loss in -concentration in the lower reaches of the rivers is due to dilution by -tributaries and sedimentation, e.g., between the end of the canal at -Lockport and the sampling point at Joliet, the entrance of the Des -Plaines River reduces the concentration of chlorine from 124.5 to 41.5 -parts per million. The entrance of the Kankakee River at Dresden Heights -further reduces the chlorine to 24.5 p.p.m. The increase of albuminoid -and ammonia nitrogen accompanied by a decrease in nitrites and nitrates, -between the upper end of the canal at Bridgeport and its lower end at -Lockport indicates the reducing action proceeding therein. The oxidizing -action over the various dams and the effect of dilution with water -containing oxygen is shown between miles 34 and 38, at mile 79, and at -mile 294. The excellent effect of quiescent sedimentation and aëration -in Peoria Lakes is shown between miles 145, 161 and 165. - - TABLE 75 - - ANALYSES OF CHICAGO, DES PLAINES AND ILLINOIS RIVERS - - (Parts per million) - - ────────────┬────────┬────────────────────────────────────────────── - Sampling │Distance│January-June, 1900, from “Sewage Disposal,” by - Point │in Miles│ Kinnicutt, Winslow and Pratt - │ from │ - │ Lake │ - │Michigan│ - ────────────┼────────┼────────┬────────┬──────────┬────────┬──────── - │ │Chlorine│ Ammonia│Albuminoid│Nitrates│Nitrates - │ │ │Nitrogen│ Nitrogen│ │ - │ │ │ │ │ │ - ────────────┼────────┼────────┼────────┼──────────┼────────┼──────── - Lake │ 0│ 3.0│ 0.03│ 60.13│ 0.002│ 0.008 - Michigan │ │ │ │ │ │ - │ │ │ │ │ │ - Canal, │ 5│ 96.6│ 8.05│ 2.05│ .021│ .074 - Bridgeport│ │ │ │ │ │ - Canal, │ 34│ 124.5│ 10.90│ 2.07│ .013│ .066 - Lockport │ │ │ │ │ │ - Joliet │ 38│ 41.5│ 4.22│ 0.83│ .021│ .086 - │ │ │ │ │ │ - │ │ │ │ │ │ - │ │ │ │ │ │ - │ │ │ │ │ │ - │ │ │ │ │ │ - Dresden │ 52│ │ │ │ │ - Heights │ │ │ │ │ │ - Dresden │ 52│ │ │ │ │ - Heights │ │ │ │ │ │ - Morris │ 62│ 24.5│ 2.46│ .60│ .075│ .424 - │ │ │ │ │ │ - Marseilles │ 79│ │ │ │ │ - Marseilles │ 79│ │ │ │ │ - Ottawa │ 85│ 15.3│ 1.55│ .41│ .197│ .966 - La Salle │ 100│ 17.5│ 1.05│ .43│ .109│ .979 - Henry │ 129│ 13.3│ .92│ .38│ .102│ .800 - Chillicothe │ 145│ │ │ │ │ - │ │ │ │ │ │ - │ │ │ │ │ │ - Averyville │ 161│ 13.5│ .81│ .37│ .004│ 1.150 - │ │ │ │ │ │ - │ │ │ │ │ │ - Wesley │ 165│ 12.0│ .57│ .41│ .083│ 1.03 - │ │ │ │ │ │ - Pekin │ 175│ 12.3│ .70│ .43│ .060│ .990 - Havana │ 205│ 11.2│ .60│ .36│ .065│ .570 - Beardstown │ 237│ 10.7│ .69│ .44│ .106│ .685 - La Grange │ 249│ │ │ │ │ - Kampsville │ 294│ 11.3│ .66│ .44│ .044│ .870 - Kampsville │ 294│ │ │ │ │ - Grafton │ 325│ 9.8│ .46│ .42│ .031│ 1.06 - │ │ │ │ │ │ - Grafton │ 325│ │ │ │ │ - │ │ │ │ │ │ - ────────────┴────────┴────────┴────────┴──────────┴────────┴──────── - - ────────────┬─────────────────────┬─────────── - Sampling │ Dissolved Oxygen │ Remarks - Point │ │ - │ │ - │ │ - │ │ - ────────────┼───────┬──────┬──────┼─────────── - │ Jan. │ July │ Nov. │ - │30–Feb.│ 8–15 │12–19,│ - │2, 1912│ 1912 │ 1912 │ - ────────────┼───────┼──────┼──────┼─────────── - Lake │ 14.1│ │ 10.8│Typical - Michigan │ │ │ │ chemical - │ │ │ │ analysis - Canal, │ │ │ 6.9│Kedzie - Bridgeport│ │ │ │ Avenue - Canal, │ 9.9│ │ 1.7│Above dam - Lockport │ │ │ │ - Joliet │ │ 1.4│ 5.6│Aëration - │ │ │ │ over dam. - │ │ │ │ Dilution - │ │ │ │by Des - │ │ │ │ Plaines - │ │ │ │ River - Dresden │ │ 1.0│ 4.1│Des Plaines - Heights │ │ │ │ River - Dresden │ │ │ 10.4│Kankakee - Heights │ │ │ │ River - Morris │ 7.8│ │ 5.7│Illinois - │ │ │ │ River - Marseilles │ 5.7│ 0.6│ 6.8│Above dam - Marseilles │ 8.2│ 4.5│ 9.3│Below dam - Ottawa │ 10.0│ │ 8.1│ - La Salle │ 5.4│ │ 7.8│ - Henry │ │ │ 7.9│ - Chillicothe │ 3.4│ 1.5│ 5.9│Above - │ │ │ │ Peoria - │ │ │ │ Lakes - Averyville │ 3.3│ 8.2│ 8.9│Below - │ │ │ │ Peoria - │ │ │ │ Lakes - Wesley │ │ │ 7.1│Below - │ │ │ │ Peoria - Pekin │ 4.9│ 3.2│ 8.9│ - Havana │ 4.8│ │ 8.8│ - Beardstown │ 6.5│ │ 9.1│ - La Grange │ │ 4.1│ 9.4│Below dam - Kampsville │ │ 4.1│ 10.0│Above dam - Kampsville │ │ 4.6│ 10.0│Below dam - Grafton │ 6.6│ 4.7│ 10.4│Illinois - │ │ │ │ River - Grafton │ │ 7.3│ 12.0│Mississippi - │ │ │ │ River - ────────────┴───────┴──────┴──────┴─────────── - - -=222. Self-Purification of Lakes.=—Sewage may be disposed of into lakes -with as great success as into running streams if conditions exist which -are favorable to self-purification. Lakes and rivers purify themselves -from the same causes; oxidation, sedimentation, etc., but in the former -the currents are much less pronounced and may be entirely absent. In -shallow lakes (20 feet or less in depth) dependence must be placed on -horizontal currents and the stirring action of the wind to keep the -water in motion in order that the sewage and the diluting water may be -mixed. In deeper bodies of water, currents induced by the wind are -helpful but entire dependence need not be placed upon them. Vertical -currents, and the seasonal turnovers in the spring and fall completely -mix the waters of the lake above those layers of water whose temperature -never rises higher than 4° C. - -In the early winter the cold air cools the surface waters of a lake. The -cooling increases the density of the surface water causing it to sink, -and allowing the warmer layers below to rise and become cooled. After -the temperature of the entire lake has reached 4° C. the vertical -currents induced by temperature cease, as continued cooling decreases -the density of the surface water maintaining the same layer at the -surface. In the spring as the temperature of the surface water rises to -4° C. and above it becomes heavier and drops through the colder water -below causing vertical currents. These phenomena are known as the fall -and spring turnovers. The former is more pronounced. These turnovers are -effective in assisting in the self-purification of lakes. - - -=223. Dilution in Salt Water.=—The oxygen content in salt water is about -20 per cent less than in fresh water at the same temperature. The -greater content of matter in solution in salt water reduces its capacity -to absorb many sewage solids. This, together with the chemical reaction -between the constituents of the salt water and those of the sewage serve -to precipitate some of the sewage solids and to form offensive sludge -banks. The evidence of the action which takes place in the absorption of -oxygen from the atmosphere by salt water and its effect on dissolved -sewage solids is conflicting, but in general fresh water is a better -diluting medium than salt water. - -Black and Phelps have made valuable studies of the relative rates of -absorption of oxygen from the air by fresh and salt water. The results -of their experiments are published in a Report to the Board of Estimate -and Apportionment of N. Y. City, made March 23, 1911.[131] Concerning -these rates they conclude: - - Therefore there is no reason to believe that the reaëration of - salt water follows any other laws than those we have determined - mathematically and experimentally for fresh water. In the absence - of fuller information on the effect of increased viscosity upon - the diffusion coefficient, it can only be stated that the rate of - reaëration of salt water is less than that of fresh water, in - proportion to the respective solubilities of oxygen in the two - waters, and still less, but to an unknown extent, by reason of the - greater viscosity and consequent small value of the diffusion - coefficient. - - -=224. Quantity of Diluting Water Needed.=—In a large majority of the -problems of disposal of sewage by dilution it is not necessary to add -sufficient diluting water to oxidize completely all organic matter -present. Ordinarily it is sufficient to prevent putrefactive conditions -until the flow of the stream, lake, or tidal current, has reached some -large body of diluting water or where putrefaction is no longer a -nuisance. It is never desirable to allow the oxygen content of a stream -to be exhausted as putrescible conditions will exist locally before -exhaustion is complete. The exact point to which oxygen can be reduced -in safety is in some dispute. Black and Phelps have assumed 70 per cent -of saturation as the allowable limit; Fuller has placed it at 30 per -cent; Kinnicutt, Winslow, and Pratt have placed it at 50 per cent. Since -the reaction between the oxygen and the organic matter is quantitative, -others have placed the limit in terms of parts per million of oxygen. -Wisner,[132] has recommended a minimum of 2.5 p.p.m. as the limit for -the sustenance of fish life, which is not far from Fuller’s limit for -hot-weather conditions. - -Formulas of various types have been devised to express the rate of -absorption of oxygen with a given quantity of diluting water which is -mixed with a given quantity and quality of sewage. The quantity of -sewage is sometimes expressed in terms of the tributary population or in -other ways. Knowing the rate at which oxygen is exhausted and the -velocity of flow of the stream, the point at which the oxygen will be -reduced to the limit allowed is easily determined. The accuracy of none -of these formulas has been proven, and their use, without an -understanding of the effect of local conditions, may lead to error. They -may be used as a check on the bio-chemical oxygen demand determinations, -which should be conclusive. - -The following formula, based on the work of Black and Phelps, is a guide -to the amount of sewage which can be added to a stream without causing a -nuisance. It is: - - _C_ = (log(_O′_⁄_O_))⁄_kt_, - - in which _C_ = per cent of sewage allowed in the water; - - _O′_ = per cent of saturation or the p.p.m. of oxygen in the - mixture at the time of dilution; - - _O_ = per cent of saturation or the p.p.m. of oxygen in the - stream after period of flow to point beyond which no - nuisance can be expected; - - _t_ = time in hours required for the stream to flow to this - point; - - _k_ = constant determined by test determinations of the - factors in the following expression: - - _k_ = (log(_O′__{1}⁄_O__{1}))⁄_C__{1}_t__{1}, - - in which _O′__{1} = per cent of saturation or the p.p.m. of oxygen in - the diluting water before mixing with the sewage; - - _O__{1} = per cent of saturation or the p.p.m. of oxygen in - an artificial mixture made in the laboratory, - after _t__{1} hours of incubation; - - _C__{1} = per cent of sewage in the mixture; - - _t__{1} = number of hours of incubation of the mixture of - sewage and diluting water under laboratory - conditions. - -In the solution of these formulas it is desired to determine the -permissible amount of sewage to discharge into a given quantity of -diluting water. This value is expressed by C in the first equation. In -solving this equation: - - _O′_ is determined by laboratory tests and should represent - the conditions to be expected during various seasons - of the year; - - _O_ is determined by judgment. It may be 30 per cent or 50 - per cent or more as previously explained; - - _t_ is determined by float tests or other measurements of - the stream flow; - - _k_ is determined by laboratory tests in which mixtures of - various strengths are incubated for various periods - of time. Different values of _k_ will be obtained for - different characteristics of the sewage; but for the - same sewage the value of _k_ should be unchanged for - different periods of incubation. - -Rideal devised the formula:[133] - - _XO_ = _C_(_M_ − _N_)_S_ - - in which _X_ = flow of the stream expressed in second-feet; - - _O_ = grams of free oxygen in one cubic foot of water; - - _S_ = rate of sewage discharge in second-feet; - - _M_ = grams of oxygen required to consume the organic matter - in one cubic foot of diluted sewage as determined by - the permanganate test with 4 hours boiling; - - _N_ = grams of oxygen available in the nitrites and nitrates - in one cubic foot of diluted sewage; - - _C_ = ratio between the amount of oxygen in the stream and - that required to prevent putrefaction. Where _C_ is - equal to or greater than one, satisfactory conditions - have been attained. - -In using this formula it is necessary to make analyses of trial mixtures -of sewage and water until the correct mixture has been found. - -Hazen’s formula is:[134] - - _D_ = _x_⁄_S_ = 4_m_⁄_O_, - - in which _D_ = dilution ratio; - - _x_ = volume of water; - - _S_ = volume of sewage; - - _m_ = result of the oxygen consumed test expressed in p.p.m. - after 5 minutes, boiling with potassium permanganate; - - _O_ = amount of dissolved oxygen in the diluting water - expressed in p.p.m. - -For comparison with Rideal’s formula the factor of 7 should be used -instead of 4 to allow for the increased time of boiling. - -Since the amount of oxygen needed is dependent on the amount of organic -matter in the sewage rather than the total volume of the sewage, and -since the amount of organic matter is closely proportional to the -population, the amount of diluting water has sometimes been expressed in -terms of the population. Hering’s recommendation for the quantity of -diluting water necessary for Chicago sewage was 3.3 cubic feet of water -per second per thousand population. Experience has proven this to be too -small. Between a minimum limit of 2 second-feet and a maximum of 8 -second-feet of diluting water per thousand population the success of -dilution is uncertain. Above this limit success is practically assured -and below this limit failure can be expected. - -Even with these carefully devised formulas and empirical guides, the -factors of reaëration, dilution, sedimentation, temperature, etc., may -have so great an effect as to vitiate the conclusions. As shown in Table -75 dilution in winter is far more successful than in summer. The lower -temperatures so reduce the activity of the putrefying organisms that -consumption of oxygen is greatly retarded. - - -=225. Governmental Control.=—A comprehensive discussion of the legal -principles governing the pollution of inland waters is contained in “A -Review of the Laws Forbidding the Pollution of Inland Waters,” by E. B. -Goodell, published by the United States Geological Survey in 1905, as -Water Supply Paper No. 152. - -The disposal of sewage by dilution is subject to statutory limitations -in many states. The enforcement of these laws is usually in the hands of -the state board of health, which is frequently given discretionary -powers to recommend and sometimes to enforce measures for the abatement -of an actual or potential nuisance. Such recommendations usually take -the form of a specification of certain forms of treatment preliminary to -disposal by dilution. No project for the disposal of sewage by dilution -should be consummated until the local, state, national, and in the case -of boundary waters, international laws have been complied with. The -attitude of the courts in different states has not been uniform. Little -guidance can be taken from the personal feeling of the persons -immediately interested. The opinion of the riparian owner 5 miles down -stream may differ materially from the popular will of the voters of a -city, and it is likely to receive a more favorable hearing from the -court. Statutes and legal precedents are the safest guides. - - -=226. Preliminary Treatment.=—If the sewage to be disposed of by -dilution contains unsightly floating matter, oil, or grease, no amount -of oxygen in the diluting water will prevent a nuisance to sight, or the -formation of putrefying sludge banks. Under such conditions it will be -necessary to introduce screens or sedimentation basins, or both, in -order to remove the floating and the settling solids. Biologic tanks, -filtration, or other methods of treatment may be necessary for the -removal of other undesirable constituents. - - -=227. Preliminary Investigations.=—Before adopting disposal of sewage by -dilution without preliminary treatment, or before considering the proper -form of treatment necessary to render disposal by dilution successful, a -study should be made of the character of the body of water into which -the sewage or effluent is to be discharged. This study should include: -measurements of the quantity of water available at all seasons of the -year; analyses of the diluting water to determine particularly the -available dissolved oxygen; observations of the velocity and direction -of currents, and the effect of winds thereon; a study of the effect on -public water supplies, bathing beaches, fish life, etc. Good judgment, -aided by the proper interpretation of such information should lead to -the most desirable location for the sewer outlet. If preliminary -treatment is found to be necessary tests should be made to determine the -necessary extent and thoroughness of the treatment. - - - - - CHAPTER XV - SCREENING AND SEDIMENTATION - - -=228. Purpose.=—The first step in the treatment of sewage is usually -that of coarse screening in order to remove the larger particles of -floating or suspended matter. Screens and sedimentation basins are used -to prevent the clogging of sewers, channels, and treatment plants; to -avoid clogging of and injuries to machinery; to overcome the -accumulation of putrefying sludge banks; to minimize the absorption of -oxygen in diluting water; and to intercept unsightly floating matter. - -By the plain sedimentation of sewage is meant the removal of suspended -matter by quiescent subsidence unaffected by septic action or the -addition of chemicals or other precipitants. In order to prevent septic -action plain sedimentation tanks must be cleaned as frequently as once -or twice a week in warm weather but not quite so often in cold weather. - -Fine screening may take the place of sedimentation where insufficient -space is available for sedimentation tanks, and it is desired to remove -only a small portion of the suspended matter. Recent American practice -has tended to restrict the field of fine screening to treatment -requiring less than 10 per cent removal of suspended matter, thus -eliminating screens from the field covered by plain sedimentation tanks. -The practice is well expressed by Potter, who states:[135] - - Where a high degree of purification is sought, the use of fine - screens is of doubtful value. A modern settling tank will give - better results and at a less cost for a given degree of - purification. A settled liquid is also superior to a screened - liquid for subsequent biological treatment in filters.... Again - the storing of large quantities of screenings must necessarily be - more objectionable than the storing of the digested sludge of a - modern settling tank. - -[Illustration: - - FIG. 150.—Types of Moving Screens. - - Trans. Am. Society Civil Engineers, Vol. 78, 1915, p. 893. -] - - -=229. Types of Screens.=—The definitions of some types of screens as -proposed by the American Public Health Association follow: A _bar -screen_ is composed of parallel bars or rods. A _mesh screen_ is -composed of a fabric, usually wire. A _grating_ consists of 2 sets of -parallel bars in the same plane in sets intersecting at right angles. A -_band screen_ consists of an endless perforated band or belt which -passes over upper and lower rollers. A _perforated plate screen_ is made -of an endless band of perforated plates similar to a band screen. A -_wing screen_ has radial vanes uniformly spaced which rotate on a -horizontal axis. A _disc screen_ consists of a circular perforated disc -with or without a central truncated cone of similar material mounted in -the center. The Reinsch Wurl screen is the best known type of disc -screen. A _cage screen_[136] consists of a rectangular box made up of -parallel bars with the upstream side of the box or cage omitted. -Allen[137] gives the following definitions: A _drum screen_ is a -cylinder or cone of perforated plates or wire mesh which rotates on a -horizontal axis. A _shovel vane screen_ is similar to a wing screen with -semicircular wings and a different method of removing the screenings. -Examples of a band screen, a wing screen, a shovel vane screen, a drum -screen and a disc screen are shown in Fig. 150. A bar screen is shown in -Fig. 151 and a cage screen is shown in Fig. 152. - -[Illustration: - - FIG. 151.—Sketch of a Bar Screen. -] - -[Illustration: - - FIG. 152.—Sketch of a Cage Screen. -] - -Screens can be classed as fixed, movable, or moving. Fixed screens are -permanently set in position and must be cleaned by rakes or teeth that -are pulled between the bars. Movable screens are stationary when in -operation, but are lifted from the sewage for the purpose of cleaning. -Moving screens are in continuous motion when in operation and are -cleaned while in motion. Fixed bar screens may be set either vertical, -inclined, or horizontal. - -Movable screens with a cage or box at the bottom are sometimes used. The -box should be of solid material to prevent the forcing of screenings -through it when the screen is being raised for cleaning. A mesh screen -should be used only under special circumstances because of the -difficulty in cleaning. Screens which must be raised from the sewage for -cleaning should be arranged in pairs in order that one may be working -when the other is being cleaned. Movable screens are undesirable for -small plants because the labor involved in raising and lowering is -greater than in cleaning with a rake and the screens are more likely to -be neglected. In a large plant rakes operated by hand are too small for -cleaning the screens. A fixed screen is sometimes used with moving teeth -fastened to endless chains. The teeth pass between the parallel bars and -comb out the screenings. If the screen chamber in a small plant is too -deep for accessibility a movable cage or box screen may be desirable. - -Moving screens are generally of fine mesh or perforated plates. They are -kept moving in order to allow continuous cleaning. They are cleaned by -brushes or by jets of air, water, or steam. - - -=230. Sizes of Openings.=—The area or size of the opening of a screen is -dependent upon the character of the sewage to be treated and upon the -object to be attained. - -Large screens, with openings between 1½ inches and 6 inches are used to -protect centrifugal pumps, tanks, automatic dosing devices, conduits, -and gate valves from large objects such as pieces of timber, dead -animals, etc., which are found in sewage. The quantity of material -removed is variable, and is usually small. - -Medium-size screens with openings from ¼ inch to 1½ inches are used to -prepare sewage for passage through reciprocating pumps, complex dosing -apparatus, contact beds, and sand filters. The amount of material -removed varies from 0.5 to 10 cubic feet per million gallons of sewage -treated, dependent on the character of the sewage and the size of the -screen. Screenings before drying contain 75 to 90 per cent moisture and -weigh 40 to 50 pounds per cubic foot. At times the amount removed may -vary widely from the limits stated. Schaetzle and Davis[138] state: - - Screenings differ greatly both in amount and character.... The - amount varies with the days of the week as well as during the - course of the day. It reaches its maximum about noon or shortly - before and commences to disappear about midnight, reaching a - minimum about 4 or 5 a.m. The material is almost wholly organic - and consists of scraps of vegetables or fruit, cloth, hair, wood, - paper and lumps of fecal matter. The amount varies so widely that - it is impossible to state just what to expect any definite size - screen to remove. The amount of water contained is small compared - with that in the sludge in sedimentation basins and amounts to - from 70 per cent to 80 per cent. On account of its organic origin - it is highly putrescible. - -Medium-size screens are sometimes placed close together with the bars of -the one opposite the openings in the other, thus approaching a fine -screen. - -Fine screens vary in size of opening from ¼ inch to 50 openings per -linear inch or 2,500 per square inch. They are used for removing solids -preparatory to disposal by dilution, to protect sprinkling filters, -complex dosing apparatus, sand filters, sewage farms, and to prevent the -formation of scum in subsequent tank treatment. In general, fine screens -will remove from 0.1 to 1 cubic yard of wet material per million gallons -of sewage treated. The wet screenings will contain about 75 per cent -moisture and will weigh about 60 pounds per cubic foot. The dry weight -of the screenings will therefore be about 10 to 400 pounds per million -gallons of sewage treated. The effect of the removal of this amount of -material is usually not detectable by methods of chemical analysis, the -amount of suspended matter before and after screening being found -unchanged. - -In his conclusions on the discussion of the results to be expected from -fine screens, Allen states:[139] - - With openings not more than 0.1 inch in size, fine screening - should remove at least 30 per cent of the suspended solids and 20 - per cent of the suspended organic solids from ordinary domestic - sewage, or 0.1 cubic yard of screenings, containing 75 per cent - water per thousand population daily. - -The effect of the use of different size openings under the same -conditions is shown in Fig. 153.[140] Some data covering the amount of -material removed by screening are given in Table 76. More extensive data -are given in Volume III of “American Sewerage Practice” by Metcalf and -Eddy. - - TABLE 76 - - DATA ON SCREENS - - (Trans. Am. Society Civil Engineers, Vol. 78, Page 942) - - ───────┬──────────┬──────────┬────────────────────────── - Type of│ Location │ Clear │ Screenings - Screen │ │ Opening, │ - │ │in Inches │ - │ │ │ - │ │ │ - │ │ │ - ───────┼──────────┼──────────┼────────────┬───────────── - │ │ │Per Million │ Per 1000 - │ │ │ Gallons, │ Population - │ │ │_y_ = Cubic │ Daily, - │ │ │ Yard │ _y_ = Cubic - │ │ │ _t_ = Tons │ Yard - │ │ │ │ _t_ = Tons - ───────┼──────────┼──────────┼────────────┼───────────── - Band │Hamburg │ 0.6 │ 0.34_y_ │ 0.018_y_ - │Göttingen │ 0.4 │ 0.35_y_ │ 0.026_y_ - │Sutton │0.375[141]│ 0.6_y_ │ - │Chicago │ │ 2.4–3.1_t_ │ - Wing │Frankfort │ 0.40 │ 0.7_y_ │ 0.040_y_ - │Elberfeld │ 0.40 │ 1.15_y_ │ 0.053_y_ - │Stralsund │ 0.20 │ │ 0.079_y_ - │Wiesbaden │ 0.60 │ 1.1_y_ │ 0.033_y_ - Shovel │Strassburg│ 0.10 │ 1.6_y_ │ 0.043_y_ - vane │ │ │ │ - │Gleiwitz │ 0.12 │ │ 0.192_y_ - │Temesvar │ 0.12 │ 0.9–1.7_y_ │0.067–.133_y_ - Drum │Bromberg │ 0.08 │ 4.75_t_ │ - │Mainz │ Note 6 │ 0.52_y_ │ - │Trier │ 0.10 │0.39–0.42_y_│ 0.13_y_ - │Osnabruck │ 0.08 │ 3.2–4.0_y_ │ 0.08–.10_y_ - Weand │Reading, │ 36[141] │ 1.0_y_ │ - │ Pa. │ │ │ - │Brockton │ 36[141] │ 1.4_t_ │ - Reinsch│Dresden │ 0.08 │ 0.97_t_ │ 0.09_y_ - Wurl │ │ │ │ - ───────┴──────────┴──────────┴────────────┴───────────── - - ───────┬────────┬───────────┬─────────┬──────────── - Type of│Per Cent│Horse-Power│ Cost of │ Remarks - Screen │Moisture│Per Screen │Operation│ - │ │ │ Per │ - │ │ │ Million │ - │ │ │Gallons, │ - │ │ │ Dollars │ - ───────┼────────┼───────────┼─────────┼──────────── - │ │ │ │ - │ │ │ │ - │ │ │ │ - │ │ │ │ - │ │ │ │ - │ │ │ │ - ───────┼────────┼───────────┼─────────┼──────────── - Band │ 87 │ 2.5 │ │Note 1 - │ │ 2.0 │ │ - │ │ │ │ - │ 79 │ │ │Stock Yard - Wing │ │ 5.0 │ │Note 2 - │ 75 │ │ │Note 3 - │ │ 4.5 │ │ - │ │hand power │ 1.64 │Note 4 - Shovel │ 89.3 │ 3.35 │ │Note 5 - vane │ │ │ │ - │ │ │ 0.90 │ - │ 60–70 │ │ small │ - Drum │ 40–60 │ │ 2.45 │Experimental - │ 75 │ 5.2–6.8 │0.89–3.42│ - │ 50–60 │ │ 2.41 │Experimental - │ │ 9.00 │ │Note 7 - Weand │ 89.5 │ 2.0 │ 1.00± │ - │ │ │ │ - │ │ │ │ - Reinsch│ 84 │ 2.5 │.325–1.76│ - Wurl │ │ │ │ - ───────┴────────┴───────────┴─────────┴──────────── - - Notes:—1. After removal of ½ this volume of grit. - - 2. After removal of 16 per cent by the grit chamber. - - 3. Including 0.6 cubic yard grit per million gallons. - - 4. After passing 1.6 inch bar screen. - - 5. After removal of 0.132 cubic yard grit and coarse - screenings per 1000 population. - - 6. 0.12, 0.04–0.08. - - 7. Before removal of 0.4 cubic yard grit per million gallons. - -[Illustration: - - FIG. 153.—Screenings Collected on Different Sized Openings. - - 1921 Report on Industrial Wastes Disposal, Union Stock Yards District, - Chicago, Illinois, to the Sanitary District of Chicago. -] - - -=231. Design of Fixed and Movable Screens.=—The determination of the -size of the opening is the first step in the design of a sewage screen. -This is followed by the computation of the net area of openings in the -screen. The final steps are the determination of the overall dimensions -of the screen; the size of the bar, wire, or support; and the dimensions -of the screen chamber. The net area of openings is fixed by the -permissible velocity of flow through the screen and the quantity of -sewage to be treated. In determining the velocity of flow the general -principle should be followed that the velocity should not be reduced -sufficiently to allow sedimentation in the screen chamber. The velocity -of grit bearing sewage in passing through coarse screens should not be -reduced below 2 or 3 feet per second. If the sewage contains no grit, or -the screen is placed below a grit chamber the velocity through a medium -or fine screen should be from ½ to 1½ feet per minute. The velocity -through the screen in a direction normal to the plane of the screen can -be reduced without reducing the horizontal velocity of the sewage by -placing the screen in a sloping position. - -The final steps are the design of the screen bar and the determination -of the dimensions of the screen and of the screen chamber. The size of -the bar in a bar screen, or as a support to a wire mesh, is dependent on -the unsupported length of the bar. The stresses in the bars are the -results of impact and bending, caused by cleaning, and of the load due -to the backing up of the sewage when the screen is clogged. Allowance -should be made for a head of 2 or 3 feet of sewage against the screen. A -generous allowance should be made in addition for the indeterminate -stresses due to cleaning. The screen should be supported only at the top -and bottom, as intermediate supports in a bar screen are undesirable -unless they are so arranged as not to interfere with the teeth of the -cleaning devices. - -Fixed screens should be placed at an angle between 30° and 60° with the -horizontal, with the direction of slope such that the screenings are -caught on the upper portion of the screen. A small slope is desirable in -order to obtain a low velocity through the screen. The slope is limited -since the smaller the slope the longer the bars of the screen and the -greater the difficulty of hand cleaning. Small slopes will tend to make -the screens self cleaning. As the screen clogs, the increasing head of -sewage will push the accumulated screenings up the screen. The use of -flat screens in a vertical position is not desirable because of the -difficulty of cleaning and the accumulation of material at inaccessible -points. If a flat screen is placed in a horizontal position with the -flow of sewage downward difficulties are encountered in cleaning and -solid matter is forced through the screen as clogging increases. An -upward flow through a horizontal screen is undesirable as the material -is caught in a position inaccessible for cleaning. Movable screens are -more easily handled when placed in a vertical position. - -In the construction of small screens, round bars are sometimes used -where the unsupported length of the bar is less than 3 or 4 feet. They -are not recommended, however, as the efficient area and the amount of -material removed by the screen are diminished. Bars which produce -openings with the larger end upstream are undesirable as particles -become wedged in the screen, and are either forced through or become -difficult to remove.[142] Rectangular bars are easily obtained and give -satisfactory service except where they are of insufficient strength -laterally. For greater lateral thickness a pear-shaped bar is sometimes -used, with the thicker side upstream. Fine mesh screens or perforated -plates are supported on grids or parallel bars of stronger material -designed to take up the heavy stresses on the screen. - -The dimensions of the bar may be selected arbitrarily. The length and -width of the screen are fixed to give desirable dimensions to the screen -chamber and to give the necessary net opening in the screen. The width -of the screen chamber and the screen should be the same. The screen -chamber should be sufficiently long to prevent swirling and eddying -around the screen. If the dimensions thus fixed permit an undesirable, -velocity in the screen chamber they should be changed. A sufficient -length of screen should be allowed to project above the sewage for the -accumulation of screenings. The bars may be carried up and bent over at -the top as shown in Fig. 151 to simplify the removal of screenings. - -Coarse screens are usually placed above all other portions of a -treatment plant. They may be followed by grit chambers or finer screens. -Coarse screens are occasionally placed as a protection above medium or -fine screens. In sewage containing grit the smaller screens are -sometimes placed below the grit chamber. It is desirable to provide some -means of diverting the sewage from a screen chamber to allow of repairs -to the screen and the cleaning of the chamber. Screen chambers are -sometimes designed in duplicate to allow for the cleaning of one while -the other is operating. - - - PLAIN SEDIMENTATION - - -=232. Theory of Sedimentation.=—Sedimentation takes place in sewage -because some particles of suspended matter have a greater specific -gravity than that of water. All particles do not settle at the same -rate. Since the weights of particles vary as the cubes of their -diameters, whereas the surface areas (upon which the action of the water -takes place) vary only as the squares of the diameters, the amount of -the skin friction on small particles is proportionally greater than that -on large particles, because of the relatively greater surface area -compared to their weight. As a result the smaller particles settle more -slowly. The velocity of sedimentation of large particles has been found -to vary about as the diameter and of small particles as the square root -of the diameter. The change takes place at a size of about 0.01 mm. - -Sedimentation is accomplished by so retarding the velocity of flow of a -liquid that the settling particles will be given the opportunity to -settle out. The slowing down of the velocity is accomplished by passing -the sewage through a chamber of greater cross-sectional area than the -conduit from which it came. The time that the sewage is in this chamber -is called the period of retention. Although the shape of a basin, the -arrangement of the baffles and other details have a marked effect on the -results of sedimentation, the controlling factors are the period of -retention and the velocity of flow. Another factor affecting the -efficiency of the process is the quality of the sewage. Usually the -greater the amount of sediment in the sewage the greater the per cent of -suspended matter removed. A method for the determination of the proper -period of sedimentation has been developed by Hazen in Transactions of -the American Society of Civil Engineers, Volume 53, 1904, page 45. The -results of his studies are summarized in Fig. 154 which shows the per -cent of sediment remaining in a treated water after a certain period of -retention. This period of retention is expressed in terms of the -hydraulic coefficient[143] of the smallest size particle to be removed. -Table 77 shows the hydraulic coefficients of various particles. In Fig. -154 _a_ represents the period of retention and _t_ the time that it -would take a particle to fall to the bottom of the basin. The different -lines of the diagram represent the results to be expected by various -arrangements of settling basins. The meaning of these lines is given in -Table 78. - - TABLE 77 - - HYDRAULIC VALUES OF SETTLING PARTICLES IN MILLIMETERS PER SECOND - - ───────────────────────────────────┬─────────────────────────────────── - Diameter in mm. │ Hydraulic Value - ───────────────────────────────────┼─────────────────────────────────── - 1.00 │ 100 - 0.80 │ 83 - 0.60 │ 63 - 0.50 │ 53 - 0.40 │ 42 - 0.30 │ 32 - 0.20 │ 21 - 0.15 │ 15 - 0.10 │ 8 - 0.08 │ 6 - 0.06 │ 3.8 - 0.05 │ 2.9 - 0.04 │ 2.1 - 0.03 │ 1.3 - 0.02 │ 0.62 - 0.015 │ 0.35 - 0.010 │ 0.154 - 0.008 │ 0.098 - 0.006 │ 0.055 - 0.005 │ 0.0385 - 0.004 │ 0.0247 - 0.003 │ 0.0138 - 0.002 │ 0.0062 - 0.0015 │ 0.0035 - 0.001 │ 0.00154 - 0.0001 │ 0.0000154 - ───────────────────────────────────┴─────────────────────────────────── - -An example will be given to illustrate the method of using the diagram -and tables to determine the size of a sedimentation basin to perform -certain required work. - - Let it be required to determine the period of retention in a - continuously operated sedimentation basin with good baffling, - corresponding to two properly baffled sedimentation basins in - series. The basins are to remove 60 per cent of the finest - particles which are to have a size of .01 mm. The quantity to be - treated daily is 3,000,000 gallons. - - 1st. Entering Table 77, we find that the hydraulic value of the - finest particles is .154 mm. per second. - - 2d. Since we wish to remove 60 per cent of the finest particles, - 40 per cent will remain. Since Fig. 154 shows the per cent - remaining after the time _a_⁄_t_ we enter Fig. 154 at 40 per cent - on the ordinates and run horizontally until we encounter Line 4 - corresponding to good baffling in Table 78. We then run down - vertically from this intersection and find that the ratio of - _a_⁄_t_ is 1.0. - - Then _a_ equals _t_, which means that the period of retention - should equal the time that it takes a particle 0.01 mm. in - diameter to drop from the top to the bottom of the basin. Since - this depends on the depth of the basin it is necessary to - determine the depth before the other dimensions of the basin can - be fixed. - -Although this method is seldom used in practice for the final design of -a sedimentation basin, it is a guide to judgment and can be used to -supplement the data obtained from tests. - -[Illustration: - - FIG. 154.—Hazen’s Diagram, Showing the Relation between the Time of - Settling and the Period of Retention in Various Types of - Sedimentation Basins. - - Trans. Am. Society Civil Engineers, Vol. 53, 1904, p. 45. -] - - TABLE 78 - - COMPARISON OF DIFFERENT ARRANGEMENTS OF SETTLING BASINS - - (From Hazen) - ────────────────────────────────────────┬────────────┬───────────────── - Description of Basins │Line in Fig.│ Values of - │ 154 │ _a_⁄_t_. - ────────────────────────────────────────┼────────────┼───────────────── - │ │ Per Cent of - │ │ Matter Removed - ────────────────────────────────────────┼────────────┼─────┬─────┬───── - │ │ 50 │ 74 │87.5 - ────────────────────────────────────────┼────────────┼─────┼─────┼───── - Theoretical maximum. Cannot be reached.│ A │ 0.50│ 0.75│0.875 - Surface skimming. Rockner Roth system. │ B │ 0.54│ 0.98│ 1.37 - Intermittent basins, reckoned on time of│ C │ │ │ - service only. │ │ 0.63│ 1.26│ 1.89 - Continuous basin. Theoretical limit. │ D │ 0.69│ 1.38│ 2.08 - Close approximation to the above. │ 16 │ 0.71│ 1.45│ 2.23 - Very well baffled basin. │ 8 │ 0.73│ 1.62│ 2.37 - Good baffling. │ 4 │ 0.76│ 1.66│ 2.75 - Two basins, tandem. │ 2 │ 0.82│ 2.00│ 3.70 - One long basin, well controlled. │ 1.5 │ 0.90│ 2.34│ 4.50 - Intermittent basin in service half time.│ E │ 1.26│ 2.50│ 3.80 - One basin, continuous. │ 1 │ 1.0│ 3.00│ 7.00 - ────────────────────────────────────────┴────────────┴─────┴─────┴───── - -The design of sedimentation basins should be based on experimental -observations made upon the quantity of sediment removed at certain rates -of flow and periods of retention in different types of basins. Hazen’s -mathematical analysis is serviceable in making preliminary estimates and -in checking the results. The shape of the tank, period of retention and -rate of flow producing the most desirable results should be duplicated -with the expectation of obtaining similar results or results but -slightly modified from those obtained in the tests. This is the most -satisfactory method of determining the proper period of retention. - - -=233. Types of Sedimentation Basins.=—A sedimentation basin is a tank -for the removal of suspended matter either by quiescent settlement or by -continuous flow at such a velocity and time of retention as to allow -deposition of suspended matter.[144] The difference between -sedimentation tanks and other forms of tank treatment is that no -chemical or biological action is depended on for the successful -operation of the tank. Sedimentation tanks may be divided into two -classes, grit chambers and plain sedimentation basins. - -A grit chamber is a chamber or enlarged channel in which the velocity of -flow is so controlled that only heavy solids, such as grit and sand, are -deposited while the lighter organic solids are carried forward in -suspension. If the velocity of flow is more than about one foot per -second, the tank is a grit chamber and below this velocity it is a plain -sedimentation basin. - - There are six general types of plain sedimentation basins: - - 1st. Rectangular flat-bottom tanks operated on the continuous-flow - principle. - - 2nd. Rectangular flat-bottom tanks operated on the fill and draw - principle. - - 3rd. Rectangular or circular hopper-bottom tanks operated on the - continuous-flow principle, with horizontal flow. - - 4th. Rectangular or circular hopper-bottom tanks operated on the - fill and draw principle, with horizontal flow. - - 5th. Rectangular or circular hopper-bottom tanks operated on the - continuous-flow principle with vertical flow. - - 6th. Circular hopper-bottom tanks operated on the continuous-flow - principle with radial flow. - - TABLE 79 - - CRITICAL VELOCITIES FOR THE TRANSPORTATION OF DEBRIS - - Sedimentation will not Occur at Higher Velocities - ───────────┬───────────────────────────────────┬────────────────────── - Diameter of│Critical Velocity, Feet per Second.