VAN NOSTRAND SCIENCE JERI ES. . f.*rict;.&Q jiff, Cents. SEWERAGE SEWAGE AND PURIFICATION BY M. N. BAKER, PH. B., C. E. ASSOCIATK EDITOM, * ENGINEERING NEWS.'* JOINT AUTHOK u SEWAGE DISPOSAL /.N THE UNITED STATES.' AUTHOR "SF.WAGE PURIFICATION IN AMERICA," isH SEV/A<;E V.'ORKS." Fifth Edition, HBHT UC-NRLF Revised and Enlarged. 157 . D, r VA]N NEW YORK: XOSTRAND COMPANY, Park 1913 Place. THE VAN NOSTRAND Allan. No. 12. Prof. THEORY OF VOUSSOIR ARCHES. Wm. Cain. By Third edition, revised and enlarged. THE VAN NOSTRAND SCIENCE SERIES No. 13. By J. GASES MET WITH "IN COAL MINES. Atkinson. Third edition, revised and enlarged, is added The Action of Coal Dusts by Edward H. Williams, Jr. to J. which No. AIR IN MINES. 14. FRICTION Atkinson. Second American edition. No. 15. C.E. No. 16. Certain Questions iu Arithmetic or Algebra. G. L. Vose. Third edition. OF By J. J. SKEW ARCHES. By Prof. E. W. Hyde, Second edition. Illustrated. GRAPHIC METHOD FOR SOLVING v *No. 17. By Prof. WATER AND WATER-SUPPLY. By W. H. Corfield, of the University College, London. Second American edition. Prof. No. IS. SEWERAGE AND SEWAGE No. N. Baker, Associate Editor "EngineerFourth edition, revised and enlarged. STRENGTH 19. Transverse Loads. of Arches." "Theory No. 20. UNDER BEAMS OF By Prof. W. Allan, author edition, revised. of Second BRIDGE AND TUNNEL CENTRES. By John B. McMaster, C.E. No. 21. PURIFI- By M. cation. ing News." Second SAFETY VALVES. By edition. Richard H. Buel, Third edition. C.E. No. 22. HIGH MASONRY DAMS. By E. Sherman Gould, M. Am. Soc. C.E. Second edition. No. 23. THE FATIGUE OF METALS UNDER Repeated Strains. With various Tables of Results and Experiments. From the German of Prof. Ludwig Spangenburg, with a Preface by S. H. Shreve, A.M. No. 24. A PRACTICAL TREATISE ON THE Teeth of Wheel?. By Prof. S. W. Robinson. Third edition, revised, with additions. No. 25. THEORY AND Cantilever Bridges. No. 26. R. CALCULATION OF M. Wilcox. PRACTICAL TREATISE ON THE PROP- erties of No. 27. By Continuous Bridges. By Charles Bender, C.E. BOILER INCRUSTATION AND CORRO- Rowan. New partly rewritten by F. E. Idell. *No. 28. TRANSMISSION OF By aion. Ropes. F. By J. Albert W. edition. Revised and POWER BY WIRE Stahl, U.S.N. Fourth edition, revised. No. 29. STEAM INJECTORS; THEIR THEORY and Use. Pochet. Translated from the French by M. Leon THE VAN NOSTRAND SCIENCE MAGNETISM OF IRON VESSELS AND No. 30. Terrestrial By Magnetism. Fairman Rogers. Prof. THE SANITARY CONDITION OF CITY No. 31. and Country Dwelling-houses. Jr. S ERIES By George E. Waring, Third edition, revised. CABLE-MAKING FOR SUSPENSION No. 32. W. Hildenbrand, C.E. B. Bridges. MECHANICS OF VENTILATION. By No. 33. George W. Rafter, C.E. Second FOUNDATIONS. No. 34. Gaudard, C.E. edition, revised. Prof. Jules Translated from the French. Second By edition. THE ANEROID BAROMETER; No. 35. ITS Construction and Use. Compiled by George Plympton. Eleventh edition, revised and enlarged. MATTER AND MOTION. No. 36. Maxwell, M.A. *No. 37. Uses, Second American By J. W. Clerk edition. GEOGRAPHICAL SURVEYING; Methods, and Results. ITS By Frank De Yeaux Carpenter, C.E. MAXIMUM STRESSES No. 38. IN FRAMED New William Cain, A.M., C.E. By Prof. Bridges. and revised edition. A HANDBOOK OF THE ELECTRO- No. 39. Magnetic Telegraph. By A. E. Loring. Fourth edi- tion, revised. TRANSMISSION OF POWER BY *No. 40. Compressed Air. By Robert STRENGTH No. 41. OF Zahner, M.E. MATERIALS. By William Kent, C.E., Assoc. Editor "Engineering News." Second edition. THEORY No. 42. OF STEEL - CONCRETE Wm. By Prof. Arches, and of Vaulted Structures. Cain. Fifth edition, thoroughly revised. WAVE AND VORTEX MOTION. No. 43. Dr. Thomas By Craig, of Johns Hopkins University. WHEELS. By Prof. W. P. No. 44. TURBINE ReTrowbridge, Columbia College. Second edition. vised. No. 45. THERMODYNAMICS. By Hirshfeld. Second edition, revised Prof. C. F. and corrected. ICE-MAKING MACHINES. From the French of M. Le Doux. Revised by Prof. J. E. Donton, D. S. Jacobus, and A. Riesenberger. Sixth edition, No. 46. revised. SEWAGE DISPOSAL IN THE UNITED STATES. BY GEO. W. RAFTER, M. Am. AND M. N. BAKER, Soc. C. E., Ph.B., ASSOCIATE EDITOR "ENGINEERING NEWS." Large Svo, 600 pages, 7 plates, 116 illustrations in tJie text. Part I. of this great work discusses the principles of the subject in detail, citing foreign experience where it will throw light upon the subject, but dealing chiefly with American ideas and practice, and with the broad principles of sewage purification, or other means of disposal, which are more or less applicable everyEach method of purification is discussed at where. length, and many allied subjects never before treated in a comprehensive manner are taken up. Part II. is an exhaustive description of about forty sewage purification plants as actually built in the United States and Canada, with many details of cost, methods of operation and the results obtained in actual Several appendices give English and Amerpractice. ican Statute Laws regarding stream pollution and its prevention, and the duties and powers lodged in State Boards of Health for the preservation of the purity of inland waters, especially where used for public water supplies. SENT POSTPAID ON KKCEIPT OF $6.00 BY THE PUBLISHEBS, D. VAN NOSTRAND CO., NEW YORK CITY. 25 PARK PLACE, SEWERAGE SEWAGE AND PURIFICATION BY M. N. BAKER, PH. B., C. E. ASSOCIATE EDITOR, "ENGINEERING NEWS." "SEWAGE DISPOSAL IN THE UNITED STATES.'