│ Size of Screen or - Particle in│ │ Number of Meshes per - Millimeters│ │ Inch - ───────────┼───────────────────────────────────┼────────────────────── - │ Specific Gravity │ - ───────────┼────────┬────────┬────────┬────────┼────────────────────── - │ 1.5 │ 2.0 │ 3.0 │ 5.0 │ - ───────────┼────────┼────────┼────────┼────────┼────────────────────── - 0.010 │0.13 │0.20 │0.22 │0.28 │ - 0.050 │0.23 │0.34 │0.39 │0.50 │More than 200 - 0.100 │0.30 │0.42 │0.50 │0.65 │More than 150 - 0.500 │0.55 │0.73 │0.91 │1.15 │More than 28 - 1.0 │0.71 │0.92 │1.18 │1.50 │More than 14 - 1.25 │0.77 │1.00 │1.30 │1.60 │ - 2.0 │0.92 │1.20 │1.50 │1.90 │More than 10 - 5.0 │1.30 │1.70 │2.20 │2.60 │More than 4 - 10 │1.70 │2.20 │2.8 │3.4 │ - │ │ │ │ │ - Diameter in Millimeters for a Velocity of 1 Foot per Second - │ │ │ │ │ - │2.5 │1.25 │0.65 │0.32 │ - ───────────┴────────┴────────┴────────┴────────┴────────────────────── - - -=234. Limiting Velocities.=—Sand, clay, bits of metal and other -particles of mineral matter will commence to deposit in appreciable -quantities when the velocity of flow falls below 3 feet per second. The -amount deposited will increase as the velocity decreases. In Table 79 -are given the approximate horizontal velocities at which certain size -particles of mineral matter will deposit. At a velocity of about one -foot per second organic matter will commence to deposit. It will be -noticed by interpolation in Table 79,[145] that particles with the same -specific gravity as sand (2.6), larger than one mm. in diameter will -deposit at a velocity of about one foot per second or less, and that -smaller and lighter particles will not deposit at velocity of one foot -per second or greater. It will also be noticed that a velocity of one -foot per minute is sufficiently slow to permit the deposit of the -smallest and lightest particles. For this reason velocities of 1 or 2 or -even 3 feet per second have been adopted as the velocities in grit -chambers and velocities less than 1 foot per minute in plain -sedimentation basins. - - -=235. Quantity and Character of Grit.=—The amount of material deposited -in grit chambers varies approximately between 0.10 and 0.50 cubic yard -per million gallons. It is to be noted that grit chambers are used only -for combined and storm sewage and for certain industrial wastes. They -are unnecessary for ordinary domestic sewage. The material deposited in -grit chambers operating with a velocity greater than one foot per second -is non-putrescible, inorganic, and inoffensive. It can be used for -filling, for making paths and roadways, or as a filtering material for -sludge drying beds. An analysis of a typical grit chamber sludge is -shown in Table 80. - - TABLE 80 - - ANALYSIS OF GRIT CHAMBER SLUDGE - - ───────────┬───────────┬───────────┬─────────────────────────────────── - Velocity │ Specific │ Per Cent │Calculated to Dry Weight, Per Cent - Feet per │ Gravity │ Moisture │ - Second │ │ │ - ───────────┼───────────┼───────────┼──────────┬──────────┬───────────── - │ │ │ Nitrogen │ Fixed │Miscellaneous - │ │ │ │ Matter │ - ───────────┼───────────┼───────────┼──────────┼──────────┼───────────── - 1.0 │ 1.5 │ 45 │ 20 │ 78 │ 2 - ───────────┴───────────┴───────────┴──────────┴──────────┴───────────── - - -=236. Dimensions of Grit Chambers.=—The quantity of sewage to be treated -and the amount and character of the settling solids which it contains -should be determined by measurement and analysis, and the amount of -settling solids to be removed should be determined by a study of the -desired conditions of disposal, in order that a grit chamber that will -accomplish the desired results may be designed. The period of retention -and the velocity of flow are the controlling features in the successful -operation of any grit chamber. These should be determined by experiment -or as the result of experience. Where neither are available, Hazen’s -method can be followed or a decision made based on a study of other grit -chambers. In general, the period of retention in grit chambers is from -30 to 90 seconds, and the velocity of flow is about one foot per second. - -After having determined the quantity of sewage to be treated, the -quantity of grit to be stored between cleanings, the period of -retention, the arrangement of the chambers, and the velocity of flow to -be used, the overall dimensions of the chambers are computed. The -capacity of the chamber is fixed as the sum of the quantity of sewage to -be treated during the period of retention and the required storage -capacity for grit accumulated between cleanings. The length of the -chamber is fixed as the product of the velocity of flow and the period -of retention. The cross-sectional area of the portion of the chamber -devoted to sedimentation is fixed as the quotient of the quantity of -flow of sewage per unit time and the velocity of flow. Only the relation -between the width and depth of the portion devoted to sedimentation and -the portion devoted to the storage of grit remain to be determined. -These should be so designed as to give the greatest economy of -construction commensurate with the required results. They will be -affected by the local conditions such as topography, available space, -difficulties of excavation, etc. Common depths in use lie between 8 and -12 feet, although wide variations can be found. A study of the -proportions of existing grit chambers will be of assistance in the -design of other basins. - - -=237. Existing Grit Chambers.=—The details of some typical grit chambers -are shown in Figs. 155 and 156. The grit chamber at the foot of 58th -Street, in Cleveland, Ohio, is shown in Fig. 155. The special feature of -this structure is the shape of the sedimentation basin, the bottom of -which is formed by sloping steel plates forming a 6–inch longitudinal -slot above the grit storage chamber. Flows between 8,000,000 and -16,000,000 gallons per day are controlled by the outlet weir so that the -velocity of flow remains at one foot per second. This is accomplished by -increasing the depth of flow in the same ratio as the increase in the -rate of flow. The bottoms of the two chambers differ, one having a -special hopper for grit and the other a flat bottom. This is due to the -method of cleaning the chambers, it being necessary in the one with a -flat bottom to shut off the flow when removing the grit while in the one -with the hopper bottom it is hoped to remove the grit by the use of sand -ejectors without stopping the sewage flow. The details of the chamber at -Hamilton, Ontario, are shown in Fig. 156. In studying these drawings the -following features should be noted: 1st, the smooth curves in the -channel to prevent eddies, undue deposition of organic matter, and -difficulties in cleaning; 2nd, the hopper in the upper end of the grit -storage chamber and the slope of the bottom of at least 1:20; and 3rd, -the simplicity of the inlet and outlet devices which may be either stop -planks or cast-iron sluice gates. - -[Illustration: - - FIG. 155.—Grit Chamber at Cleveland, Ohio. - - Eng. Record, Vol. 73, 1916, p. 409. -] - -[Illustration: - - FIG. 156.—Grit Chamber at Hamilton, Ontario. - - Eng. News, Vol. 73, 1915, p. 425. -] - -The drawings shown are merely representative of some satisfactory types. -The number and variety of grit chambers in existence is great. In -designing grit chambers consideration must be given to the method of -cleaning. They are ordinarily cleaned by such methods as have been -described for the cleaning of catch-basins in Chapter XII. Continuous -bucket scrapers similar to excavating machines are sometimes used for -the cleaning of large grit chambers. The period between cleanings is -variable. The design should be such as not to require more frequent -cleanings than twice a month under the worst conditions. The -fluctuations in quality and quantity of grit will vary the period -between cleanings. - - -=238. Number of Grit Chambers.=—The period of retention in grit chambers -is so short and the velocity of flow so near the maximum and minimum -limitations that the wide fluctuations in the rate of discharge in storm -and combined sewers necessitates the construction of a number of -chambers which should be operated in parallel in order to maintain the -velocity between the proper limits. Unless arrangements are made -permitting the cleaning of grit chambers during operation, more than one -grit chamber should be installed in order that when one is being cleaned -the others may be in operation. The number of grit chambers must be -determined by the desired conditions of operation and the cost of -construction. The larger the number of basins the more nearly the flow -in any one basin can be maintained constant, but the more expensive the -construction. The increase in velocity of flow with increasing quantity -is dependent on the outlet arrangements. In a shallow chamber with -vertical sides and a standard sharp-crested rectangular weir at the -outlet the velocity will vary approximately as the cube root of the rate -of flow. Similarly if the outlet is a V notch the velocity will vary as -the fifth root of the rate of flow. In all cases the deeper the basin -the more nearly the velocity varies directly as the rate of flow. The -outlet weir can be arranged as at Cleveland, so that the velocity -remains constant for all rates of flow within certain limits. It is -seldom that more than three grit chambers are necessary to care for the -fluctuations in flow. - - -=239. Quantity and Characteristics of Sludge from Plain -Sedimentation.=—The sludge removed from plain sedimentation basins is -slimy, offensive, not easily dried, and is highly putrescible and -odoriferous. It contains about 90 per cent moisture and has a specific -gravity from 1.01 to 1.05. The amount removed varies between 2 and 5 -cubic yards per million gallons of sewage. The percentage of suspended -matter removed varies between 20 and 60. The total amount removed and -the percentage removal depend on the character of the sewage, the type -of basin, and the period of detention. - - -=240. Dimensions of Sedimentation Basins.=—The dimensions of a -sedimentation basin are determined by a method similar to the one given -for the determination of the dimensions of a grit chamber in Art. 236. -The capacity of the basin is first fixed upon to give the required -period of sedimentation and sludge storage capacity. The length of the -basin is the product of the velocity and the period of retention. The -length, width, and depth of the basin are normally fixed by -considerations of economy and the limitations of the local conditions, -such as available area, topography, foundations, etc., and examples of -good practice. A study of basins in use shows the relation between -length and width to vary normally between 2:1 and 4:1. Widths greater -than 30 to 50 feet are undesirable because of the danger of cross -currents and back eddies which will reduce the efficiency of the -sedimentation. Depths used in practice vary too widely to act as guides -for any particular design. Theoretically the shallower the basin the -better the result. Tanks abroad have been built as shallow as 3 feet and -some in this country as deep as 16 feet. The economical dimensions can -be determined by trial or by calculus. They will serve as a guide in the -adoption of the final dimensions. - -The method to be pursued in determining the economical dimensions of any -engineering structure are: - - I. Express the total cost of the structure in terms of as few - variables as possible. - - II. Express all of the variables in terms of any one and rewrite - the expression for the total cost in terms of this one variable. - - III. Equate the first derivative of the expression with regard to - this variable to zero and solve for the variable. The result will - be the economical value of the variable. The values of the other - variables can be computed from the relations already expressed. - -[Illustration: - - FIG. 157.—Diagram for the Computation of Economical Basin Dimensions. -] - -For example, let it be desired to determine the dimensions of two -continuous-flow sedimentation basins as shown in Fig. 157, in which the -period of retention in each is to be 2 hours, the velocity of flow is -not to exceed one foot per second, and the sludge accumulated will be 3 -cubic yards per million gallons of sewage treated. The quantity of -sewage to be treated is 18,000,000 gallons per day. The shortest time -between cleanings will be 2 weeks. - -The capacity of each basin must be 2/24 of 18,000,000 gallons, or -200,000 cubic feet in order to allow a period of retention of 2 hours. -To this volume should be added sufficient capacity to allow for the 2 -weeks of sludge storage between cleanings. When a basin is being cleaned -the load must be put on the remaining basins. Then if _Q_ represents the -rate of accumulation of sludge per day, _n_ represents the number of -days between cleanings, _m_ represents the number of basins, and _S_ the -sludge capacity of one basin, then - - _S_ = (_Q_(_n_ − 1))⁄_m_ + _Q_⁄(_m_ − 1) - -The sludge storage capacity for the example given will be approximately -11,000 cubic feet. - -In expressing the total cost of the basins let - - _h_ = the depth in feet. - _l_ = the length in feet. - _b_ = the width in feet. - - The cost of land, floor, etc., per square foot = _p_ dollars. - The cost of wall per foot length = _qh_^2 dollars. - The cost of pipes, valves and appurtenances = _P_ dollars. - - Then the total cost _C_ = (3_l_ + 4_b_)_qh_^2 + 2_plb_ + _P_. - - It is now necessary to express the three variables _b_, _l_, and - _h_, in terms of one of them. From the relation _Q_ = 2_blh_ it is - possible to rewrite the expression for the total cost as: - - _C_ = (3_Q_⁄(2_bh_) + 4_b_)_qh_^2 + (_pQ_)⁄_h_ + _P_. - - _C_ = (3_l_ + 2_Q_⁄(_lh_))_qh_^2 + (_pQ_)⁄_h_ + _P_. - - Holding _h_ constant and differentiating with regard to _b_ in the - first expression and with regard to _l_ in the second expression, - equating to zero and solving we get: - - _b_ = √((3_Q_)⁄(8_h_)) and _l_ = √((2_Q_)⁄(3_h_)). - - The economical relation between _b_ and _l_ is therefore - - _b_ = 0.75_l_ - - regardless of the value of _h_. - - Substituting these values of _l_ and _b_ in the original - expression for the total cost, it becomes - - _C_ = (3√((2_Q_)⁄(3_h_)) + 4√((3_Q_)⁄(8_h_)))_qh_^2 + (_pQ_)⁄_h_ + - _P_. - - Differentiating with regard to _h_, equating to zero, and solving - - _h_ = 0.45((_pQ_^½)⁄_q_)^⅔. - - In the example given if _q_ = 0.2 and _p_ = 1.0 then - - _h_ = 11.6 feet, _b_ = 120 feet and _l_ = 160 feet. - -Since these are reasonable dimensions and in accord with good practice -they should be used, unless other conditions are unsuitable or the -velocity of flow is too great. A width of channel of 120 feet as -compared to a length of 160 feet is conducive to a poor distribution of -velocity across the basin. A ratio of width to length of about 1:4 is -desirable. In this case, by the use of three baffles parallel to the -length of the basin, thus dividing it into channels 40 feet wide and -11.6 feet deep, the ratio of width to length is changed to 1:4 and the -velocity will be increased only to 0.06 foot per second or 3.6 feet per -minute, which is a reasonable velocity. It could be reduced by -increasing the spacing of the baffles or the depth of the chamber. - -Complicated baffling is undesirable. Two or three overflow baffles may -be used to permit quiescent sedimentation in the space thus formed, and -hanging baffles may be placed before the inlet and outlet to break up -surface currents, or to prevent the movement of scum. The hanging -baffles should not extend more than 12 to 18 inches below the water -surface. The inlet and outlet are sometimes arranged to permit the -reversal of flow, and the connecting channels between basins to allow -the operation of any number of basins in series or in parallel, although -such arrangements are more important in water purification. Sewage -should enter and leave at the top of the basin. - -[Illustration: - - FIG. 158.—Section through a Dortmund Tank. - - Depth 20 to 30 feet. -] - -Cleaning is facilitated by the location of a central gutter in the -bottom of the basin with the slope of the bottom of the basin towards -the gutter from 1:25 to 1:80 or steeper. A pipe, 2 inches or larger in -diameter, containing water under pressure with connections for hose -placed at frequent intervals is a useful adjunct in flushing the sludge -from the sedimentation basins. For equal capacity, deep vertical flow -tanks are more expensive and difficult to construct than the shallower -rectangular type. Deep tanks are advantageous, however, in that sludge -can sometimes be removed by gravity or by pumping without stopping the -operation of the tank. They will also operate successfully with shorter -periods of detention and higher velocities. The upward velocity should -not be greater than the velocity of sedimentation of the smallest -particle to be removed. The efficiency of sedimentation in them will be -increased by the sedimentation of the larger particles which drag some -of the smaller particles down with them. The Dortmund tank shown in Fig. -158 is an example of this type. - -Ordinarily it is not necessary to roof sedimentation basins as the odors -created are not strong, and difficulties with ice are seldom serious. - - - CHEMICAL PRECIPITATION - - -=241. The Process.=—Chemical precipitation consists in adding to the -sewage such chemicals as will, by reaction with each other and the -constituents of the sewage, produce a flocculent precipitate and thus -hasten sedimentation. The advantages of this process over plain -sedimentation are a more rapid and thorough removal of suspended matter. -Its disadvantages include the accumulation of a large amount of sludge, -the necessity for skilled attendance, and the expense of chemicals. The -process is not in extensive use as the conditions under which the -advantages outweigh the disadvantages are unusual. Sewage containing -large quantities of substances which will react with a small amount of -an added chemical to produce the required precipitate are the most -favorable for this method of treatment. - -Chemical precipitation accomplishes the same result as plain -sedimentation, although the effluent from the chemically precipitated -sewage may be of better quality than that from a plain sedimentation -basin. - - -=242. Chemicals.=—Lime is practically the only chemical used for the -precipitation of the solid matter in sewage. Commercial lime used for -precipitation consists of calcium oxide (CaO), with large quantities of -impurities. It should be stored in a dry place and protected from undue -exposure to the air to prevent the formation of calcium carbonate -(CaCO_{3}), the formation of which is commonly known as air slacking. -The active work in the formation of the precipitate is performed by the -lime (CaO) or calcium hydroxide (Ca(OH)_{2}). The lime should therefore -be purchased on the basis of available CaO, which may be as low as 10 to -15 per cent in some commercial products. The amount of lime necessary -depends on the quality of the sewage, the period of retention in the -sedimentation basin, the method of application, the required results, -and other less easily measured factors. Full scale tests for the amount -of lime needed to produce certain results are the most satisfactory. In -practice the amount of lime necessary when lime alone is used as a -precipitant has been found to be about 15 grains per gallon. This may be -markedly different, dependent on the quality of the sewage. For acid -sewages, lime alone is not suitable as a precipitant since it is -necessary to add sufficient lime to neutralize the sewage before the -calcium carbonate will be precipitated. - -The use of copperas (FeSO_{4}) together with lime, leads to economy in -the use of chemicals as the flocculent precipitate of ferrous hydroxide -(Fe(OH)_{2}) is more voluminous than the precipitate of calcium -carbonate. This is commonly known as the lime and iron process. The -presence of iron in certain trade wastes may reduce the cost of chemical -precipitation, as the necessary amount of copperas is reduced. Where 15 -grains of lime alone will be needed per gallon of sewage, the total -amount of chemicals used will be reduced to 8 to 10 grains per gallon -with the use of lime and iron. This combination is less expensive than -the use of lime alone, and is even cheaper where the iron is already -present in the sewage. Such a condition is well illustrated by the -sewage at Worcester, Mass., where the oldest and best known chemical -precipitation plant in the United States is located. The amount of lime -used at this plant has varied between 6 and 10 grains per gallon of -sewage, the normal amount being about 7 grains. No iron is added because -of the amount already in solution. - -The results of a series of experiments on the chemical precipitation of -sewage by Allen Hazen, are given in the 1890 Report of the Massachusetts -State Board of Health, on p. 737 of the volume on the Purification of -Water and Sewage. Hazen concludes as the result of his experiments: -concerning lime, - - There is a certain definite amount of lime ... which gives as good - or better results than either more or less. This amount is that - which exactly suffices to form normal carbonates with all the - carbonic acid of the sewage. This amount can be determined in a - few minutes by simple titration. - -Concerning lime and iron (copperas) he states: - - Ordinary house sewage is not sufficiently alkaline to precipitate - copperas, and a small amount of lime must be added to obtain good - results. The quantity of lime required depends both upon the - composition of the sewage and the amount of copperas used, and can - be calculated from titration of the sewage. Very imperfect results - are obtained from too little lime, and, when too much is used, the - excess is wasted, the result being the same as with a smaller - quantity. - - In precipitation by ferric sulphate and crude alum, the addition - of lime was found unnecessary, as ordinary sewage contains enough - alkali to decompose these salts. Within reasonable limits the more - of these precipitants used the better is the result, but with very - large quantities the improvement does not compare with the - increased cost. - - Using equal values of different precipitants, applied under the - most favorable conditions for each, upon the same sewage, the best - results were obtained from ferric sulphate. Nearly as good results - were obtained from copperas and lime used together, while lime and - alum each gave somewhat inferior effluents.... When lime is used - there is always so much lime left in solution that it is doubtful - if its use would ever be found satisfactory except in case of an - acid sewage. - - It is quite impossible to obtain effluents by chemical - precipitation which will compare in organic purity with those - obtained by intermittent filtration through sand. - - It is possible to remove from one-half to two-thirds of the - organic matter by precipitation ... and it seems probable that ... - a result may be obtained which will effectually prevent a public - nuisance. - - -=243. Preparation and Addition of Chemicals.=—Lime is not readily -soluble in water. Therefore, it is not best to add the lime as a powder -to the sewage, but to form a milk of lime, that is, a supersaturated -solution containing from 2,000 to 4,000 grains per gallon, although dry -slaked lime has sometimes been applied directly. The solution is -prepared in tanks in a quantity sufficient for some part of the day’s -run, commonly sufficient to last through one shift of 8 or 10 hours. The -lime is prepared by placing the amount necessary to fill one storage -tank into a slaking tank containing some cold water. Sufficient water is -added to keep the solution just at the boiling point, or steam may be -added to make it boil. After slaking, it is run into the milk-of-lime -solution tank and sufficient water added to bring to the proper -strength. The milk of lime is added in measured quantities, being -controlled by a variable head on a fixed orifice or weir, so that it may -be varied with the amount of sewage flowing through the plant. The -amount of lime to be added is determined by titration with -phenolphthalein, experience indicating the color to be obtained when the -proper amount of lime has been added. - -The use of either copperas or alum has been so rare, for the -precipitation of sewage, that a description of the methods of handling -these chemicals as a sewage precipitant is not warranted. An excellent -description of the methods of handling these chemicals in water -purification will be found in “Water Purification” by Ellms. - - TABLE 81 - - RESULTS OF CHEMICAL PRECIPITATION AT WORCESTER, MASSACHUSETTS[146] - - ──────────────────────────────────────┬──────────┬──────────┬────────── - │ 1900 │ 1910 │ 1920 - ──────────────────────────────────────┼──────────┼──────────┼────────── - Amount of sewage treated, million │ 4,781 │ 5,317 │ 8,893 - gallons │ │ │ - Amount of sewage chemically treated, │ 3,650 │ 3,574 │ 7,300 - million gallons │ │ │ - Gallons of wet sludge per million │ 4,450 │ 4,185 │ - gallons of sewage treated │ │ │ - Per cent of solids in sludge │ 4.42 │ 8.20 │4.64[147] - Tons of solids │ 7,294 │ 4,182 │6,431[147] - Pounds of lime added per million │ 999[148] │ 762[147] │ 534 - gallons of sewage pumped │ │ │ - Per cent of organic matter removed: │ │ │ - By albuminoid ammonia: │ │ │ - Total │52.7[149] │ 58.4 │ 51.9 - Suspended │90.0[149] │ 88.7 │ 83.6 - By oxygen consumed: │ │ │ - Total │62.8[149] │ 61.1 │ 62.5 - Suspended │86.6[149] │ 89.7 │ 86.2 - ──────────────────────────────────────┴──────────┴──────────┴────────── - - -=244. Results.=—The results of Hazen’s experiments indicate that a -greater amount of suspended matter can be removed in the same time by -chemical precipitation than by plain sedimentation. The percentage of -removal of suspended matter may be as high as 80 to 90 per cent with a -period of retention of 6 to 8 hours and the addition of a proper amount -of chemical. That the method is not always a success is shown by the -results of some tests at Canton, Ohio.[150] The report states: - - ... lime treatment removes about 50 per cent of the suspended - matter, and in the main about 50 per cent of the organic - matter.... These data are instructive as indicating that the - addition of lime to the Canton sewage in quantities as previously - stated does not materially improve the character of the resulting - effluent over and above that which could be produced by plain - sedimentation alone. - -The plant at Worcester, Mass., is the largest in the United States and -information from it is of value. A summary of the results at Worcester -for 1900, 1910, and 1920 are shown in Table 81. - - - - - CHAPTER XVI - SEPTICIZATION - - -=245. The Process.=—Septic action is a biological process caused by the -activity of obligatory or facultative anaërobes as the result of which -certain organic compounds are reduced from higher to lower conditions of -oxidation, some of the solid organic substances are rendered soluble, -and a quantity of gas is given off. Among these gases are: methane, -hydrogen sulphide, and ammonia. The biologic process in the septic tank -represents the downward portion of the cycle of life and death, in which -complex organic compounds are reduced to a more simple condition -available as food for low forms of plant life. The disposal of sewage by -septic action, when introduced, promised the solution of all problems in -sewage treatment. Septic action is now better understood, and it is -known that some of the early claims were unfounded. - -The principal advantage of septic action in sewage treatment is the -relatively small amount of sludge which must be cared for compared to -that produced by a plain sedimentation tank. The sludge from a septic -tank may be 25 to 30 per cent and in some cases 40 per cent less in -weight, and 75 to 80 per cent less in volume than the sludge from a -plain sedimentation tank. The most important results of septic action -and the greatest septic activity occur in the deposited organic matter -or sludge. The biologic changes due to septic action which occur in the -liquid portion of the tank contents are of little or no importance. The -installation of a septic tank, although it may fail to prevent the -nuisance calling for abatement, has a remarkable psychological effect in -stilling complaints. Among other advantages are the comparative -inexpensiveness of the tanks and the small amount of attention and -skilled attendance required. The tanks need cleaning once in 6 months to -a year. If properly designed no other attention is necessary. - -The septic tank has fallen into some disrepute because of the better -results obtainable by other methods, the occasional discharge of -effluents worse than the influent, the occasional discharge of sludge in -the effluent caused by too violent septic boiling, and on account of -patent litigation. This last difficulty has been overcome as the Cameron -patents expired in 1916. Occasionally the odors given off by the septic -process are highly objectionable and are carried for a long distance. -These odors can be controlled to a large extent by housing the tanks. -Over-septicization must be guarded against as an over-septicized -effluent is more difficult of further treatment or of disposal than a -comparatively fresh, untreated sewage. An over-septicized or stale -sewage is indicated by the presence of large quantities of ammonias, -either free or albuminoid, frequently accompanied by hydrogen sulphide -and other foul-smelling gases. The oxygen demand in an over-septicized -sewage is greater than that in a fresh or more carefully treated sewage. - - -=246. The Septic Tank.=—A septic tank is a horizontal, continuous-flow, -one-story sedimentation tank through which sewage is allowed to flow -slowly to permit suspended matter to settle to the bottom where it is -retained until anaërobic decomposition is established, resulting in the -changing of some of the suspended organic matter into liquid and gaseous -substances, and a consequent reduction in the quantity of sludge to be -disposed of.[151] It is to be noted that a continuous flow is essential -to a septic tank. Small tanks containing stagnant household sewage are -called cesspools, although sometimes erroneously spoken of as septic -tanks. - -Septic and sedimentation tanks differ in their method of operation only -in the period of storage and the frequency of cleaning. The period of -flow in a septic tank is longer and it is cleaned less frequently. The -results obtained by the two processes differ widely. A septic tank can -be converted into a sedimentation tank, or vice versa, by changing the -method of operation, no constructional features requiring alteration. -The purpose of the tank is to store the sludge for such a period of time -that partial liquefaction of the sludge may take place, and thus -minimize the difficulty of sludge disposal. For this reason the sludge -storage capacity of a septic tank is sometimes greater than would be -necessary for a plain sedimentation tank. - - TABLE 82 - - EFFICIENCIES AND PERFORMANCE OF SEPTIC TANK AT COLUMBUS, OHIO - - (Report of Sewage Purification, by G. A. Johnson, Nov. 10, 1905) - ──────────────┬────┬─────┬────┬────┬────┬────┬────┬─────┬─────┬───┬────┬──── - Month, │Aug.│Sept.│Oct.│Nov.│Dec.│Jan.│Feb.│March│April│May│June│Avg. - 1904–1905 │ │ │ │ │ │ │ │ │ │ │ │ - ──────────────┼────┼─────┼────┼────┼────┼────┼────┼─────┼─────┼───┼────┼──── - Temperature, │ │ │ │ │ │ │ │ │ │ │ │ - degrees F. │ │ │ │ │ │ │ │ │ │ │ │ - Influent │ 69 │ 70 │ 65 │ 60 │ 54 │ 51 │ 48 │ 50 │ 57 │61 │ 67 │ - Effluent │ 69 │ 68 │ 64 │ 59 │ 52 │ 48 │ 45 │ 49 │ 57 │62 │ 68 │ - Oxygen │ │ │ │ │ │ │ │ │ │ │ │ - consumed, │ │ │ │ │ │ │ │ │ │ │ │ - parts per │ │ │ │ │ │ │ │ │ │ │ │ - million: │ │ │ │ │ │ │ │ │ │ │ │ - Influent │ 49 │ 50 │ 52 │ 47 │ 43 │ 51 │ 44 │ 47 │ 53 │33 │ 40 │ 47 - Effluent │ 40 │ 36 │ 40 │ 39 │ 37 │ 35 │ 37 │ 39 │ 50 │34 │ 33 │ 38 - Per cent │ 18 │ 28 │ 23 │ 15 │ 16 │ 31 │ 16 │ 17 │ 6 │–3 │ 18 │ 19 - removal │ │ │ │ │ │ │ │ │ │ │ │ - Organic │ │ │ │ │ │ │ │ │ │ │ │ - nitrogen, │ │ │ │ │ │ │ │ │ │ │ │ - parts per │ │ │ │ │ │ │ │ │ │ │ │ - million: │ │ │ │ │ │ │ │ │ │ │ │ - Influent │6.5 │ 8.2 │9.3 │8.4 │8.8 │8.5 │6.7 │ 6.4 │ 7.9 │6.1│6.7 │7.8 - Effluent │7.3 │ 5.5 │6.0 │7.4 │8.2 │7.0 │5.4 │ 5.5 │ 5.2 │ │ │ - Per cent │–12 │ 32 │ 35 │ 12 │ 7 │ 18 │ 19 │ 14 │ 25 │30 │ 19 │ 19 - removal │ │ │ │ │ │ │ │ │ │ │ │ - Free ammonia, │ │ │ │ │ │ │ │ │ │ │ │ - parts per │ │ │ │ │ │ │ │ │ │ │ │ - million: │ │ │ │ │ │ │ │ │ │ │ │ - Influent │9.7 │12.2 │12.4│16.3│14.7│10.8│8.3 │ 9.9 │12.3 │6.9│8.3 │11.7 - Effluent │10.5│11.5 │12.4│17.2│14.3│11.1│8.9 │10.7 │14.9 │9.0│8.7 │12.1 - Per cent │ –8 │ 6 │ 0 │ –6 │ 3 │ –3 │ –7 │ –8 │ –21 │–23│ –5 │ –3 - removal │ │ │ │ │ │ │ │ │ │ │ │ - │ │ │ │ │ │ │ │ │ │ │ │ - Residue on │ │ │ │ │ │ │ │ │ │ │ │ - Evaporation,│ │ │ │ │ │ │ │ │ │ │ │ - parts per │ │ │ │ │ │ │ │ │ │ │ │ - million: │ │ │ │ │ │ │ │ │ │ │ │ - Total: │ │ │ │ │ │ │ │ │ │ │ │ - Influent │990 │ 952 │993 │961 │989 │949 │890 │ 850 │1067 │912│945 │946 - Effluent │935 │ 891 │893 │916 │925 │886 │843 │ 782 │ 895 │800│835 │873 - Per cent │ 6 │ 6 │ 10 │ 5 │ 6 │ 6 │ 5 │ 8 │ 16 │12 │ 12 │ 8 - removal │ │ │ │ │ │ │ │ │ │ │ │ - Volatile: │ │ │ │ │ │ │ │ │ │ │ │ - Influent │231 │ 184 │162 │175 │156 │167 │156 │ 168 │ 212 │122│162 │166 - Effluent │206 │ 160 │129 │148 │137 │137 │134 │ 137 │ 147 │103│144 │139 - Per cent │ 11 │ 13 │ 20 │ 15 │ 12 │ 18 │ 14 │ 18 │ 31 │16 │ 11 │ 16 - removal │ │ │ │ │ │ │ │ │ │ │ │ - Mineral: │ │ │ │ │ │ │ │ │ │ │ │ - Influent │759 │ 768 │831 │786 │833 │782 │734 │ 682 │ 855 │700│783 │780 - Effluent │729 │ 731 │764 │768 │788 │749 │709 │ 645 │ 748 │697│691 │734 - Per cent │ 4 │ 5 │ 8 │ 2 │ 5 │ 4 │ 3 │ 5 │ 11 │ 1 │ 12 │ 6 - removal │ │ │ │ │ │ │ │ │ │ │ │ - Cubic yards │ │ │0.10│1.24│1.09│1.17│0.65│0.63 │0.57 │ │1.34│ - wet sludge │ │ │ │ │ │ │ │ │ │ │ │ - per million │ │ │ │ │ │ │ │ │ │ │ │ - gallons: │ │ │ │ │ │ │ │ │ │ │ │ - Per cent │ │ │ │ │ │ │ │ │ │ │ │ - removal of │ │ │ │ │ │ │ │ │ │ │ │ - suspended │ │ │ │ │ │ │ │ │ │ │ │ - matter: │ │ │ │ │ │ │ │ │ │ │ │ - Total │ 59 │ 54 │ 56 │ 51 │ 42 │ 48 │ 32 │ 47 │ 56 │67 │ 53 │ 50 - Volatile │ 60 │ 41 │ 48 │ 52 │ 44 │ 55 │ 47 │ 47 │ 62 │80 │ 15 │ 48 - Fixed │ 75 │ 65 │ 60 │ 51 │ 40 │ 38 │ 19 │ 48 │ 53 │64 │ 67 │ 51 - Gas evolved, │ │ │ │ │ │ │ │ 29 │ 14 │41 │ 50 │ - cubic feet │ │ │ │ │ │ │ │ │ │ │ │ - per day: │ │ │ │ │ │ │ │ │ │ │ │ - ──────────────┴────┴─────┴────┴────┴────┴────┴────┴─────┴─────┴───┴────┴──── - - -=247. Results of Septic Action.=—The results obtained from the septic -tanks at the Columbus Sewage Experiment Station are given in Table 82. -The effluent is higher than the influent in free ammonia, but the -reduction of other constituents, particularly suspended matter, is -marked. - -Septic action is sensitive to temperature changes, and to certain -constituents of the incoming sewage. Cold weather or an acid influent -will inhibit septicization. In winter the liquefaction of sludge may -practically cease, whereas in summer liquefaction may exceed deposition. -The amount of gas generated is a measure of the relative amount of -septic action. The rapid generation of gas in warm weather disturbs the -settled sludge and may cause a deterioration of the quality of the -effluent because of the presence of decomposed sludge. The results in -Table 82 show the effect of cold weather on the process. In warm weather -the violent ebullition of gas sometimes causes the discharge of sludge -in the effluent, resulting in a liquid more difficult of disposal than -the incoming sewage. Since septic action is dependent on the presence of -certain forms of bacteria, where these are absent there will be no -septic action. Sewage generally contains the forms of bacteria necessary -for this action but it has occasionally been found necessary to seed new -tanks in order to start septic action. - -The sludge from septic tanks is usually black, with a slight odor, -though in some cases this odor may be highly offensive. The sludge will -flow sluggishly. It can be pumped by centrifugal pumps and it will flow -through pipes and channels. It has a moisture content of about 90 per -cent and a specific gravity of about 1.03. It is dried with difficulty -on open-air drying beds, and it is worthless as a fertilizer. The -composition of some septic sludges are shown in Table 83. - - -=248. Design of Septic Tanks.=—The sedimentation chambers of a septic -tank are designed on the same principles as the sedimentation basins -described in Art. 240. The velocity of flow should not exceed one foot -per minute. The channels should be straight and free from obstructions -causing back eddies. The ratio of length to width of channel should be -between 2 : 1 to 4 : 1 with a width not exceeding 50 feet, and desirably -narrower. The depths used vary between 5 and 10 feet, exclusive of the -sludge storage capacity. Hanging baffles should be placed, one before -the inlet and the other in front of the outlet, so as to distribute the -incoming sewage over the tank, and to prevent scum from passing into the -outlet. The baffles should hang about 12 inches below the surface of the -sewage. Intermediate baffles are sometimes desirable to prevent the -movement of sludge or scum towards the outlet. The placing of baffles -must be considered carefully as injudicious baffling may lessen the -effectiveness of a tank by so concentrating the currents as to prevent -sedimentation or the accumulation of sludge. Baffles should be built of -concrete or brick, as wood or metal in contact with septic sewage -deteriorates rapidly. In designing the sludge storage chambers it may be -assumed that one-half of the organic matter and none of the mineral -matter will be liquefied or gasified. The net storage volume allowed is -about 2 to 3 cubic yards per million gallons of sewage treated. -Variations between 0.1 and 10.0 cubic yards have been recorded, however. -If grit is carried in the sewage to be treated, it should be removed by -the installation of a grit chamber before the sewage enters the septic -tank. - - TABLE 83 - - ANALYSIS OF TANK SLUDGES - - ──────────┬────────┬────────┬──────────────────────────── - Place │Specific│Per Cent│ Per Cent in Terms of Dry - │Gravity │Moisture│ Matter - │ │ │ - │ │ │ - │ │ │ - ──────────┼────────┼────────┼────────┬─────┬────────┬──── - │ │ │Volatile│Fixed│Nitrogen│Fat - ──────────┼────────┼────────┼────────┼─────┼────────┼──── - Mansfield,│ 1.11│ 80.8│ │ │ │ - O. │ │ │ │ │ │ - │ │ │ │ │ │ - │ │ │ │ │ │ - Chicago, │ 1.03│ 90│ 40│ 60│ 1.9│ 7.0 - Ill. │ │ │ │ │ │ - │ │ │ │ │ │ - Columbus, │ 1.09│ 83.3│ 4.4│ 16.7│ 0.25│0.94 - O. │ │ │ │ │ │ - │ │ │ │ │ │ - │ │ │ │ │ │ - Atlanta, │ 1.02│ 87.1│ 39.1│ 60.9│ 1.25│6.11 - Ga. │ │ │ │ │ │ - │ │ │ │ │ │ - Baltimore,│ 1.02│ 91.9│ 66.2│ │ 2.45│4.02 - Md. │ │ │ │ │ │ - │ │ │ │ │ │ - │ │ │ │ │ │ - │ │ │ │ │ │ - Baltimore,│ 1.02│ 92.4│ 62.7│ │ 2.75│ - Md. │ │ │ │ │ │ - Baltimore,│ │ 79.2│ 73.8│ │ 2.64│9.00 - Md. │ │ │ │ │ │ - Baltimore,│ │ 92.4│ 58.0│ 3.19│ │ - Md. │ │ │ │ │ │ - ──────────┴────────┴────────┴────────┴─────┴────────┴──── - - ──────────┬────────┬────────┬─────────┬──────────── - Place │ Cubic │ Pounds │ Kind of │ Reference - │Yard per│ per │ Sludge │ - │Million │Million │ │ - │Gallons,│Gallons,│ │ - │ Wet │ Dry │ │ - ──────────┼────────┼────────┼─────────┼──────────── - │ │ │ │ - ──────────┼────────┼────────┼─────────┼──────────── - Mansfield,│ │ │Septic │1908 Report, - O. │ │ │ │ State - │ │ │ │ Board of - │ │ │ │ Health - Chicago, │ 1.0│ 200│Septic │ - Ill. │ │ │ │ - │ 1.5│ 300│ │ - Columbus, │ │ │Septic │G. A. - O. │ │ │ │ Johnson - │ │ │ │ 1905 - │ │ │ │ Report - Atlanta, │ │ │Imhoff │Eng. Rec., - Ga. │ │ │ │ V. 72, - │ │ │ │ 1915, p. 4 - Baltimore,│ │ │Digestion│Eng. - Md. │ │ │ Tank │ News-Rec., - │ │ │ │ V. 87, - │ │ │ │ 1921, p. - │ │ │ │ 98 - Baltimore,│ │ │Imhoff │ do. - Md. │ │ │ │ - Baltimore,│ │ │Raw │ do. - Md. │ │ │ Sludge │ - Baltimore,│ │ │Settling │ do. - Md. │ │ │ Basin │ - ──────────┴────────┴────────┴─────────┴──────────── - -Two or more tanks should be constructed to allow for the shut down of -one for cleaning and to increase the elasticity of the plant. The number -of tanks to be used is dependent on the total quantity of sewage and the -fluctuations in rate of flow. An average period of retention of about 9 -to 10 hours with a minimum period of 6 hours during maximum flow is a -fair average to be assumed for design. The period of retention should -not exceed about 24 hours, as the sewage may become over-septicized. The -sludge storage period should be from 6 to 12 months. - -A cover is not necessary to the successful operation of a septic tank. -Covers are sometimes used with success, however, in reducing the -dissemination of odors from the tank. They are also useful in retaining -the heat of the sewage in cold weather and thus aid in promoting -bacterial activity. Types of covers vary from a building erected over -the tank to a flat slab set close to the surface of the sewage. In the -design of a cover, good ventilation should be provided to permit the -escape of the gases, and easy access should be provided for cleaning. -Tightly covered tanks or tanks with too little ventilation have resulted -in serious explosions, as at Saratoga Springs in 1906 and at -Florenceville, N. C., in 1915.[152] - -The sludge may be removed through drains in the bottom of the tank as -described for sedimentation basins, or where such drains are not -feasible the sludge and sewage are pumped out. For this purpose a pump -may be installed permanently at the tank, or for small tanks portable -pumps are sometimes used. Septic tanks should be cleaned as infrequently -as possible without permitting the overflow of sludge into the effluent. -The less frequent the cleaning the less the amount of sludge removed -since digestion is continuous throughout the sludge. It is necessary to -clean when the tank becomes so filled with sludge, that the period of -retention is materially reduced, or sludge is being carried over into -the effluent. - -The details of the septic tank at Champaign, Illinois, are shown in Fig. -159. This tank was designed by Prof. A. N. Talbot, and was put in -service on Nov. 1, 1897. It was among the first of such tanks to be -installed in the United States. The tank shown in Fig. 159 is an example -of present day practice in single-story septic tank design. - -[Illustration: - - FIG. 159.—Septic Tank at Champaign, Illinois. -] - -[Illustration: - - FIG. 160.—Design for a Residential Septic Tank for a Family of Ten. - Illinois State Board of Health. -] - -Small septic tanks for rural homes of 5 to 15 persons, or on a slightly -larger scale for country schools and small institutions, are little more -than glorified cesspools. Nevertheless much attention has been given to -the construction of such tanks by the National Government and by state -boards of health.[153] The recommendations of some of these boards have -been compiled in Table 84. A typical method for the construction of such -tanks, as recommended by the Illinois State Board of Health, is shown in -Fig. 160. A subsurface filter, into which the effluent is discharged, is -an important adjunct where no adequate stream is available to receive -the discharge from the tank. - - TABLE 84 - - CAPACITIES OF SEPTIC TANKS FOR SMALL INSTALLATIONS - - ──────────────┬─────────────┬─────────┬─────────┬────────────────────── - Rule │ Number, │Capacity,│Period of│ Remarks - Recommended by│ Persons │ Gallons │Retention│ - State Board of│ │ per │ │ - Health │ │ Person │ │ - ──────────────┼─────────────┼─────────┼─────────┼────────────────────── - Wisconsin │ │ 30 │24 hours │ - Ohio │ 4 to 10 │ 50 │ │Not less than 560 - │ │ │ │ gallons - Kentucky │ │ │24 to 48 │Not more than 5 feet - │ │ │ hours │ deep - Texas │ │ │24 hours │ - Illinois │ │ 45 │24 hours │ - U.S. Dept. │ │ 40 │24 hours │25 per cent additional - Agriculture.│ │ │ │ - │ │ │ │capacity for sludge - North Carolina│Large Schools│ 15 │ │Not less than 500 - │ │ │ │ gallons - North Carolina│ 20 pupils │ 25 │ │ - North Carolina│Medium School│ 20 │ │ - North Carolina│ Homes │25 to 30 │ │ - ──────────────┴─────────────┴─────────┴─────────┴────────────────────── - - -=249. Imhoff Tanks.=—In the discussion of septic tanks it has been -brought out that one of the objections to their use is the unloading of -sludge into the effluent which occasionally causes a greater amount of -suspended matter in the effluent than in the influent. The Imhoff tank -is a form of septic tank so arranged that this difficulty is overcome. -It combines the advantages of the septic and sedimentation tanks and -overcomes some of their disadvantages. An Imhoff tank is a device for -the treatment of sewage, consisting of a tank divided into 3 -compartments. The upper compartment is called the sedimentation chamber. -In it the sedimentation of suspended solids causes them to drop through -a slot in the bottom of the chamber to the lower compartment called the -_digestion_ chamber. In this chamber the solid matter is humified by an -action similar to that in a plain septic tank. The generated gases -escape from the digestion chamber to the surface through the third -compartment called the _transition_ or _scum_ chamber. Sections of -Imhoff tanks are shown in Fig. 161. It is essential to the construction -of an Imhoff tank that the slot in the bottom of the sedimentation -chamber does not permit the return of gases through the sedimentation -chamber, and that there be no flow in the digestion chamber. - -[Illustration: - - FIG. 161.—Typical Sections through Imhoff Tanks. - - Eng. News, Vol. 75, p. 15. -] - -The Imhoff tank was invented by Dr. Karl Imhoff, director of the Emscher -Sewerage District in Germany. Its design is patented in the United -States, the control of the patent being in the hands of the Pacific -Flush Tank Co. of Chicago, which collects the royalties which are -payable when construction work begins. The fee for a tank serving 100 -persons is $10, for 1,000 persons is $80 and for 100,000 persons is -$2550. The rate of the royalty reduces in proportion as the number of -persons served increases.[154] As designed by Imhoff and used in Germany -the tanks were of the radial flow type and quite deep. The depth, as -explained by Imhoff, is one of the chief requirements for the successful -operation of the tank. As adapted to American practice the tanks are -generally of the longitudinal flow type and are not made so deep. An -isometric view of a radial flow Imhoff tank is shown in Fig. 162. The -sewage enters at the center of the tank near the surface and flows -radially outward under the scum ring and over a weir placed near the -circumference of the tank. One type of longitudinal flow tank is shown -in isometric view in Fig. 163. - -[Illustration: - - FIG. 162.—Sketch of Radial Flow Imhoff Tank at Baltimore, Maryland. - - Eng. Record, Vol. 70, p. 5. -] - -[Illustration: - - FIG. 163.—Isometric View of Longitudinal Flow Imhoff Tank at Cleburne, - Texas. - - Eng. News, Vol. 76, p. 1029. -] - - -=250. Design of Imhoff Tanks.=—The velocity of flow, period of -retention, and the quantity of sewage to be treated determine the -dimensions of the _sedimentation chamber_ as in other forms of tanks. -The velocity of flow should not exceed one foot per minute, with a -period of retention of 2 to 3 hours. A greater velocity than one foot -per minute results in less efficient sedimentation. A longer period of -retention than the approximate limit set may result in a septic or stale -effluent, and a shorter period may result in loss of efficiency of -sedimentation. The bottom of the sedimentation chamber should slope not -less than 1½ vertical to 1 horizontal, in order that deposited material -will descend into the sludge digestion chamber. Provision should be made -for cleaning these sloping surfaces by placing a walk on the top of the -tank from which a squeegee can be handled to push down accumulated -deposits. It is desirable to make the material of the sides and bottom -of the sedimentation chamber as smooth as possible to assist in -preventing the retention of sludge in the sedimentation chamber. Wood, -glass, and concrete have been used. The latter is the more common and -has been found to be satisfactory. The length of the sedimentation -chamber is fixed by the velocity of flow and the period of retention. -Tanks are seldom built over 100 feet in length, however, because of the -resulting unevenness in the accumulation of sludge. Where longer flows -are desired two or more tanks may be operated in series. The width of -the chamber is fixed by considerations of economy and convenience. It -should not be made so great as to permit cross currents. In general a -narrow chamber is desirable. Satisfactory chambers have been constructed -at depths between 5 and 15 feet. The depth of the sedimentation chamber -and the depth of the digestion chamber each equal about one-half of the -total depth of the tank. This should be made as deep as possible up to a -limit of 30 to 35 feet, with due consideration of the difficulties of -excavation. C. F. Mebus states:[155] - - In 9 of the largest representative United States installations, - the depth from the flow line to the slot varies from 10 feet 10 - inches to 13 feet 6 inches. - -Imhoff states, concerning the depth of tanks: - - Deep tanks are to be preferred to shallow tanks because in them - the decomposition of the sludge is improved. This is so because in - the deeper tanks the temperature is maintained more uniformly and - because the stirring action of the rising gas bubbles is more - intense. - -The stirring action of the gas bubbles is desirable as it brings the -fresh sludge more quickly under the influence of the active bacterial -agents. The greater pressure on the sludge in deep tanks also reduces -its moisture content. - -Two or more sedimentation chambers are sometimes used over one sludge -digestion chamber in order to avoid the depths called for by the sloping -sides of a single sedimentation chamber. An objection to multiple-flow -chambers is the possibility of interchange of liquid from one chamber to -another through the common digestion chamber. - -The inlet and outlet devices should be so constructed that the direction -of flow in the tank can be reversed in order that the accumulated sludge -may be more evenly distributed in the hoppers of the digestion chamber. -The sewage should leave the sedimentation chamber over a broad crested -weir in order to minimize fluctuations in the level of sewage in the -tank. The gases in the digesting sludge are sensitive to slight changes -in pressure. A lowering of the level of sewage will release compressed -gas and will too violently disturb the sludge in the digestion chamber. -Hanging baffles, submerged 12 to 16 inches and projecting 12 inches -above the surface of the sewage, should be placed in front of the inlet -and outlet, and in long tanks intermediate baffles should be placed to -prevent the movement of scum or its escape into the effluent. An Imhoff -tank which is operating properly should not have any scum on the surface -of the sewage in the sedimentation chamber. - -The _slot_ or opening at the bottom of the sedimentation chamber should -not be less than 6 inches wide between the lips. Wider slots are -preferable, but too wide a slot will involve too much loss of volume in -the digestion chamber. One lip of the slot should project at least 3 -inches horizontally under the other so as to prevent the return of gases -through the sedimentation chamber. A triangular beam may be used as -shown in Fig. 161 A. This method of construction is advantageous in -increasing the available capacity for sludge storage. - -The _digestion chamber_ should be designed to store sludge from 6 to 12 -months, the longer storage periods being used for smaller installations. -In warm climates a shorter period may be used with success. The amount -of sludge that will be accumulated is as uncertain as in other forms of -sewage treatment. A widely quoted empirical formula, presented in -“Sewage Sludge” by Allen, states: - - _C_ = 10.5 _PD_ for combined sewage; - _C_ = 5.25 _PD_ for separate sewage, - - in which _C_ = the effective capacity of the digestion chamber in - cubic feet; - - _P_ = the population served, expressed in thousands; - - _D_ = the number of days of storage of sludge. - -The effective capacity of the chamber is measured as the entire volume -of the chamber approximately 18 inches below the lower lip of the slot. -The capacity as computed from the above formula is assumed as -satisfactory for a deep tank. Frank and Fries[156] recommend the -increase of the capacity for shallow tanks to compensate for the -decreased hydrostatic pressure. In any event the formula can be no more -than a guide to design. No formula can be of equal value to data -accumulated from tests on the sewage to be treated. The Illinois State -Board of Health requires 3 cubic yards of sludge digestion space per -million gallons of sewage treated. Frank and Fries recommend an -allowance of 0.007 cubic foot of storage per inhabitant per day for -combined sewage and one-half that amount for separate sewage. If this is -based on 80 per cent moisture content, the volume for other percentages -of moisture can be easily computed. An average figure used in the -Emscher District is one cubic foot capacity for each inhabitant for the -combined system, and three-fourths of this for the separate system. -Metcalf and Eddy[157] recommend the following method for the -determination of the sludge storage capacity: (1) From analyses of the -sewage or study of the sources ascertain the amount of suspended matter. -(2) Assume, or determine by test, the amount which will settle in the -period of detention selected, say 60 per cent in 3 hours. (3) Estimate -the amount which will be digested in the sludge chamber at about 25 per -cent, leaving 75 per cent to be stored. (4) Estimate the percentage -moisture in the sludge conservatively, say 85 per cent. The total volume -of sludge can then be computed. This method is more rational than the -use of empirical formulas, but because of the estimates which must be -made its results will probably be of no greater accuracy than those -obtained empirically. - -The digestion chamber is made in the form of an inverted cone or pyramid -with side slopes at most about 2 horizontal to 1 vertical and preferably -much steeper without necessitating too great a depth of tank. The -purpose of the steep slope is to concentrate the sludge at the bottom of -the hopper thus formed. Concrete is ordinarily used as the material of -construction as a smooth surface can be obtained by proper workmanship. -Where flat slopes have been used, a water pipe perforated at intervals -of 6 to 12 inches may be placed at the top of the slopes, and water -admitted for a short time to move the sludge when the tank is being -cleaned. - -A cast-iron pipe, 6 to 8 inches in diameter, is supported in an -approximately vertical position with its open lower end supported about -12 inches above the lowest point in the digestion chamber. This is used -for the removal of sludge. A straight pipe from the bottom of the tank -to a free opening in the atmosphere is desirable in order to allow the -cleaning of the pipe or the loosening of sludge at the start, and to -prevent the accumulation of gas pockets. The sludge is led off through -an approximately horizontal branch so located that from 4 to 6 feet of -head are available for the discharge of the sludge. A valve is placed on -the horizontal section of the pipe. A sludge pipe is shown in Fig. 162 -and 163. Under such conditions, when the sludge valve is opened the -sludge should flow freely. The hydraulic slope to insure proper sludge -flow should not be less than 12 to 16 per cent. Where it is not possible -to remove the sludge by gravity an air lift is the best method of -raising it. - -The volume of the _transition_ or _scum_ chamber should equal about -one-half that of the digestion chamber. The surface area of the scum -chamber exposed to the atmosphere should be 25 to 30 per cent of the -horizontal projection of the top of the digestion chamber. Some tanks -have operated successfully with only 10 per cent, but troubles from -foaming can usually be anticipated unless ample area for the escape of -gases has been provided. - -All portions of the surface of the tank should be made accessible in -order that scum and floating objects can be broken up or removed. The -gas vents should be made large enough so that access can be gained to -the sludge chamber through them when the tank is empty. - -Precautions should be taken against the wrecking of the tank by high -ground water when the tank is emptied. With an empty tank and high -ground water there is a tendency for the tank to float. The flotation of -the tank may be prevented by building the tank of massive concrete with -a heavy concrete roof, by underdraining the foundation, or by the -installation of valves which will open inwards when the ground water is -higher than the sewage in the tank. Dependence should not be placed on -the attendant to keep the tank full during periods of high ground water. - -Roofs are not essential to the successful operation of Imhoff tanks. -They are sometimes used, however, as for septic tanks, to assist in -controlling the dissemination of odors, to minimize the tendency of the -sewage to freeze, and to aid in bacterial activity. In the construction -of a roof, ventilation must be provided as well as ready access to the -tank for inspection, cleaning, and repairs. - - -=251. Imhoff Tank Results.=—The Imhoff tank has the advantage over the -septic tank that it will not deliver sludge in the effluent, except -under unusual conditions. The Imhoff tank serves to digest sludge better -than a septic tank and it will deliver a fresher effluent than a plain -sedimentation tank. Imhoff sludge is more easily dried and disposed of -than the sludge from either a septic or a sedimentation tank. This is -because it has been more thoroughly humified and contains only about 80 -per cent of moisture. As it comes from the tank it is almost black, -flows freely and is filled with small bubbles of gas which expand on the -release of pressure from the bottom of the tank, thus giving the sludge -a porous, sponge-like consistency which aids in drying. When dry it has -an inoffensive odor like garden soil, and it can be used for filling -waste land, without further putrefaction. It has not been used -successfully as a fertilizer. - -Offensive odors are occasionally given off by Imhoff tanks, even when -properly operated. They also have a tendency to “boil” or foam. The -boiling may be quite violent, forcing scum over the top of the -transition chamber and sludge through the slot in the sedimentation -chamber, thus injuring the quality of the effluent. The scum on the -surface of the transition chamber may become so thick or so solidly -frozen as to prevent the escape of gas with the result that sludge may -be driven into the sedimentation chamber. - -Some chemical analyses of Imhoff tank influents and effluents are given -in Table 86 and the analyses of some sludges from Imhoff tanks are given -in Table 83. It is to be noted that the nitrites and nitrates are still -present in the effluent, whereas they are seldom present in the effluent -from septic tanks. The per cent of moisture in the Imhoff sludge is less -than that in the septic tank sludge, and its specific gravity is higher. -It is heavier and more compact because of the longer time and the -greater pressure it has been subjected to in the digestion chamber of -the Imhoff tank. - - -=252. Status of Imhoff Tanks.=—The introduction of the Imhoff tank into -the United States, like the introduction of the Burkli-Ziegler Run-Off -Formula, and Kutter’s Formula, is to be credited to Dr. Rudolph Hering. -He advised Dr. Imhoff to come to the United States to introduce his tank -and gave him material aid through recommendations and introductions to -engineers. Shortly after its introduction, in 1907, the tank became very -popular and installations were made in many cities. This popularity was -caused by a growing dissatisfaction with the septic tank, the litigation -then progressing over septic patents, the production of inoffensive -sludge, and the promising results which had been obtained in Germany. As -a result of the extended experience obtained in the use of Imhoff tanks -American engineers have learned that, like all other sewage treatment -devices introduced up to the present time, the Imhoff tank requires -experienced attention for its successful operation. These tanks are now -being installed in the place of septic tanks, and they are frequently -used in conjunction with sprinkling filters. - - -=253. Operation of Imhoff Tanks.=—The important feature in the -successful operation of an Imhoff tank is the proper control of the -sludge and transition chambers. During the ripening process, which may -occupy 2 weeks to 3 months after the start of the tank, offensive odors -may be given off, the tank may foam violently, and scum may boil over -into the sedimentation chamber. This is usually due to an acid condition -in the digestion chamber which may possibly be overcome by the addition -of lime. A very fresh influent will have a similar effect. Too violent -boiling is not likely to occur where the area for the escape of gas has -been made large and the gas is not confined. Any accumulation of scum -should be broken up and pushed down into the digestion chamber, or -removed from the tank. The stream from a fire hose is useful in breaking -up scum. The side walls of the sedimentation chamber should be squeegeed -as frequently as is necessary to keep them free from sludge, which may -be as often as once or twice a week. Material floating on the surface of -the sedimentation chamber should be removed from the tank or sunk into -the digestion chamber through the gas vents in the transition chamber. - -No sludge should be removed, except for the taking of samples, until the -tank is well ripened. The ripening of the sludge can be determined by -examining a sample and observing its color and odor. An odorless, black, -granular, well humified sludge is indicative of a ripened tank. After -the tank has ripened, sludge should be removed in small quantities at 2 -to 3–week intervals, except in cold or rainy weather. The sludge should -be drawn off slowly to insure the removal of the oldest sludge at the -bottom of the digestion chamber. After the drawing off of the sludge has -ceased the pipe should be flushed with fresh water to prevent its -clogging with dried sludge in the interim until the next removal. Under -no circumstances should all the sludge in the tank be removed at any -time. The removal of some sludge during foaming after ripening may -reduce or stop the foaming. The ripening of a tank can be hastened by -adding some sludge from a tank already ripened. - -Sludge should not be allowed to accumulate within 18 inches of the slot -at the bottom of the digestion chamber. The elevation of the surface of -the sludge can be located by lowering into the tank, a stoppered, -wide-mouthed bottle on the end of a stick. The stopper is pulled out by -a string when the bottle is at some known elevation. The bottle is then -carefully raised and observed for the presence of sludge. The process is -repeated with the bottle at different elevations until the surface of -the sludge has been discovered. Another method is to place the suction -pipe of a small hand pump at known points, successively increasing in -depth, and to pump in each position until one position is found at which -sludge appears in the pump. When the sludge in one portion of the -digestion chamber has risen higher than in another portion, the -direction of flow in the sedimentation chamber should be reversed if -possible. In the ordinary routine of operation it is never necessary to -shut down an Imhoff tank. Sludge is removed while the tank is operating. -The shut down of a tank will be caused by accidents and breaks to the -structure or control devices. - - -=254. Other Tanks.=—The Travis Hydrolytic Tank represents a step in the -development from the septic tank to the Imhoff tank. The Doten tank and -the Alvord tank are recent developments, and are somewhat similar in -operation to the Imhoff tank. - -The Travis Hydrolytic Tank when first designed differed from the later -design of the Imhoff tank in the slot between the sedimentation chamber -and the digestion chamber which was not trapped against the escape of -gas from the latter to the former, and in operation a small quantity of -fresh sewage was allowed to flow through the digestion chamber. The tank -is called a hydrolytic tank because some solids are liquefied in it. The -tank is mainly of historic interest as designs similar to it are rarely -made to-day. Better results are obtained from the use of the Imhoff -tank. Recent developments have altered the original design of the Travis -tank so that it is hardly recognizable. The Travis tank at Luton, Eng., -is shown in Fig. 164. The detailed description given in the _Engineering -News_ in connection with this illustration shows that the governing -object of the design is to separate as quickly as possible the sludge -deposited by the sewage without septic action being set up. To aid in -the collection and settlement of flocculent matter vertical wooden grids -or colloiders are used. The suspended matter strikes these and forms a -slimy deposit on them that in a short time slips off in pieces large -enough to settle readily. - -[Illustration: - - FIG. 164.—Plan and Section of Hydrolytic Tank at Luton, England. - - Eng. News, Vol. 76, 1916, p. 194. -] - -[Illustration: - - FIG. 165.—Doten Tank for Army Cantonment Sewage Disposal. - - Eng. News-Record, Vol. 79, 1917, p. 931. -] - -The Doten tank[158] is a single-storied, hopper-bottomed septic tank, -views of which are shown in Fig. 165. It was devised by L. S. Doten for -army cantonments during the War. Its chief purpose was to avoid the -foaming and frothing so common to Imhoff tanks when overdosed with fresh -sewage. The first Alvord tank was constructed in Madison, Wis., in -1913.[159] As now constructed the tank consists of three deep, -single-story compartments with hopper bottoms. These compartments are -arranged side by side in any one unit. Sewage enters at the surface of -one of the compartments and is retained here during one-half of the -total period of retention. It leaves the first compartment over a weir -and passes in a channel over the top of the intermediate compartment to -the third or effluent compartment, where it is held for the remainder of -the period of detention. Accumulated scum and sludge are drawn off into -the intermediate compartment at the will of the operator, this -compartment being used for sludge digestion only. Such tanks as the -Doten and the Alvord have been used for plants receiving very fresh -sewages such as is discharged from military cantonments, in order to -assist in the prevention of the foaming to be expected from an Imhoff -tank receiving such a fresh influent. The tanks are suitable for small -installations, or where excavation to the depth required for an Imhoff -tank is not practicable. - - - - - CHAPTER XVII - FILTRATION AND IRRIGATION - - -=255. Theory.=—The cycle through which the elements forming organic -matter pass from life to death and back to life again has been described -in Chapter XIII. It has been shown in Chapter XVI that septic action -occupies that portion of the cycle in which the combinations of these -elements are broken down or reduced to simpler forms and the lower -stages of the cycle are reached. The action in the filtration of sewage -builds up the compounds again in a more stable form and almost complete -oxidation is attained, dependent on the thoroughness of the filtration. -In the filtration of sewage only the coarsest particles of suspended -matter are removed by mechanical straining. The success of the -filtration is dependent on biologic action. The desirable form of life -in a filter is the so-called nitrifying bacteria which live in the -interstices of the filter bed and feed upon the organic matter in the -sewage. Anything which injures the growth of these bacteria injures the -action of the filter. In a properly constructed and operated filter, all -matter which enters in the influent, leaves with the effluent, but in a -different molecular form. A slight amount may be lost by evaporation and -gasification but this is more than made up by the nitrogen and oxygen -absorbed from the atmosphere. The nitrifying action in sewage filtration -is shown by the analysis of sewage passing through a trickling filter, -as given in Tables 86 and 87. It is shown by the reduction of the -content of organic nitrogen, free ammonia, oxygen consumed, and the -increase in nitrites, nitrates, and dissolved oxygen. The reduction of -suspended matter is interrupted periodically when the filter “unloads.” -The suspended matter in the effluent is then greater than in the -influent. - -The nitrifying organisms have been isolated and divided into two -groups—_nitrosomonas_, the nitrite formers, and _nitrobacter_, the -nitrate formers. Experiments indicate that the growth of the nitrobacter -organisms is dependent on the presence of the nitrosomonas organisms, -which are in turn dependent on the presence of the putrefactive -compounds resulting from the action of putrefying bacteria. The -existence of these organisms is an example of symbiotic action in -bacterial growth. The organisms have been found to grow best on rough -porous material on which their zoögleal jelly can be easily deposited -and affixed. Sewage filters were constructed to provide these ideal -conditions before the action of a filter was thoroughly understood. - -The action in irrigation is similar to that in filtration. Although more -strictly a method of final disposal rather than preliminary treatment, -the similarity of the actions which take place, and the grading of sand -filtration into broad irrigation with no distinct line of difference has -resulted in the inclusion of the discussion of irrigation in the same -chapter with filtration. - - -=256. The Contact Bed.=—A contact bed is a water-tight basin filled with -coarse material, such as broken stone, with which sewage and air are -alternately placed in contact in such a manner that oxidation of the -sewage is effected. A contact bed has some of the features of a -sedimentation tank and an oxidizing filter. As such it marks a -transitory step from anaërobic to aërobic treatment of sewage. A plan -and a section of a contact bed are shown in Fig. 166. - -Because of its dependence on biologic action a contact bed must be -ripened before a good effluent can be obtained. The ripening or maturing -occurs progressively during the first few weeks of operation, the -earlier stages being more rapidly developed. The time required to reach -such a stage of maturity that a good effluent will be developed will -vary between one and six or eight weeks, dependent on the weather and -the character of the influent. During the period of maturing the load on -the bed should be made light. - -The use of contact beds has been extensive where a more stable effluent -than could be obtained from tank treatment has been desired, yet the -best quality of effluent was not required. The sewage to undergo -treatment in a contact bed should be given a preliminary treatment to -remove coarse suspended matter. The efficiency of the contact treatment -can be increased by passing the sewage through two or three contact beds -in series. In double contact treatment the primary beds are filled with -coarser material and operate at a more rapid rate than the secondary -beds. Double contact gives better results than single contact, but -triple contact treatment, though showing excellent results, is hardly -worth the extra cost. An advantage which contact treatment has over all -other methods of sewage filtration is that the bed can be so operated -that the sewage is never exposed to view. As a result the odors from -well-operated contact beds are slight or are entirely absent and there -should be no trouble from flying insects. Such a method of treatment is -favorable to plants located in populous districts and to the fancies of -a landscape architect. Another advantage of the contact bed is the small -amount of head required for its operation, which may be as low as 4 to 5 -feet. This low head consumption by a sewage filter is equaled only by -the intermittent sand filter. - -[Illustration: - - FIG. 166.—Plan and Section of Treatment Plant at Marion, Ohio, Showing - Septic Tank, Contact Bed, and Sand Filter. - - 1908 Report Ohio State Board of Health. -] - -The quality of the effluent from some contact beds is shown in Table 85. -It is to be noted that nitrification has been carried to a fair degree -of completion, and that the reduction of oxygen consumed has been -marked. In comparison with the effluent from filters, contact effluent -contains a smaller amount of nitrogen as nitrites and nitrates, and -suspended solids. Contact effluent is usually clear and odorless, but it -is not stable without dilution. The absence of nitrites and nitrates is -sometimes advantageous as the effluent will not support vegetable -growths dependent on this form of nitrogen. The absence of suspended -solids obviates the use of secondary sedimentation basins which are -needed with trickling filters. The head of 5 to 8 feet required for -contact treatment is low in comparison to the 10 to 15 feet required for -trickling filters, but is slightly higher than the head required for -intermittent sand filtration. The cost of contact treatment is higher -than the cost of trickling filters but is lower than the cost of -intermittent sand filtration, as shown in Table 90. - - TABLE 85 - - QUALITY OF EFFLUENTS FROM CONTACT BEDS - - Report on Sewage Purification at Columbus, Ohio, by G. A. Johnson, 1905. - - ──────┬──────┬─────────┬───────┬────────┬───────────────────────────────── - Filter│Depth,│ Size of │ Rate, │ Oxygen │ Nitrogen as - │ Feet │Material │Million│Consumed│ - │ │in Inches│Gallons│ │ - │ │ │ per │ │ - │ │ │ Acre │ │ - │ │ │per Day│ │ - ──────┼──────┼─────────┼───────┼────────┼───────┬───────┬────────┬──────── - │ │ │ │ │Organic│ Free │Nitrites│Nitrates - │ │ │ │ │ │Ammonia│ │ - ──────┼──────┼─────────┼───────┼────────┼───────┴───────┴────────┴──────── - │ │ │ │ │ Parts per Million - │ │ │ │ │ │ │ │ - A │ 5│0.25–1.00│ 0.953│ 23│ 3.5│ 8.7│ 0.20│ 1.6 - B │ 5│0.25–2.00│ 1.514│ 21│ 4.0│ 8.4│ 0.15│ 1.4 - C │ 5│0.25–1.50│ 1.222│ 24│ 3.5│ 10.8│ 0.11│ 0.6 - D │ 5│0.50–1.50│ 1.405│ 22│ 3.3│ 9.5│ 0.13│ 0.9 - │ │ │ │ │ │ │ │ - │ │ │Per Cent Removal of Constituents of Applied Sewage - │ │ │ │ │ │ │ │ - A │ 5│0.25–1.00│ 0.953│ 48│ 49│ 10│ │ - B │ 5│0.25–2.00│ 1.514│ 52│ 40│ 11│ │ - C │ 5│0.25–1.50│ 1.222│ 47│ 31│ 12│ │ - D │ 5│0.50–1.50│ 1.405│ 46│ 37│ 19│ │ - ──────┴──────┴─────────┴───────┴────────┴───────┴───────┴────────┴──────── - - ──────┬──────┬────────────────────┬───────── - Filter│Depth,│ Suspended Matter │Dissolved - │ Feet │ │ Oxygen - │ │ │ - │ │ │ - │ │ │ - │ │ │ - ──────┼──────┼─────┬────────┬─────┼───────── - │ │Total│Volatile│Fixed│ - │ │ │ │ │ - ──────┼──────┴─────┴────────┴─────┴───────── - │ Parts per Million - │ │ │ │ │ - A │ 5│ 832│ 94│ 737│ 0.3 - B │ 5│ 831│ 85│ 746│ 0.1 - C │ 5│ 826│ 92│ 734│ 0.8 - D │ 5│ 810│ 91│ 717│ 0.9 - │ │ │ │ │ - │ Per Cent Removal of Constituents of Applied Sewage - │ │ │ │ │ - A │ 5│ 73│ 70│ 76│ - B │ 5│ 80│ 77│ 83│ - C │ 5│ 70│ 70│ 70│ - D │ 5│ 67│ 61│ 72│ - ──────┴──────┴─────┴────────┴─────┴───────── - -The depth of the contact bed is generally made from 4 to 6 feet. The -deeper beds are less expensive per unit of volume, to construct, as the -cost of the underdrains and the distribution system is reduced in -relation to the capacity of the filter. The increased depth reduces the -aëration, and the periods of filling and emptying are so increased as to -limit the depths to the figures stated. The other dimensions of the bed -are controlled by economy and local conditions, as the success of the -contact treatment is not affected by the shape of the bed. Contact units -are seldom constructed larger than one-half an acre in area, as larger -beds require too much time for filling and emptying. A large number of -small units is also undesirable because of the increased difficulty of -control. In general it is well to build as large units as are compatible -with efficient operation, elasticity of plant, and which can be filled -within the time allowed at the average rate of sewage flow, or from -dosing tanks in which the storage period is not so long as to produce -septic conditions. - -The interstices in a contact bed will gradually fill up, due to the -deposition of solid matter on the contact material, the disintegration -of the material, and the presence of organic growths. The period of rest -allowed every five or six weeks tends to restore partially some of this -lost capacity through the drying of the organic growths. It is -occasionally necessary to remove the material from the bed and wash it -in order to restore the original capacity. It may be necessary to do -this three or four times a year, in an overloaded plant, or as -infrequently as once in five or six years in a more lightly loaded bed. -The period is also dependent on the character of the contact material -and the quality of the influent. This loss of capacity may reduce the -voids from an original amount of 40 to 50 per cent of voids to 10 to 15 -per cent. If the bed is not overloaded the loss of capacity will not -increase beyond these figures. - -The rate of filtration depends on the strength of the sewage, the -character of the contact material, and the required effluent. It should -be determined for any particular plant as the result of a series of -tests. For the purposes of estimation and comparison the approximate -rate of filtration should be taken at about 94 gallons per cubic yard of -filtering material per day on the basis of three complete fillings and -emptyings of the tank. This is equivalent to 150,000 gallons per acre -foot of depth per day, or for a bed 5 feet deep to a rate of 750,000 -gallons per acre per day. The net rate for double or triple filtration -is less than these figures, but on each filter the rates are higher. - -The material of the contact bed should be hard, rough, and angular. It -should be as fine as possible without causing clogging of the bed. -Materials in successful use are: crushed trap rock or other hard stone, -broken bricks, slag, coal, etc. Soft crumbling materials such as coke -are not suitable as the weight of the superimposed material and the -movement of the sewage crushes and breaks it into fine particles which -accumulate in the lower portion of the filter and clog it. Roughness, -porosity, and small size are desirable, as the greater the surface area -the more rapid the deposition of material. After a short time, however, -the advantages of roughness and porosity are lost, as the sediment soon -covers all unevenness alike. The minimum size of the material is limited -by the tendency towards clogging. The sizes in successful use vary -between ¼ and ¾ of an inch, ½ inch being a common size. The same size of -material is used throughout the depth of the bed except that the upper 6 -inches may be composed of small white pebbles or other clean material, -which does not come in contact with the sewage and which will give an -attractive appearance to the plant. In double or triple contact beds 3 -or 4–inch material is sometimes used for the primary beds, and ¼-inch -material in the final bed. - -Sewage may be applied at any point on or below the surface. The sewage -is withdrawn from the bottom of the bed. It is undesirable to have too -few inlet or outlet openings as the velocity of flow about the openings -will be so great as to disturb the deposit on the contact material. The -distribution system and the underdrains for the bed at Marion, Ohio, are -shown in Fig. 166. - -The cycle of operation of a contact bed is divided into four periods. A -representative cycle might be: time of filling, one hour; standing full, -2 hours; emptying, one hour; standing empty, 4 hours. The length of -these periods is the result of long experience based on many tests and -are an average of the conclusions reached. Wide variations from them may -be found in different plants, and tests may show successful results with -different periods. The combination of these four periods is known as the -contact cycle. - -The period of filling should be made as short as possible without -disturbing the material of the bed nor washing off the accumulated -deposits. The sewage should not rise more rapidly than one vertical foot -per minute. During the contact or standing full period sedimentation and -adsorption of the colloids are occurring on the area of surface exposed -to the sewage. This period should be of such length that septic action -does not become pronounced, and long enough to permit of thorough -sedimentation. The period of emptying should be made as short as -possible without disturbing the bed, on the same basis that the period -of filling is determined. During the period of standing empty, air is in -contact with the sediment deposited in thin layers on the contact -material, and the oxidizing activities of the filter are taking place. -The filter is given a rest period of one or two days every five or six -weeks, in order that it may increase its capacity and its biologic -activity. - -The control of a contact bed may be either by hand or automatic, the -latter being the more common. Hand control requires the constant -attention of an operator and results in irregularity of operation, -whereas automatic control will require inspection not more than once a -day and insures regularity of operation. A number of automatic devices -have been invented which give more or less satisfaction. The air-locked -automatic siphons, without moving parts, have proven satisfactory and -are practically “fool-proof.” The operation of these devices is -explained in Chapter XXI. - - -=257. The Trickling Filter.=—A trickling or sprinkling filter is a bed -of coarse, rough, hard material over which sewage is sprayed or -otherwise distributed and allowed to trickle slowly through the filter -in contact with the atmosphere. A general view of a trickling filter in -operation at Baltimore is shown in Fig. 167. The action of the trickling -filter is due to oxidation by organisms attached to the material of the -filter. The solid organic matter of the sewage deposited on the surface -of the material, is worked over and oxidized by the aërobic bacteria, -and is discharged in the effluent in a more highly nitrified condition. -At times the discharge of suspended matter becomes so great that the -filter is said to be unloading. The action differs from that in a -contact bed in that there is no period of septic or anaërobic action and -the filter never stands full of sewage. - -The effluent from a trickling filter is dark, odorless, and is -ordinarily non-putrescible. Analyses of typical effluents are given in -Tables 86 and 87. The unloading of the filter may occur at any time, but -is most likely to occur in the spring or in a warm period following a -period of low temperatures. It causes higher suspended matter in the -effluent than in the influent and may render the effluent putrescible. -The action is marked by the discharge of solid matter which has sloughed -off of the filter material and which increases the turbidity of the -effluent. Where the diluting water is insufficient to care for the -solids so carried in the effluent, they can be removed by a 2–hour -period of sedimentation. The effluent may become septic during this -time, however. The nitrogen in the effluent is almost entirely in the -form of nitrates, and the percentage of saturation with dissolved oxygen -is high. The effluent is more highly nitrified than that from a contact -bed, and its relative stability is also higher, thus demanding a smaller -volume of diluting water. - -[Illustration: - - FIG. 167.