* AUTHOR "SEWAGE PURIFICATION IN AMERICA," "BRITISH SEWAGE WORKS." JOINT AUTHOR Fifth Edition, B, Revised and Enlarged. NEW YORK: VAN NOSTRAND COMPANY, . ?5 Park 1913 Place. COPTBIOHT, BY D. 1905, VAN NOSTRAND COMPANY. ^IK Rights Reserved. PREFACE. One of the earliest volumes in this series was " Sewerage and Sewage Utilization," by W. H. Corfield, of the UniverLondon. of Appearing in 1875, when sity American cities had sewscore a few only and when the name, erage systems worthy was nractically unsewage purification known in this country, the little book was Professor and for many years continued to be of great service this side the water. When, after twenty years, the publishers requested the author to revise the book, he found revision, or even re-writirg, entirely out of the question, so ill-suited were its matter and method to modern American conditions. There being a strong demand for a brief but comprehensive book on the subject, it was decided that an entirely new one should be written. Professor Corfield entitled his discussion 365610 TV " Sewerage and Sewage Utilization." The " Purificapresent author prefers to use " rather than tion," Utilization," in his In making this change he does not wish to detract from the importance or possibilities of utilization, but simply to title. put purification, or the sanitary problem, commercial first, and utilization, or the problem, second. In addition, utilization is only one of several processes of purifi- cation. There are now in the United States some fifty cities and villages, many institutions, manufactories and houses, employing one or another system of sewage purification. studies of the Massachusetts State The Board of Health have given an impetus to intermittent filtration of late, but chemical precipitation is practiced in and broad pecially in many places common, esthe West, where " Water is irrigation is King," and the sewage quite is used for plant drink rather than plant food. It is hoped that this little book will be some engineers, especially those of use to whose practice has been in other lines of V. engineering, and to that vast and rapidly growing body of sewer commissioners and superintendents, boards of public works, boards of health, mayors and city council- men, and public spirited citizen in general, are of late taking a growing and most promising interest in sanitary all of whom problems. M. N. B. 104 Tribune Building, New York, Dec. 31, 1895. PREFACE TO THE SECOND EDITION. In the nearly ten years that have elapsed since the appearance of the first edition of this little book, the newer and so-called sewage treatment have been announced, passed through an bacterial processes of experimental stage and come into extensive Meanwhile the author has improved many opportunities to visit American sewuse. VI. age purification works, old and new, and during 1904 spent several months abroad, chiefly in Great Britain, visiting sewage works and meeting a number of the men prominently connected with British progress in this field. As a consequence of the events named above, the section of this book which deals with the purification of sewage has been largely rewritten and somewhat extended. Few changes in the other section, on sewerage systems as contrasted with disposal works, have been deemed necessary. M. N. B. 220 Broadway, New York, May 5, 1905. CONTENTS. Page. Sewerage System is Needed The Value of a Sewerage System Good Engineering Advice Essential. Preliminary Reports and Plans Why a Separate or Combined System Subsoil Drainage 14 15 21 25 28 Final Disposal of Sewage Population, Water Consumption, Sewage, Rainfall 5 12 Volume of Method of Meeting the Cost Design and Construction of the Conduit System Manholes Sewer Grades Flushing Devices Y-Branches for House Connections Ventilation of Sewers 34 46 58 63 64 64 66 68 Misapprehensions Regarding So-called Sewer Gas 72 Dr. Billings' Opinion on Sewer Air and Ventilation 74 Features Peculiar to the Combined System.. Oatch Basins or Rainwater Inlets 80 Storm Overflows 81 77 vm. Page. Pumping Stations, Keceiving Reservoirs and Force Mains 82 Tidal Chambers 84 Final Plans and Specifications Securing Bids and Awarding Contracts The Proper Lxecution . of the Contract Operating the System 8i 86 90 92 Sewarge Commission, Board of Public Works or City Council Sewage 93 Purification in its General Aspects.... Sedimentation Mechanical Straining Chemical Precipitation The Septic Tank Artificial Aeration. " Electrical" Processes. 95 104 106 108 116 121 Broad Irrigation or Sewage Farming 125 Sub-Surface Irrigation 131 Intermittent Filtration 131 Contact Beds Percolating Filters 142 147 Sewage Purification Plants not Nuisances Status of Sewage Purification.... 