—Sprinkling Filter in Operation in Winter at Baltimore. -] - -The principal advantage of a trickling filter over other methods of -treatment is its high rate which is from two to four times faster than a -contact bed, and about seventy times faster than an intermittent sand -filter. The greatest disadvantage is the head of 12 to 15 feet or more -necessary for its operation. Sedimentation of the effluent is usually -necessary to remove the settleable solids. During the period of -secondary sedimentation the quality of the filter effluent may -deteriorate in relative stability. In winter the formation of ice on the -filter results in an effluent of inferior quality, but as the diluting -water can care for such an effluent at this time the condition is not -detrimental to the use of the trickling filter. In summer the filters -sometimes give off offensive odors that can be noticed at a distance of -half a mile, and flying insects may breed in the filter in sufficient -quantities to become a nuisance if preventive steps are not taken. The -dissemination of odors is especially marked when treating a stale or -septic sewage. The treatment of a fresh sewage seldom results in the -creation of offensive odors. - - TABLE 86 - - ANALYSIS OF CRUDE SEWAGE, IMHOFF TANK, AND SPRINKLING FILTER EFFLUENTS - AT ATLANTA, GEORGIA - - (Engineering Record, Vol. 72, p. 4) - - ─────────┬───────────┬────────────────────────────────────────── - │Temperature│ Parts per Million - │Fahrenheit │ - │ │ - │ │ - ─────────┼───────────┼─────────────────────────────────┬──────── - │ │ Nitrogen as │ Oxygen - │ │ │Consumed - ─────────┼───────────┼───────┬───────┬────────┬────────┼──────── - │ │Organic│ Free │Nitrites│Nitrates│ - │ │ │Ammonia│ │ │ - ─────────┴───────────┴───────┴───────┴────────┴────────┴──────── - - _Crude Sewage_ - - ─────────┬───────────┬───────┬───────┬────────┬────────┬──────── - 1913 │ │ │ │ │ │ - Maximum │ 77│ 15.6│ 21.8│ 0.1│ 3.0│ 100.0 - Minimum │ 61│ 10.4│ 16.5│ 0.1│ 1.4│ 78.3 - Average │ 70│ 12.8│ 18.8│ 0.1│ 2.2│ 90.6 - 1914 (7 │ │ │ │ │ │ - months)│ │ │ │ │ │ - Maximum │ 74│ 16.0│ 33.4│ │ 2.3│ - Minimum │ 60│ 9.5│ 18.1│ │ 1.6│ - Average │ 66│ 13.4│ 27.1│ │ 2.0│ - ─────────┴───────────┴───────┴───────┴────────┴────────┴──────── - - _Imhoff Effluent_ - - ─────────┬───────────┬───────┬───────┬────────┬────────┬──────── - 1913 │ │ │ │ │ │ - Maximum │ 78│ 13.2│ 21.9│ 0.2│ 3.1│ 68.0 - Minimum │ 58│ 6.5│ 16.8│ 0.1│ 1.1│ 53.1 - Average │ 68│ 9.0│ 20.0│ 0.2│ 2.1│ 60.1 - 1914 (7 │ │ │ │ │ │ - months)│ │ │ │ │ │ - Maximum │ 77│ 10.3│ 30.3│ │ 2.0│ - Minimum │ 59│ 4.1│ 18.0│ │ 1.5│ - Average │ 65│ 7.7│ 25.9│ │ 1.8│ - ─────────┴───────────┴───────┴───────┴────────┴────────┴──────── - - _Sprinkling Filter Effluent_ - - ─────────┬───────────┬───────┬───────┬────────┬────────┬──────── - 1913 │ │ │ │ │ │ - Maximum │ 79│ 5.6│ 14.2│ 0.8│ 11.3│ 32.1 - Minimum │ 55│ 2.6│ 6.2│ 0.5│ 5.8│ 23.6 - Average │ 66│ 3.8│ 9.9│ 0.7│ 8.2│ 28.2 - 1914 (7 │ │ │ │ │ │ - months)│ │ │ │ │ │ - Maximum │ 77│ 8.5│ 20.7│ │ 11.2│ - Minimum │ 55│ 4.4│ 8.8│ │ 3.6│ - Average │ 63│ 5.7│ 15.2│ │ 7.2│ - ─────────┴───────────┴───────┴───────┴────────┴────────┴──────── - - ─────────┬────────────────────┬──────────┬───────── - │ Parts per Million │ Per Cent │Relative - │ │Saturation│Stability - │ │Dissolved │ - │ │ Oxygen │ - ─────────┼────────────────────┼──────────┼───────── - │ Suspended Matter │ │ - │ │ │ - ─────────┼─────┬────────┬─────┼──────────┼───────── - │Total│Volatile│Fixed│ │ - │ │ │ │ │ - ─────────┴─────┴────────┴─────┴──────────┴───────── - - _Crude Sewage_ - - ─────────┬─────┬────────┬─────┬──────────┬───────── - 1913 │ │ │ │ │ - Maximum │ 371│ 154│ 163│ 47│ - Minimum │ 222│ 98│ 112│ 11│ - Average │ 285│ 126│ 138│ 28│ - 1914 (7 │ │ │ │ │ - months)│ │ │ │ │ - Maximum │ 431│ │ │ 48│ - Minimum │ 279│ │ │ 12│ - Average │ 351│ │ │ 30│ - ─────────┴─────┴────────┴─────┴──────────┴───────── - - _Imhoff Effluent_ - - ─────────┬─────┬────────┬─────┬──────────┬───────── - 1913 │ │ │ │ │ - Maximum │ 90│ 50│ 41│ │ - Minimum │ 35│ 42│ 21│ │ - Average │ 68│ 46│ 33│ │ - 1914 (7 │ │ │ │ │ - months)│ │ │ │ │ - Maximum │ 73│ │ │ 48│ - Minimum │ 49│ │ │ 34│ - Average │ 65│ │ │ 43│ - ─────────┴─────┴────────┴─────┴──────────┴───────── - - _Sprinkling Filter Effluent_ - - ─────────┬─────┬────────┬─────┬──────────┬───────── - 1913 │ │ │ │ │ - Maximum │ 60│ 31│ 28│ 76│ 99 - Minimum │ 33│ 26│ 28│ 52│ 88 - Average │ 49│ 28│ 28│ 64│ 89 - 1914 (7 │ │ │ │ │ - months)│ │ │ │ │ - Maximum │ 106│ │ │ 79│ 99 - Minimum │ 40│ │ │ 55│ 89 - Average │ 62│ │ │ 65│ 95 - ─────────┴─────┴────────┴─────┴──────────┴───────── - - TABLE 87 - - EFFICIENCY OF SPRINKLING FILTER CHICAGO, ILLINOIS - - Depth of Filter 9 feet. Size of stone 2 in. to 3 in. - - ────────┬───────────────────────────┬─────────────────────────── - Month │ Organic Nitrogen │ Free Ammonia - │ │ - ────────┼───────────────────────────┼─────────────────────────── - │ │ - ────────┼─────────┬─────────┬───────┼─────────┬─────────┬─────── - │Influent,│Effluent,│ Per │Influent,│Effluent,│ Per - │Parts per│Parts per│ Cent │Parts per│Parts per│ Cent - │ Million │ Million │Removed│ Million │ Million │Removed - ────────┼─────────┼─────────┼───────┼─────────┼─────────┼─────── - 1910 │ │ │ │ │ │ - October │ 5.1│ 2.8│ 45│ 12.0│ 4.6│ 62 - November│ 5.9│ 2.5│ 58│ 12.0│ 5.9│ 51 - December│ 4.6│ 3.0│ 35│ 12.0│ 6.9│ 42 - │ │ │ │ │ │ - 1911 │ │ │ │ │ │ - January │ 6.3│ 4.8│ 24│ 11.0│ 7.0│ 36 - February│ 9.0│ 4.8│ 47│ 10.0│ 7.2│ 28 - March │ 8.3│ 3.5│ 58│ 9.9│ 6.4│ 35 - April │ 6.4│ 4.0│ 37│ 8.3│ 3.6│ 69 - May │ 7.6│ 5.4│ 29│ 9.2│ 2.4│ 74 - June │ 5.9│ 3.2│ 46│ 11.0│ 0.6│ 95 - July │ 6.2│ 4.2│ 32│ 11.0│ 1.3│ 88 - ────────┴─────────┴─────────┴───────┴─────────┴─────────┴─────── - - ────────┬───────────────────────────┬─────────────────────────── - Month │ Oxygen Consumed │ Nitrites - │ │ - ────────┼───────────────────────────┼─────────────────────────── - │ │ - ────────┼─────────┬─────────┬───────┼─────────┬─────────┬─────── - │Influent,│Effluent,│ Per │Influent,│Effluent,│ Per - │Parts per│Parts per│ Cent │Parts per│Parts per│ Cent - │ Million │ Million │Removed│ Million │ Million │Removed - ────────┼─────────┼─────────┼───────┼─────────┼─────────┼─────── - 1910 │ │ │ │ │ │ - October │ 30│ 15│ 50│ │ .90│ - November│ 35│ 15│ 57│ │ .76│ - December│ 39│ 20│ 49│ .07│ .45│ 6.4 - │ │ │ │ │ │ - 1911 │ │ │ │ │ │ - January │ 42│ 20│ 52│ .08│ .15│ 1.9 - February│ 46│ 20│ 56│ .09│ .15│ 1.7 - March │ 47│ 21│ 56│ .09│ .15│ 1.7 - April │ 38│ 21│ 45│ .16│ .21│ 1.3 - May │ 33│ 31│ 6│ .08│ .38│ 4.8 - June │ 28│ 16│ 43│ .00│ .30│ ∞ - July │ 34│ 26│ 24│ .00│ .36│ ∞ - ────────┴─────────┴─────────┴───────┴─────────┴─────────┴─────── - - ────────┬───────────────────────────┬─────────────────────────── - Month │ Nitrates │ Dissolved Oxygen - │ │ - ────────┼───────────────────────────┼─────────────────────────── - │ │ - ────────┼─────────┬─────────┬───────┼─────────┬─────────┬─────── - │Influent,│Effluent,│ Per │Influent,│Effluent,│ Per - │Parts per│Parts per│ Cent │Parts per│Parts per│ Cent - │ Million │ Million │Removed│ Million │ Million │Removed - ────────┼─────────┼─────────┼───────┼─────────┼─────────┼─────── - 1910 │ │ │ │ │ │ - October │ │ 7.8│ │ 0.0│ 8.5│ ∞ - November│ │ 5.9│ │ 0.0│ 8.1│ ∞ - December│ .15│ 2.6│ 17│ 2.0│ 8.4│ 4.2 - │ │ │ │ │ │ - 1911 │ │ │ │ │ │ - January │ .27│ 2.2│ 8.2│ 3.0│ 7.8│ 2.9 - February│ .50│ 2.6│ 5.2│ 2.6│ 8.0│ 3.1 - March │ .34│ 3.2│ 9.4│ 2.2│ 6.6│ 3.0 - April │ .53│ 4.5│ 8.5│ 2.1│ 7.1│ 3.4 - May │ .15│ 7.5│ 4.3│ 0.1│ 7.7│ 77 - June │ .16│ 8.3│ 5.2│ 0.0│ 7.6│ ∞ - July │ .09│ 7.7│ 8.0│ 0.0│ 6.5│ ∞ - ────────┴─────────┴─────────┴───────┴─────────┴─────────┴─────── - - ────────┬───────────┬─────────────────────────────────────────────────────── - Month │ Per Cent │ Suspended Matter - │Putrescible│ - ────────┼───────────┼───────────────────────────┬─────────────────────────── - │ │ Total │ Volatile - ────────┼───────────┼─────────┬─────────┬───────┼─────────┬─────────┬─────── - │ │Influent,│Effluent,│ Per │Influent,│Effluent,│ Per - │ │Parts per│Parts per│ Cent │Parts per│Parts per│ Cent - │ │ Million │ Million │Removed│ Million │ Million │Removed - ────────┼───────────┼─────────┼─────────┼───────┼─────────┼─────────┼─────── - 1910 │ │ │ │ │ │ │ - October │ 0│ 75│ 40│ 47│ 54│ 25│ 54 - November│ 5│ 61│ 16│ 74│ 52│ 15│ 71 - December│ 35│ 85│ 40│ 53│ 60│ 26│ 57 - │ │ │ │ │ │ │ - 1911 │ │ │ │ │ │ │ - January │ 38│ 112│ 43│ 63│ 68│ 29│ 57 - February│ 29│ 100│ 49│ 51│ 64│ 32│ 50 - March │ 28│ 106│ 37│ 65│ 63│ 22│ 65 - April │ 9│ 113│ 68│ 40│ 59│ 35│ 41 - May │ 6│ 88│ 150│ _1.7_│ 54│ 70│ _1.3_ - June │ 1│ 92│ 77│ 18│ 56│ 36│ 36 - July │ 4│ 155│ 130│ 16│ 74│ 61│ 18 - ────────┴───────────┴─────────┴─────────┴───────┴─────────┴─────────┴─────── - - ────────┬─────────────────────────── - Month │ Suspended Matter - │ - ────────┼─────────────────────────── - │ Fixed - ────────┼─────────┬─────────┬─────── - │Influent,│Effluent,│ Per - │Parts per│Parts per│ Cent - │ Million │ Million │Removed - ────────┼─────────┼─────────┼─────── - 1910 │ │ │ - October │ 21│ 15│ 29 - November│ 9│ 1│ 89 - December│ 25│ 14│ 44 - │ │ │ - 1911 │ │ │ - January │ 44│ 13│ 70 - February│ 37│ 17│ 53 - March │ 43│ 15│ 65 - April │ 54│ 33│ 39 - May │ 34│ 80│ _2.4_ - June │ 36│ 41│ _1.1_ - July │ 81│ 69│ 15 - ────────┴─────────┴─────────┴─────── - - NOTE.—Italic figures represent increases. - -Raw sewage cannot be treated successfully on a trickling filter. Coarse -solid particles should be screened and settled out, in order that the -distributing devices or the filter may not become clogged. The effluent -from an Imhoff tank has proven to be a satisfactory influent for a -trickling filter. A septic tank effluent may be so stale as to be -detrimental to the biologic action in the filter. - -In the operation of a trickling filter the sewage is sprayed or -otherwise distributed as evenly as possible in a fine spray or stream, -over the top of the filtering material. The sewage then trickles slowly -through the filter to the underdrains through which it passes to the -final outlet. The distribution of the sewage on the bed is intermittent -in order to allow air to enter the filter with the sewage. The cycle of -operation should be completed in 5 to 15 minutes, with approximately -equal periods of rest and distribution. Cycles of too great length will -expose the filter to drying or freezing and will give poorer -distribution throughout the filter. Cycles which are too short will -operate successfully only with but slight variation in the rate of -sewage flow. In some plants it has been found advantageous to allow the -filters to rest for one day in 3 to 6 weeks or longer, dependent on the -quality of the effluent. - -The rate of filtration may be as high as 2,000,000 gallons per acre per -day, which is equivalent to 200 gallons per cubic yard of material per -day in a bed 6 feet deep. This is more than double the rate permissible -in a contact bed. The exact rate to be used for any particular plant -should be determined by tests. It is dependent on the quality of the -sewage to be treated, on the depth of the bed, the size of the filling -material, the weather, and other minor factors. - -The filtering material is similar to that used in a contact bed. It -should consist of hard, rough, angular material, about 1 to 2 inches in -size. Larger sizes will permit more rapid rates of filtration, but will -not produce so good an effluent. Smaller sizes will clog too rapidly. - -The depth of the filter is limited by the possibility of ventilation and -the strength of the filtering material to withstand crushing. The deeper -the bed the less the expense of the distribution and collecting system -for the same volume of material, and the more rapid the permissible rate -of filtration. The depths in use vary between 6 and 10 feet, with 6 to 8 -feet as a satisfactory mean. From a biologic standpoint the action of -the filter seems to be proportional to the volume of the filtering -material and therefore proportional to the depth of the bed, being -limited to a minimum depth of about 5 feet, below which sewage may pass -through the filter without treatment. The shape and other dimensions of -the filter depend on the local conditions and the economy of -construction. The filters need not be broken up into units by -water-tight dividing walls. One filter can be constructed sufficient for -all needs and various portions of it can be isolated as units by the -manipulation of valves in the distribution system. Ventilation is -provided by the air entrained with the sewage as it falls upon the -surface. If the sides of the filter are built of open stone crib work -the ventilation will be greatly improved, but it will not be possible to -flood the filters to keep down flies, and in cold climates these -openings must be covered in winter to prevent freezing. Filters have -been constructed without side walls, the filtering material being -allowed to assume its natural angle of repose. This has usually been -found to be more expensive than the construction of side retaining -walls, due to the unused filling material and the extra underdrains -required. - -The distribution of sewage is ordinarily effected by a system of pipes -and spray nozzles as shown in Fig. 168 and 169. Other methods of -distribution have been used. At Springfield, Mo.,[160] a moving trough -from which the sewage flows continuously is drawn back and forth across -the bed by means of a cable. In England circular beds have been -constructed and the sewage distributed on them through revolving -perforated pipes. At the Great Lakes Naval Training Station[161] the -distributing pipes in the plant, now abandoned, were supported above the -surface of the filter. The sewage fell from holes in the lower side of -these pipes on to brass splash plates 14 inches above the filter. It was -deflected horizontally from these plates over the filter surface. Pipes -and spray nozzles have been adopted almost universally in the United -States. Splash plates, traveling distributors, and other forms of -distribution have been used only in exceptional cases. In a distributing -system consisting of pipes and nozzles, a network of pipes is laid out -somewhat as shown in Fig. 168, in such a manner that the head loss to -all points is approximately equal. The number of valves required should -be reduced to a minimum. The pipes may be laid out with the main feeders -leading from a central point and branches at right angles to them, -somewhat on the order of a spider’s web, or they may be laid out on a -rectangular or gridiron system. The radial system is advantageous -because of the central location of the control house, but it does not -always lend itself favorably to the local conditions, and the piping and -nozzle location are not so simple. The gridiron system lends itself -favorably to the equalization of head losses. The pipes used should be -larger than would be demanded by considerations of economy alone, both -for the purpose of reduction of head loss and ease in cleaning. No pipe -less than 6 inches in diameter should be used, and the average velocity -of flow should not exceed one foot per second. Cast-iron, concrete, or -vitrified clay pipe may be used, but cast iron is the material commonly -used. The system should be arranged for easy flushing and cleaning and -the pipes so sloped that the entire system can be drained in case of a -shut down in cold weather. - -[Illustration: - - FIG. 168.—Section through Sprinkling Filter at Fitchburg, Mass., - Showing Distribution System. - - Eng. Record, Vol. 67, p. 634. -] - -The pipes are placed far enough below the surface of the filling -material so that the top of the spraying nozzle is 6 to 12 inches above -the surface of the filter. If the pipes are placed near the surface they -are accessible for repairs, but are exposed to temperature changes. If -the pipes are large their presence near the surface of the filter may -seriously affect the distribution of the sewage through the filter. If -the distributing pipes are placed near the bottom of the filter they are -inaccessible for repairs and the nozzles must be connected to them by -means of long riser pipes. The distributing pipes should be supported by -columns extending to the foundation of the filter bed, there being a -column at every pipe joint with such intermediate supports as may be -required. In some plants the pipes have been supported by the filtering -material. Although slightly less expensive in first cost the practice of -so supporting the pipes is poor, as settling of the material may break -the pipe or cause leaks, and if the bed becomes clogged, removal of the -material is made more difficult. Valves should be placed in the -distributing system in such a manner that different sets of nozzles can -be cut out at will, thus resting those portions of the filter and -permitting repairs without shutting down the entire filter. - -The spacing of the nozzles is fixed by the type and size of the nozzle, -the available head, and the rate of filtration. Various types of -sprinkler nozzles are shown in Fig. 169 and the discharge rates, head -losses, and distances to which sewage is thrown for the Taylor nozzles, -are shown in Fig. 170. Nozzles are available which will throw circular, -square, or semicircular sprays. In the use of circular sprays there is -necessarily some portion of the filter which is underdosed if the -nozzles are placed at the corners of squares with the sprays tangent, -and there is an overdosing of other portions if the sprays are allowed -to overlap so that no portion of the filter is left without a dose. -Rectangular sprays will apparently overcome these difficulties, but -studies have shown that circular sprays with some overlapping, and the -nozzles placed at the apexes of equilateral triangles as shown in Fig. -172 will give as satisfactory distribution as other forms. - -[Illustration: - - FIG. 169.—Sprinkling Filter Nozzles. - - Bulletin No. 3, Engineering Experiment Station, Purdue University. -] - -[Illustration: - - FIG. 170.—Diagram Showing the Discharge and Spacing of Taylor Nozzles. -] - -The nozzles should be selected to give the best distribution, to consume -all of the head available, and to give the proper cycle of operation. -The entire head available should be consumed in order that the fewest -number of nozzles may be used. An excellent study of the characteristics -of various types of nozzles has been published in Bulletin No. 3 of the -Engineering Experiment Station at Purdue University, 1920. As a result -of the tests on the nozzles shown in Fig. 169, it was determined for all -nozzles, except No. 8, that - - _Q_ = _Ca_√(2_gh_); - - in which _Q_ = the rate of discharge in cubic feet per second; - - _C_ = a coefficient shown in Table 88; - - _a_ = the net cross-sectional opening of the nozzle in square - feet; - - _h_ = the pressure on the nozzle in feet of water. - - TABLE 88 - - COEFFICIENTS OF DISCHARGE FOR SPRINKLER NOZZLES SHOWN IN FIG. 169 - - ──────────────────────┬──────┬──────┬──────┬──────┬──────┬──────┬────── - Nozzle Number │ 1 │ 2 │ 3 │ 4 │ 5 │ 6 │ 7 - ──────────────────────┼──────┼──────┼──────┼──────┼──────┼──────┼────── - Coefficient │ .648 │ .756 │ .696 │ .666 │ .675 │ .598 │ .569 - ──────────────────────┴──────┴──────┴──────┴──────┴──────┴──────┴────── - -It is evident that if the head on the nozzles is constant and the nozzle -throws a circular spray, the intensity of dosing at the circumference -will be greater than nearer the center. This difficulty is overcome by -so designing the dosing tank from which the sewage is fed that the head -on the nozzle and the quantity thrown will vary in such a manner that -the distribution over the bed is equalized. Intermittent action is -obtained by an automatic siphon which commences to discharge when the -tank is full and empties the tank in the period allowed for dosing. -Under such conditions the tank should discharge for a longer time at the -higher heads than at the lower heads as there is more territory to be -covered at the higher heads. The design of the tank to do this with -exactness is difficult, and the construction of the necessary curved -surfaces is expensive. Where a dosing tank is used for such conditions -it has been found satisfactory to construct the tank with plane sides -sloping at approximately 45 degrees from the vertical (or horizontal). A -tank with curved surfaces is shown in Fig. 171. The dosing siphon is -usually placed in the tank as shown in the figure. The head and quantity -of discharge through the nozzles can be varied also by maintaining a -constant depth in a dosing tank by means of a float feed valve, and -varying the head and quantity discharged to the nozzles by a butterfly -valve in the main feed line, or by the use of a Taylor undulating valve -designed for this purpose. The butterfly valve is opened and closed by a -cam so designed and driven at such a rate that the required distribution -is obtained. The Taylor undulating valve is opened and closed at a -constant rate, the shape of the valve giving the required variations in -head and discharge. Other methods of control have been attempted but -have not been used extensively. - -[Illustration: - - FIG. 171.—Section of 12–inch Siphon and Dosing Tank, for King’s Park, - Long Island. -] - -An example of the design of the nozzle layout and dosing tank for a -sprinkling filter follows: - - Let it be required to determine the nozzle layout for one acre of - sprinkling filters with 5 feet available head on the nozzles. - - The selection of the type of nozzle and the size of opening is a - matter of judgment and experience. Nozzles with large openings are - less liable to clog and fewer nozzles are needed than where small - nozzles are used, but the distribution of sewage is not so even as - with the use of small nozzles. In this example Taylor circular - spray nozzles will be selected. Fig. 170 shows that a Taylor - circular spray nozzle will discharge 22.3 g.p.m. under a head of 5 - feet, and that the economical nozzle spacing will be 15.3 feet. - The least number of nozzles at this spacing required for a bed of - one acre in area is found as follows: In Fig. 172, let _n_ equal - the number of nozzles in a horizontal row, counting half-spray - nozzles as ½, and let _m_ equal the number of rows counting rows - of half-spray nozzles as half rows.[162] Then the number of - nozzles, _N_, equals _mn_, and 15.3_m_ × 13.2_n_ equals 43,560 or - _mn_ equals 215. - -[Illustration: - - FIG. 172.—Typical Sprinkler Nozzle Layout. -] - -The next step should be the design of the dosing tank and siphon. It is -possible to design a tank which will give equal distribution over equal -areas of filter surface. It has been found, however, that the expense of -this refinement is unwarranted as there are a number of outside factors -which tend to overcome the theoretical design. The effect of wind, -unequal spacing, and irregularities in the elevation of the nozzles have -a tendency to offset refinements in the design of a dosing tank. It is -therefore the general practice to slope the sides of the tank at an -angle of about 45 degrees as previously stated. The dosing tank is -generally designed to have a capacity which will give a complete cycle -of operation once in 15 minutes. In the ordinary design the factors -given are the rate of inflow and the given time of filling. In the -following example the time of filling will be taken as 10 minutes, the -time of emptying as 5 minutes, and the rate of flow as 1,000,000 gallons -per day. The capacity of the tank will therefore be (1,000,000)⁄24 x 6 = -7,000 gallons. The diameter of the siphon to be selected can be computed -as follows: - - Let _Q_ = the capacity of the tank in cubic feet; - _q__{1} = the rate of discharge of the siphon in cubic feet per - second; - _q__{2} = the rate of inflow to the tank in cubic feet per second; - _q_ = the rate of emptying the tank in cubic feet per second = - (_q__{1} − _q__{2}); - _A_ = the cross-sectional area of the free surface of the water - in the tank at any instant, in square feet; - _a_ = the cross-sectional area of the siphon in square feet; - _b_ = the small dimension of the base of the tank in feet; - _h_ = the head of water, in feet, on the discharge siphon; - _h__{1} = the initial head of water, in feet, on the siphon; - _h__{2} = the final head of water in feet, on the siphon; - _t_ = the time, in seconds, required to empty the tank, - - then _dQ_ = -_Adh_ = _q__{1}_dt_ − _q__{2}_dt_, - - and _dt_ = (_dQ_)⁄_q_ = − _Adh_⁄(_q__{1} − _q__{2}), - - but _q__{1} = 0.4 _A_ √((2_gh_)),[163] - - therefore _t_ = ∫_{_h__{2}}^{_h__{1}} -_Adh_⁄(0.4_a_√(2_gh_) − - _q__{2}), - - but _A_ = 4_h_^2 + 4_bh_ + _b_^2, - - therefore _t_ = ∫_{_h__{1}}^{_h__{2}} ((_b_^2 + 4_bh_ + - 4_h_^2)_dh_)⁄0.4_a_√(2_gh_) − _q__{2}. - -The integration of this expression is tedious. Its solution for siphons -between 6 inches and 12 inches operating under heads commencing from 3 -feet to 6 feet, with a time of emptying of 5 minutes and time of filling -of 10 minutes is given in Fig. 173. In the example given the rate of -inflow is 1.55 sec. feet and the head is 5 feet. Then from Fig. 173 the -size of the siphon to be used is 12 inches. Where a siphon of the size -required to empty the tank in the time fixed is not available, -combinations of available sizes can sometimes be used. - -[Illustration: - - FIG. 173.—Diagram for the Determination of the Capacities of Dosing - Tanks for Trickling Filters. - - Time of emptying, 5 minutes. Time of filling, 10 minutes. Shape of - tank is a right pyramid or a truncated right pyramid with all four - sides making an angle of 45 degrees with the vertical. All - horizontal cross-sections are squares. -] - - For example, if the given head is 6 feet, and the rate of inflow - is 1.4 sec. feet, it is evident from Fig. 173 that a 6,300–gallon - dosing tank and two 8–inch siphons will give the required cycle. - -The method used for the design of the setting of Taylor nozzles by the -Pacific Flush Tank Co., is less rational but more simple and probably as -satisfactory. In this method the steps are as follows: - - (1) Divide the maximum daily rate of sewage flow by 1,000 to get - the maximum minute inflow. - - (2) The number of nozzles required is determined by dividing the - preceding figure by 6. Generally a Taylor nozzle with an orifice - of ⅞ of an inch will discharge about 20 g.p.m. at the high head - and about 8 g.p.m. at the low head, and as the nozzles must have a - capacity which will take care of the inflow at the low head, the - divisor 6 is used as a factor of safety instead of using 8 as the - divisor. - - (3) The type of nozzle to be used is selected from experience or - as a matter of judgment. Circular-spray nozzles are more generally - used. - - (4) The spacings are determined from Fig. 170. - - (5) The dosing tank of the shape described is then designed. The - capacity is such as to give a complete cycle once every 15 - minutes. The method of this design is similar to that followed - previously. - - (6) The dosing siphons are designed so that they will have a - capacity at the minimum head of from 40 to 50 per cent in excess - of the maximum minute inflow, and the draining depth of the siphon - will be limited to a maximum of 5 to 5½ feet. The siphons are all - made adjustable with a variation of 6 inches or more on either - side of the normal discharge line so that the spraying area and - cycle can be varied to secure the best results. - -The underdrainage of a trickling filter should consist of some form of -false bottom such as the types shown in Fig. 174. Where possible the -underdrains should be open at both ends for the purpose of ventilation -and flushing. It is desirable that the drains be so arranged that a -light can be seen through them in order that clogging can be easily -located. The drains should be placed on a slope of approximately 2 in -100 towards a main collector. The length of the drains is limited by -their capacity to carry the average dose from the area drained by them. -The main collecting conduits must be designed in accordance with the -hydraulic principles given in Chapter IV. No valves, or other -controlling apparatus, are placed on the underdrains or outlets from the -filter. - -Covers have been provided in winter for some trickling filters in cold -climates. The Taylor sprinkling nozzle has been found to work -successfully in extremely cold weather, and it is generally accepted -that the covering of filters is unnecessary, if the filter is not to be -shut down for any length of time in cold weather. - -The operation of devices for automatically controlling the operation of -a trickling filter is explained in Chapter XXI. - -[Illustration: - - FIG. 174.—Types of False Bottoms for Trickling Filters. - - Eng. News, Vol. 74, p. 5. -] - - -=258. Intermittent Sand Filter.=—An intermittent sand filter is a -specially prepared bed of sand, or other fine grained material, on the -surface of which sewage is applied intermittently, and from which the -sewage is removed by a system of underdrains. It differs from broad -irrigation in the character of the material, the care and preparation of -the bed, and the thoroughness of the underdrainage. A distinctive -feature of the intermittent sand filter is the quality of the effluent -delivered by it. In a properly designed and operated plant the effluent -is clear, colorless, odorless, and sparkling. It is completely -nitrified, is stable and contains a high percentage of dissolved oxygen. -It contains no settleable solids except at widely separated periods when -a small quantity may appear in the effluent. The percentage removal of -bacteria may be from 98 to 99 per cent. Some analyses of sand filter -effluents are given in Table 89. The dissolved solids, the remaining -bacteria, and the antecedents of the effluent are the only differences -between it and potable water. An effluent from an intermittent sand -filter is the most highly purified effluent delivered by any form of -sewage treatment. The effluent can be disposed of without dilution, on -account of its high stability. The treatment of sewage to so high a -degree is seldom required, so that the use of intermittent filters is -not common. Other drawbacks to their use are the relatively large area -of land necessary and the difficulty of obtaining good filter sand in -all localities. - - TABLE 89 - - QUALITY OF EFFLUENTS FROM SAND FILTERS - - (Report on Sewage Purification at Columbus, Ohio, by G. A. Johnson, 1905) - ────────────┬───────────────────────────────────────────────────────┬─────── - Source of │ Parts per Million │Rate of - Sample │ │Filtra- - │ │ tion - │ │Gallons - │ │ per - │ │ Acre, - │ │per Day - ────────────┼────────────────────────────────────┬────────┬─────────┼─────── - │ Nitrogen as │ Oxygen │ Oxygen │ - │ │Consumed│Dissolved│ - ────────────┼───────┬──────────┬────────┬────────┼────────┼─────────┼─────── - │ Free │Albuminoid│Nitrites│Nitrates│ │ │ - │Ammonia│ Ammonia │ │ │ │ │ - ────────────┼───────┼──────────┼────────┼────────┼────────┼─────────┼─────── - Filter │ 11.0 │ 8.6 │ │ │ 59. │ │ - influent │ │ │ │ │ │ │ - from grit │ │ │ │ │ │ │ - chamber │ │ │ │ │ │ │ - Filter │ 1.12 │ 0.88 │ 0.08 │ 11.5 │ 6.9 │ 6.3 │ 0.081 - effluent │ │ │ │ │ │ │ - Filter │ 0.81 │ 0.88 │ 0.10 │ 12.6 │ 6.5 │ 6.2 │ 0.118 - effluent │ │ │ │ │ │ │ - ────────────┼───────┼──────────┼────────┼────────┼────────┼─────────┼─────── - Filter │ 9.7 │ 5.4 │ │ │ 33. │ │ - influent │ │ │ │ │ │ │ - from plain│ │ │ │ │ │ │ - settling │ │ │ │ │ │ │ - tank │ │ │ │ │ │ │ - Filter │ 0.62 │ 0.77 │ 0.11 │ 14.9 │ 6.0 │ 8.2 │ 0.139 - effluent │ │ │ │ │ │ │ - Filter │ 0.99 │ 1.10 │ 0.10 │ 12.6 │ 7.8 │ 6.5 │ 0.274 - effluent │ │ │ │ │ │ │ - Filter │ 2.61 │ 1.39 │ 0.09 │ 9.0 │ 9.7 │ 3.9 │ 0.357 - effluent │ │ │ │ │ │ │ - ────────────┼───────┼──────────┼────────┼────────┼────────┼─────────┼─────── - Filter │ 10.7 │ 5.6 │ │ │ 38. │ │ - influent │ │ │ │ │ │ │ - from │ │ │ │ │ │ │ - septic │ │ │ │ │ │ │ - tank │ │ │ │ │ │ │ - Filter │ 1.63 │ 1.16 │ 0.09 │ 11.2 │ 8.0 │ 5.8 │ 0.357 - effluent │ │ │ │ │ │ │ - ────────────┼───────┼──────────┼────────┼────────┼────────┼─────────┼─────── - Filter │ 13.4 │ 4.7 │ │ │ 40. │ │ - influent │ │ │ │ │ │ │ - from coke │ │ │ │ │ │ │ - strainer │ │ │ │ │ │ │ - Filter │ 2.24 │ 1.35 │ 1.03 │ 14.6 │ 10.1 │ 6.9 │ 0.372 - effluent │ │ │ │ │ │ │ - ────────────┼───────┼──────────┼────────┼────────┼────────┼─────────┼─────── - Filter │ 8.6 │ 3.6 │ 0.19 │ 1.6 │ 24. │ 0.3 │ - influent │ │ │ │ │ │ │ - from │ │ │ │ │ │ │ - contact │ │ │ │ │ │ │ - bed │ │ │ │ │ │ │ - Filter │ 2.62 │ 1.35 │ 0.31 │ 8.1 │ 8.3 │ 5.8 │ 0.516 - effluent │ │ │ │ │ │ │ - Filter │ 2.44 │ 2.41 │ 0.16 │ 9.4 │ 12.5 │ 5.0 │ 0.525 - effluent │ │ │ │ │ │ │ - Filter │ 3.40 │ 1.15 │ 0.20 │ 10.9 │ 9.7 │ 5.2 │ 0.525 - effluent │ │ │ │ │ │ │ - ────────────┼───────┼──────────┼────────┼────────┼────────┼─────────┼─────── - Filter │ 9.0 │ 4.8 │ 0.42 │ 1.3 │ 27. │ 3.4 │ - influent │ │ │ │ │ │ │ - from │ │ │ │ │ │ │ - sprinkling│ │ │ │ │ │ │ - filter │ │ │ │ │ │ │ - after │ │ │ │ │ │ │ - sedimen- │ │ │ │ │ │ │ - tation │ │ │ │ │ │ │ - Filter │ 2.95 │ 1.25 │ 0.19 │ 7.0 │ 8.8 │ 3.8 │ 0.675 - effluent │ │ │ │ │ │ │ - Filter │ 4.77 │ 2.63 │ 0.51 │ 4.6 │ 11.8 │ 2.5 │ 0.749 - effluent │ │ │ │ │ │ │ - Filter │ 3.47 │ 1.61 │ 0.31 │ 7.2 │ 11.9 │ 3.7 │ 1.129 - effluent │ │ │ │ │ │ │ - ────────────┴───────┴──────────┴────────┴────────┴────────┴─────────┴─────── - -The action in an intermittent sand filter is more complete than in other -forms of filters because a greater surface is exposed to the passage of -sewage by the fine sand particles, and the sewage is in contact with the -filtering material a longer time due to the lower rate of filtration and -the slow velocity of flow through the filter. It is essential that the -sewage be applied to the bed intermittently in order that air shall be -entrained in the filter. The period between doses should not be so long -that the filter becomes dry. - -In the operation of an intermittent sand filter one dose per day is -considered an ordinary rate of application, although some plants operate -with as many as four doses per day per filter, and others on one dose at -long and irregular intervals. It is not always necessary to rest the -filter for any length of time unless signs of overloading and clogging -are shown. The intermittent dosing action may be obtained by the action -of an automatic siphon as is described in Chapter XXI. The sewage is -distributed on the beds through a number of openings in the sides of -distributing troughs resting on the surface of the filter. The sewage is -withdrawn from the bottom of the filter through a system of underdrains, -into which it enters after its passage through the bed. There are no -control devices on the outlet, as the rate of filtration is controlled -by the action of the dosing apparatus and the rate at which sewage is -delivered to it. The action of the dosing apparatus should respond -quickly to variations in sewage flow. As the doses are applied to a sand -filter, a mat of organic matter or bacterial zoöglea is formed on the -surface of the bed. The mat is held together by hair, paper, and the -tenacity of the materials. It may attain a thickness of ¼ to ½ an inch -before it is necessary to remove it. So long as the filter is draining -with sufficient rapidity this mat need not be removed, but if the bed -shows signs of clogging, the only cleaning that may be necessary will be -the rolling up of this dried mat. It is believed that the greater -portion of the action in the filter occurs in the upper 5 to 8 inches of -the bed, but occasionally the beds become so clogged that it is -necessary to remove ¾ of an inch to 2 inches of sand in addition to the -surface mat, or to loosen up the surface by shallow plowing or -harrowing. The necessity for such treatment may indicate that the filter -is being overloaded as a result of which the rate of filtration should -be decreased or the preliminary treatment should be improved. The -plowing of clogging material into the bed should be avoided as under -these conditions the final condition of the bed will be worse than its -condition when trouble was first observed. - -In winter the surface of the bed should be plowed up into ridges and -valleys. The freezing sewage forms a roof of ice which rests on the -ridges and the subsequent applications of sewage find their way into the -filter through the valleys under the ice. In a properly operated bed the -filtering material will last indefinitely without change. If a filter is -operated at too high a rate, however, although the quality of the -effluent may be satisfactory, it will be necessary at some time to -remove the sand and restore the filter. - -The rate of filtration depends on the character of the influent, the -desired quality of the effluent, and the depth and character of the -filtering material. Filters can be found operating at rates of 50,000 -gallons per acre per day and others at eight times this rate. For sewage -which has had some preliminary treatment, the rate should not exceed -100,000 gallons per acre per day, whereas the rate for raw sewage should -be less than this. For rough estimates made without tests of the sewage -in question, the rate should not be taken at more than 1,000 persons per -acre. If the preliminary treatment of the sewage has been thorough and -the material of the sand filter is coarser than ordinary the rate of -filtration can be high. For less careful preliminary treatment and fine -filtering material the rates must be reduced. The sewage must undergo -sufficient preliminary treatment to remove large particles of solid -matter which would otherwise clog the dosing apparatus and the filter. -This treatment should include grit removal, screening, and some form of -tank treatment. Some plants have operated successfully with a stale -sewage and no preliminary treatment, as at Brockton, Mass. Septic tank -effluent can be treated successfully on an intermittent sand filter, but -not so satisfactorily as the effluent from a tank delivering a fresh -sewage. - -The material of the filter should consist of clean, sharp, quartz or -silica sand with an effective size[164] of 0.2 to 0.4 mm., preferably -about 0.25 to 0.35 mm., and a uniformity coefficient[165] of 2 to 4. -Within the limits mentioned no careful attention need be given to the -size of the material. Natural sand found in place has been underdrained -and used successfully for sewage treatment. The size of the sand is -fixed by the rate of filtration rather than the bacteriological action -of the filter. A coarse sand will permit the sewage to pass through the -bed too rapidly, and a fine sand will hold it too long or will become -clogged. The same size of material should be used throughout the bed, -except that a layer of gravel from 6 to 12 inches thick, graded from -very small sizes to stones just passing a 2–inch ring should be placed -at the bottom to facilitate the drainage of the bed. - -The thickness of the sand layer should not be less than 30 inches to -insure complete treatment of the sewage. In shallower beds the sewage -might trickle through without adequate treatment. Beds are ordinarily -made from 30 to 36 inches deep, but when deeper layers of sand are found -in place there is no set limit to the depth which may be used. The shape -and overall dimensions of the bed should conform to the topography of -the site and the rate of filtration adopted. A plan and cross-section of -an intermittent sand filter showing the distribution and under drainage -systems are given in Fig. 166 and 175. - -The distribution system consists of a system of troughs on the surface -of the filter, laid out in a branching form, as shown in the figure. The -openings in the troughs should be so located that the maximum distance -from any point on the bed to the nearest opening should not exceed 20 to -30 feet. If the filters are small enough, troughs need not be used, the -sewage being distributed from one corner, or from mid-points on the -sides. Where troughs are used they should be supported from the bottom -of the filter in order to prevent uneven settling due to the washing of -the sand. The openings in the troughs are made adjustable by swinging -gates as shown in Fig. 176, or by other means so that after the filter -is in operation the intensity of the dose on any portion of the filter -can be changed. The troughs may be placed with their bottoms level with -the surface of the sand and with sides of sufficient height to give the -required gradient to the water surface, or they may be built up above -the surface of the filter and given the required slope so that the -surface of the flowing water is parallel to the bottom of the trough. In -either case a splash plate should be placed at each opening, so that not -less than 2 feet of the surface of the sand is protected in all -directions from the opening. A stone or concrete slab 2 to 4 inches -thick makes a satisfactory splash plate. Either wood or concrete may be -used for the construction of the troughs. The former is less durable, -but also less expensive in first cost. The capacity of the troughs may -be computed by Kutter’s formula with the quantity to be carried equal to -the maximum rate of discharge of the feeding siphon, with a reduction in -size below each branch or outlet proportional to the amount which will -be discharged above this point. - -[Illustration: - - FIG. 175.—Plan and Section of an Intermittent Sand Filter Showing - Central Location of Control House. -] - -The operation of automatic devices for dosing the bed is explained in -Chapter XXI. The dosing tank should have a capacity sufficient to cover -the bed to a depth of about 1 to 3 inches at one dose, and the siphon -should discharge at a rate of about one second-foot for each 5,000 -square feet of filter area. A dose should disappear within 20 minutes to -half an hour after it is applied to the filter. With the rate stated and -four applications per day to a depth of 1 inch at each dose, the rate -per acre per day will be 109,000 gallons. - -[Illustration: - - FIG. 176.—Distributing Trough with Adjustable Openings. -] - -The filtration of sewage through sand in a manner similar to the _rapid -sand filtration_ of water is being attempted at the Great Lakes Naval -Training Station. No results of this treatment have been published and -the practical success of the method has not been assured. - - -=259. Cost of Filtration.=—Only comparative figures can be given in -stating the costs of filtration, as most data available are based on -pre-war conditions, and are therefore unreliable for present conditions. -The variations from the figures given may be very large but in general -the relative costs have not changed. The figures given in Table 90 are -suggestive of the relative costs of the different forms of filtration. - - TABLE 90 - - RELATIVE COSTS OF DIFFERENT METHODS OF SEWAGE TREATMENT - - Costs in Dollars per Million Gallons per Day - ─────────────────────────┬───────────────┬──────────────┬────────────── - Form of Treatment │First Cost[166]│Operation and │ Total - │ │ Maintenance │ - ─────────────────────────┼───────────────┼──────────────┼────────────── - Coarse screens │ │ │ 0.20 - Fine screens │ │ │ 3.00 - Plain sedimentation │ 7.00│ 3.00│ 10.00 - Chemical precipitation │ │ │ 22.00[167] - Septic tank │ 7.00│ 1.00│ 8.00 - Imhoff tank │ 10.00│ 1.00│ 11.00 - Contact bed │ 8.00│ 2.00│ 10.00 - Trickling filter │ 4.00│ 2.00│ 6.00 - Intermittent sand filter │ 15.00│ 10.00│ 25.00 - Activated sludge │ 6.50│ 8.50│ 15.00[168] - ─────────────────────────┴───────────────┴──────────────┴────────────── - - - IRRIGATION - - -=260. The Process.=—Broad irrigation is the discharge of sewage upon the -surface of the ground, from which a part of the sewage evaporates and -through which the remainder percolates, ultimately to escape in surface -drainage channels. Sewage farming is broad irrigation practiced with the -object of raising crops. Broad irrigation can be accomplished -successfully without the growing of crops, but it is seldom attempted as -some return and sometimes even a profit can be obtained from the crops -raised. Broad irrigation and sewage farming differ from intermittent -sand filtration in the intensity of the application of the sewage, the -method of preparing the area on which the sewage is to be treated, and -the care in operation. In broad irrigation and intermittent sand -filtration the paramount consideration is successful disposal of the -sewage. In sewage farming the paramount consideration is the growing of -crops. The growing of crops may be combined with irrigation and -filtration, however, but the crop should be sacrificed to the successful -disposal of the sewage. - -The change which occurs in the characteristics of the sewage due to its -filtration through the ground is the same as occurs in aërobic -filtration. The effect on the crops is mainly that of an irrigant, as -the manurial value of the sewage is small. - - -=261. Status.=—The disposal of sewage by broad irrigation was practiced -in England previous to the development of any of the more intensive -biologic methods of treatment. It was considered the only safe and -sanitary method for the disposal of sewage, and as a result, areas -irrigated by sewage were common throughout England. Crops were grown on -these areas as a minor consideration, and sewage farming gained some of -its popularity from the apparent success of these disposal areas. The -success of sewage farms is due more to generous irrigation in dry years -than to fertilization by sewage. - -The sewage farms of Paris and Berlin are frequently cited as examples of -the successful and remunerative disposal of sewage by farming in -connection with broad irrigation. Kinnicutt, Winslow, and Pratt[169] -state: - - The Berlin Sewage farms offer examples of broad irrigation under - better conditions ... of 21,008 acres receiving sewage, 16,657 - acres were farmed by the city, 3,956 acres were leased to farmers, - and only 395 acres were unproductive. The contributing population - at this time was 2,064,000 and the average amount of sewage - treated was 77,000,000 gallons, giving a daily rate of treatment - of about 3,700 gallons per acre of prepared land. The soil is - sandy and of excellent quality. A quarter of the area operated by - the authorities is devoted to pasturage, and about a third to the - cultivation of cereals, of which winter rye and oats are the most - important. Potatoes and beets are grown in considerable amounts - and a wide variety of other crops in smaller proportions.... Even - fish ponds are made to yield a part of the revenue, and the drains - on some of the farms have been successfully stocked with breed - trout. - - The cost of the Berlin farms to March 31, 1910, was $17,470,000, - somewhat more than half being the purchase price of the land. The - expenses for this year amounted to $1,300,385 for maintenance, and - $741,818 for interest charges. The receipts were $1,240,773 and - there was an estimated increase of $122,593 in value of live stock - and other property. - -The conditions at Berlin are quoted at length to indicate the success -which can accompany broad irrigation, and as an example of what is being -done abroad, where the rainfall is light and the soil is suitable. - -In the United States success in sewage farming has not been marked. This -may be due partially to the relative weakness of American sewages, to -the cost of labor, to lack of satisfactory irrigation areas, and to -inattention to details. An attempt was made to grow crops on the sand -filters at Brockton, Mass., but it was finally abandoned as the -interests of the crops and the successful treatment of the sewage could -not both be satisfied. At Pullman, Illinois,[170] in 1880, there was -commenced probably the most extensive attempt at sewage farming in -eastern United States. The farm was a failure from the start, because of -the clay soil, and it was subsequently abandoned. Sewage farming, mainly -as a subsidiary consideration to the filtration of sewage, is practiced -in a few cities in the eastern portion of the United States to-day. -Among the cities mentioned by Metcalf and Eddy[171] are Danbury, Conn., -and Fostoria, Ohio. In the western portion of the United States where -water is scarce and the ground is porous, sewage has been used as an -irrigant with some success. Such use of sewage cannot be considered as a -method of treatment since the prime consideration is the growing of -crops. In this process all sewage not used as an irrigant is discharged -without treatment into water courses. According to Metcalf and Eddy -there were 35 cities in California in 1914 that were operating sewage -farms. Among these are Pasadena, Fresno, and Pomona. Other farms, -notably the pioneer farm at Cheyenne, Wyo., have been abandoned because -of the local nuisance created and the lack of financial success. - - -=262. Preparation and Operation.=—A porous sandy soil on a good slope -and with good underdrainage is most suitable for broad irrigation. -Impervious clay or gumbo soils are unsuitable and should not be used. -They become clogged at the surface, forming pools of putrefying sewage, -or in hot weather form cracks which may permit untreated sewage to -escape into the underdrains. - -The sewage may be distributed to the irrigated area in any one of five -ways which are known as: flooding, surface irrigation, ridge and furrow -irrigation, filtration, and subsurface irrigation. In flooding, sewage -is applied to a level area surrounded by low dikes. The depth of the -dose may be from 1 inch to 2 feet. In surface irrigation the sewage is -allowed to overflow from a ditch over the surface of the ground into -which it sinks or over which it flows into another ditch placed lower -down. This ditch conducts it to a point of disposal or to another area -requiring irrigation. Ridge and furrow irrigation consists in plowing a -field into ridges and furrows and filling the furrows with sewage while -crops are grown on or between the ridges. In filtration the sewage is -distributed in any desired fashion on the surface and is collected by a -system of underdrains after it has filtered through the soil. In -subsurface irrigation the sewage is applied to the land through a system -of open-joint pipes laid immediately below the surface, similarly to a -system of underdrains. Combinations of and modifications to these -methods are sometimes made. Underdrains may be used in connection with -any of these forms of distribution. - -The preparation of the ground consists in: the construction of ditches -or dikes to permit of any of the above described methods of application, -grading of the surface to prevent pooling, the laying of underdrains, -and the grubbing and clearing of the land. The main carriers may be -excavated in open earth or earth lined with an impervious material. The -distribution of the sewage from the main carriers to groups of laterals -may be controlled by hand-operated stop planks. If the soil has a -tendency to become waterlogged it may be relieved by installing -underdrains at depths of 3 to 6 feet, and 40 to 100 feet apart. The tile -underdrains may discharge into open ditches excavated for the purpose -which serve also to drain the land. Drains should be used where the -ground water is within 4 feet of the surface, and the open ditches -should be cut below the drains to keep the ground water out of them. -Four or 6–inch open-joint farm tile may be used for underdrains. The -porosity of the soil will be increased by cultivation. Where particular -care is taken in the cultivation of the soil so that sewage can be -applied at a high rate, broad irrigation merges into the more intensive -intermittent filtration through sand. - -Before being turned on to the land, sewage should be screened and -heavy-settling particles should be removed. The rate of application may -be increased as the intensity of the preliminary treatment is increased. -The rate at which sewage may be applied is dependent also on the -character of the soil, and may vary between 4,000 and 30,000 gallons per -acre per day, although higher rates have been used with the effluent -from treatment plants and on favorable soil. The sewage should be -applied intermittently in doses, the time between doses varying between -one day and two or three weeks or more, dependent on the weather and the -condition of the soil. The methods of dosing vary as widely as the -rates. The dose may be applied continuously for one or two weeks with -correspondingly long rests, or it may be applied with frequent -intermittency alternated with short rests, interspersed with long rest -periods at longer intervals of time. When applying the sewage to the -land the rate of application of the dose is about 10,000 to 150,000 -gallons per acre per day. The area under irrigation at any one time may -be as much as 10 to 15 acres. The rate of the application of the sewage -is also dependent on the weather and may vary widely between seasons. It -is obvious that a rain-soaked pasture cannot receive a large dose of -sewage without danger of undue flooding. One of the principal -difficulties with the treatment or disposal of sewage by broad -irrigation is that the greatest load of sewage must be cared for in wet -seasons when the ground is least able to absorb the additional moisture. - - -=263. Sanitary Aspects.=—A well-operated sewage farm should cause no -offense to the eye or nose, and is not a danger to the public health. In -Berlin, a portion of the sewage farms are laid out as city parks. The -liquid in the drainage ditches or underdrains may be clear, odorless, -and colorless, high in nitrates and non-putrescible. Where the farm has -been improperly managed or overdosed the condition may be serious from -both esthetic and health considerations. Sewage may be spread out to -pollute the atmosphere and to supply breeding places for flying insects -which will spread the filth for long distances surrounding the farm. The -character of the crop is also a sanitary consideration. - - -=264. The Crop.=—From a sanitary viewpoint no crops which come in -contact with the sewage should be cultivated on a sewage farm. Such -products as lettuce, strawberries, asparagus, potatoes, radishes, etc., -should not be grown. Grains, fruits, and nuts are grown successfully and -as they do not come in contact with the sewage there is no sanitary -objection to their cultivation in this manner. Italian rye grass and -other forms of hay are grown with the best success as they will stand a -large amount of water without injury. The raising of stock is also -advisable for sewage farms where hay and grain are cultivated. The stock -should be fed with the fodder raised on the irrigated lands and should -not be allowed to graze on the crops during the time that they are being -irrigated. This is due as much to the danger of injury to the -distributing ditches and the formation of bogs by the trampling of the -cattle, as to the danger to the health of the cattle. - - - - - CHAPTER XVIII - ACTIVATED SLUDGE - - -=265. The Process.=—In the treatment of sewage by the activated sludge -process the sewage enters an _aëration tank_ after it has been screened -and grit has been removed. As it enters the aëration tank it is mixed -with about 30 per cent of its volume of activated sludge. The sewage -passes through the aëration tank in about two to four hours during which -time air is blown through it in finely divided bubbles. The effluent -from the aëration tank passes to a _sedimentation tank_ where it remains -for one-half an hour to an hour to allow the sedimentation of the -activated sludge. The supernatant liquid from the sedimentation tank is -passed to the point of final disposal. A portion of the sludge removed -from the tank is returned to the influent of the aëration tank. The -remainder may be sent to any or all of the following: the _sludge drying -process_, the reaëration tanks, or to some point for final disposal. -Sections of the activated sludge plant at Houston, Texas, are shown in -Fig. 177. - -The biological changes in the process occur in the aëration tank. These -changes are dependent on the aërobic organisms which are intensively -cultivated in the activated sludge. When placed in intimate contact with -fresh sewage, brought about by the agitation caused by the rising air, -and in the presence of an abundance of oxygen, the organic matter is -partially oxidized. The putrefactive stage of the organic cycle is -avoided. Colloids and bacteria are partially removed probably by the -agitation effected in the presence of activated sludge but the exact -action which takes place is not well understood. - -[Illustration: - - FIG. 177.—Activated Sludge Plant at Houston, Texas. - - Eng. News, Vol. 77, p. 236. -] - - -=266. Composition.=—Activated sludge is the material obtained by -agitating ordinary sewage with air until the sludge has assumed a -flocculent appearance, will settle quickly, and contain aërobic and -facultative bacteria in such numbers that similar characteristics can be -readily imparted to ordinary sewage sludge when agitated with air in the -presence of activated sludge. Copeland described activated sludge as -follows:[172] - - The sludge embodied in sewage and consisting of suspended organic - solids, including those of a colloidal nature, when agitated with - air for a sufficient period assumes a flocculent appearance very - similar to small pieces of sponge. Aërobic and facultative - bacteria gather in these flocculi in immense numbers—from 12 to 14 - million per c.c.—some having been strained from the sewage and - others developed by natural growth. Among the latter are species - that have the power to decompose organic matter, especially of an - albuminoid or nitrogenous nature, setting the nitrogen free; and - others absorbing the nitrogen convert it into nitrites and - nitrates. These biological processes require time, air, and - favorable environment such as suitable temperature, food supply - and sufficient agitation to distribute them throughout all parts - of the sewage. - -Ardern states that the sludge differs entirely from the usual tank -sludge. It is inoffensive and flocculent in character. The percentage of -moisture is from 95 to 99 per cent. American experience has generally -been that the sludge does not readily separate from its moisture by -treatment on fine-grain filters, but the results in England and at -Milwaukee, Wisconsin, are in conflict with this general experience. Upon -standing 24 hours or more partially dried activated sludge may start to -decompose accompanied by the production of offensive odors. - -Duckworth states: - - The activated sludge at Salford contained three times as much - nitrogen, twice as much phosphoric acid and one-half as much fatty - matter as ordinary sludge. - - TABLE 91 - - COMPOSITION OF SEWAGE, IMHOFF SLUDGE, AND ACTIVATED SLUDGE AND EFFLUENT AT - MILWAUKEE - - (W. R. Copeland, Eng. News, Vol. 76, p. 665) - ──────┬──────────┬──────────────────────────────────────────────────────────── - Period│Source of │ Parts per Million - of │ Sample │ - Test │ │ - ──────┼──────────┼──────┬──────────────────────────────────────┬────────────── - │ │ Sus- │ Nitrogen as │Nitrogen - │ │pended│ │ Reported as - │ │Matter│ │ Ammonia on a - │ │ │ │ Basis of - │ │ │ │ Sludge Dried - │ │ │ │ to 10 Per - │ │ │ │ Cent - │ │ │ │ Moisture. - │ │ │ │ Three - │ │ │ │ samples of - │ │ │ │ Sludge - ──────┼──────────┼──────┼───────┬───────┬────────┬──────┬──────┼────────────── - │ │ │ Free │ Albu- │Organic │ Ni- │ Ni- │ - │ │ │Ammonia│minoid │Nitrogen│trites│trates│ - │ │ │ │Ammonia│ │ │ │ - ──────┼──────────┼──────┼───────┼───────┼────────┼──────┼──────┼────┬────┬──── - Aug., │Sewage │ 253│ 14.6│ 7.88│ 29│ 0.15│ 0.13│ │ │ - 1915│ │ │ │ │ │ │ │ │ │ - │Imhoff │ 105│ 16.2│ 6.10│ 27│ 0.19│ 0.13│2.87│3.82│ - │ effluent│ │ │ │ │ │ │ │ │ - │Activated │ 14│ 3.8│ 3.19│ 6│ 0.29│ 6.00│5.71│4.97│7.04 - │ sludge │ │ │ │ │ │ │ │ │ - │ effluent│ │ │ │ │ │ │ │ │ - ──────┼──────────┼──────┼───────┼───────┼────────┼──────┼──────┼────┼────┼──── - Sept.,│Sewage │ 300│ 13.5│ 8.81│ 29│ 0.25│ 0.14│ │ │ - 1915│ │ │ │ │ │ │ │ │ │ - │Imhoff │ 116│ 15.4│ 7.10│ 27│ 0.12│ 0.09│3.88│ │ - │ effluent│ │ │ │ │ │ │ │ │ - │Activated │ 8│ 5.7│ 2.22│ 9│ 0.24│ 5.01│8.69│9.00│ - │ sludge │ │ │ │ │ │ │ │ │ - │ effluent│ │ │ │ │ │ │ │ │ - ──────┴──────────┴──────┴───────┴───────┴────────┴──────┴──────┴────┴────┴──── - -These results have been roughly checked by American experimenters as -shown in Table 91.[173] In the recovery of nitrogen from sewage the -activated sludge process is the most promising for satisfactory results. -In all other processes of sewage treatment the sludge is digested to -some extent and nitrogen lost in the gases or in the soluble matter -which passes off with the effluent. In the activated sludge process a -negligible amount of gasification and liquefaction take place and only a -small amount of nitrogen passes off with the effluent as compared with -the loss from the Imhoff process as shown in Table 91. The percentage of -nitrogen in dried activated sludge is shown in Table 92. - - TABLE 92 - - NITROGEN CONTENT OF DRY ACTIVATED SLUDGE AND SLUDGE FROM OTHER - PROCESSES - - (G. W. Fuller, Eng. News, Vol. 76, p. 667) - ────────────────────────────────────────┬────────────────────────────── - Source │ Per Cent Nitrogen - ────────────────────────────────────────┼────────────────────────────── - Milwaukee (Copeland) │ 4.40 - Manchester, England (Ardern) │ 4.60 - Salford, England (Melling) │ 3.75 - Urbana, Illinois (Bartow) │ 3.5 to 6.4 - Armour and Co. (Noble) │ 4.6 - Approximate range of all other processes│ 1.0 to 3.0 - ────────────────────────────────────────┴────────────────────────────── - These figures are expressed in terms of nitrogen and not of ammonia. - Nitrogen is only 82 per cent of the ammonia content. - -Nitrifying bacteria and other species which have the power of destroying -organic matter have been isolated from the sludge. An analysis of the -dried sludge at Urbana[174] showed the following results after the -weight had been reduced 95.5 per cent by drying: 6.3 per cent nitrogen, -4.00 per cent fat, 1.44 per cent phosphorus, and 75 per cent volatile -matter or loss on ignition. Analyses of other domestic sewages have not -shown such high contents of these desirable constituents. - -The dewatering of activated sludge is a problem which offers serious -obstacles to the successful operation of the process. It is its greatest -disadvantage. Five to ten times the volume of sludge may be produced by -the activated sludge process as by an Imhoff tank, and the activated -sludge contains a greater percentage of water. According to Copeland: - - The best information now available points to a combination of - settling and decantation as a preliminary dewatering process. By - this means the water will be cut down from about 99 per cent to 96 - per cent. On passing the concentrated residue through a pressure - filter the moisture can be cut down to 75 per cent. The press cake - can be dewatered in a heat drier to 10 per cent moisture or - less.[175] - -The quantity of sludge produced at Milwaukee[176] is about 15 cubic -yards per million gallons of sewage, the sludge having about 98 per cent -moisture. On the basis of 10 per cent moisture it produces ½ ton of dry -sludge per million gallons of sewage treated. At Cleveland,[177] 20 -cubic yards per million gallons at 97.5 per cent moisture are produced. -Methods of drying sludge are discussed in Chapter XX. - -Chemical analyses and biological tests indicate that the fertilizing -value of the sludge is appreciable. Professor C. B. Lipman states, as -the result of a series of tests in which a sludge and a soil were -incubated for one month, as follows:[178] - - The amounts of nitrates produced in one month’s incubation from - the soil’s own nitrogen and from the nitrogen from the sludge - mixed with the soil in the ratio of one part of sludge to 100 of - soil is, in milligrams of nitrate, as follows: Anaheim soil - without sludge 6.0, with sludge 10.0; Davis soil without sludge - 4.2, with sludge 14.0; Oakley soil without sludge 2.2, with sludge - 4.0. - -The effect of the sludge on plant growth is shown in Table 93.[179] The -results represent the growth obtained after fifteen weeks from the -planting of 30 wheat seeds in each pot. - - -=267. Advantages and Disadvantages.=—Some of the advantages of the -process are: a clear, sparkling, and non-putrescible effluent is -obtained; the degree of nitrification is controllable within certain -limits; the character of the effluent can be varied to accord with the -quantity and character of the diluting water available; more than 90 per -cent of the bacteria can be removed; the cost of installation is -relatively low; and the sludge has some commercial value. - - TABLE 93 - - FERTILIZING VALUE OF ACTIVATED SLUDGE - - (E. Bartow, Journal Am. Water Works Ass’n, Vol. 3, p. 327) - ───────────────────────────────────────┬─────────────────────────────── - Cultivating Medium │Grams Contained in Experimental - │ Pot - ───────────────────────────────────────┼───────┬───────┬───────┬─────── - │ 1 │ 2 │ 3 │ 4 - ───────────────────────────────────────┼───────┼───────┼───────┼─────── - White sand │ 19,820│ 19,820│ 19,820│ 19,820 - Dolomite │ 60│ 60│ 60│ 60 - Bone meal │ 6│ 6│ 6│ 6 - Potassium sulphate │ 3│ 3│ 3│ 3 - Activated sludge │ 0│ 0│ 20│ 0 - Activated sludge extracted with Ligroin│ 0│ 0│ 0│ 20 - Dried blood │ 0│ 8.61│ 0│ 0 - ───────────────────────────────────────┼───────┼───────┼───────┼─────── - Number of heads of wheat │ 14│ 15│ 22│ 23 - Number of seeds │ 85│ 189│ 491│ 518 - Weight of seeds, grams │ 2.38│ 5.29│ 13.748│ 14.504 - Bushels per acre, calculated │ 6.20│ 13.6│ 35.9│ 38.7 - Average length of stalk, inches │ 19.40│ 23.0│ 35.4│ 37.1 - Weight of straw, grams │ 2.25│ 8.25│ 26.75│ 26.21 - Tons per acre, calculated │ 0.18│ 0.68│ 2.23│ 2.18 - ───────────────────────────────────────┴───────┴───────┴───────┴─────── - -Among the disadvantages of the process can be included, uncertainty due -to the lack of information concerning the results to be expected under -all conditions, high cost of operation under certain conditions, the -necessity for constant and skilled attendance, and the difficulty of -dewatering the sludge. - - -=268. Historical.=—The most notable work in the aëration of sewage -within recent years was that performed by Black and Phelps for the -Metropolitan Sewerage Commission of New York, in 1910,[180] and by Clark -and Gage at the Lawrence, Massachusetts, Sewage Experiment Station in -1912 and 1913.[181] The results of these investigations showed that the -treatment of sewage by forced aëration might give a satisfactory -effluent, but that the time and expense in connection thereto rendered -the method impractical. - -It remained for Messrs. Ardern and Lockett of Manchester, England, to -introduce the process of the aëration of sewage in the presence of -activated sludge, as a result of their connection with Dr. Fowler, who -attributes his inspiration to his visit to the Lawrence Experiment -Station and observing the work of Clark and Gage. Ardern and Lockett -commenced their experiments in 1913. Their results were published in the -_Journal of the Society of Chemical Industry_, May 30, 1914, Vol. 33, p. -523. Shortly thereafter experiments were started at the University of -Illinois by Dr. Edw. Bartow and Mr. F. W. Mohlmann of the Illinois State -Water Survey. At about the same time an experimental plant was started -at Milwaukee, by T. C. Hatton, Chief Engineer of the Milwaukee Sewerage -Commission. The United States Public Health Service became actively -interested in December, 1914, and on February 20, 1915, announced its -intention to co-operate with the Baltimore Sewerage Commission in the -conduct of experiments. In May, 1915, patent number 1,139,024 was -granted to Leslie C. Frank, Sanitary Engineer of the U. S. Public Health -Service, covering certain features of the process. Mr. Frank generously -donated this patent to the public for the use of municipalities. - -The first full sized plant for the treatment of sewage by this method -was erected in Milwaukee in December, 1915. This plant had a capacity of -1,600,000 gallons per day. It was used for experimental purposes and is -not now in use. The Champaign, Illinois, septic tank, among the first of -its kind in the country, was converted into an activated sludge tank on -April 13, 1916. The changes, developments, and the results obtained from -these and other plants have been reported in the technical press from -time to time. - - -=269. Aëration Tank.=—The sewage on leaving the screen and grit chamber -enters the aëration tank, which is usually operated on the -continuous-flow principle, although in the early days of experimentation -the fill and draw method was practiced. This tank should be rectangular -with a depth of about 15 feet and a width of channel not to exceed 6 to -8 feet. Such proportions allow better air and current distribution than -larger tanks. The bottom should be level to insure an even distribution -of air. The velocity of flow of sewage through the tank is usually in -the neighborhood of 5 feet per minute, dependent on the length of the -tank and the period of retention. The period of retention is in turn -dependent on the desired quality of the effluent. The process is -flexible and the quality of the effluent can be changed by changing the -period of retention or by changing the rate of application of the air, -or both. The period of retention in the aëration tank is usually about 4 -hours. - -The bottom of the aëration tank is usually made of concrete arranged in -ridges and valleys, or small shallow hoppers, at the bottom of which the -air-diffusing devices are located, as shown in Fig. 177. The inlet and -outlet devices are similar to those in a plain sedimentation tank. - - -=270. Sedimentation Tank.=—It is evident that as no sedimentation is -permitted in the aëration tank, the settleable particles will be -discharged in the effluent unless some provision is made for their -detention. The effluent from the aëration tank is therefore run through -a plain sedimentation tank, usually with a hopper bottom, which has been -arranged to permit frequent and easy cleaning. An air lift or a -centrifugal sludge pump is satisfactory for this purpose. Another type -of sedimentation tank which has been used has a smooth bottom with a -slight slope towards the center. A revolving scraper collects the sludge -continuously, scraping it towards the center of the tank. Although this -arrangement gives better results than the hopper-bottom tank, its -expense has usually prevented its installation.[182] - -The period of sedimentation in different plants varies from 30 minutes -to one hour, although the longer periods usually give the better -results. Approximately 65 per cent of the sludge will settle in the -first 10 minutes, 80 per cent in the first 30 minutes, and about 5 per -cent more in the next half hour. - -The effluent from the sedimentation tank is ready for final disposal or -if desired, for further treatment by some other method. The sludge, or a -portion of it, is pumped back into the influent of the aëration tank, -provided the sludge is in a satisfactory state of nitrification. -Otherwise it should be pumped to the reaëration tanks. The remainder of -the sludge which is not to be used in the process is ready for drying -and final disposal. - - -=271. Reaëration Tank.=—The purpose of the reaëration or sludge aëration -tank is to reactivate the sludge which has gone through the aëration -tank. During the process of the aëration of the sewage in the aëration -tank the activated sludge may lose some of its qualities because of the -deficiency of oxygen to maintain aërobic conditions. By blowing air -through the sludge in the reaëration tank these properties are returned -and the sludge made available to be pumped back into the aëration tank. -The reactivation of the sludge obviates the necessity for supplying -sufficient air to the entire mass of the sewage to maintain aërobic -conditions, and results in an economy in the use of air. The use of -mechanical agitators has also been attempted both in the reaëration and -the aëration tanks with the expectation of saving in the use of air, but -with indifferent success. - -It is difficult to say, without experimentation, what the size of the -reaëration tank should be, as the necessary amount or reactivation is -uncertain. In the experimental plant at Milwaukee, there were eight -units of aëration tanks, one sedimentation tank, and two reaëration -tanks, all of the same capacity and general design. This represents a -ration of about one reaëration tank to four aëration tanks. - - -=272. Air Distribution.=—Air is applied to the sewage at the bottom of -the aëration tank at a pressure in the neighborhood of 5.5 to 6.0 pounds -per square inch, dependent on the depth of the sewage, the loss of head -through the distributing pipes, and the rate of application. In -different experimental plants the pressure has varied from 3 to 30 -pounds per square inch. Such pressures are on the line which divides the -use of direct blowers for low pressures from turbo and reciprocating -pressure machines for pressures above 10 pounds per square inch. -Positive-pressure blowers or direct blowers operate on the principle of -a centrifugal pump and because of the lighter specific gravity of air -they rotate at a very high speed. The Nash Hytor Turbo Blower consists -of a rotor with a large number of long teeth slightly bent in the -direction of rotation. The rotor, which has a circular circumference, -revolves in an elliptical casing. At the commencement of operation the -rotor and casing are partially filled with water. The revolution of the -rotor throws the water to the outside of the elliptical casing thus -forming a partial vacuum between any two teeth as the water is thrown -from near the center of the short diameter of the casing to the -extremity of the long diameter of the casing. Air is allowed to enter -through the inlet port to relieve the vacuum. As the teeth pass from the -long diameter to the short diameter of the ellipse, the water again -approaches the center of the rotor compressing the air trapped between -the teeth and forcing it out under pressure into the exhaust pipe. Among -the advantages of this compressor are the washing of the air, cooling, -and ease in operation. Reciprocating air compressors operate similarly -to direct-acting steam pumps or crank-and-fly-wheel pumps but at much -higher speeds, and they require more floor space than either of the -other types. Fig. 178 shows the field of serviceability of various types -of air compression machinery. - -[Illustration: - - FIG. 178.—Economic Range of Air Compressors. - - From Eng. News, Vol. 74, p. 906. -] - -For pressures up to about 10 pounds per square inch the positive blower -seems most desirable. It has a low first cost and a relatively high -efficiency of about 75 to 80 per cent of the power input. No oil or dirt -is added to the air to clog the distributing plates, as in the -reciprocating machine. A disadvantage is the difficulty of varying the -pressure or quantity of the output of the machine. As the required -pressure and volume of air increases the turbo blower becomes more and -more desirable within the limits of pressure which are ordinarily used -in this process. For small installations the best form of power is -probably the electric drive, but when the capacity becomes such as to -make turbo blowers advisable they should be driven by directly connected -steam turbines. - -The quantity of air required varies between 0.5 to 6.0 cubic feet per -gallon of sewage, with from 3 to 6 hours of aëration. The quantity of -air depends on the degree of treatment required, the strength of the -sewage, the depth of the tank, and the period of aëration. The deeper -the tank the less the amount of air needed because of the greater travel -of the bubble in passing through the sewage, but the higher the pressure -at which the air must be delivered. Shallow tanks usually require a -longer period of retention. The depth of the tank then has very little -to do with economy in the use of air. Hatton states:[183] - - The purification of sewage obtained varies decidedly with the - volume of air applied. Small volumes applied for 5 or 6 hours do - as well as larger volumes applied for 3 or 4 hours, but the time - of aëration required to obtain a like effluent does not vary - directly with the volume of air applied per unit of time. For - instance air applied at a rate of 2 cubic feet per minute purifies - the sewage in less time than one cubic foot of air per minute, but - will not accomplish an equal degree of purification in half the - time. - -It has been found that although a low temperature has a deleterious -effect on the process, by the use of an additional quantity of air good -results can be maintained. The effect of changing the quantity of air -and the period of aëration are shown in Table 94 taken from Hatton. - -The velocity of the air in the pipes should be about 1,000 feet per -minute. There should be relatively few sharp turns in the line, and the -distributing mains should be arranged without dead ends. It is desirable -to use as little piping as possible and at the same time to make the -travel of the sewage long in order to maintain a non-settling velocity -and intimate contact with the air. The piping should be accessible and -well provided with valves. It should be non-corrodible, particularly on -the inside, as flakes of rust will quickly clog the air diffusers. It -should drain to one point in order that it can be emptied when flooded, -as occasionally happens. - - TABLE 94 - - EFFECT OF VARIOUS RATES AND PERIODS OF APPLICATION OF AIR ON THE RESULTS - OBTAINED FROM THE TREATMENT OF SEWAGE BY THE ACTIVATED SLUDGE PROCESS - - (Milwaukee Results) - - ─────────┬──────┬──────┬──────────┬──────── - Time of │Cubic │Cubic │Appearance│Per Cent - Aëration,│ Feet │ Feet │of Settled│Removal - Hours │ Free │ Air │ Liquid │Bacteria - │ Air │ per │ │ - │ Per │Gallon│ │ - │Minute│ of │ │ - │ │Sewage│ │ - ─────────┼──────┼──────┼──────────┼──────── - │ │ │ │ - │ │ │ │ - ─────────┼──────┼──────┼──────────┼──────── - │ │ │ │ - │ │ │ │ - ─────────┼──────┼──────┼──────────┼──────── - 0│ 0│ 0.0│ Turbid │ 0 - 1│ 160│ 0.67│ Clear │ 52 - 2│ 160│ 1.32│ Clear │ 81 - 3│ 160│ 1.98│ Clear │ 92 - 4│ 160│ 2.64│ Clear │ 94 - 5│ 160│ 3.31│ Clear │ 98 - 2.5│ 90│ 1.07│ │ 92 - 3│ 90│ 1.28│ │ 96 - 4│ 90│ 1.71│ │ 98 - 4│ 80│ 1.82│ │ 97.7 - 4│ 70│ 1.60│ │ 99.6 - 4│ 46│ 1.67│ │ 88.3 - 4│ 105│ 1.75│ │ 92.7 - 3│ 140│ 1.75│ │ 91.2 - 2.5│ 168│ 1.74│ │ 96.7 - │ │ 1.80│ │ 98.1 - │ │ 1.53│ │ 99 - │ │ 1.12│ │ 91 - ─────────┴──────┴──────┴──────────┴──────── - - ─────────┬─────────────────────────────────────────────────────┬────────── - Time of │ Parts per Million │Stability, - Aëration,│ │ Hours - Hours │ │ - │ │ - │ │ - │ │ - │ │ - ─────────┼─────────────────────────────────┬─────────┬─────────┼────────── - │ Nitrogen as │Dissolved│Suspended│ - │ │ Oxygen │ Matter │ - ─────────┼───────┬────────┬────────┬───────┼─────────┼─────────┼────────── - │ Free │Nitrites│Nitrates│Organic│ │ │ - │Ammonia│ │ │ │ │ │ - ─────────┼───────┼────────┼────────┼───────┼─────────┼─────────┼────────── - 0│ 22│ 0.08│ 0.08│ │ 0.00│ │ 000 - 1│ 17│ 0.00│ 0.04│ │ 0.30│ │ 2 - 2│ 15│ 0.95│ 0.70│ │ 1.90│ │ 33 - 3│ 11│ 1.75│ 2.80│ │ 4.30│ │ 120 - 4│ 7│ 2.20│ 5.60│ │ 5.90│ │ 120 - 5│ 5│ 2.50│ 8.20│ │ 6.70│ │ 120 - 2.5│ 11│ 0.05│ 2.00│ │ │ │ 69 - 3│ 9.9│ 0.12│ 2.9│ │ │ │ 95 - 4│ 1.8│ 0.14│ 5.2│ │ │ │ 120 - 4│ 1.95│ 0.08│ 8.5│ │ │ │ 120 - 4│ 5.79│ 0.14│ 9.0│ │ │ │ 120 - 4│ 7.90│ 0.02│ 2.0│ │ │ │ 61 - 4│ 4.86│ 0.36│ 4.9│ │ │ │ 120 - 3│ 9.39│ 0.60│ 3.0│ │ │ │ 120 - 2.5│ 11.2│ 0.36│ 1.1│ │ │ │ 84 - │ │ │ 8.5│ 4│ │ 11│ 120 - │ 5.79│ │ 9.0│ 8│ │ 9│ 120 - │ 10.1│ │ 2.3│ 14│ │ 42│ 73 - ─────────┴───────┴────────┴────────┴───────┴─────────┴─────────┴────────── - - TABLE 95 - - COMPARATIVE RESULTS FROM THE AËRATION OF SEWAGE IN THE PRESENCE OF - ACTIVATED SLUDGE WITH THE USE OF DIFFERENT DISTRIBUTING MEDIA - - (T. C. Hatton, Eng. Record, Vol. 73, p. 255) - ─────────────┬──────────┬────────┬────────┬────────┬─────────┬───────── - Diffusers │Months in │ Pounds │ Air, │Per Cent│Nitrates,│Stability - │ 1915 │ per │ Cubic │Bacteria│Parts per│Effluent - │ │ Square │Feet per│Removed │ Million │in Hours - │ │ Inch │ Gallon │ │ │ - ─────────────┼──────────┼────────┼────────┼────────┼─────────┼───────── - Filtros plate│June 1 to│ 4.3│ 2.06│ 91│ 3.4│ 78 - │ Aug. 15 │ │ │ │ │ - Air jet │June 1 to│ 3.5│ 1.94│ 91│ 2.2│ 52 - │ Aug. 15 │ │ │ │ │ - Filtros plate│Nov. 18 to│ 4.6│ 1.71│ 90│ 0.3│ 113 - │ Dec. 7 │ │ │ │ │ - Monel metal │Nov. 18 to│ 3.0│ 1.71│ 80│ 0.2│ 63 - │ Dec. 7 │ │ │ │ │ - ─────────────┴──────────┴────────┴────────┴────────┴─────────┴───────── - -It is desirable to diffuse the air in small bubbles as by this means the -greatest efficiency seems to be obtained from the amount of air added. A -diameter 1/16 to ⅛ of an inch is approximately the maximum limit for the -size of an effective bubble. Monel metal cloth, porous wood blocks, open -jets, paddles, and other forms of diffusers have been tried, but none -have given the satisfaction of the filtros plate. The relative value of -different types of diffusers is shown in Table 95 taken from -Hatton.[184] The Filtros plates are a proprietary article manufactured -by the General Filtration Company of Rochester, N. Y. They are made of a -quartz sand firmly cemented together and can be obtained with -practically any degree of porosity, size of pore opening or dimension of -plate, but they are made in a standard size 12 inches square by 1½ -inches thick. The frictional loss through the plate is not very great -for the amount of air ordinarily used. The plates are classified in -accordance with the volume of air which will pass through them, when -dry, per minute when under a pressure of 2 inches of water. These -classes run from ½ to 12 cubic feet of air per minute. The type usually -specified passes about 2 cubic feet of air per minute. The loss of head -through these plates as tested at Milwaukee showed an initial loss of ¾ -of a pound and an additional loss of about ¼ of a pound for every cubic -foot of air per minute per square foot of surface. It is necessary to -screen and wash the air before blowing it through the filtros plate as -ordinary air is so filled with dirt as to clog the pores of the diffuser -quite rapidly. - -The area of filtros plates required in the bottom of the tank is usually -expressed in terms of the free surface of the tank or as a ratio -thereto. In the Urbana tests the best ratio was found to be less than 1 -: 3 and more than 1 : 9. In Milwaukee[185] the ratio adopted is in the -neighborhood of 1 : 4 or 1 : 5. At Fort Worth the ratio will be about 1 -: 7 and at Chicago it will be 1 : 8. The exact ratio should be -determined by experiment and will depend on the construction of the tank -and the character of the raw sewage and the desired effluent. It is -essential that the filtros plates be placed level and at the same -elevation as otherwise the distribution of air will be uneven. - - -=273. Obtaining Activated Sludge.=—After a plant is once started -activated sludge is generated during the process of treatment and with -careful management a stock of activated sludge can be kept on hand. When -a plant is new, or if shut down for such a length of time that the -sludge loses its activation, it is necessary to activate some new -sludge. This is done by blowing air continuously through sewage either -on the fill and draw method with periodic decantations of the -supernatant liquid, or by the continuous-flow process, but more -preferably by the latter. Where activated sludge is to be obtained from -fresh sewage alone the time required is in the neighborhood of 10 to 14 -days, and purification begins at the start. An estimate of the quantity -which will be obtained can not be made with accuracy. After the initial -quantity of sludge has been obtained activated sludge can be maintained -during the process of aëration of the raw sewage, or by means of the -reaëration tanks previously described. - -The volume of activated sludge present in the aëration tank should be -about 25 per cent of the volume of the tank. The volume of the sludge is -measured in a somewhat arbitrary manner as the amount by volume which -will settle in 30 minutes in an ordinary test tube. It is found that -this is almost 90 per cent of the solids settling in 4 to 6 hours. - - -=274. Cost.