150 The Present 140 SEWERAGE AND SEWAGE PURI- FICATION. WHY A SEWERAGE SYSTEM is NEEDED. An abundant supply of pure water is one of the greatest advantages which any community can possess. This is so generally recognized that every American town with a population reaching into the thousands has, or is planning to obtain, a public Such a supply having been through the streets and houses, used and enjoyed, what dispo- water supply. distributed secured, be made of it ? Obviously may be the very reverse of its sition shall its removal in- troduction. As it was'distributed through a network of conduits diminishing in size with their ramifications, so it may be collected again by similar conduits, increasing in size, as one after another they unite in a common volume The is But the outgoing from the incoming. was pure and limpid the outlet. far different influent ; effluent has been fouled in performing the demanded of it, and should it accumulate and remain at any point it would decompose and give rise to offensive services odors. Moreover, in various fields of its usefulness, the once pure water may have taken up germs of disease which formerly habited the human body, causing sickness and perhaps death, and which might give rise to like dire results should they again secure access to man. What, then, shall be done with the fouled water that has been collected ? two answers Either : In general, there are but it must (1) be turned body of water so large as to'dilute beyond all possibility of offence, and where it cannot endanger human life by into a it polluting a public water supply, or (2) must in some manner be This fouled water conduits which sewerage system is it purified. called sewage; the it constitute the collect ; and the means adopted is termed The terms sewerage and to get rid of the collected matter sewage disposal. sewage, it may be noted here, are often confounded, even among engineers. The use of sewerage to indicate the matter carby a sewer, is obsolete, so that one ried as properly write or speak of water- works as of purifying might about purifying sewerage. To go a it may little further with definitions, be stated that conduits which cany water collected from street surfaces, during and after rains, or ground water collected from beneath the are called drains. surface, or both, Where one set of con- removes sewage and another carries surface and ground water, it is said that duits the separate system of sewerage is in use, a term which may be applied where the drainage system has not yet been constructed, but only sanitary sewers, as they often called, have been provided. set of conduits conveys both and drainage water, it is called the sewage are Where one combined system of sewerage. Obviously, various modifications of those two systems are possible, both for whole cities and for limited areas within one municipality. To make the distinction between sewers and drains more complete, it may be said s that sewers carry water fouled with organic wastes from the human system, from various cleansing processes common to households, and also manufacturing wastes; while drains convey rain or ground all water only. The drainage, however, may much organic matter gathered by the rain in passing over roofs, yards and streets, or by the ground water as it percontain through polluted soil; but this matter, in most cases, is far less likely to give offense or menace health than that colates contained in sewage. Before entering into a discussion of sewerage systems it will be well to consider briefly why they are needed, for the engineer and the sanitarian must for many years to come meet the objections to this class of improvements put forth by men either ignorant of the principles involved or, is worse yet> of those whose first impulse to strenuously resist any new demand upon the public treasury, without regard to its character. Public water supplies and sewerage systems naturally go hand in hand. Where neither exists water from wells, privies often and sink is generally drawn close proximity to drains, and subject to in gross pollution from them. Should there be a case of typhoid fever in a given house typhoid germs, which always exist in great numbers in the dejecta of the patient, might readily find their way into the and thus into the digestive system of well, members of the family, of visitors, or of neighbors using the well. Thus the disease is spread from one member of a other family to another and from family to Besides this danger, there is family. always the more remote one from the dreaded cholera, should it visit the country, and the ever present one of poor health and consequent greater susceptibility to all forms of disease. A sanitary sewerage system cannot be installed until a public water supply has been provided. It is needed as soon as that is accomplished, for while the wells can then be abandoned the volume of waste water is greatly augmented Its foulness water-works system. by the is also 10 greatly increased through the introduc- Without