=—The available information on the cost of the activated -sludge process is meager and unreliable. The factors entering into the -cost are: the price of fuel, the size of the plant, the period of -sedimentation, the amount of air per gallon of sewage, the air pressure, -and the percentage of sludge to be aërated in the mixture. In -Milwaukee[186] the cost of construction is estimated at $44,000 per -million gallons, and $4.75 per million gallons for operation. At -Houston, Texas, the cost is estimated at $24,000 per million gallons, -exclusive of the sludge drying plant, which may cost $40,000 per million -gallons. At Milwaukee, the cost of pressing the sludge is $4.82 per dry -ton and of drying is $3.93 per dry ton. The sludge may be sold at the -normal rate of $2.50 per unit of nitrogen. Based on the normal value the -evident profit will be $3.75 per ton. The net cost of disposing of -Milwaukee sewage is estimated at $9.64 per million gallons of which -$4.89 is chargeable to overhead and $4.75 to repairs, operation and -renewal. In a comparison of the costs of activated sludge and Imhoff -tanks with sprinkling filters,[187] the information given by Eddy has -been summarized in Table 96. In comparing the relative areas required -for different methods of sewage treatment, activated sludge should be -allowed about 15 million gallons per acre per day on the basis of -aëration tanks 15 feet deep. This figure represents approximately the -gross area of the plants at Milwaukee and at Cleveland. - - TABLE 96 - - COMPARATIVE COSTS OF ACTIVATED SLUDGE, AND OF IMHOFF TANKS FOLLOWED BY - SPRINKLING FILTERS - - (H. P. Eddy, Eng. Record, Vol. 74, p. 557) - ─────────────┬─────────────┬─────────────┬───────────────────────────── - Process │ First Cost │Operation per│Total Annual Cost at 4 Per - │ per Million │ Million │ Cent with Sinking Fund at - │ Gallons, │ Gallons, │ 2.5 Per Cent per - │ Dollars │ Dollars │ - ─────────────┼─────────────┼─────────────┼──────────────┬────────────── - │ │ │ Million │ Capita, - │ │ │ Gallons, │ Dollars - │ │ │ Dollars │ - ─────────────┼─────────────┼─────────────┼──────────────┼────────────── - Activated │ 57,100│ 20.00│ 29.85│ 1.09 - sludge │ │ │ │ - Imhoff tank │ 78,500│ 8.50│ 21.84│ 0.80 - and │ │ │ │ - sprinkling │ │ │ │ - filter │ │ │ │ - ─────────────┴─────────────┴─────────────┴──────────────┴────────────── - - - REFERENCES AND BIBLIOGRAPHY ON ACTIVATED SLUDGE - -The following abbreviations will be used: A.S. for Activated Sludge, -E.C. for Engineering and Contracting, E.N. for Engineering News, E.R. -for Engineering Record, E.N.R. for Engineering News-Record, p. for page, -and V. for volume. - - No. - - 1. Cooperation Sought in Conducting A.S. Experiments at Baltimore, by - Franks and Hendrick. E.R. V. 71, 1915, pp. 521, 724, and 784. V. - 72, 1915, pp. 23, and 640. - - 2. Sewage Treatment Experiments with Aëration and A.S., by Bartow and - Mohlman. E.N. V. 73, 1915, p. 647, and E.R. V. 71, 1915, p. 421. - - 3. A.S. Experiments at Milwaukee, Wisconsin, by Hatton. E.N. V. 74, - 1915, p. 134. - - 4. A.S. in America, An Editorial Survey, by Baker. E.N. V. 74, 1915, - p. 164. - - 5. Choosing Air Compressors for A.S., by Nordell, E.N. V. 74, 1915, p. - 904. - - 6. A Year of A.S. at Milwaukee, by Fuller. E.N. V. 74, 1915, p. 1146. - - 7. A.S. Experiments at Urbana. E.N. V. 74, 1915, p. 1097. - - 8. Experiments on the A.S. Process, by Bartow and Mohlman. E.C. V. 44, - 1915, p. 433. - - 9. Milwaukee’s A.S. Plant, the Pioneer Large Scale Installation, by - Hatton. E.R. V. 72, 1915, p. 481 and E.C. V. 44, 1915, p. 322. - - 10. A.S. Experiments at Milwaukee, by Hatton. Journal American - Waterworks Association and Proceedings Illinois Society of - Engineers, 1916. Also E.R. V. 73, 1916, p. 255. E.C. V. 45, 1916, - p. 104, and E.N. V. 75, 1916, pp. 262 and 306. - - 11. A.S. Defined. E.N. V. 75, 1916, p. 503, and E.N.R. V. 80, 1918, p. - 205. - - 12. Status of A.S. Sewage Treatment, by Hammond. E.N. V. 75, 1916, p. - 798. - - 13. Trial A.S. Unit at Cleveland, by Pratt. E.N. V. 75, 1916, p. 671. - - 14. Air Diffuser Experience with A.S. E.N. V. 76, 1916, p. 106. - - 15. Nitrogen from Sewage Sludge, Plain and Activated, by Copeland, - Journal American Chemical Society, Sept. 28, 1916. E.N. V. 76, - 1916, p. 665. E.R. V. 74, 1916, p. 444. - - 16. Tests Show A.S. Process Adapted to Treatment of Stock Yards Wastes. - E.R. V. 74, 1916, p. 137. - - 17. Aëration Suggestions for Disposal of Sludge, by Hammond. Journal - American Chemical Society, Sept. 25, 1916. E.R. V. 74, 1916, p. - 448. - - 18. Cost Comparison of Sewage Treatment. Imhoff Tank and Sprinkling - Filters vs. A.S., by Eddy. E.R. V. 74, 1916, p. 557. - - 19. Large A.S. Plant at Milwaukee. E.N. V. 76, 1916, p. 686. - - 20. A.S. Novelties at Hermosa Beach, Cal. E.N. V. 76, 1916, p. 890. - - 21. A.S. Experiments at University of Illinois, by Bartow, Mohlman, and - Schnellbach. E.N. V. 76, 1916, p. 972. - - 22. A.S. Results at Cleveland Reviewed, by Pratt and Gascoigne. E.N. V. - 76, 1916, pp. 1061 and 1124. - - 23. Sewage Treatment by Aëration and Activation, by Hammond. - Proceedings American Society Municipal Improvements, 1916. - - 24. A.S., by Bartow and Mohlman, Proceedings Illinois Society of - Engineers, 1916. - - 25. The Latest Method of Sewage Treatment, by Bartow. Journal American - Waterworks Association, V. 3, March, 1916, p. 327. - - 26. Winter Experiences with A.S., by Copeland. Journal American Society - of Chemical Engineers, April 21, 1916. E.C. V. 45, 1916, p. 386. - - 27. A.S. Process Firmly Established, by Hatton. E.R. V. 75, 1917, p. - 16. - - 28. Operate Continuous Flow A.S. Plant, by Bartow, Mohlman, and - Schnellbach. E.R. V. 75, 1917, p. 380. - - 29. Chicago Stock Yards Sewage and A.S., by Lederer. Journal American - Society of Chemical Engineers, April 21, 1916. E.C. V. 45, 1916, - p. 388. - - 30. The Patent Situation Concerning A.S. E.C. V. 45, 1916, p. 208. - - 31. “Sewage Disposal” by Kinnicutt, Winslow, and Pratt, published by - John Wiley & Sons. 2d Edition, Chapter 12. - - 32. A.S. Tests Made by California Cities. E.N.R. V. 79, 1917, p. 1009. - - 33. Conclusions on the A.S. Process at Milwaukee. Journal American - Public Health Association, 1917. E.N.R. V. 79, 1917, p. 840. - - 34. Dewatering A.S. at Urbana, by Bartow. Journal American Institute of - Chemical Engineers, 1917. E.N.R. V. 79, 1917, p. 269. - - 35. Milwaukee Air Diffusion Studies in A.S. E.N.R. V. 78, 1917, p. 628. - - 36. A.S. Bibliography (up to May 1, 1917) by J. E. Porter. - - 37. Air Diffusion in A.S. E.N.R. V. 78, 1917, p. 255. - - 38. A.S. Plant at Houston, Texas. E.N. V. 77, 1917, p. 236, E.N.R. 83, - 1919, p. 1003, and V. 84, 1920, p. 75. - - 39. A.S. Power Costs, by Requardt. E.N. V. 77, 1917, p. 18. - - 40. A.S. at San Marcos, Texas, by Elrod. E.N. V. 77, 1917, p. 249. - - 41. Filtros Plates Made the Best Showing in Air Diffuser Tests. E.N.R. - V. 79, 1917, p. 269. - - 42. Results of Experiments on A.S., by Ardern and Lockett. Journal - Society for Chemical Research, V. 33, May 30, 1914, p. 523. - - 43. Final Plans at Milwaukee. E.N.R. V. 84, 1920, p. 990. - - 44. A.S. Bibliography, published by General Filtration Co., Rochester, - N. Y., 1921. - - 45. A.S. at Manchester, Eng. by Ardern. Journal Society Chemical - Industry, 1921. E.C. V. 55, 1921, p. 310. - - 46. The Des Plaines River A.S. Plant, by Pearse. E.N.R. V. 88, 1920, p. - 1134. - - 47. Sewage Treatment by the Dorr System, by Eagles. Proceedings, Boston - Society of Engineers, 1920. Public Works V. 50, 1920, p. 53. - - - - - CHAPTER XIX - ACID PRECIPITATION, LIME AND ELECTRICITY, AND DISINFECTION - - -=275. The Miles Acid Process.=—The Miles Acid Process for the treatment -of sewage was devised and patented by G. W. Miles. It was tried -experimentally at the Calf Pasture sewage pumping station, Boston, -Mass., 1911 to 1914. In 1916 it was tried experimentally at the -Massachusetts Institute of Technology, and it has been tested -subsequently at other places, notably at New Haven, Conn., in 1917 and -1918. It is one of the most recent developments in sewage treatment and -no extensive experience has been had with it. The process consists in -the acidification of sewage with sulphuric or sulphurous acid, as the -result of which the suspended matter and grease are precipitated and -bacteria are removed. The equipment required for the process consists of -devices for the production of sulphur dioxide (SO_{2}), and for feeding -niter cake or other forms of acid; subsiding basins; sludge-handling -apparatus; sludge driers; grease extractors; grease stills; and tankage -driers and grinders. - -The first step is the acidification of the sewage. The period of contact -with the acid is about 4 hours. Sulphurous acid seems to give better -results than sulphuric because of the ease in which it can be -manufactured on the spot. It seems also to be more virulent in attacking -bacteria than an equal strength of sulphuric acid. In experimental -plants the acidulation has been accomplished in different ways such as: -by the addition of compressed sulphur dioxide from tanks; by the -addition of sulphur dioxide made from burning sulphur; or by the -roasting of iron pyrite (FeS_{2}). The acidulation precipitates most of -the grease as well as the suspended matter and results in a sludge which -gives some promise of commercial value. In referring to the process R. -S. Weston states:[188] - - (1) It disinfects the sewage by reducing the numbers of bacteria - from millions to hundreds per c.c. - - (2) If the drying of the sludge and the extraction of the grease - can be accomplished economically, it is possible that a large - part, if not all, of the cost of the acid treatment may be met by - the sale of the grease and fertilizer recovered from the sewage. - - (3) The use of so strong a deodorizer and disinfectant as sulphur - dioxide would prevent the usual nuisances of treatment works. - - (4) The addition of sulphur dioxide to the sewage also avoids any - fly nuisance, which is a handicap to the operation of Imhoff tanks - and trickling filters. - -The amount of acid used varies with the quality of the sewage and the -desired character of the effluent. At Bradford, England,[189] 5,500 -pounds of sulphuric acid are used per million gallons, producing about -2,340 pounds of grease or 0.43 pound of grease per pound of sulphuric -acid. At Boston only 0.215 pound of grease were produced per pound of -sulphuric acid. The difference is probably due to the great difference -in the amount of grease in the raw sewage. In the East Street sewer at -New Haven, Conn.,[190] only 700 pounds of acid are used per million -gallons of sewage as the alkalinity is only 50 p.p.m. This amount of -acid secures an acidity of 50 p.p.m. whereas in the Boulevard sewer -1,130 pounds of acid had to be added to produce the same result. The -results obtained by the experiments conducted by the Massachusetts -State Board of Health in 1917 are shown in Table 97. The character of -the sludge from the same tests is shown in Table 98. After -acidification[191] the sewage contains bisulphites and some free -sulphurous acid, with some lime and magnesium soaps which are attacked -by the acid liberating the free fatty acids. Part of the bisulphites -and sulphurous acid are oxidized to bisulphates and sulphuric acid. It -was found as a result of the New Haven[191] experiments that the -presence of sulphur dioxide in the effluent caused an abnormal oxygen -demand from the diluting water and that this difficulty could be -partly overcome by the aëration of the effluent after acidulation and -sedimentation, without prohibitory expense. The effluent and sludge -are both stable for appreciable periods of time and are suitable for -disposal by dilution. The character of the sludge as determined by the -New Haven tests[192] is shown in Table 99. - - TABLE 97 - - AVERAGE ANALYSIS OF SEWAGE ENTERING BOSTON HARBOR, BEFORE AND AFTER - TREATMENT, JULY 17 TO SEPTEMBER 27, 1917 - - (Eng. News-Record, Vol. 80, p. 319) - ─────────┬───────────────────────────────────────────────┬─────────────── - Sample │ Parts per Million │ Bacteria, - │ │ Millions - ─────────┼─────────────────┬───────────┬────────┬────────┼─────┬───────── - │ Ammonia │ Kjeldahl │Chlorine│ Oxygen │ │ - │ │ Nitrogen │ │Consumed│ │ - ─────────┼─────┬───────────┼─────┬─────┼────────┼────────┼─────┼───────── - │Free │Albuminoid │ │ │ │ │ │ - ─────────┼─────┼─────┬─────┼─────┼─────┼────────┼────────┼─────┼───────── - │Total│Total│Diss.│Total│Diss.│ │ │ 20° │ 37° - ─────────┴─────┴─────┴─────┴─────┴─────┴────────┴────────┴─────┴───────── - - _Paddock’s Island_ - - ─────────┬─────┬─────┬─────┬─────┬─────┬────────┬────────┬─────┬───────── - Raw │ 14.0│ 3.3│ 1.8│ 6.8│ 3.6│ 134│ 23.1│1.86 │ 4.15 - sewage │ │ │ │ │ │ │ │ │ - Settled │ 12.2│ 1.6│ 1.1│ 3.5│ 2.2│ │ 15.4│ │ - Sewage │ │ │ │ │ │ │ │ │ - Acidified│ 20.9│ 5.2│ 3.9│ 10.0│ 7.5│ │ │units│units 91 - and │ │ │ │ │ │ │ │ 94 │ - settled│ │ │ │ │ │ │ │ │ - sewage │ │ │ │ │ │ │ │ │ - ─────────┴─────┴─────┴─────┴─────┴─────┴────────┴────────┴─────┴───────── - - _Deer Island_ - - ─────────┬─────┬─────┬─────┬─────┬─────┬────────┬────────┬─────┬───────── - Raw │ 23.3│ 8.2│ 4.8│ 16.8│ 8.9│ 3100│ 87.3│2.63 │ 1.50 - sewage │ │ │ │ │ │ │ │ │ - Settled │ 21.1│ 5.6│ 3.9│ 10.7│ 7.3│ │ 62.2│ │ - sewage │ │ │ │ │ │ │ │ │ - Acidified│ 20.9│ 5.2│ 3.9│ 10.0│ 7.5│ │ │units│units 85 - and │ │ │ │ │ │ │ │ 147 │ - settled│ │ │ │ │ │ │ │ │ - sewage │ │ │ │ │ │ │ │ │ - ─────────┴─────┴─────┴─────┴─────┴─────┴────────┴────────┴─────┴───────── - - _Calf Pasture_ - - ─────────┬─────┬─────┬─────┬─────┬─────┬────────┬────────┬─────┬───────── - Raw │ 18.0│ 4.5│ 2.0│ 9.7│ 4.1│ 3254│ 41.2│1.89 │ 0.98 - sewage │ │ │ │ │ │ │ │ │ - Settled │ 19.1│ 2.3│ 1.4│ 4.9│ 3.3│ │ 25.8│ │ - sewage │ │ │ │ │ │ │ │ │ - Acidified│ 17.8│ 2.4│ 1.6│ 4.9│ 3.3│ │ │units│units 149 - and │ │ │ │ │ │ │ │ 277 │ - settled│ │ │ │ │ │ │ │ │ - sewage │ │ │ │ │ │ │ │ │ - ─────────┴─────┴─────┴─────┴─────┴─────┴────────┴────────┴─────┴───────── - -The success of the Miles Acid Process in comparison with other processes -is dependent on the commercial value of the sludge produced. The New -Haven experiments indicate that 16 to 21 per cent of the grease in the -sludge is unsaponifiable and seriously impairs the value of the process. - - TABLE 98 - - AVERAGE AMOUNT OF SLUDGE AND FATS OBTAINED FROM SEWAGE ENTERING BOSTON - HARBOR AFTER EIGHTEEN HOURS SEDIMENTATION WITH AND WITHOUT - ACIDIFICATION - - (Eng. News-Record, Vol. 80, p. 319) - ────────────────────┬────────────────┬────────────────┬──────────────── - │Paddock’s Island│ Deer Island │ Calf Pasture - ────────────────────┼────────────────┼────────────────┼──────────────── - │ Sedimentation │ Sedimentation │ Sedimentation - ────────────────────┼─────┬──────────┼─────┬──────────┼─────┬────────── - │Plain│Acidulated│Plain│Acidulated│Plain│Acidulated - ────────────────────┼─────┼──────────┼─────┼──────────┼─────┼────────── - Pounds of SO_{2} │ │ 818│ │ 1513│ │ 1189 - used per million │ │ │ │ │ │ - gallons of sewage │ │ │ │ │ │ - treated │ │ │ │ │ │ - Dry sludge per │ 782│ 959│ 1709│ 1939│ 1208│ 1427 - million gallons │ │ │ │ │ │ - Per cent Nitrogen in│ 3.10│ 3.38│ 3.57│ 3.45│ 3.18│ 2.83 - sludge │ │ │ │ │ │ - Per cent fats in │27.30│ 27.30│24.60│ 19.40│24.30│ 26.30 - sludge │ │ │ │ │ │ - ────────────────────┴─────┴──────────┴─────┴──────────┴─────┴────────── - - TABLE 99 - - CHARACTER OF MILES ACID SLUDGE AT NEW HAVEN - - (Eng. News-Record, Vol. 81, p. 1034) - ─────────────────────────┬───────────────────────────────────┬───────── - │ East Street Sewer │Boulevard - │ │ Sewer - ─────────────────────────┼────────┬────────┬────────┬────────┼───────── - Length of run in days │ 25│ 24│ 44│ 70│ 29 - Total sewage treated, │ 260│ 239.4│ 407.8│ 602.2│ 145.5 - thousand gallons │ │ │ │ │ - Gallons wet sludge per │ 3750│ 4025│ 3200│ 2600│ 5375 - million gallons sewage │ │ │ │ │ - Specific gravity │ 1.067│ 1.048│ 1.054│ 1.061│ - Per cent moisture │ 86.6│ 88│ 86.3│ 85.7│ 92.5 - Pounds of dry sludge per │ 503│ 483│ 439│ 368│ 403 - million gallons sewage │ │ │ │ │ - Ether extract, per cent │ 23.7│ 24.0│ 29│ 32.6│ 30.9 - dry sludge │ │ │ │ │ - Ether extract, pounds per│ 119│ 116│ 127│ 120│ 124 - million gallons │ │ │ │ │ - Volatile matter, per cent│ 47.2│ 51.2│ 57.3│ 63.8│ 78.5 - dry sludge │ │ │ │ │ - Nitrogen, per cent dry │ 1.6│ 1.6│ 2.4│ 2.0│ 3.0 - sludge │ │ │ │ │ - ─────────────────────────┴────────┴────────┴────────┴────────┴───────── - -The conclusions reached as a result of the New Haven experiments -are:[193] - - Our experience with New Haven sewage lends no color to the hope - that a net financial profit can be obtained by the use of the - Miles Acid Process, except with sewage of exceptionally high - grease content and low alkalinity. They do, however, suggest that - for communities where clarification and disinfection are - desirable—where screening would be insufficient and nitrification - unnecessary—the process of acid treatment comes fairly into - competition with the other processes of tank treatment, and that - it is particularly suited to dealing with sewages that contain - industrial wastes, and to use in localities where local nuisances - must be avoided at all costs and where sludge disposal could be - provided for only with difficulty. - -The conclusions reached as a result of the Chicago experiments are:[194] - - The results on hand indicate that treatment of this sewage with - acid results in a somewhat greater retention of fat. An apparent - reduction in the oxygen demand over that resulting from plain - sedimentation, while remarkable, is probably not real, being - simply due to a retardation of decomposition by the sterilization - of the bacteria present, the organic matter being left in - solution.... However, there appears the added cost of acid - treatment and the cost of recovery of the grease, as well as the - uncertainty of the price to be received for the grease recovered. - -The cost of the treatment is estimated by Dorr to be $18 per million -gallons, and the value of the sludge obtained from the Boston sewage as -$24 per million gallons, giving a net margin of profit of $6 per million -gallons. At New Haven, the total return is estimated at $7.09 per -million gallons. Based on the production of sulphur dioxide by burning -sulphur (assumed to cost $36 per long ton) and on drying from 85 per -cent to 10 per cent moisture with coal assumed to cost $7.50 per ton, it -appears that the acid treatment of sewage should be materially cheaper -than either the Imhoff treatment or fine screening under the local -conditions. A comparison of the cost of the treatment of the East Street -and the Boulevard sewage at New Haven and the Calf Pasture sewage in -Boston is given in Table 100. The cost of construction was estimated by -Dorr and Weston in 1919 as greater than $15,000 per million gallons of -sewage per day capacity. - - TABLE 100 - - ESTIMATED COST OF SEWAGE TREATMENT AT NEW HAVEN AND BOSTON BY THREE - DIFFERENT PROCESSES - - Cost in Dollars per Million Gallons Treated - - (Engineering and Contracting, Vol. 51, p. 510) - ────────────────┬────────────────────┬────────────────────┬──────────── - │ Miles Acid Process │ Imhoff Tank and │Fine Screens - │ │ Chlorination │ and - │ │ │Chlorination - ────────────────┼──────┬─────┬───────┼──────┬─────┬───────┼──────┬───── - │ East │Boul-│ Calf │ East │Boul-│ Calf │ East │Boul- - │Street│evard│Pasture│Street│evard│Pasture│Street│evard - ────────────────┼──────┼─────┼───────┼──────┼─────┼───────┼──────┼───── - Tanks and │ 2.47│ 2.47│ 2.47│ 5.28│ 4.44│ │ 4.60│ 4.60 - Buildings Int.│ │ │ │ │ │ │ │ - and Dep. │ │ │ │ │ │ │ │ - Acid treatment │ 6.93│10.74│ 18.65│ │ │ │ │ - Drying sludge │ 2.09│ 2.04│ 10.34│ │ │ │ │ - Degreasing │ 1.78│ 1.91│ 9.12│ │ │ │ │ - sludge │ │ │ │ │ │ │ │ - Superintendence │ 1.06│ 2.65│ 1.06│ 0.46│ 1.15│ │ 0.47│ 1.15 - Labor on tanks │ 1.00│ 1.00│ 1.00│ 1.20│ 1.50│ │ 1.42│ 2.05 - and screens │ │ │ │ │ │ │ │ - Disposal of │ │ │ │ 1.00│ 1.00│ │ 0.50│ 0.50 - sludge or │ │ │ │ │ │ │ │ - screenings │ │ │ │ │ │ │ │ - Chlorination │ │ │ │ 4.05│ 4.05│ │ 4.05│ 4.05 - Gross cost │ 15.50│20.98│ 42.75│ 11.99│12.14│ │ 11.03│12.35 - Revenue │ 6.57│10.66│ 47.59│ │ │ │ │ - Net cost │ 8.93│10.32│ 4.84│ 11.99│12.14│ │ 11.03│12.35 - ────────────────┴──────┴─────┴───────┴──────┴─────┴───────┴──────┴───── - - - ELECTROLYTIC TREATMENT - - -=276. The Process.=—This process has been generally unsuccessful in the -treatment of sewage and has grown into disrepute. In the words of the -editor of the _Engineering News-Record_:[195] - - Thirty years of experiments and demonstrations with only a few - small working plants built and most of them abandoned—such in - epitome is the record of the electrolytic process of sewage - treatment. - -It is probably true that the process has never received a thorough and -exhaustive test on a large scale, but the small-scale tests have not -been promising of good results. Among the most extensive tests have been -those at Elmhurst, Long Island,[196] Decatur, Ill.,[197] and Easton, -Pa.[198] - -Whatever degree of popularity the method has possessed has been due -possibly to the mystery and romance of “electricity” and to the -personality of its promoters. The process should, nevertheless, be -understood by the engineer in order that it may be explained -satisfactorily to the layman interested in its adoption. - -In this process, sometimes called the direct-oxidation process, all grit -is removed and the sewage is passed through fine screens before entering -the electrolytic tank. In the electrolytic tank the sewage passes in -thin sheets between electrodes and an electric current is discharged -through it. A recent development has been the addition of lime to the -sewage at some point in its passage through the electrolytic tank. From -the electrolytic tank the sewage flows to a sedimentation tank, where -sludge is accumulated, and from which the liquid effluent is finally -disposed of. - -It is claimed that the action of the electricity electrolyzes the -sewage, releasing chlorine, which acts as a powerful disinfectant. The -constituents of the sewage are oxidized so that the dissolved oxygen, -nitrates, and relative stability are increased and the sludge is -rendered non-putrescible. It is said that the addition of lime increases -the efficiency of sedimentation and enhances the effect of the electric -current. The results obtained by tests at Easton, Pa., are shown in -Table 101. It will be observed from this table that the combination of -lime and electricity does not have a more beneficial effect than either -one of them alone. The amount of sludge produced by the combination is -about the same as by chemical precipitation alone, but the character of -the sludge produced with electricity is less putrescible. The cost of -the treatment as estimated at Elmhurst is shown in Table 102. - -As a result of the tests at Decatur, comparing lime alone with lime and -electricity together, Dr. Ed. Bartow stated: - - The purification by treatment with lime alone was greater than - that obtained in several of the individual samples treated with - lime and electricity. - - TABLE 101 - - COMPARATIVE RESULTS OBTAINED FROM THE TREATMENT OF SEWAGE BY LIME - ALONE, ELECTRICITY ALONE, AND LIME AND ELECTRICITY COMBINED - - (Creighton and Franklin, Journal of the Franklin Institute, August, - 1919) - ───────────────────────┬───────────────┬───────────────┬─────────────── - │ Lime and │ Lime Alone │ Electricity - │ Electricity │ │ Alone - ───────────────────────┼───────┬───────┼───────┬───────┼───────┬─────── - │Change,│Change,│Change,│Change,│Change,│Change, - │ Parts │ Per │ Parts │ Per │ Parts │ Per - │ per │ Cent │ per │ Cent │ per │ Cent - │Million│ │Million│ │Million│ - ───────────────────────┼───────┼───────┼───────┼───────┼───────┼─────── - Chlorine │ +1.2│ +1.9│ +12.3│ +18.2│ +1.6│ +2.2 - Nitrites │ +0.014│ +58.3│ -.005│ –10.0│ –0.01│ –20.0 - Nitrates │ +0.13│ +23.6│ +.005│ +0.8│ –0.15│ –20.0 - Ammonia │ –3.3│ –18.3│ +0.2│ +1.3│ +0.9│ +6.6 - Albuminoid ammonia │ –3.6│ –12.1│ –0.4│ –1.7│ –0.5│ –2.3 - Oxygen demand │ –13.0│ –20.5│ –7.7│ –8.9│ –6.5│ –10.0 - Dissolved oxygen │ +1.78│ +40.9│ –0.93│ –19.1│ +1.61│ +40.1 - Total bacteria at 37° │ –343│ –92.7│ –373│ –82.4│ –165│ –37.8 - (Thousands) │ │ │ │ │ │ - Total bacteria at 20° │ –688│ –92.7│ –1074│ –90.1│ –635│ –70.0 - (Thousands) │ │ │ │ │ │ - B. Coli (Thousands) │ –77.9│ –99.85│ –96.3│ –92.3│ –45│ –81.8 - Oxygen absorbed in 5 │ –3.40│ –81.6│ –1.03│ –21.│ +1.24│ +31 - days │ │ │ │ │ │ - ───────────────────────┴───────┴───────┴───────┴───────┴───────┴─────── - - - DISINFECTION - - -=277. Disinfection of Sewage.=—Sewage is disinfected in order to protect -public water supplies, shell fish, and bathing beaches; to prevent the -spread of disease; to keep down odors, and to delay putrefaction. -Disinfection is the treatment of sewage by which the number of bacteria -is greatly reduced. Sterilization is the destruction of all bacterial -life, including spores. Ordinarily even the most destructive agents do -not accomplish complete sterilization. Chlorine and its compounds are -practically the only substances used for the disinfection of sewage. The -lime used in chemical precipitation, the acid used in the Miles Acid -Process, the aëration in the activated sludge process, all serve to -disinfect sewage, but are not used primarily for that purpose. Copper -sulphate has been used as an algaecide but never on a large scale as a -bactericide.[199] Heat has been suggested, but its high cost has -prevented its practical application to the disinfection of sewage. - - TABLE 102 - - COST OF ELECTROLYTIC TREATMENT, ELMHURST, LONG ISLAND, AND EASTON, - PENNSYLVANIA - - ────────────────────────────────────────┬───────────────────┬───────── - │ │ Three - Item │One Million Gallon │ Million - │ │ Gallon - ────────────────────────────────────────┼─────────┬─────────┼───────── - │ unit at │ unit at │ unit at - │ Easton, │Elmhurst,│Elmhurst, - │ Dollars │ Dollars │ Dollars - ────────────────────────────────────────┼─────────┼─────────┼───────── - Hydrated lime: │ │ │ - Elmhurst, 1300 pounds at $7.90 ton. │ 12.56│ 5.14│ 15.42 - Easton, 3720 pounds at $6.75 ton. │ │ │ - Electric power electrolysis: │ │ │ - Elmhurst, 85 kw-h. at 4 cents │ 4.19│ 3.40│ 9.60 - Easton, 6.25 kw-h. at 8.05 cents │ │ │ - Electric power, light and agitation: │ │ │ - Elmhurst, 60 kw-h. at 4 cents │ 0.50│ 2.40│ 7.20 - Easton, 6.25 kw-h at 8.05 cents │ │ │ - Heating │ 1.25│ │ - Labor and supervision │ 15.00│ 12.50│ 15.00 - Maintenance, repairs and supplies │ 1.50│ 1.00│ 3.00 - Sludge pressing and removal │ │ 5.11│ 15.33 - ────────────────────────────────────────┼─────────┼─────────┼───────── - Total │ 35.00│ 29.55│ 65.55 - Cost per million gallons │ 35.00│ 29.55│ 21.85 - ────────────────────────────────────────┴─────────┴─────────┴───────── - -The action which takes place on the addition to sewage of chlorine or -its compounds is not well understood. The idea that the bacteria are -burned up with “nascent” or freshly born oxygen, has been exploded.[200] -Likewise the idea that the toxic properties of chlorine have no effect -has not been borne out by experiments. It has been demonstrated, -particularly by tests on strong tannery wastes, that the action of -chlorine gas is more effective than the application of the same amount -of chlorine in the form of hypochlorite. All that we are certain of at -present is that the greater the amount of chlorine added under the same -conditions, the greater the bactericidal effect. - -Chlorine is applied either in the form of a bleaching powder or a gas. -In ordinary commercial bleach (calcium hypochlorite) the available -chlorine is about 35 to 40 per cent by weight. In order to add one part -per million of available chlorine to sewage it is necessary to add about -25 pounds of bleaching powder or 8½ pounds of liquid chlorine per -million gallons of sewage. This can be computed as follows: - - The molecular weight of calcium hypochlorite is 127.0. This reacts - to produce two atoms of available chlorine with a molecular weight - of 70.9. If the bleaching powder were pure the available chlorine - would therefore represent 70.9 ÷ 127, or 56 per cent of its - weight. Then to obtain one pound of chlorine it would be necessary - to have 1.79 pounds of pure bleaching powder. Since 1,000,000 - gallons of water weigh approximately 8,300,000 pounds, in order to - apply one part per million of chlorine to 1,000,000 gallons of - sewage it is necessary to apply 1.79 × 8.3 or 14.9 pounds of pure - bleaching powder. Commercial bleaching powder is only about 60 per - cent calcium hypochlorite. It is therefore necessary to add 14.9 ÷ - 0.60 or about 25 pounds of commercial bleach. - - Since liquid chlorine is very nearly pure, approximately 8½ pounds - of it applied to 1,000,000 gallons of sewage are equivalent to a - dose of one part per million. - -Commercial bleaching powder is a dry white powder which absorbs moisture -slowly, and which loses its strength rapidly when exposed to the air. It -is packed in air-tight sheet iron containers, which should be opened -under water, or emptied into water immediately on being opened. The -strength of the solution should be from ½ to 1 per cent. The rate of the -application of the solution to the sewage may be controlled by automatic -feed devices, or by hand-controlled devices. - -Commercial liquid chlorine is sold in heavy cast steel containers, which -hold 100 to 140 pounds of liquid chlorine under a pressure of 54 pounds -per square inch at zero degrees C. or 121 pounds per square inch at 20 -degrees. - -The amount of chlorine used is dependent on the character of the sewage -to be treated, the stage of decomposition of the organic matter, the -desired degree of disinfection, the period of contact, and the -temperature. The amount of chlorine is expressed in parts per million of -available chlorine, regardless of the form in which the chlorine is -applied. In general about 15 to 20 parts per million of available -chlorine with 30 minutes’ contact at a temperature of about 15° C. will -effect an apparent removal of 99 per cent of the bacteria from the raw -sewage. The effect is only apparent because many of the bacteria encased -in the solid matter of the sewage escape the effect of the chlorine, or -detection in the bacterial analysis. Stronger and older sewages, higher -temperatures, and shorter periods of contact will demand more chlorine -to produce the same results. A septic effluent will require more -chlorine than a raw sewage because of the greater oxygen demand by the -septic sewage. The results of experiments on disinfection made at -different testing stations have shown such wide variations in the amount -of chlorine necessary, as to demonstrate the necessity for independent -studies of any particular sewage which is to be chlorinated. For -instance, at Milwaukee approximately 13 p.p.m. of available chlorine -applied to an Imhoff tank effluent effected a 99 per cent removal of -bacteria, whereas the same result was obtained at Lawrence, Mass., on -crude sewage with only 6.6 p.p.m. and at Marion, Ohio, only 9 per cent -removal of bacteria was obtained by the addition of 4,815 p.p.m. to -crude sewage. The Ohio and Massachusetts reports show irrational -variations among themselves. For instance, 6.2 p.p.m. applied to a -septic effluent effected 88 per cent removal whereas in another case 7.6 -p.p.m. effected only 36 per cent removal. At Lawrence in one case it -took 8.6 p.p.m. to remove 99 per cent from a sand filter effluent, but -only 6.3 p.p.m. to effect the same result in the effluent from a septic -tank. The most consistent results are those found at Milwaukee which -show a steadily increasing percentage removal with increasing amounts of -chlorine. - -Some time after sewage has received its dose of chlorine the number of -bacteria may be greater than in the raw sewage. Such bacteria are called -aftergrowths. Certain forms of bacteria, particularly the pathogenic or -body temperature types, are most susceptible to disinfecting agents. -These are killed off and leave the sewage in a condition more favorable -to the growth of more resistant forms of bacteria. As the latter are -non-pathogenic and are generally aërobic their presence is usually more -beneficial than detrimental, as they hasten the action of -self-purification. - - - REFERENCES - -The following abbreviations will be used: E.C. for Engineering and -Contracting, E.N. for Engineering News, E.R. for Engineering Record, -E.N.R. for Engineering News-Record, M.J. for Municipal Journal, p. for -page, and V. for volume. - - No. - - 1. Grease and Fertilizer Base for Boston Sewage, by Weston, E.N. V. - 75, 1916, p. 913 and Journal American Public Health Association, - April, 1916. - - 2. Getting Grease and Fertilizer from City Sewage, by Allen. E.N. V. - 75, 1916, p. 1005. - - 3. New Haven Tests Five Processes of Sewage Treatment. E.N.R. V. 79, - 1917, p. 829. - - 4. Recovery of Grease and Fertilizer from Sewage Comes to the Front. - E.N.R. V. 80, 1916, p. 319. - - 5. Miles Acid Process may Require Aëration of Effluent, by Mohlman. - E.N.R. V. 81, 1918, p. 235. - - 6. Promising Results with Miles Acid Process in New Haven Tests. - E.N.R. V. 81, 1918, p. 1034. - - 7. Baltimore Experiments on Grease from Sewage. E.N. V. 75, 1916, p. - 1155. - - 8. Report on Industrial Wastes from the Stock Yards and Packingtown in - Chicago to the Trustees of the Sanitary District of Chicago, - 1914, pp. 187–195. - - 9. The Separation of Grease from Sewage, by Daniels and Rosenfeld. - Cornell Civil Engineer. V. 24, p. 13. - - 10. The Separation of Grease from Sewage Sludge with Special Reference - to Plants and Methods Employed at Bradford and Oldham, England, - by Allen. E.C. V. 40, 1913, p. 611. - - 11. Acid Treatment of Sewage, by Dorr and Weston. Journal Boston - Society of Civil Engineers, April, 1919. E.C. V. 51, 1919, p. - 510. M.J. V. 46, 1919, p. 365. - - 12. The Miles Acid Process for Sewage Disposal. Metallurgical and - Chemical Engineering, V. 18, p. 591. - - 13. Miles Acid Treatment of Sewage, by Winslow and Mohlman. Journal - American Society Municipal Improvements, Oct., 1918. M.J. V. 45, - 1918, pp. 280, 297, and 321. - - 14. New Electrolytic Sewage Treatment. M.J. V. 37, 1914, p. 556. - - 15. Electrolytic Sewage Treatment. M.J. V. 47, 1919, p. 131. - - 16. Electrolytic Treatment of Sewage at Durant, Oklahoma, by Benham. - E.N. V. 76, 1916, p. 547. Municipal Engineering, V. 49, 1916, p. - 141. - - 17. Electrolytic Treatment of Sewage at Elmhurst, Long Island, by - Travis. Report to the President of the Borough of Queens, Aug. - 31, 1914. E.R. V. 70, 1914, pp. 292, 315, and 429. M.J. V. 39, p. - 551. Municipal Engineering, V. 47, p. 281. - - 18. Tests of the Electrolysis of Sewage at Toronto, by Nevitt. E.N. V. - 71, 1914, p. 1076. - - 19. Electrolytic Treatment of Sewage Little Better than Lime Alone, by - Bartow. E.R. V. 74, 1916, p. 596. - - 20. Electrolytic Sewage Treatment Not Yet an Established Process. - E.N.R. V. 83, 1919, p. 541. - - 21. Tests of Electrolytic Sewage Treatment Process at Easton, Pa. - Journal of the Franklin Institute, Aug., 1919. E.N.R. V. 83, - 1919, p. 569. - - 22. The Disinfection of Sewage. U. S. Geological Survey, Water Supply - Paper, No. 229. - - 23. Sewage Disinfection in Actual Practice, by Orchard. E.R. V. 70, - 1914, p. 164. - - 24. Water and Sewage Purification in Ohio. Report of the Ohio State - Board of Health, 1908, pp. 738–762. - - 25. Water Purification, by Ellms. Published in 1917 by McGraw-Hill Book - Co. - - 26. Electrolytic Sewage Treatment, A Half Century of Invention and - Promotion. E.N.R. V. 86, 1921, p. 25. - - - - - CHAPTER XX - SLUDGE - - -=278. Methods of Disposal.=—Sludge is the deposited suspended matter -which accumulates as the result of the sedimentation of sewage. The -methods for the disposal of sludge as discussed herein will include the -disposal of scum. Scum is a floating mass of sewage solids buoyed up in -part by entrained gas or grease, forming a greasy mat which remains on -the surface of the sewage.[201] The sludges formed by different methods -of sewage treatment are described in the chapter devoted to the -particular method. The disposal of sludge is a problem common to all -methods of sewage treatment involving the use of sedimentation tanks. - -Sludge is disposed of by: dilution, burial, lagooning, burning, filling -land, and as a fertilizer or fertilizer base. Certain methods of -disposal, such as burning or as a fertilizer, demand that the sludge be -dried preparatory to disposal. Sludge is dried on drying beds, in a -centrifuge, in a press, in a hot-air dryer, or by acid precipitation. - - -=279. Lagooning.=—This is a method of sludge disposal in which fresh -sludge is run on to previously prepared beds to a depth of 12 to 18 -inches or more, and allowed to stand without further attention. The -preparation of the lagoons requires leveling the ground, building of -embankments, and, if the ground is not porous, the placing of -underdrains laid in sand or gravel. At Reading, Pa.,[202] approximately -one acre was required for 1,700 cubic yards of wet sludge. The results -of lagooning at Philadelphia are given in Table 103.[202] - - TABLE 103 - - RESULTS OF DRYING SLUDGE IN LAGOONS AT PHILADELPHIA - - (“Sewage Sludge” by Allen) - ─────────────────────┬─────────┬─────────┬─────────┬─────────┬───────── - Treatment │ Days │ Depth, │Per Cent,│Rainfall,│ Cubic - │ │ Inches │Moisture │ Inches │Yards per - │ │ │ │ │ Acre - ─────────────────────┼─────────┼─────────┼─────────┼─────────┼───────── - Screened │ 0│ 12.20│ 82.8│ 0│ 1600 - Screened │ 26│ 7.67│ 57.0│ 0│ 1000 - Screened │ 49│ 3.50│ 51.6│ 0.43│ 470 - Screened │ 0│ 13.50│ 90.1│ 0│ 1800 - Screened │ 62│ 7.00│ 61.0│ 3.14│ 950 - Crude │ 0│ 12.00│ 88.7│ 0│ 1600 - Crude │ 59│ 4.70│ 62.8│ 2.59│ 640 - ─────────────────────┴─────────┴─────────┴─────────┴─────────┴───────── - -During the period of standing in the lagoon the moisture drains out and -evaporates and the organic matter putrefies, giving off gases and foul -odors. In the course of three to six months, biological action ceases -and the sludge has become humified and reduced to about 75 per cent -moisture. In the utilization of this method of disposal the lagoons must -be removed from settled districts and should occupy land of little value -for other purposes. The odors created at the lagoons may be intense and -offensive. The land so used is rendered unfit for other purposes for -many years. - -The digestion of sludge in special tanks is a form of lagooning in which -an attempt is made to maintain septic action as a result of which a -portion of the sludge is gasified or liquefied, leaving less to be cared -for by some of the other methods of treatment or disposal. The results -obtained by digestion tanks have not been entirely satisfactory. A -partial drying and consolidation of the sludge may be effected, however, -by the process of decantation, in which the supernatant liquid is run -off, followed by further sedimentation, rendering the final product more -compact. - - -=280. Dilution.=—In the disposal of sludge by dilution, as in the -disposal of sewage by dilution, there must be sufficient oxygen -available in the diluting water to prevent putrefaction, and a swift -current to prevent sedimentation. Such conditions exist in localities -along the sea coast, and in communities situated near rivers, when the -rivers are in flood. In some seacoast towns, for example at London and -Glasgow, the sludge is taken out to sea in boats, and dumped. Since it -is not necessary to discharge sludge continuously, it can be stored to -advantage in the digestion chamber of a tank, until the conditions in -the body of diluting water are suitable to receive it. - -The amount of diluting water to receive sewage sludge has not been -sufficiently well determined to draw reliable general conclusions. A -dilution of 1,500 to 2,000 volumes may be considered sufficiently safe -to avoid a nuisance provided there is a sufficient velocity to prevent -sedimentation. Johnson’s Report on Sewage Purification at Columbus, Ohio -(1905), states that a dilution of 1 to 800 is sufficient to avoid a -nuisance. The character of the sludge has a marked effect on the proper -ratio of dilution, the sludge from septic and sedimentation tanks -requiring a greater dilution than that from Imhoff tanks. - - -=281. Burial.=—Sludge can be disposed of by burial in trenches about 24 -inches deep with at least 12 inches of earth cover, without causing a -nuisance. The ground used for this purpose should be well drained. This -method of disposal is generally used as a makeshift and has not been -practiced extensively because of the large amount of land required. -Insufficient information is available to generalize on the amount of -land required or the time before the land can be used for further sludge -burial, or for other purposes. Indications are that the sludge may -remain moist and malodorous for years and that the land may be rendered -permanently unfit for further sludge burial. Under some conditions the -land may be used again for the same or other purposes. For example, -Kinnicutt, Winslow and Pratt[203] state that 500 tons of wet sludge can -be applied per acre and: - - The same land, it is claimed, can be used again after a period of - a year and a half to two years, if in two months or so after - covering the sludge with earth, the ground is broken up, planted, - and, when the crop is removed, again plowed and allowed to remain - fallow for about a year. - - -=282. Drying.=—Before sludge can be disposed of to fill land, by -burning, or for use as a fertilizer filler it must be dried to a -suitable degree of moisture. The removal of moisture from the sludge -decreases its volume and changes its characteristics so that sludge -containing 75 per cent moisture has lost all the characteristics of a -liquid. It can be moved with a shovel or fork, and can be transported in -non-watertight containers. A reduction in moisture from 95 to 90 per -cent will cut the volume in half. - -The change in volume on the removal of moisture can be represented as: - - _V__{1} = _V_(100 − _P_)⁄(100 − _P__{1}), - - in which _P_ = the original percentage of moisture; - - _P__{1} = the final percentage of moisture; - - _V_ = the original volume; - - _V__{1} = the final volume. - -The drying of sludge on coarse sand filter beds is more particularly -suited to sludge from Imhoff tanks. This sludge does not decompose -during drying, and is sufficiently light and porous in texture to permit -of thorough draining. The sludge from plain sedimentation or chemical -precipitation tanks is high in moisture, putrescible, and when placed on -a filter bed it settles into a heavy, compact, impervious mass which -dries slowly. In order to avoid this condition the sludge is run on to -the beds as quickly as possible, to a depth of not more than 6 to 10 -inches. Lime is sometimes added to the sludge at this time as it aids -drying by assisting in the maintenance of the porosity of the sludge, -and it is advantageous in keeping down odors and insects. - -Sludge filter beds are made up of 12 to 24 inches of coarse sand, -well-screened cinders, or other gritty material, underlaid by 6 inches -of coarse gravel and 6 or 8–inch open-joint tile underdrains, laid 4 to -10 feet apart on centers, dependent on the porosity of the subsoil. The -side walls of the filters are made of planks or of low earth -embankments. The sludge filters at Hamilton, Ontario, are shown in Fig. -179. - -[Illustration: - - FIG. 179.—Sludge drying Beds at Hamilton, Ontario. - - Eng. News, Vol. 73, p. 426. -] - -The size of the bed is dependent mainly upon the characteristics of the -sludge. For Imhoff tank sludge which comes from the tank with about 85 -per cent moisture, the practice is to allow about 350[204] square feet -of filter surface per 1,000 population contributing sludge. For other -types of sludge the area varies from 900 to 9,000 square foot per 1,000 -population contributing sludge, and only experiments with the sludge in -hand can determine the proper allowance. Imhoff recommends 1,080 square -feet per 1,000 population for septic tank sludge, and 6,480 square feet -for sludge from plain sedimentation tanks.[205] Kinnicutt, Winslow, and -Pratt in their book on Sewage Disposal state: - - With an average depth of 10 inches per dose of sludge of 87 per - cent water content, one square foot of covered (glass) bed should - dry to a spadable condition one cubic yard of sludge per year. - -The sludge is run on the bed in small quantities at periods from two -weeks to a month apart. In favorable weather Imhoff sludge will dry in -two weeks or less to approximately 50 to 60 per cent moisture. It is -then suitable for use as a filling material on waste land, for burning, -or for further drying by heat. Glass roofs, similar to those used on -green-houses, have been used to speed the drying process by preventing -the moistening of partly dried sludge during rainy weather. In some -instances sludge has dried to 10 per cent moisture on such beds. Imhoff -sludge can be removed from the drying beds with a manure or hay fork. It -has an odor similar to well-fertilized garden soil. It is stable, dark -brownish-gray in color, is of light coarse material, and is granular in -texture. - -Sludge presses are suitable for removing moisture from the bulky wet -sludge obtained from plain sedimentation, chemical precipitation, and -the activated sludge process. The details of a typical sludge press are -shown in Fig. 180. The press shown is made up of a number of corrugated -metal plates about 30 inches in diameter with a hole in the center about -8 inches in diameter. The corrugations run vertically except for a -distance about 3 inches wide around the outer rim, which is smooth. To -this smooth portion is fastened, on each side of the plate, an annular -ring about an inch thick and 2 to 3 inches wide, of the same outside -diameter as the plate. A circular piece of burlap, canvas, or other -heavy cloth is fastened to this ring, covering the plate completely. A -hole is cut in the center of the cloth slightly smaller in diameter than -the center hole in the plate, and the edges of the cloth on opposite -sides of the plate are sewed together. The plates are then pressed -tightly together by means of the screw motion at the left end of the -machine, thus making a water-tight joint at the outer rim. Sludge is -then forced under pressure into the space between the plates, passing -through the machine by means of the central hole. The pressure on the -sludge may be from 50 to 100 pounds per square inch. This pressure -forces the water out of the sludge through the porous cloth from which -it escapes to the bottom of the press along the corrugations of the -separating plate. After a period of 10 to 30 minutes the pressure is -released, the cells are opened, and the moist sludge cake is removed. -The liquid pressed from the sludge is highly putrescible and should be -returned to the influent of the treatment plant. The pressing of wet -greasy sludges is facilitated by the addition of from 8 to 10 pounds of -lime per cubic yard of sludge. The cake thus formed is more cohesive and -easy to handle. The output of the press depends so much on the character -of the sludge that a definite guarantee of capacity is seldom given by -the manufacturer. - -[Illustration: - - FIG. 180.—Filter Press. -] - -The simplest form of centrifugal sludge dryer is a machine which -consists of a perforated metal bowl lined with porous cloth in which the -sludge is placed. Surrounding this bowl is a second water-tight metal -bowl so arranged as to intercept the water thrown from the sides of the -inner bowl as it revolves. The peripheral velocity of the inner bowl is -about 6,000 feet per minute, which makes the effective weight of each -particle about 250 times its normal weight when at rest. Very few data -are available on the operation of such machines, and their use has not -been extensive because of the difficulty of starting and stopping the -machine at each filling, and the difficulty of removing the partially -dried sludge from the inner basket. The Besco-ter-Meer centrifuge, -manufactured by the Barth Engineering and Sanitation Co., can be -operated continuously and the difficulties of removing the dried sludge -from the machine have been overcome. According to the manufacturers the -centrifuge has been operated very successfully in Germany on plain -septic tank sludge. A removal of 70 per cent of suspended solids in the -raw sludge and a production of 3,600 pounds of sludge per hour, -containing 60 to 70 per cent of moisture, can be obtained at less than -900 r.p.m. with a consumption of 15 horse-power. Extensive tests of the -machine were made at Milwaukee from October, 1920, to September, 1921, -on activated sludge, but results of these tests are not as yet -available. Indications are that the centrifuge has acted as a -classifier. The coarser particles of sludge have been removed but the -finer particles have been continuously returned with the liquid to the -sedimentation tank, ultimately filling this tank with fine particles of -sludge. An illustration of the unit tested at Milwaukee is shown on this -page. - -[Illustration: - - Besco-ter-Meer Sludge Drying Centrifuge at Milwaukee, Wisconsin - Courtesy, Barth Engineering and Sanitation Co. -] - -Experiments on the drying of sludge by acid flotation have not -progressed sufficiently to allow the installation of a working unit. The -method, which has been applied principally to activated sludge, consists -in adding a small amount of sulphuric acid to the sludge as it leaves -the storage tank. The sludge is coagulated by this action, the -coagulated material rising to the surface as a scum containing about 86 -per cent moisture. The consistency is such that it can be removed with a -shovel. The liquid can be withdrawn continuously from below the scum. - -[Illustration: - - FIG. 181.—Direct-Indirect Sludge Dryer. - - Courtesy, the Buckeye Dryer Co. -] - -The moisture content of sludge to be used in the manufacture of -fertilizer must be reduced to 10 per cent or less. None of the methods -of drying described so far can be relied upon for such a product and it -becomes necessary to use direct or indirect heat dryers. There are -various types of dryers on the market. The details of a Buckeye dryer -are shown in Fig. 181. In the operation of this machine moist sludge is -fed in at the left end at the point marked “feed.” The hot gases pass -from the fire box up and around the cylinder which revolves at about -eight r.p.m. The gases are drawn into the inner cylinder through the -openings marked A which revolve with the two cylinders. The gases escape -from the inner cylinder through the openings to the right and flow -towards the left in the outer cylinder. They come in contact with the -sludge at this point. The gases then pass off through the fan at the -left. The sludge is lifted by the small longitudinal baffles fastened to -the outer cylinder, as the drying cylinders revolve. The right end of -the cylinder is placed lower than the left so that the drying sludge is -lifted and dropped through the cylinder at the same time that it moves -slowly toward the right hand end of the cylinder. These dryers require -about one pound of fuel for 10 pounds of water evaporated. The odors -from the dryer can be suppressed by passing the gases through a dust -chamber and washer. - -A summary of the results from methods of sludge drying at Milwaukee[206] -follows: - - Excess sludge produced, 12,100 gallons, having 97.5 per cent - moisture, per million gallons of sewage treated. - - Sludge cake produced (by presses), 10,083 pounds having 80.3 per - cent moisture, per million gallons of sewage treated. - - Dried sludge (from heat driers) produced, 2,521 pounds having 10 - per cent moisture, per million gallons of sewage treated. - - Press will produce 3 pounds of cake per square foot of filter - cloth in four and a half hours, or five operations per twenty-four - hours. - - Dryers will reduce 6,700 pounds of sludge cake at 80 per cent - moisture to 10 per cent moisture, and will evaporate 8 pounds of - water per pound of combustible. - -Thickening devices known as Dorr thickeners, patented and manufactured -by the Dorr Co. and originally intended for metallurgical purposes, have -been adapted to the thickening of sewage sludge. These thickeners are -circular sedimentation tanks, from 8 to 12 feet deep, more or less, and -are made in any diameter up to 200 feet or more. An arm, pivoted in the -center and extending to the circumference, is provided at the bottom -with a number of baffles or squeegees set at an angle with the arm. The -arm revolves at from one to fifteen revolutions per hour, and the -squeegees, in contact with the bottom of the tank, scrape the deposited -sludge towards a central sump, from which it is removed by a pump or by -gravity, without interrupting the operation of the thickener. The sludge -so thickened may be reduced to 95 or 96 per cent moisture. These devices -are ordinarily used only in the activated sludge process in which they -have been a pronounced success. - - - - - CHAPTER XXI - AUTOMATIC DOSING DEVICES - - -=283. Types.=—Automatic dosing devices are used to apply sewage to -contact beds, trickling filters, and intermittent sand filters. These -devices can be separated into two classes; those with moving parts and -those without moving parts. The latter are better known as air-locked -dosing devices. Simple devices without moving parts are less liable to -disorders and are nearer “fool-proof” than any device depending on -moving parts for its operation. - -No one type of moving part device has been used extensively in different -sewage treatment plants. Designing engineers have exercised their -ingenuity at different plants, resulting in the production of different -types.[207] Among the best known forms is the apparatus designed by J. -W. Alvord for the intermittent sand filters at Lake Forest, -Illinois.[208] In its operation.... - - A float in the dosing chamber lifts an iron ball in one of a - series of wooden columns, and at a certain height the ball rolls - through a trough from one column to the next, in its passage - striking a catch, which opens an air valve attached to one of ten - bell-siphons in the dosing chamber. Each of the siphons discharges - on one of the ten sand beds, which are thus dosed in rotation. - -Since air-locked dosing devices are in more general use their operation -will be explained in greater detail. - - -=284. Operation.=—The simplest form of these devices is the automatic -siphon used for flush-tanks, the operation of which is described in Art. -61. - -In the operation of sand filters, sprinkling filters, or other forms of -treatment where there are two or more units to be dosed it is desirable -that the dosing of the beds be done alternately. A simple arrangement -for two siphons operating alternately is shown in Fig. 182. They operate -as follows: with the dosing tank empty at the start water will stand at -_bb′_ in siphon No. 2 and at _aa′_ in siphon No. 1. As the water enters -through the inlet on the left the tank fills. When the water rises -sufficiently, air is trapped in the bells, and as the water continues to -rise in the tank, surfaces _a_ and _b_ are depressed an equal amount. -When _b_ has been depressed to _d_, _a_ has been depressed to _c_. Air -is released from siphon No. 2 through the short leg, and siphon No. 2 -goes into operation. Surface _c_ rises in siphon No. 1 as the tank -empties and when the action of Siphon No. 2 is broken by the admission -of air when the bottom of the bell is uncovered the water in siphon No. -1 has assumed the position of _bb′_ and that in No. 2 is at _aa′_. The -conditions of the two siphons are now reversed from that at the -beginning of the operation and as the tank refills siphon No. 1 will go -into operation. It is to be noted that these siphons are made to -alternate by weakening the seal of the next one to discharge and by -strengthening the seal of the one which has just discharged. - -[Illustration: - - FIG. 182.—Diagram Showing the Operation of Two Alternating Siphons. -] - -[Illustration: - - FIG. 183.—Diagram Showing the Operation of Three Alternating Siphons. -] - - -=285. Three Alternating Siphons.=—This principle can be extended to the -operation of three alternating siphons as shown in Fig. No. 183. These -operate as follows: with the dosing tank empty at the start and water at -_aa′_ in siphons 1 and 2, and at _bb′_ in siphon No. 3, the dosing tank -will be allowed to fill. As the water rises in the tank air is trapped -in all the bells and surfaces _a_ and _b_ are depressed. When surface -_b_ has been depressed to _d_, _a_ has been depressed to _c_. Air is -released from siphon No. 3 and this siphon goes into action. Surface _c_ -rises in siphons 1 and 2 to the position _b_, as the dosing tank is -emptied. At the same time a small amount of water is passed from siphon -No. 3 to the short leg of siphon No. 1, through the small pipes shown, -thus filling this leg so that when siphon No. 3 ceases to operate the -water in siphons 1 and 3 stands at _aa′_ and that in No. 2 stands at -_bb′_. Siphon No. 2, having the weaker seal, will be the next to -operate. During its operation it will fill siphon No. 3, leaving No. 1 -weak. When No. 1 operates it will refill No. 2, leaving No. 3 weak, thus -completing a cycle for the three siphons. This principle has not been -applied to the operation of more than three alternating siphons and is -seldom used on recent installations. - -[Illustration: - - FIG. 184.—Miller Plural Alternating Siphons. - - Courtesy, Pacific Flush Tank Co. -] - - -=286. Four or More Alternating Siphons.=—An arrangement for the -alternation of four or more siphons is illustrated in Fig. 184. At the -commencement of the cycle it will be assumed that all starting wells are -filled with water except well No. 1, and that all main and all blow-off -traps are filled with water. The following description of the operation -of the siphons is taken from the catalog of the Pacific Flush Tank -Company: - - The liquid in the tank gradually rises and finally overflows into - the starting well No. 1 and the starting bell being filled with - air, pressure is developed which is transmitted, as shown by the - arrows, to the blow-off trap connected with siphon No. 2. When the - discharge line is reached, sufficient head is obtained on the - starting bell to force the seal in blow-off trap No. 2, thus - releasing the air confined in siphon No. 2 and bringing it into - full operation. - - During the time that siphon No. 2 is operating, siphonic action is - developed in the draining siphon connected with starting well No. - 2 and as soon as the level in the tank is below the top of the - well it is drained down to a point below the bottom of starting - well No. 2. It can now be seen that after the first discharge - starting well No. 2 is empty, whereas the other three are full.... - Therefore when the tank is filled the second time, pressure is - developed in starting bell No. 2, which forces the seal of - blow-off trap No. 3, thus starting siphon No. 3.... - -This alternation can be continued for any number of siphons. Other -arrangements have been devised for the automatic control of alternating -siphons, but these principles of the air-locked devices are fundamental. - - -=287. Timed Siphons.=—In the operation of a number of contact beds not -only must the dosing of the tanks be alternated, but some method is -needed by which the beds shall be automatically emptied after the proper -period of standing full. To fulfill this need the principle of the timed -siphon must be employed in conjunction with the alternating siphons. -Fig. 185 illustrates the operation of the Miller timed siphon. Its -operation is as follows: water is admitted to the contact bed and -transmitted to the main siphon chamber through the “opening into bed.” -Water flows from the main siphon chamber into the timing chamber at a -rate determined by the timing valve. The contact bed is held full during -this period. As the timing chamber fills with water air is caught in the -starting bell and the pressure is increased until the seal in the main -blow-off trap is blown and the main siphon is put into operation. As the -water level in the main siphon chamber descends, water flows from the -timing chamber into the main siphon through the draining siphon and the -timing chamber is emptied, ready to commence another cycle. - - -=288. Multiple Alternating and Timed Siphons.=[209]—The alternating and -timing of a number of beds is more complicated. The arrangement -necessary for this is shown in Fig. 186. It will be assumed at the start -that all beds are empty and that all feeds are air locked as shown in -Section _AB_ except that to bed No. 4 into which sewage is running. As -bed No. 4 fills, sewage is transmitted through the opening in the wall -into the timed siphon chamber No. 4. When the level of the water in the -bed and therefore in this chamber has reached the top of the withdraw -siphon leading to the compression dome chamber No. 4, this latter -chamber is quickly filled. The air pressure in starting bell No. 4_a_ is -transmitted to blow-off trap No. 1_a_. The seal of this trap is blown, -releasing the air lock in feed No. 1 and the flow into bed No. 1 is -commenced. At the same time the air pressure in compression dome No. 4 -is transmitted to feed No. 4, air locking this feed and stopping the -flow into bed No. 4. The alternation of the feed into the different beds -is continued in this manner. - -[Illustration: - - FIG. 185.—Miller Timed Siphon. - - Courtesy, Pacific Flush Tank Co. -] - -Bed No. 4 is now standing full and No. 1 is filling. When compression -dome chamber No. 4 was filled, water started flowing through timing -siphon valve No. 4 into timing chamber No. 4 at a rate determined by the -amount of the opening of the timing valve. As this chamber fills -compression is transmitted to blow-off trap 4_b_ and when sufficiently -great this trap is blown and timed siphon No. 4 is put into operation. -Bed No. 4 is emptied by it, and compression dome chamber No. 4 is -emptied through the withdraw siphon at the same time. This completes a -cycle for the filling and emptying of one bed and the method of passing -the dose on to another bed has been explained. The principle can be -extended to the operation of any number of beds. - -[Illustration: - - FIG. 186.—Plural Timed and Alternating Siphons for Contact Bed - Control. - - Courtesy, Pacific Flush Tank Co. -] - - - - - INDEX - - - A. B. C. process of sewage treatment, 4 - - Abandonment of contract, 225 - - Access to work, 228, 229 - - Accident, contractor’s responsibility, 221, 224 - - Acetylene, explosive, 347 - - Acid precipitation. _See_ Miles Acid Process. - of sludge, 503 - - Acids as disinfectants, 489, 490 - - Activated sludge. Chapter XVIII, 465–479 - advantages and disadvantages, 469, 470 - aëration tank, 471, 472 - air diffusion, 475, 477 - air distribution, 473–478 - air quantity, 475, 476 - area of filtros plates, 478 - colloid removal, 358 - composition, 465–469 - cost, 478, 479 - definition, 466 - dewatering, 468, 469, 497–505 - fertilizing value, 469, 470 - historical, 470, 471 - how obtained, 478 - nitrogen content, 468 - patent, 471 - process, 465 - quantity, 469 - reaëration tank, 473 - results, 467, 468, 476 - sedimentation tank, 472 - - Advertisement, 214 - - Aëration, effect on oxygen dissolved, 373–375 - of sewage, 371, 376, 465–479 - - Aërobes, 363 - - Aërobic decomposition, 366, 367 - - Aftergrowths, 492 - - Aggregates, specifications, 172–174 - - Air, see also ventilation, activated sludge, compressed air, etc. - ejectors, 150 - lock dosing apparatus. Chap. XXI, 506–512 - machinery for activated sludge, 473, 474 - - Algæ, 363 - - Alkalinity, 358 - - Alleys, sewers in, 80 - - Alum, 407, 408 - - Alvord tank, 427, 429 - - Ammonia, 366, 367, 374, 375, 410 - explosives, 297 - - Analyses, bacteriological, 364 - chemical, 354, 355 - mechanical of sand, 182 - physical, 352–354 - sewage, 352–364 - - Anaërobes, 363, 365–367 - - Anaërobic, action, 410 - bacteria, 363 - conditions, 367 - decomposition, 365–367 - - Ann Arbor, Michigan, Population, 14 - - Annual expense, method of financing, 157, 158 - - Ansonia air ejector, 150, 151 - - Antibiosis, definition, 363 - - Appurtenances to sewers. Chap. VI, 99–115 - - Arch, analyses, 204–208 - elastic method, 206–208 - vouissoir analysis, 204–206 - brick construction, 312, 313 - centers for brick sewers, 313 - concrete construction, 318–321 - - Ardern and Lockett, development of activated sludge, 467, 468, 471 - - Area of cities, 31 - - Asphyxiation in sewer gas, 336 - - Assessments, special, 15, 16 - - Augers, earth, 21 - - Automatic, regulators, 117–121 - siphons, flush-tanks, 110 - double alternating, 507 - multiple alternating, 508–512 - timed, 510 - timed and multiple alternating, 510–512 - triple alternating, 508 - - - Bacillus, definition and morphology, 362, 363 - - Backfilling, 328–331 - - Backfill, puddling, 330 - weight of, 199, 201 - - Backwater curve, 73 - - Bacteria, definition and morphology, 362, 363 - good and bad, 363, 364 - nature of, 362, 363 - nitrifying, 431, 432 - sanitary significance of, 364 - in sewage, 362, 363 - total count, 364 - - Bacterial analyses, results in sewage, 364 - - Baffles, scum, 404, 413, 414, 421 - in sedimentation tanks, 404 - in septic tanks, 413, 414 - in Imhoff tanks, 421 - - Balls, for cleaning sewers, 338 - - Band screen, 384 - - Barring, definition, 263 - - Bars for screens, 390 - - Basins, sedimentation, baffling, 404 - bottoms, 404 - cleaning arrangements, 404 - depth, 401 - economical dimensions, 401–403 - inlets and outlets, 404 - scum boards, 404 - types, 395 - - Basket handle sewer section, 67, 69 - - Bathing beaches, pollution, 381 - - Bazin’s formula, 54 - - Bearings, for centrifugal pumps, 131, 137, 138 - thrust, 138 - - Bellmouth, 121, 122 - - Bends in pipe, loss of head in, 116 - - Berlin, sewage farm, 460, 461 - sewers, date of, 3 - - Bids, proposal, 217–219 - - Bidder’s duties, 215–217 - - Bio-chemical oxygen demand, 359–361 - - Biolysis of sewage, 366, 367 - - Black and Phelps dilution formulas, 377–379 - - Blasting and explosives, 294–304 - caps, 297, 299, 300 - detonators, 294, 297–300 - firing, 302–304 - fuses and detonators, 297–300 - fuses, delayed action, 291, 300 - fuses, electric, 299, 300 - splicing, 303 - gelatine, 296 - loading holes, 303 - powder, 295 - precautions, 300–302 - priming and loading, 303 - rock, 269 - size of charge, 304, 305 - tunneling, 290, 291 - - Bleach, characteristics of for disinfection, 491 - - Block sewer, construction, 311–314 - hollow tile as underdrains, 126 - - Blocks, vitrified clay, 189, 190 - - Boilers, steam, 147–150 - - Boilers, efficiencies, 149 - horse-power, 149 - - Bond, contractor’s, 213, 214, 232 - issues, 14 - - Bonds, definition and types, 14–16 - - Boring underground, 20 - - Bottom, activated sludge aëration tank, 472 - Imhoff tanks, 423 - sedimentation tanks, 404 - trickling filter, 451, 452 - - Box sheeting, 272 - - Branch sewer, defined, 7 - - Breast boards, 288 - - Brick, arch construction, 312, 313 - and block sewer construction, 311–315 - invert construction, 311, 312 - sewer construction, 311–315 - arch centers, 313 - invert, 311–312 - organization, 314, 315 - progress, 314 - row lock bond, 312 - specifications, 188, 189 - sewers, life of, 351 - - Bricks for sewers, 316 - - British Royal Commission on Sewage Disposal, 4 - - Broad irrigation. _See_ under Irrigation. - - Bucket excavators, 246, 255, 256 - - Building material, weight of, 201 - - Burkli-Ziegler formula, 47, 425 - - Butyrine, 366 - - - Cableway excavators, 246, 250–252 - - Cage screen, 384, 385 - - Caisson excavation, 285, 286 - - Calcium carbide, explosive, 347 - - Calumet pumping station, 128, 142 - - Cameron septic patent, 411 - - Capacity of sewers, diagrams, 57–60 - - Capital, private invested in sewers, 17 - - Capitalization, method of financing, 157–160 - - Caps, blasting. _See_ blasting. - - Carbohydrate, 366, 367 - - Carbon, analysis for, 356 - dioxide, 366, 367 - - Carson Trench machine, 250, 251 - - Cast-iron pipe, 122, 164, 190, 191 - joints, 164 - quality, 101, 102, 190 - - Castings, iron, 101, 102 - - Catch-basins, 99, 107–108, 217 - cleaning, 343, 344 - inspection, 337 - - Catenary sewer section, 69 - - Cellars, depth of, 88 - - Cellulose, 367 - - Cement. _See also_ Concrete, - pipe, specifications, manufacture and sizes, 171–179 - vs. concrete, 164 - - Centrifugal pumps. _See_ pumps, centrifugal. - - Centrifuge for sludge drying, 501, 502 - - Cesspool, 411, 416, 417 - - Champaign, Illinois, septic tank, 415, 416 - - Changes in plan, 222, 223 - - Channeling, definition, 263 - - Character of surface, 44 - - Chemical analyses, 354–362 - - Chemical precipitation, 371, 405–409 - chemicals used, 405–407 - preparation of chemicals, 407, 408 - results, 408, 409 - at Worcester, 408 - - Chezy formula, 52, 53 - - Chicago. _See also_ Sanitary District of Chicago. - drainage canal, 374, 375 - dilution requirement for sewage, 380 - early sewers, 3 - method of sewage disposal, 374 - population and density, 29, 30 - trench excavation in, 248 - - Chlorine. _See also_ Disinfection. - disinfectant, 489–493 - in sewage, 358, 374, 375 - - Chlorine liquid, application, 491, 492 - - Cholera, transmittable disease, 364 - - Chromatin, 365 - - Chutes for concrete, 187 - - Circular sewer section, hydraulic elements, 65, 66, 69 - types, 70, 71 - - City, growth of area, 31 - growth of population, 24–28 - legal powers, 219 - - Clay, life of pipe, 349–351 - manufacture of pipe, 165–167 - specifications for pipe, 168–170 - unglazed for pipe, 165 - vitrified blocks, 167, 189, 190 - vitrified pipe, 165–171 - - Cleaning, grit chambers, 398, 400 - sedimentation basins, 404 - sewers, cost, 341 - in N. Y. City, 332 - methods, 337–343 - tools, 338–340 - up after completion of work, 228 - - Coccus, 362 - - Coefficient of uniformity of sand, 456 - - Coffin sewer regulator, 117, 118 - - Colloid, nature of, 358 - treatment for, 358 - - Color of sewage, 352, 353 - - Combined sewer system, 78, 79 - - Commercial districts, characteristics of and sewage from, 32, 34, 35 - - Compensators for pumps, 142 - - Compressed air. _See also_ ventilation, tunneling, drilling, etc. - activated sludge, 473–475 - for drilling, 264–268 - in tunnels, 292–294 - transporting concrete, 320, 321 - - Concentration, time of flood flow, 41–43, 96, 97 - - Concrete, aggregates, 172–174 - mixing and placing, 184–188 - pipe, details, 175–179 - manufacture, 171–179 - reinforcement, 177, 178, 209, 210 - pipe, steam process, 176 - sizes, 175 - pressure against forms, 232, 323 - - Concrete, proportioning, 179–183 - qualities, 179, 180 - reinforcement, placing, 178, 326, 327 - reinforcing steel, quality, 191 - sewer construction, 314–328 - arch, 318–321 - form length, 319 - labor costs, 327, 328 - in open cut, 314–320 - in tunnel, 320, 321 - invert, 315–320 - organization for, 328 - working joints, 319 - sewer costs, 327–329 - strength, 181 - waterproofing, 184 - - Conduits, special sections, 67, 70, 71 - - Connections to sewers, ordinances, 344, 345 - record of 92, 238 - - Construction of sewers, Chap. XI, 233–331 - - Construction, elements of, 233 - organizations, 315, 328 - - Contact bed, 432–437, 506 - advantages and disadvantages, 432–434 - automatic control, 437, 506 - cleaning, 435 - clogging, 435 - construction, 434–436 - control, 437, 506 - cycle, 436, 437 - depth, 434 - description, 432, 433 - design, 434–436 - dimensions, 434, 435 - loss of capacity, 435 - material, 435, 436 - multiple, 433, 435 - operating conditions, 432–437 - rate, 435 - results, 433, 434 - ripening, 432 - - Continuous bucket excavators, 246–250 - - Contour interval on maps, 79, 80 - - Contracts, Chap. X, 211–232 - abandonment of, 225 - assignment, 228 - completion of, 222, 228 - bond, 213, 222 - content, 213, 230, 231 - cost-plus, 212, 213 - disputes, 220 - divisions of, 213 - drawings, 213 - engineer as an arbitrator, 220 - the instrument, 230, 231 - interpretation of, 220, 234, 235 - lump sum, 212 - nature of, 211, 212 - sample, 230, 231 - time allowed, 222 - types, 212, 213 - unit-price, 213 - - Contractor, absence of, 222 - bond, 232 - claims against, 228 - duties, 221 - liability, 224 - relations with other contractors, 228, 229 - - Contractor’s powder, 294 - - Control devices, automatic, for sewers, 117–121 - for filters, 500–512 - inspection of, 336, 337 - - Copper sulphate, disinfectant, 490 - - Copperas, precipitant, 406–408 - - Cordeau Bickford, 298, 303 - - Corrugated iron pipe, 165 - - Cost. _See_ under item wanted. - - Cost, annual. Method of financing, 157–160 - capitalized. Method of financing, 157–160 - classification of, 235–238 - comparisons of. Methods for - making, 157–160 - collection of data, 10–14, 235–238 - estimate. Method of making, 10–14 - overhead, 237, 238 - - Couplings, flexible for shafts, 138 - - Covers, Imhoff tanks, 424 - septic tanks, 415 - trickling filters, 451 - - Crops on sewage farms, 463, 464 - - Cunette, 67, 70 - - Cut, depth of excavation, 88, 92 - - Cycle, contact bed, 436 - life and death, 367, 431 - nitrogen, 367, 368 - trickling filter, 441 - - Cylinders, stresses in, 194, 202–204 - - Cytoplasm, 365 - - - Damages, liquidated, 222 - material, 221, 224 - - Darcy’s formula, 52 - - Day labor, 211 - - Decomposition of sewage, 365–367 - - Definitions. _See_ word defined. - - Deflagration, definition, 294 - - Delays in contract work, 228 - - Delayed action fuses, 291, 300 - - Densities. _See_ population. - - Depreciation, of sewers, 348–351 - rate of, financial, 158 - - Depth of sewers, 88 - - Design conditions, 88–92 - economical, mathematics of, 401–403 - preparations for, 17–23 - - Detention period, grit chamber, 397 - Imhoff tank, 419 - plain sedimentation, 392–395, 401 - septic tank, 415 - - Detonation, definition, 294 - - Detonator. _See_ blasting cap. - - Diameter of sewers, 57–60, 72, 88–92 - - Diaphragm pump, 257, 258 - - Diesel engine, 152, 154 - - Digestion chamber, Imhoff tank, 422, 423 - - Digestion of sludge in separate tank, 427–430, 497 - - Dilution, amount needed, 377–380 - conditions for success, 372, 373 - - Dilution, definition, 372 - formulas for quantity, 378–380 - governmental control, 380, 381 - preliminary studies, 381, 382 - in salt water, 376, 377 - in streams, 372–376 - of sewage, 370 and Chap. XIV, 372–382 - - Diseases, water-borne, 364 - - Disinfection, 489–493 - action of, 489–491 - bleaching powder, 491 - chlorine, liquid, 491 - amount of, 492 - disinfectants, 489, 490 - purpose, 489 - selective action of disinfectants, 492, 493 - - Disk screen, 384 - - Disposal of sewage, _See_ sewage treatment. - - Disputes, engineer to settle, 220 - - Dissolved oxygen. _See_ Oxygen dissolved. - - Distribution of sewage, - contact beds, 436 - irrigation, 461, 462 - nozzles, 442–449 - sand filter, 450–458 - traveling distributor, 442 - trickling filters, 441–451 - - Districts, character of, 29, 30, 32–37 - classification of, 34, 35 - - Domestic sewage, defined, 6, 7, 352 - - Dorr Thickeners, 472, 504 - - Dortmund tank, 404 - - Dosing devices, 506–512 - alternating and timed siphons, 500–512 - Alvord device at Lake Forest, 506 - four or more alternating siphons, 509 - operation of automatic siphon, 110 - three alternating siphons, 508 - timed siphons, 510 - two alternating siphons, 507 - types, 506 - - Dosing tank design, for trickling - filter, 446–450 - - Doten tank, 429, 430 - - Drag line excavators, 255, 256 - - Drainage areas, 81, 84, 94 - - Drills, electric, 267 - jack hammer, 264, 265 - punch, 20 - size of cylinder for, 266 - tripod, 264, 265 - - Drilling, methods, 20–23, 264–270 - depth, diameter and spacing of - holes, 268–270 - power for, 267, 268 - rate of, in rock, 267 - steam and air, 267, 268 - - Drop manhole, 100, 101 - - Drop-down curve, 73, 77 - - Drum screen, 384 - - Dry weather flow, 24, 38 - - Drying sludge. _See_ sludge drying. - - Dualin, 296 - - Duty of contractor. _See_ Contractor, duties - - Duty of engineer. _See_ Engineer, duties. - - Duty of inspector. _See_ Inspector, duties. - - Duty of a pump, defined, 135 - - Dynamite, 296–298, 300–302, 304, 305 - cartridge, 268, 296, 302 - thawing, 301, 302 - - Dysentery, 365 - - - Earth pressures, theories, 274, 275 - - Economical dimensions, mathematics of, 401–403 - - Effective size of sand, defined, 456 - - Efficiency of a pump, defined, 135 - - Effluents, character of - activated sludge, 467, 468 - chemical precipitation, 408 - contact bed, 434 - Imhoff tank, 414, 424, 425, 432 - lime and electricity, 489 - Miles acid process, 484, 485 - sand filter, 453 - - Effluents, sedimentation tank, 401 - septic tank, 412–414 - - Egg-shaped section, 67, 68, 70 - - Ejectors, air, 150, 151 - - Elastic arch analysis, 206–208 - - Electric motors, 150–152 - - Electrolytic treatment, 487–489 - - Elevations, method of recording, 92 - - Emergencies, duties of engineer, 235 - - Emerson pump, 261 - - Engines, internal combustion, 152–154 - steam, types, 142–144. - - Engineer, absence of, 221 - defined, 220 - disputes settled by, 220, 234 - duties of, 9, 10, 220, 233, 234, 238 - individuality and personality, 9, 234 - qualifications, 9 - sanitary, definition, 2 - - Engineering News pile formula, 125, 126 - - Entering sewers, precautions, 335, 336 - - Enzymes, 365 - - Equipment for construction, 237 - - Equivalent sections, defined, 72 - solution of problems in, 67–72 - - Estimates, cost and work done, 10–14 - when made, 226 - data for, 235 - - Excavation, depth of open cut, 284 - drainage, 252, 262 - hand, 242–245, 249 - economy, 245 - laborer’s ability, 243 - lay out of tasks, 243 - - Excavation, hand, opening trench, 243 - vs. machine, 245, 249 - tools, 242 - machine, 244–246 - economy, 245 - limitations, 246 - vs. hand, 245, 249 - specifications, 240, 241 - - Excavating machines, bucket, 246, 255 - cableway and trestle, 246, 250–252 - Carson machine, 250, 251 - continuous belt, 246 - bucket, 246, 247 - drag line, 255 - Potter machine, 251 - steam shovel, 252–254 - tower cableway, 252 - wheel excavators, 246–250 - - Excavation, machine, organization, 249 - pumping and drainage, 256, 257 - quicksand, 256 - rock, 263, 264 - payment for, 230 - specifications, 240, 241 - trench bottom, 241, 304, 311 - - Explosions in sewers, 108, 336, 346–348 - causes of, 346 - historical, 346 - prevention, 108, 348 - - Explosives. _See also_ Blasting. - - Explosives, and blasting, 294–304 - ammonia compounds, 297 - blasting gelatine, 296 - contractor’s powder, 294 - deflagrating, 294 - detonating, 294 - detonators, 294, 297–300 - “Don’ts,” 300, 301 - dynamite, 296–298, 300–302, 304, 305 - fuses and detonators, 297–300 - gelatine dynamite, 296 - gunpowder, 295 - handling, 300–302 - nitro-glycerine, 295 - nitro-substitution compounds, 295 - permissible, 297 - quantity, 304, 305 - requirements, 294 - strength of, 297, 298 - T.N.T., 295 - types, 294–297 - - Exponential formulas for flow of water, 54, 55 - - Extra work, compensation, 227 - - - Facultative bacteria, 363 - - Fanning’s run-off formula, 49 - - Farms, septic tanks for, 416, 417 - - Farming with sewage. _See_ irrigation. - - Fats in sewage, 357–359, 366, 367 - from Miles acid process, 485–487 - - Feathers, for splitting rock, 264 - - Ferrous sulphate, precipitant, 406–408 - - Fertilizer from sludge, 470, 495, 497 - - Fertilizing value of, activated sludge, 470 - sewage, 459, 460 - - Filter press for sludge, 500, 501 - - Filters. _See_ under name of filter. - - Filtration, of sewage, 370, 371, 431–459 - action in, theory of, 431 - cost, 458, 459 - - Filtros plates, 477, 478 - - Finances, mathematics of, 157–160 - - Financing, methods of, 14–17 - - Flamant’s formula, 54, 56 - - Flies on trickling filters, 438 - - Flight sewer, 101, 102 - - Flood, crest velocities, 42, 43 - flow computations, 94–98 - McMath formula, 94, 96, 97 - Rational method, 95–98 - - Flow, laws of, 52 - velocity of, 52, 90, 91 - - Fluctuations, in rate of sewage flow, 33–38 - in quality of sewage, 368–370 - - Flush-tanks, automatic, 109–113 - capacity, 111 - details, 110, 112 - inspection of, 336, 337 - payment for, 217 - siphon sizes, 111 - - Flushing, 109–113, 341–343 - amount of water needed, 112 - methods, 341–343 - manhole, 109 - sewer, defined, 8 - - Foaming of Imhoff tanks, 425, 426 - - Foot valves, 141 - - Force main, defined, 8 - - Forms, design of, 322, 323 - length of, 319 - materials, 321, 322 - oiling, 174, 186, 322 - specifications, 322 - steel, 325, 326 - steel-lined, 325 - support for, 316, 318 - time in place, 319 - wooden, 323, 324 - - Formulas, hydraulic, methods for solution, 55–61 - for flow of water, 52–55 - for rainfall. _See_ Rainfall, - for run-off. _See_ Run-off. - - Foundations, 99, 124–126 - - Franchises for sewers, 17 - - Free ammonia, 366, 367, 374, 375, 410 - - Freezing, catch-basins, 108 - concrete, 186, 187 - dynamite, 301, 302 - - Fresh sewage, characteristics, 352–354 - - Friction losses. _See_ Head losses. - flow in pipe, 51, 52 - - Fuel, consumption by prime movers, 153 - costs, 153 - heat value, 150 - - Fungus growth in sewers, 333 - - Fuses. _See_ blasting fuses. - - - Ganguillet and Kutter’s formula, 52–65 - - Gas, chamber in Imhoff tank. _See_ Scum chamber. - engines, 152–154 - illuminating, explosive, 347 - sewer, 335, 336 - - Gasoline, explosive, 108, 109, 335, 346, 347 - engines, 152–154 - and oil separator, 109 - odors, significance, 335, 353 - - Gearing, reduction for turbines, 140, 146 - - Gelatine dynamite, 296 - - Glycerol, 366 - - Gothic section, 67 - - Governmental control, stream pollution, 380, 381 - - Grade, of sewers. _See also_ Slope. - how given, 281–284 - selection of, 90 - stakes, 221, 281–283 - - Gravel, specifications, 172 - - Grease, in sewers, 99, 108, 333, 345 - cutter, 340 - ordinance concerning, 345 - traps, 99, 108 - - Gregory’s imperviousness formulas, 44, 46 - - Grit, clogs sewers, 333 - chambers, 127, 397–401 - description, 395, 398 - design, 397, 398 - dimensions, 397, 398 - existing, 398–400 - outlet arrangements, 400 - results, 397 - retention period, 397 - sludge analyses, 397 - units, number of, 400, 401 - velocity of flow in, 396–398 - quantity and character of, 397 - - Grooves in concrete, working joints, 319 - - Ground water in sewers, 38, 39, 85, 87, 256, 352 - - Gun cotton, 296 - - Gunpowder, 295 - - - Hazen, theory of sedimentation, 392–395 - dilution formula, 380 - - Hazen and William’s formula, 55, 57 - - Head loss, in bends, 116 - entrance, 115 - friction in straight pipe, 51, 52, 115 - - Hercules powder, 296 - - Hering, Rudolph, dilution recommendations, 380 - - Hering, Rudolph, introduction of Imhoff tank and hydraulic formulas, - 425 - - Historical résumé of sewerage and sewage treatment, 2–5 - - Hitch, tunnel frame, 286, 287 - - Holes, drill. _See_ Drill holes. - - Holidays, work on, 221 - - Hook for lifting pipe, 304, 306 - - Horse-power, boiler, 149, 150 - of pumps, 144–146 - - Horseshoe sewer section, 71 - - House, connections, record of, 92, 234 - drains, 7, 88, 90 - sewer, defined, 7 - - Hydraulic, elements, 65, 69 - formulas, 52–55 - jump, 73–74 - principles, 51, 52, 72, 73 - value of settling particles, 393 - - Hydraulics of, sewers, Chap. IV, 51–77 - circular pipes partly full, 65, 66 - equivalent sections, 72 - non-uniform flow, 72–77 - sections other than circular, 67–72 - use of diagrams, 61–65 - - Hydrocarbon, 367 - - Hydrogen sulphide, 353, 366, 410 - - Hydrolytic tank, 427, 428 - - “Hypo” as a disinfectant, 491 - - Hytor Turbo blower, 473, 474 - - - Illinois River, self-purification, 374–376 - - Imhoff tank, and chlorination, costs, 487 - cover, 424 - description, 417–419 - design, 419–424 - digestion chamber, 422 - inlet and outlet, 421 - operation, 426–427 - patent, 418 - results, 414, 424, 425, 439, 467 - sedimentation chamber, 419–422 - scum chamber, 424 - slot, 422 - sludge, 414, 467 - sludge pipe, 423, 424 - status, 425, 426 - and trickling filter, cost, 479 - - Impeller, for centrifugal pump, 131, 136 - - Imperviousness, relative, 40, 42, 44–46, 95–97 - - Industrial, districts, 32–37 - wastes, defined, 7, 352 - tannery, 491 - - Information and instructions for bidders, 213, 215–217 - - Inlets, street, 93, 94, 99, 104–107 - - Inspection, contract stipulations, 221–224 - during construction, 233, 234 - for maintenance, 104, 333–337, 348, 349 - - Inspector, absence of, 221, 222 - duties, 233–234 - qualifications, 234 - - Institutional sewage treatment plants, 416, 417 - - Intercepting sewer, defined, 7 - - Intermittentsand filter. _See_ Sand filter. - - Internal combustion engines, 152–154 - - Inverted siphon, 113–116 - - Iron, ferrous sulphate, precipitant, 406–408 - cast. _See_ cast iron. - - Irrigation. _See also_ Farming and Sewage farming. - area required, 463 - Berlin sewage farm, 460, 461 - crops, 463, 464 - description, 459 - fertilizing value of sewage, 460, 470, 495, 498 - vs. farming, 459 - operation, 461–463 - preliminary treatment, 462, 463 - preparation for, 461–463 - process, 459, 460 - sanitary aspects 463 - status, 460, 461 - theory, 432 - in the United States, 461 - - - Jack hammer drill, 264, 265 - - Jetting method, 21–23 - - Jet pump, 259, 341, 343 - - Joints, bituminous, 309–311 - in cast-iron pipe, 164 - cement, 307, 308 - inspection of, 234 - lead, 164 - mortar, 307 - open, 307 - poured, 309–311 - cement, 309, 311 - riveted steel, 195, 196 - sulphur and sand, 309 - types, for pipe, 307 - working, in concrete, 319 - - Junctions, 99 - - - Kuichling, run-off rules, 46, 47, 49 - storm intensity formulas, 50 - - Kutter’s formula, 52–65 - - - Labor, day vs. contract, 211 - costs on concrete sewer, 328, 329 - - Labyrinth packing rings, 136, 137 - - Lagging, tunnel frames, 287 - for forms, 322 - - Lagooning sludge, 495–497 - - Laitance, 186, 188 - - Lakes, self-purification of, 376 - - Lampé’s formula, 54 - - Lampholes, 99, 104 - - Lateral sewer, defined, 7 - - Lawrence Experiment Station, 4 - - Leaping weir, 118–121, 337 - - Legal requirements, construction, 224 - dilution, 380, 381 - in design, 9 - - Liernur system, 5 - - Life, organic in sewage, 363, 364 - of sewers, 348–351 - - Lime as a precipitant, 405–408 - with electricity, 488, 489 - with iron, 406, 407 - - Line and grade, 281–284 - how given, 281–283 - - Liquefaction of sludge, 411–413, 496, 497 - - Liquid chlorine. _See also_ Chlorine, 491 - - Liquidated damages, 222 - - Loads on, pipe, 198–202 - Marston’s method, 198–202 - trench, 199–202 - - Lock bar pipe, 197 - - Lock-joint pipe, 177 - - Long loads, 201 - - - Machine excavation. _See_ Excavation. - - Macroscopic organisms, 363, 368 - - Main sewer, defined, 7 - - Maintenance of sewers, Chap. XII, 332–351 - catch-basin cleaning, 343, 344 - cleaning sewers, 337–343 - complaints, 333 - cost, 341 - entering sewers, 335, 336 - flushing, 109–113, 341–343 - hand cleaning, 341 - inspection, 333–337 - organization, 332 - protection of sewers, 344, 345 - repairs, 337 - tools, 338–341 - troubles, 333 - work involved, 332 - - Man, shoveling ability, 243 - - Manholes, 81, 99–104 - bottom, 100 - cover, 102–103 - drop, 101 - flushing, 109, 342 - location and numbering, 81 - payment methods, 217, 218 - steps, 100, 103, 104 - - Manning’s formula, 55 - - Map, preliminary, 17, 79, 80, 82, 83 - - Marsh gas, 347, 366, 367, 410, 415 - - Marston’s methods for external loads on buried pipe, 198–202 - - Materials, for sewers, Chap. VIII, 164–193 - measurement of, 236, 237 - record of, 237 - unit weights, 201, 202 - - McMath’s formula, 47, 48, 94, 95 - - Meem’s theory of earth pressure, 274, 275 - - Mercaptan, 367 - - Metabolism, 365 - - Methane, 347, 366, 367, 410, 415 - - Methylene blue, 360 - - Microscopic organisms, 363, 364, 368 - - Miles acid process, costs, 487 - amount of acid, 483 - analyses of sludge, 485 - description, 482 - results, 483–487 - sludge, 485 - - Mineral matter in sewage, 357 - - Mirror, inspecting device, 334 - - Money retained by city, 227 - - Mosquitoes in catch-basins, 108 - - Motors, electric, 150–152 - - Municipal, bond, 14, 15 - corporations, 15 - - - _n_, value of in Kutter’s formula, 53 - - New York City, density of population, 29, 31 - siphons under subway, 114 - grease and gasoline trap, 108, 109 - aëration of sewage, 377, 470 - cleaning sewers, 332 - depreciation of sewers, 348–351 - - Needle beam, 286, 287 - - Night, soil, 5 - work, 221 - - Nitrates, 355, 356 - - Nitrites, 355, 356 - - Nitrifying organisms, 431, 432 - - Nitrobacter, 431, 432 - - Nitro explosives, 295, 296 - - Nitrogen, cycle, 367, 368 - organic, 355, 356 - - Nitro-glycerine, 295 - - Nitrosomonas, 431, 432 - - Nomograph, 55, 56 - - Non-uniform flow, 72–77 - - Nozzles. _See also_ Trickling filters. - coefficients of discharge, 446 - types, 445 - - Numbering, drainage areas, 81, 94 - manholes, 81 - - Nye steam pump, 260, 263 - - - Obstructions to construction, 235 - - Odor of sewage, 353 - - Oil in sewage, 108, 344–348 - - Oiling forms, 174, 186, 322 - - Olein, 366 - - Ordinances, for protection of sewers, 344, 345 - - Organisms in sewage, 363, 364, 368 - - Organic matter, composition, 366 - - Organizations for construction, 315, 317, 328 - - Orders, to whom given, 222 - - Outfall sewer, defined, 8 - - Outlets, 99, 122–124, 373 - - Overflow weir, 118–121 - inspection of, 337 - - Overhead, costs, division of, 10, 237, 238 - -track excavators, 246, 250, 251 - - Oxidation in streams, 373–376 - - Oxygen, absorption of, 374–377 - consumed, 355, 356 - demand, 359–361 - computation of, 360 - bio-chemical, 359–361 - - Oxygen dissolved - exhaustion of, 366 - in dilution, 381 - solubility, 362 - supersaturation, 361 - concentration for successful dilution, 377–380 - formulas for concentration, 378–380 - significance of in sewage, 359–362 - - Oysters, contamination of, 372, 489 - - - Packing rings, labyrinth type, 136, 137 - - Palmatin, 366 - - Parasites, 365 - - Paris sewage farm, 460 - - Patents. Protection of City by contractor, 224, 225 - - Pathogenic bacteria, 364 - - Pavement, replacing, 329 - - Payment, final on contract, 228 - - Payments, methods of making, 217, 218 - - Periscope inspecting device, 334, 335 - - Permissible explosives, 297 - - Phenolphthalein indicator, 408 - - Photographic records, 238 - - Piles for foundations, 123–126 - - Pills for cleaning sewers, 338 - - Pipe, bedding, 230, 304, 328 - cast-iron. _See_ under cast-iron pipe. - design of ring, Chap. IX, 194–210 - external loads on, 198–202 - joints. _See_ Joints. - sewer construction, 304–311 - laying, line and grade, 282–284 - organization, 311 - method of laying, 304, 306, 307 - steel, design, 195–197 - stresses in, external forces, 194, 202–204 - stresses due to internal pressure, 194 - stresses in buried pipe, 198–204 - stresses in circular ring, 202–204 - wood design, 197, 198 - - Plankton, defined, 363 - in sewage, 368 - - Plans, changes in contract, 222, 223 - - Plug and feathers for splitting rock, 264 - - Pneumatic, collection system, 5 - concreting, 320, 321 - - Poling boards, in open cut, 271, 272 - in tunnel, 287 - - Pollution, legal features, 380, 381 - - Population, density, 28–31 - predictions, 24–27 - served by sewers in the U. S., 3 - sources of information, 27, 28 - and quantity of sewage, 31, 32 - - Potter trench machine, 251 - - Powder. _See_ Blasting. - - Power pump, 132, 133 - - Precautions in entering sewers, 335, 336 - - Precipitants, chemical, 405–407 - - Preliminary, map, 17, 79, 80, 82, 83 - work, 9, 17–23 - - Present worth, 158, 160 - - Pressing sludge, 500, 501 - - Priming explosives, 302–304 - - Private, capital, 17 - sewers, 17 - - Privy, 5 - - Profile, for brick sewers, 312 - sewer, 92 - surface, 88 - - Progress, rate of, 222 - reports, 238 - - Promotion (inception of sewers), 9 - - Proportioning concrete. _See_ Concrete proportioning. - - Proposal (contract), 213, 217–219 - - Protection of sewers (ordinances), 344, 345 - - Protein, 366 - - Puddling, backfill, 330 - - Pulsometer pump, 260, 261 - - Pumping, in excavations, 256–263 - selection of machinery, 154–156 - equipment, cost comparison, 162 - station, 128, 142 - costs, 156–163 - equipment, 127, 128 - - Pumps, air ejector, 150, 151 - capacity, 129, 160–163 - capacity of units, 160–163 - centrifugal, details, 130, 131, 136–138 - automatic control, 141, 142 - characteristics, 138–140 - efficiency, 140 - for excavation, 262 - motors for driving, 150–152 - performance, 138–140 - protection of, by screens, 386 - selection of, 154–156 - setting, 140–142 - turbine, 130–132, 154 - types, 130, 131 - - Pumps, centrifugal, volute, 130–132, 154 - character of load, 129 - costs, 156, 157 - description of types, 130–134 - for construction work, 256–263 - diaphragm, 257, 258 - direct-acting, 133 - duty of, 135, 136 - efficiencies, 135, 136 - ejector, 134, 150, 151, 259, 341, 343 - jet, 259 - need for, 127 - number of units, 160–163 - packing of, 133, 134 - piston, 133 - speed, 133, 134 - plunger, 133 - power, 132, 133 - reciprocating, 130, 132–135, 154–156 - for excavation, 262 - reliability, 127 - sizes, 135 - steam, 134, 135, 142–146 - consumption, 144, 145 - vacuum, 259, 262 - improvised for trench work, 257 - turbine, 130–132, 154 - volute, 130–132, 154 - - Putrescibility, 359, 360 - - - Quantity, of sewage, 24–50, 84–87 - variations, 33–38 - storm water, 40–50, 94–98 - - Quicksand, definition, 256 - excavation in, 256 - safeguards, 235 - - Quiescent water, self-purification, 374 - - - Racks. _See_ Screens. - - Rainfall, 17, 40, 41, 50, 96, 97 - data, 17 - rate, 96, 97 - - Rangers, 270–274, 276–279 - - Rankine’s theory of earth pressure, 275 - - Rapid sand filtration of sewage, 458 - - Rational method of run-off determination, 40, 95–98 - - Reaëration tank in activated sludge, 473 - - Receiving well, capacity, 129, 130 - - Reciprocating pumps. _See_ Pumps, reciprocating. - - Records, character of, on construction, 238–240 - - Rectangular sewer section, 67–69 - - Regulators, 99, 117–121, 337 - inspection of, 337 - - Reinforced concrete sewer design, 209, 210 - - Reinforcing steel, specifications, 191 - placing, 326, 327 - - Reinsch Wurl screen, 384 - - Relative stability numbers, 359 - - Relief sewer, defined, 7 - - Repairs to sewers, 337 - - Report, engineer’s preliminary, 10 - - Reservoir, collecting capacity, 129, 130 - - Residences, septic tanks for, 416, 417 - - Residential districts, characteristics, 32–37 - - Residue on evaporation, 356, 357 - - Rideal’s dilution formula, 379 - - Ring, design. Chap. IX, 194–210 - stresses in circular, 202–204 - - River pollution, legal features, 380, 381 - - Rivers, self-purification of, 373–376 - - Riveted joints, properties, 196 - - Rock, blasting, 268, 290, 291 - definition, 263 - drill, data on, 266, 267 - drilling. _See_ also Drilling. - by hand, 264 - by power, 264–268 - rates, 267 - excavation. _See also_ Excavation. - payment for, 230 - measurement of, in place, 235 - tunnels, 290, 291 - - Rods, sewer, 338 - - Roman ordinance relative to sewers, 2 - - Roofs. _See_ Covers. - - Root cutters, 340 - - Roots, 333, 340 - - Row lock bond for bricks, 312 - - Running water, self-purification, 373–376 - - Run-off, computations, 17, 40, 46–50, 94–98 - - - Safeguards during construction, 221, 241 - - Salt water, dilution in, 376, 377 - - Sand, effective size, 456 - uniformity coefficient, 456 - filters, 452–459 - action in, 431, 432, 452–454 - control, 458, 506–510 - description, 452 - dimensions, 456 - distribution systems, 433, 456–458 - dosing, 454–456 - dosing devices, 506–510 - materials, 456 - operation, 454, 455 - preliminary treatment, 455 - rate, 455 - results, 452, 453 - size of sand for, 456 - thickness, 456 - in winter, 455 - - Sanitary District of Chicago, - dilution factor, 380 - specifications, for manhole covers, 101, 102 - tunnel cover, 284 - tunnel ventilation, 291 - - Sanitary engineering, 1, 2 - - Sanitary sewage, defined, 7, 352 - - Saph and Schoder’s formula, 54 - - Saprophytes, 365 - - Screed, 316 - - Screens, 383–391 - chlorination and fine screens, costs, 487 - coarse, 386, 391 - data on fine, 388, 389 - design of, 389–391 - fine, 381, 382, 387–389 - fixed, 385, 390 - medium, 386 - movable, 385, 386, 389–391 - moving, 384–386 - openings, 386–389 - protection to pumps, 127, 141 - purpose, 383 - results, 386–389 - sewage treatment by, 371, 381 - size and performance, 386–389 - sizes, 386–391 - types, 384–386 - - Screening, vs. sedimentation, 383 - purpose, object, 383 - - Screenings, character of, 386–389 - - Scum, boards for, septic tanks, 413, 414 - Imhoff tanks, 421 - chamber in an Imhoff tank, 424 - definition, 495 - - Sediment, velocity of transportation, 396, 397 - - Sedimentation, 383–405 - definition, 383 - Hazen’s analysis, 392–395 - hydraulic values, 393 - a method of treatment, 370 - object, 383 - Peoria Lakes, 376 - protection of siphons, 113, 114 - results from plain sedimentation, 401 - theory of, 391–395 - transportation of debris, 396 - velocity of, 392, 393 - vs. screening, 383 - velocities, limiting, 396, 397 - - Sedimentation, basins, arrangement, 394 - baffling, 404 - cleaning, 404 - dimensions, 401–403 - inlet and outlet, 404 - operation, 411 - types, 395 - chamber, Imhoff tank, 419–422 - - Self-purification of lakes, 376 - - Self-purification of streams, 373–376 - - Separate sewer systems, 78–80 - - Septic action, 353, 365–368, 371, 410, 411, 496, 497 - results, 412, 413 - vs. sedimentation, 411 - - Septic tank, 411 - baffling, 413, 414 - capacities of small tanks, 417 - for country homes, 416, 417 - covers for, 415 - definition, 411 - design, 413–417 - explosions in, 415 - results, 412, 413 - seeding, 413 - sludge storage, 414 - small, 416, 417 - units, 415 - - Septic sludge analysis, 414 - - Septicization. Chap. XVI, 410–430 - a method of treatment, 371 - the process, 410, 411 - results, 412, 413 - - Settling solids, 357 - - Sewage and water supply, 32 - aëration, 371, 376, 465–479 - alkalinity of, 358 - analyses, chemical, 355, 369, 467 - interpretation of, 356–362 - physical, 352–354 - average, 352–355 - bacteria, 362–365 - biolysis of, 366, 367 - changes in, rate of discharge of, 33–38 - characteristics, 368–370 - characteristics of, 352–354 - chemical constituents, 354–356 - classification of, 6, 7, 352 - collection, 5 - color, 352, 353 - components and properties, 352–356 - decomposition of, 365–367 - definition, 6, 7, 352 - disposal. _See also_ Sewage treatment. - methods, 6, 370, 371 - purposes, 370, 371 - domestic, 7, 352 - farming. _See_ Irrigation. - fertilizing value, 459, 460 - flow fluctuations, 33–38 - ratio of maximum to average, 36, 37, 85 - fresh, 352–354 - gas, 335, 336, 353 - industrial, defined, 7, 352 - life in, 363–365, 368 - odor, 353 - physical, analyses, 352–354 - characteristics, 352–354 - quality variations, 368–370 - quantity. Chap. III, 24–50, and 84, 87 - and population, 31, 32 - of sanitary, 24–40 - variations, 33–38 - sanitary, defined, 7, 352 - septic, 353, 365–368, 371, 410, 411, 496, 497 - stability, 359, 360 - stale, 353 - storm, defined, 7, 352 - strong, 355 - temperature, 353 - turbidity, 353 - treatment processes, 370, 371 - A. B. C., 4 - activated sludge, Chap. XVIII, 465–479 - biological, 371 - chemical, 371 - contact bed, 432–437, 506 - costs, 459 - dilution. Chap. XIV, 372–382 - disinfection, 489–493 - electrolytic, 487–489 - filtration, 431–459 - increase of, 3 - irrigation, 431, 459–464 - mechanical, 471 - Miles acid process, 482–487 - purpose of, 6, 370 - résumé, 6, 370, 371 - sand filter, 452–458 - screening, 383–391 - sedimentation, 391–409, 411 - septicization. Chap. XVI, 410–430 - trickling filters, 437–452 - weak, 355 - and water supplies, 31, 32 - - Sewerage, definition, 7 - demand for, 2 - design, 78–98 - growth of, 2–4 - historical, 2–4 - - Sewers, ancient, 2, 3 - capacity, diagrams, 56–60 - cost, 10–14 - definitions of various types, 7, 8 - depth of, 88 - diameter, 58–60, 88–92 - flat grades, 73, 109 - flight, 101, 102 - inspection of, 333–337 - life of, 348–351 - location of, 80, 81, 94 - materials. Chap. VIII, 164–193 - medieval, 3 - pipe, properties of concrete, 175 - design. Chap. IX, 194–210 - vitrified clay, properties, 169–171 - profile, 89, 92 - section of different types, 67–72 - separate system, 78, 79, 82, 86, 87 - slope, 88–92 - storm-water system, 78, 79, 83, 93, 94 - stresses in, 194, 198–204 - - Shafts, for tunnels, 284–287 - - Sheeting, 270–280 - alignment, 240, 241 - backfilling, 330 - box, 272 - design, 275–280 - driving, 273 - length, 273 - lumber, 277 - moving, 248 - poling boards, 271, 272, 287 - pulling, 274 - skeleton, 270, 271 - stay bracing, 270 - steel, 252, 280, 281 - thickness, 276–278 - types, 270 - vertical, 270, 272–274 - Wakefield piling, 273 - - Shellfish contamination, 372, 489 - - Shields, tunnel, 288–290 - - Short loads on trenches, 202 - - Shovels, for hand excavation, 242 - steam. _See_ Steam shovels. - - Shovel vane screen, 384 - - Shoveling by hand, height raised, 244 - performance by one man, 243 - - Symbiosis, definition, 363 - example, 432 - - Sinking fund, 158 - - Siphons, automatic. Chap. XXI, 506–512. _See also under_ Dosing - devices. - in flush-tanks, 109–110 - inspection, 337 - operation, 109–110, 506–512 - for trickling filter, 448–451 - true and inverted, 113–117 - - Skeleton sheeting, 270, 271 - - Slope, of sewers, 88–92 - of tank bottoms, Imhoff, 419, 423 - sedimentation tank, 404 - - Skewback, 204 - - Sludge. Chap. XX, 495–505 - activated. Chap. XVIII, 465–479. _See also under_ Activated sludge. - analyses, 414, 467, 468, 485, 496 - characteristics, 495 - definition, 495 - digestion tanks, 427–430, 497 - disposal methods, 495 - drying, 497–505 - acid flotation, 503 - beds, 498, 500 - centrifuge, 501–502 - heat, 502, 503 - press, 500–501 - thickeners, 504, 505 - fertilizing value, 470, 495, 497 - - Sludge, filters, 498–500 - lagooning, 495, 496 - measurement, 427 - press, 500, 501 - sedimentation, 401 - septic analysis, 434 - treatment methods, 495 - - Soaps, 357 - - Soil, bearing value, 125 - stack, definition, 7 - - Solids in sewage, 356–368 - - Special assessment, 15, 16 - - Specifications. Chap. X, 211–232 - general, 219–229 - special, 230 - technical, 229, 230 - - Spiling. _See_ Piles. - - Spirillum, 362 - - Spores, 363 - - Springing line, 204 - - Sprinkling filter. _See_ Trickling filter - - Square sewer section, 68, 69 - - Stability, relative, 359–361 - - Stagnant water, 374 - - Stakes, contractor to provide, 221 - where driven, 281, 282 - - Stationing, 92 - - Stay bracing, 270 - - Steam boilers, 147–150 - - Steam, consumption by, pumps, 144, 145 - turbines, 144, 147 - engines, 144, 145 - pumping engines, 142–146 - pumps. _See_ Pumps, steam. - shovels, 246, 252–254 - turbines, 146, 147 - - Stearin, 366 - - Steel, forms. _See_ Forms, steel. - pipe, 164, 191, 192 - design, 195–197 - specifications, 191 - reinforcement for concrete, 191, 326–327 - sheet piling, 252, 280, 281 - - Stench, historic in London, 4 - - Sterilization. _See_ Disinfection. - - Storm, sewage, definition, 7, 352 - Storm, sewer system design, 93–98 - water, quantity, 40–50 - - Storms, extent and intensity, 50 - - Stream pollution, regulation, 380, 381 - - Streams, self-purification, 373–376 - - Street, inlet. _See_ Inlets. - wash, definition, 352 - - Stresses, in buried pipe, 198–204 - in circular ring, 194, 202–204 - - Sub-main, defined, 7 - - Subsurface surveys, 18–20 - - Suction for centrifugal pump, 141 - - Sulphur and sand joint compound, 309 - - Sunday work, 221 - - Surface, elevation, 92 - of ground, character, 44–46 - profile, 88 - water, 7, 352 - - Surveys, underground, 18–20 - - Suspended matter, 357 - - - Talbot’s run-off formula, 49 - - Tamping, backfilling, 328–331 - - Tannery wastes, disinfection, 491 - - Taxation, general, 16, 17 - - Taylor nozzles, 444, 445 - - Temperature of sewage, 353 - - Templates, brick sewers, 312 - - Thawing dynamite, 301, 302 - - Tide gate, 122 - - Timbering tunnels, 286–288 - - Timber, strength of, 277 - - Time of concentration, 41–43, 95–97 - - Tools, for cleaning sewers, 337–341 - excavating, 242, 246 - - Tower cableways, 252 - - Trade wastes. _See_ Industrial wastes. - - Traps, in catch-basins, 107 - grease, gasoline, and oil, 108, 109 - in street inlets, 104, 105 - - Travis tank, 427, 428 - - Tree roots, 333, 340 - - Tremie, 187, 188 - - Trench, backfilling, 328–331 - blasting in, 244, 269 - bottom, shape of, 241, 304, 311 - breaking surface, 243, 244 - drainage, 256–263 - excavating, by hand, 242–245 - machine, 244–256 - guarding and lighting, 221 - layout of tasks, 243 - length of open, 241, 248 - line and grade, 281–284 - location, 243, 281 - opening, 243, 244 - pumps, 256–263 - sheeting, 270–280 - width, 240, 241, 246 - - Trestle excavators, 250, 251 - - Trickling filter, 437–452 - advantages, 438, 439 - covers for, 451 - depth, 441, 442 - description, 437, 438 - dimensions, 442 - distribution of sewage, 442–451 - dosing siphon, 446–451 - dosing tank, 446–451 - head lost, 438 - insects, 438 - material, 441 - nozzles, 442–451 - layout, 447–451 - odors, 438, 439 - operation, 441 - rate, 441 - results, 439, 440 - siphon size, 449–451 - underdrainage, 451, 452 - unloading, 431, 437 - - Tripod drill, 265 - - Triton, 295 - - Troubles with sewers, causes, 333 - - Trumpet arch, 121 - - Trunk sewer, defined, 7 - - Tunnels, 283–294 - backfilling, 331 - breast boards, 288 - brick invert, 313 - compressed air in, 292–294 - concrete construction, 320, 321 - depth of cover, 284 - line and grade in, 283 - machines, 290 - rock, 290–292 - shafts, 284–286 - shield, 288–290 - timbering, 284–288 - ventilation, 291, 292 - - Turbidity of sewage, 353 - - Turbine, for cleaning sewers, 340 - pumps, 130, 132 - steam, 146, 147 - - Typhoid fever, 364 - - - U-shaped sewer section, 67, 69, 71 - - Underdrains for, sewers, 126 - trickling filters, 451, 452 - - Underground surveys, 18–20 - - Unexpected situations, 235 - - Uniformity coefficient of sand, 456 - - Unloading of filters, 431, 437 - - Urea, 367 - - - Valuation of sewers, 332, 348–351 - - Velocities, depositing, 395–397 - distribution of, 51 - flow in sewers, 90 - over surface of ground, 42 - limiting for sedimentation, 396, 397 - limiting in sewers, 396, 397 - principles of flow in sewers, 51 - transporting, 396 - - Ventilation, air pressures, 291 - compressed air, 292–294 - pipes, 291 - - Ventilation, of sewers, 102, 103, 335 - tunnel, 291 - - Vertical sheeting, 270–274 - - Vitrified clay. _See_ Clay vitrified. - - Volatile matter in sewage, 357 - - Volute pumps, 130, 132, 154 - - Vouissoir arch analysis, 204 - - - Wakefield piling, 273 - - Wales, 288 - - Waste pipe, defined, 7 - - Wastes. _See_ Industrial wastes. - - Water consumption, 31–33 - flow of, 51–77 - rate of steam engines, 144, 145 - supply and sewage flow, 31–33 - - Watershed. _See_ Drainage area. - - Weight, of backfill, 199 - of building material, 201 - of moving loads, 200, 202 - - Well, hole, 101 - points, 262, 263 - - Wheel excavator, 246–250 - - Wing screen, 384 - - Wood, forms. _See_ Forms. - pipe, materials, 164, 165, 190, 192, 193 - design, 197, 198 - working strength of, 277 - - Work, extra, 227 - preliminary to design, 9 - Sunday, night, and holiday, 221 - - Workmen, competent, 227 - dishonesty, 233, 234 - ------ - -Footnote 1: - - Frontinus and the Water Supply of Rome, p. 81, by Clemens Herschel. - -Footnote 2: - - Estimated by G. W. Fuller, Trans. Am. Society of Civil Engineers, Vol. - 44, 1905, p. 148. The total population connected with sewerage systems - was assumed to be the total population in the United States in cities - over 4000 in population. - -Footnote 3: - - Estimated by Metcalf and Eddy, American Sewerage Practice, Vol. III, - p. 240. - -Footnote 4: - - Computed from report of the United States Census, 1920, on the same - basis as Fuller’s estimate for 1905. - -Footnote 5: - - Cosgrove, History of Sanitation. - -Footnote 6: - - Sedgwick: Sanitary Science and Public Health. - -Footnote 7: - - No detrimental effect on the public health was noted as a result of - this condition however. It has never been conclusively proven that - such nuisances are detrimental to the public health. - -Footnote 8: - - Moore and Silcock, Sanitary Engineering, p. 67, 1909. - -Footnote 9: - - Similar to the definition proposed by the Am. Public Health Assn. - -Footnote 10: - - Definition recommended by Am. Public Health Assn. - -Footnote 11: - - Ibid. - -Footnote 12: - - Ibid. - -Footnote 13: - - Eng. News, Vol. 76, 1916, p. 781. See also Eng. News-Record, Vol. 85, - 1920, pp. 22, 1175. - -Footnote 14: - - For a more extensive treatment of the subject see Principles and - Methods of Municipal Administration by W. B. Munro, 1916. - -Footnote 15: - - Eng. Record, Vol. 74, 1916, p. 263. - -Footnote 16: - - Professional paper No. 46, United States Geological Survey, 1906, p. - 97. - -Footnote 17: - - United States Geological Survey, Water Supply paper No. 257, 1911. - -Footnote 18: - - From Eng. Cont., Vol. 41, 1914, p. 698. - -Footnote 19: - - Max. represents only the average maximum, not the greatest maximum. - -Footnote 20: - - Eng. News-Record, Vol. 80, page 1233, 1918. - -Footnote 21: - - Infiltration of Ground Water into Sewers. Transactions of the American - Society of Civil Engineers, Vol. 76, 1913, p. 1909. - -Footnote 22: - - A comprehensive discussion of rainfall formulas will be found in Vol. - 54 of the Transactions Am. Society of Civil Engineers, 1905. - -Footnote 23: - - Formula devised by H. E. Babbitt from Allen’s 25–year curve. - -Footnote 24: - - See Note under Table 14. - -Footnote 25: - - Sewerage by A. P. Folwell. - -Footnote 26: - - From an article by E. Kuichling in Transactions American Society of - Civil Engineers, Vol. 65, 1909, p. 399. - -Footnote 27: - - Trans. Am. Society Civil Engineers, Vol. 58, 1907, p. 483. - -Footnote 28: - - Trans. American Society of Civil Engineers, Vol. 58, 1907, p. 498. - -Footnote 29: - - Ibid. - -Footnote 30: - - The principles governing the run-off from large areas are explained in - Elements of Hydrology, by A. F. Meyer, 1917. - -Footnote 31: - - Transactions of the American Society of Civil Engineers, Vol. 51, - 1903, p. 11. - -Footnote 32: - - Municipal and County Engineering, Vol. 58. 1920, p. 164. - -Footnote 33: - - Industrial waste Treated as ground water. - -Footnote 34: - - For diagrams for the Solution of the Rational Method, see Eng. - News-Record, Vol. 83, 1919, p. 868 and Vol. 85, 1920, p. 151. - -Footnote 35: - - Municipal and County Engineering, October, 1909. - -Footnote 36: - - “Cleaning and Flushing Sewers.” Journal of the Association of - Engineering Societies, Vol. 33, 1904, p. 212. - -Footnote 37: - - Notes on the Design and Principles of Sewage Siphons, Eng. - News-Record, Vol. 85, 1920, p. 1041. - -Footnote 38: - - From A. E. Phillips, Trans. Am. Society of Municipal Improvements, - 1898, p. 70. - -Footnote 39: - - Trans. Am. Society of Civil Engineers, Vol. 15, 1886. - -Footnote 40: - - True Siphon at East Providence, Eng. News-Record, Vol. 85, 1920, p. - 862. - -Footnote 41: - - “The Effect of Mouthpieces on The Flow of Water Through a Submerged - Short Pipe,” by F. B. Seely. Bulletin No. 96, 1917, of the Eng’g. - Experiment Station of the University of Illinois. - -Footnote 42: - - Trans. Am. Society of Civil Engineers, Vol. 49, 1902. - -Footnote 43: - - Described by W. L. Stevenson before the Boston Society of Civil - Engineers in 1916. - -Footnote 44: - - Multiple Outlet for Calumet Intercepting Sewer, by S. T. Smetters, - Eng. News-Record, Vol. 83, 1919, p. 728. - -Footnote 45: - - “Direct Acting Steam Pumps,” by F. R. Nickel, 1915. - -Footnote 46: - - From Heat Engines, by Allen and Bursley. - -Footnote 47: - - “The Economy Resulting from the Use of Variable Speed Induction Motors - for Driving Centrifugal Pumps” by M. L. Enger and W. J. Putnam. - Journal Am. Water Works Ass’n., 1920, Vol. 7, p. 536. - -Footnote 48: - - C. A. Hague in Trans. Am. Society of Civil Engineers, Vol. 74, 1911, - p. 20. - -Footnote 49: - - Includes screen chamber, collecting reservoir, and building. - -Footnote 50: - - Computed on the assumption that the pumps may be operated at 50 per - cent overload for short periods, the rated capacity being equal to the - loads given in Table 33. - -Footnote 51: - - For description of type see note under Table 35. - -Footnote 52: - - Proceedings Illinois Society of Engineers, 1916, page 81. - -Footnote 53: - - Municipal Engineers’ Journal for April, 1918. - -Footnote 54: - - Workability involves ease in placing and smoothness of working. - -Footnote 55: - - Johnson’s Materials of Construction, 5th Edition, 1918, p. 432. - -Footnote 56: - - Trans. Am. Society of Civil Engineers, Vol. 59, 1907, p. 146. - -Footnote 57: - - L. N. Edwards, Trans. Am. Society Testing Materials, 1918, and R. B. - Young, Eng. News-Record, Vol. 82, 1919, p. 33. - -Footnote 58: - - Bulletin No. 1, Structural Materials Research Laboratory, Lewis - Institute, Chicago, Illinois. - -Footnote 59: - - Proportioning Concrete by Voids in the Mortar, A. N. Talbot, read - before Am. Society Testing Materials, June 22, 1921. Abstract in Eng. - News-Record, Vol. 87, 1921, p. 147. - -Footnote 60: - - Trans. Am. Society of Civil Engineers, Vol. 81, 1917, p. 1122. - -Footnote 61: - - See also Tentative Specifications for Concrete and Reinforced Concrete - submitted by the Joint Committee to its Constituent Organizations, - June 4, 1921. - -Footnote 62: - - Journal Illinois Society of Engineers for 1916, p. 75. - -Footnote 63: - - See A. S. T. M. Standards for 1918, p. 148. - -Footnote 64: - - Trans. Am. Society Civil Engrs., Vol. 82, 1918, p. 459. - -Footnote 65: - - See Trans. Am. Society Civil Eng., Vol. 82, 1918, p. 482. - -Footnote 66: - - See Trans. Am. Society Civil Engr., Vol. 41, 1899, p. 76, and Vol. 82, - 1918, p. 433, Eng. News, Vol. 74, 1915, p. 400, and Vol. 75, 1916, p. - 911. - -Footnote 67: - - Trans. Am. Soc. Civil Engrs., Vol. 82, 1918, p. 433. - -Footnote 68: - - Bulletin No. 31 of the Engineering Experiment Station of the Iowa - State College of Agriculture. - -Footnote 69: - - From bulletin No. 31, Engineering Experiment Station, Iowa State - College of Agriculture. - -Footnote 70: - - From Bulletin No. 31, Engineering Experiment Station, Iowa State - College of Agriculture. - -Footnote 71: - - From Bulletin No. 31, Engineering Experiment Station, Iowa State - College of Agriculture. - -Footnote 72: - - From Vouissoir Arches by Cain. - -Footnote 73: - - Baker’s Masonry, 10th Edition, p. 676. - -Footnote 74: - - Business Law for Engineers, C. Frank Allen, McGraw-Hill, 1917; - Engineering Contracts and Specifications, J. B. Johnson, McGraw-Hill, - 1904; Contracts in Engineering, J. I. Tucker, McGraw-Hill, 1910; The - Law Affecting Engineers, W. V. Ball, Archibald Constable, 1909; Law - and Business of Engineering and Contracting, C. E. Fowler, - McGraw-Hill, 1909; The Economics of Contracting, D. J. Hauer, E. H. - Baumgartner, 1915; The Elements of Specification Writing, R. S. Kirby, - John Wiley & Son, 1913; Contracts, Specifications and Engineering - Relations, D. W. Mead, McGraw-Hill, 1916; Engineering and - Architectural Jurisprudence, J. C. Wait, John Wiley, 1912. - -Footnote 75: - - See article by E. W. Bush in Eng. News-Record, Vol. 85, 1920, p. 122. - -Footnote 76: - - An unbalanced proposal is one in which the bids on some of the items - are obviously low and on other items are obviously or suspiciously - high. The purpose of submitting unbalanced bids is to keep secret the - true or supposed cost of the work to the contractor or to obtain more - money by bidding high on those items which are believed to have been - underestimated by the Engineer. A low bid is made on other items in - order to keep down the total amount of the bid. - -Footnote 77: - - Taken mainly from specifications of the Sanitary District of Chicago - and the Baltimore Sewerage Commission, with miscellaneous selections - from other sources. - -Footnote 78: - - Restrictions are placed on work done outside of ordinary working hours - in order that the Contractor may not perform work in the absence of an - engineer or inspector. - -Footnote 79: - - Cost Keeping and Management, by Gillette and Dana. Practical Cost - Keeping for Contractors, by F. R. Walker. Cost Keeping in Sewer Work, - by K. O. Guthrie in Eng. Contracting, Vol. 28, p. 238, 1905. Sewer - Construction Records at Scarsdale, Eng. News-Record, Vol. 83, p. 111, - 1919. - -Footnote 80: - - See Planning and Progress on a Big Construction Job, by Chas. Penrose, - Eng. News-Record, Vol. 84, 1920, pp. 554 and 627. - -Footnote 81: - - See also “Ownership and Operation of Trench Excavators by the Water - Department of Baltimore,” by V. B. Seims, presented before Am. Water - Works Association, June 9, 1921. - -Footnote 82: - - Eng. and Contracting, Vol. 48, 1917, p. 492. - -Footnote 83: - - Earth Excavation by A. B. McDaniel. - -Footnote 84: - - Courtesy, Sanitary District of Chicago. - -Footnote 85: - - See article by J. R. Gow, Journal New England Waterworks Ass’n, Sept., - 1920, also Public Works, Vol. 50, p. 98. - -Footnote 86: - - Diameter of diaphragm. - -Footnote 87: - - Gallons per minute. - -Footnote 88: - - Eng. News, Vol. 75, 1916 p. 1050. - -Footnote 89: - - Mun. Engineering, Vol. 53, p. 6. - -Footnote 90: - - For types of drill bits see article by T. H. Proske, Mining and - Scientific Press, March 5, 1910. - -Footnote 91: - - These intermediate holes are seldom more than 3 feet apart. - -Footnote 92: - - Earth Pressures, Old Theories and New Test Results, Eng. News-Record, - Vol. 85, 1920, p. 632. - -Footnote 93: - - Trans. Am. Society Civil Eng’rs, Vol. 60, 1908. - -Footnote 94: - - Adopted by the Am. Ry. and Maintenance of Way Ass’n in 1907. - -Footnote 95: - - Tunneling Machines Successful on Detroit Sewers, Eng. News-Record, - Vol. 84, 1920, p. 329. - -Footnote 96: - - Rules on Compressed-Air Work of N. Y. State Industrial Commission, - Eng. News-Record, Vol. 85, 1920, p. 1225. - -Footnote 97: - - Taken mainly from the Engineer Field Manual of the U. S. Army; Safety - Factors in the Use of Explosives by W. O. Snelling, Technical Paper - No. 18, U. S. Bureau of Mines; and an article in Eng’g and - Contracting, Vol. 52, 1919, p. 585. - -Footnote 98: - - See paper by C. T. Hall before Am. Inst. Chemical Engineers. - -Footnote 99: - - Per cubic yard of material displaced. - -Footnote 100: - - Eng. News, Vol. 75, 1916, p. 592. - -Footnote 101: - - Pressure of Concrete on Forms Measured in Tests, by E. B. Smith, - before Am. Concrete Institute, Feb. 15, 1920. Abstracted in Eng. - News-Record, Vol. 84, 1920, p. 665. - -Footnote 102: - - See, also, Concrete Form Design, by E. F. Rockwood, Eng. and - Contracting, Vol. 55, 1921, p. 528. - -Footnote 103: - - Includes 6 cents per foot for excavation. Labor for this was 58 per - cent of the total labor cost. - -Footnote 104: - - Cement at $1.25 per barrel. - -Footnote 105: - - Mun. Journal, Vol. 36, 1914, p. 736. - -Footnote 106: - - Mun. Journal, Vol. 39, 1915, p. 911. - -Footnote 107: - - Formerly the Municipal Journal. - -Footnote 108: - - See Eng. Record, Vol. 75, 1917, p. 463. - -Footnote 109: - - Eng. Record, Vol. 73, 1916, p. 141, and Eng. News-Record, Vol. 79, - 1917, p. 1019. - -Footnote 110: - - Eng. Record, Vol. 72, 1915, p. 690. - -Footnote 111: - - Eng. Record, Vol. 71, 1915, p. 256. - -Footnote 112: - - Eng. and Contr., Vol. 41, 1914, p. 250. - -Footnote 113: - - H. J. Kellogg in Journal Connecticut Society of Civil Engineers, 1914, - and Technical Paper 117, U. S. Bureau of Mines. - -Footnote 114: - - Eng. News, Vol. 70, 1913, p. 1157. - -Footnote 115: - - Technical Paper No. 117, U. S. Bureau of Mines. - -Footnote 116: - - Eng. News, Vol. 71, 1914, p. 84. - -Footnote 117: - - Eng. News, Vol. 71, 1914, p. 82. - -Footnote 118: - - Similar to definition proposed by the Am. Public Health Ass’n. - -Footnote 119: - - Economic Values in Sewage and Sewage Sludge, by Raymond Wells, - Proceedings Am. Society Municipal Improvements, Nov. 12, 1919. Eng. - News-Record, Vol. 83, 1919, p. 948. - -Footnote 120: - - Sample boiled for five minutes. - -Footnote 121: - - Sample immersed in boiling water for 30 minutes. - -Footnote 122: - - Four months. - -Footnote 123: - - One week in March, 1914. - -Footnote 124: - - R represents any chemical element such as K, Na, etc. - -Footnote 125: - - Standard Methods of Water Analysis, American Public Health - Association, 1920. - -Footnote 126: - - Routine tests are ordinarily incubated for this period only, and if - not decolorized in this time are recorded as stable. - -Footnote 127: - - Determination of the Biochemical Oxygen Demand of Sewage and - Industrial Wastes, by E. J. Theriault, Report of the U. S. Public - Health Service, Vol. 35, May 7, 1920, No. 19, p. 1087. - -Footnote 128: - - Standard Methods of Water Analysis, American Public Health - Association, 1920. - -Footnote 129: - - Jordan, General Bacteriology, 1909, p. 91. - -Footnote 130: - - Ibid. - -Footnote 131: - - Reprinted in Vol. III of Contributions from the Sanitary Research - Laboratory of Massachusetts Institute of Technology. - -Footnote 132: - - Formerly Chief Engineer of the Sanitary District of Chicago. - -Footnote 133: - - From “Sewage,” by Samuel Rideal, 1900, p. 16. - -Footnote 134: - - See Am. Civil Engineers’ Pocket Book, Second Edition, p. 982. - -Footnote 135: - - Trans. Am. Society Civil Engineers, Vol. 58, 1907, p. 988. - -Footnote 136: - - Not defined by the American Public Health Association. - -Footnote 137: - - Trans. Am. Society Civil Engineers, Vol. 78, 1915, p. 892. - -Footnote 138: - - Removal of Suspended Matter by Sewage Screens, Cornell Civil Engineer, - 1914. Abstracted in Engineering and Contracting, Vol. 41, 1914, p. - 451. - -Footnote 139: - - “The Clarification of Sewage by Fine Screens,” Trans. Am. Society - Civil Engineers, Vol. 78, 1915, p. 1000. - -Footnote 140: - - Langdon Pearse, Trans. Am. Society Civil Engineers, Vol. 78, 1915, p. - 1000. - -Footnote 141: - - Meshes per inch. - -Footnote 142: - - See article by Henry Ryon in Cornell Civil Engineer, 1910. - -Footnote 143: - - The hydraulic coefficient is defined as the rate of settling in mm. - per second. - -Footnote 144: - - Definition suggested by the American Public Health Association. - -Footnote 145: - - Computed from formula by Gilbert in “Transportation of Debris by - Running Water,” U. S. Geological Survey, Professional Paper No. 86, - 1914. Diameter in mm. = (1.28 (velocity)^{2.7})⁄(Sp. gv. − 1). - -Footnote 146: - - Computed from Annual Report of the Superintendent of Sewers, Nov. 30, - 1919, and 1920. - -Footnote 147: - - These figures are for 1919. - -Footnote 148: - - These figures are for 1905. - -Footnote 149: - - These figures are for 1902. - -Footnote 150: - - Report of the Ohio State Board of Health, 1908, page 425. - -Footnote 151: - - Definition proposed by the Am. Public Health Assn. - -Footnote 152: - - See Eng. News. Vol. 73, 1915, p. 410. - -Footnote 153: - - Sewage Treatment from Single Houses and Small Communities, by L. C. - Frank. U. S. Public Health Service, Bulletin 101, 1920. - -Footnote 154: - - Eng. News-Record, Vol. 78, 1917, p. 566. - -Footnote 155: - - Municipal Engineering, Vol. 54, p. 149. - -Footnote 156: - - Eng. Record, Vol. 68, 1913, p. 452. - -Footnote 157: - - Am. Sewerage Practice, Vol. III, p. 437. - -Footnote 158: - - Trans. Am. Society Civil Engineers, Vol. 83, 1920, p. 337. - -Footnote 159: - - Eng. News-Record, Vol. 83, 1919, p. 510. - -Footnote 160: - - See Eng. News, Vol. 70, 1913, p. 1112; Eng. Record, Vol. 68, 1913, p. - 440, and Eng. News, Vol. 75, 1916, p. 1028. - -Footnote 161: - - See Eng. Record, Vol. 67, 1913, p. 232. - -Footnote 162: - - The use of half-spray nozzles is not always advocated as it is - considered that their use does not markedly improve the distribution. - Where half nozzles are used, a margin of 18 inches to 2 feet should be - allowed between the edge of the filter and the nozzle, to prevent the - blowing of raw sewage from the filter. - -Footnote 163: - - From paper by E. G. Bradbury in Proceedings of the Ohio Eng. Society, - 1910, p. 79. - -Footnote 164: - - The effective size of sand is the diameter in millimeters of the - largest grain in that 10 per cent, by weight, of the material which - contains the smallest grains. - -Footnote 165: - - The uniformity coefficient is the ratio of the diameter of the largest - particle of the smallest 60 per cent, by weight, to the effective - size. - -Footnote 166: - - Interest at 6 per cent. - -Footnote 167: - - Worcester figures. - -Footnote 168: - - This method may show a profit from the sale of sludge. - -Footnote 169: - - Sewage Disposal, 1919, p. 223. - -Footnote 170: - - See Eng. News, Vol. 9, 1883, p. 203, and Vol. 29, 1893, p. 27. - -Footnote 171: - - American Sewerage Practice, Vol. III. - -Footnote 172: - - Reference 11, at end of this chapter. - -Footnote 173: - - Reference 15. - -Footnote 174: - - Reference 2. - -Footnote 175: - - For mechanical methods of drying sludge, see Reference 22, p. 1127, - and No. 33, p. 843. - -Footnote 176: - - Reference 10. - -Footnote 177: - - Reference 13. - -Footnote 178: - - University of California, Bulletin 251, 1915. - -Footnote 179: - - Reference 25. - -Footnote 180: - - See Report by Black & Phelps of Metropolitan Sewerage Commission, - 1911, reprinted as Vol. VII of Contributions from the Sanitary - Research Laboratory of the Massachusetts Institute of Technology. - -Footnote 181: - - See Reports, Mass. State Board of Health. - -Footnote 182: - - Reference 47. - -Footnote 183: - - Reference 10. - -Footnote 184: - - Reference 10. - -Footnote 185: - - Reference 10. - -Footnote 186: - - Hatton, reference 33. - -Footnote 187: - - Reference 18. - -Footnote 188: - - Reference 1, at end of this chapter. - -Footnote 189: - - Reference 2. - -Footnote 190: - - Reference 6. - -Footnote 191: - - Reference 5. - -Footnote 192: - - Reference 6. - -Footnote 193: - - Reference 6. - -Footnote 194: - - Reference 8. - -Footnote 195: - - Reference 20. - -Footnote 196: - - Reference 17. - -Footnote 197: - - Reference 19. - -Footnote 198: - - Reference 21. - -Footnote 199: - - Reference 24. - -Footnote 200: - - Inorganic Chemistry, by Alexander Smith. - -Footnote 201: - - American Public Health Association definition. - -Footnote 202: - - Sewage Sludge by Allen. - -Footnote 203: - - Sewage Disposal by Kinnicutt, Winslow and Pratt. - -Footnote 204: - - Sewage Disposal by Fuller. - -Footnote 205: - - Sewage Sludge by Allen. - -Footnote 206: - - From Eng. News-Record, Vol. 84, 1920, p. 995. - -Footnote 207: - - A Simple Mechanical Control for Dosing Sewage Beds, by P. Thompson, - Eng. News-Record, Vol. 84, 1920, p. 1018. - -Footnote 208: - - Sewage Disposal by Kinnicutt, Winslow and Pratt. - -Footnote 209: - - Design of Siphon by G. H. Bayles, Eng. News-Record, Vol. 84, 1920, p. - 974. - ------------------------------------------------------------------------- - - - - - TRANSCRIBER’S NOTES - - - 1. Silently corrected typographical errors and variations in spelling. - 2. Archaic, non-standard, and uncertain spellings retained as printed. - 3. Enclosed italics font in _underscores_. - 4. Enclosed bold font in =equals=. - 5. Superscripts are denoted by a caret before a single superscript - character or a series of superscripted characters enclosed in - curly braces, e.g. M^r. or M^{ister}. - 6. 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