sewers and with a public water supply cesspools must tion of water closets. be employed. With cesspools begins a continuous and far-reaching pollution of the soil, much more serious than that which commonly results from privies and the surface disposal of slops. The pores of the ground become clogged with organic waste; nature's beneficent process of oxidation is arrested ; putrefaction sets in ; and poisonous gases are gene- These gases may find their way through foundations into houses and also rated. directly into the outer air, especially during sudden rises in the ground watrr level. The cellars of houses on small lots may be made damp by leaching cesspools. Such wells as still remain in use are also liable to pollution from cesspools on neighboring premises. Water tight cesspools, while possible in theory and often demanded by health ordinances, are a luxury that only a few can afford, owing to the Even in percost of frequent emptyings. meable 'soils the emptying of leaching 11 cesspools as often as health and decency demand will generally cost more than the increase in taxes due to the construction and maintenance of a sewerage system. A village or town without water-works and sewers is at great disadvantage as compared with communities having these conveniences and safeguards. Industries and population are not so quickly attracted the municipality is almost sure to be poorer and its death rate These statements hold, only in higher. lesser degree, where a public water sup- to it; the health of ply but no sewerage system has been provided. The full benefits of water-works cannot be enjoyed until sewers are put in, because many people will make the absence of sewers an excuse for the non-use or limited use of the water supply. can describe the trials and tribula- Who tions which beset health authorities in their efforts to secure the proper disposal of privy and cesspool matter ? If there is little but privy matter to be removed the not so great, because in this difficulties are country such a condition seldom exists, 12 except in small communities, where the houses are set in ample lots, with gardens, and with an abundance of farm land near by, so that the vault matter for fertilizing purposes. is in demand With denser populations and larger areas, the emptying of vaults is a more serious matter, requir- ing the greatest care to prevent nuisances, and often, if not generally, entailing expense upon the householder. Cesspools are unmitigated nuisances, and however well built or frequently emptied, the satisfactory disposal of their contents cally impossible. paratively little is practi- The matter has com- value as a fertilizer and is met with if the land is even increasing protests, located in remote and sparsely settled dumping upon unoccupied land towns. THE VALUE OF A SEWERAGE SYSTEM. To express the value of a good sewerage system in lives or dollars saved is simply Other sanitary improvements impossible. precede, accompany and follow this, each 13 adding to the healthfullness of the community. The decrease in the death rate for a term of years can be given, but no man can express in percentages the part played by each factor. We know that pure air, pure water, and a pure soil are essential good health and long to life. the greatest polluters of air and and by all odds the greatest enemy to Among soil, pure water, is the contaminating matter from privies, cesspools and improper systems of sewerage and sewage disposal. These are such truisms that to expand upon them in these days of progress seems almost absurd. Only one be attempted. a year are caused by typhoid fever in the United States. Keep from the lips of our people all water illustration will More than 35,000 deaths containing germs from the excreta of typhoid patients, and milk diluted with such water, or contaminated with it through washing milk cans and bottles it, and the disease would soon be prac- in tically wiped out. This can be effected only by providing every one with a pure 14 water supply, which, with other much desired ends, would be greatly advanced by the provision of properly designed sewer- age and sewage disposal systems town and country.* for both GOOD ENGINEERING ADVICE ESSENTIAL. Simple and convincing as the arguments for efficient sewerage systems seem, years of agitation are often necessary to awaken sufficient interest in the subject to secure their introduction. One cause of this is the failure to present to the people a wellconsidered scheme, capable of beingunderstood in citizen its and broad outlines by the average in all but its most technical details by any live business or professional man. How rarely this is done until years have been spent in well nigh useless effort, money as well as time often being wasted * For the salutary effect upon the general health of individuals, and especially of women, conferred by the abolition of outside privies, more or less exposed to the public view, cold in winter, insufferably hot and odorous in summtr, impossible of access without getting wet dur" How to Drain a ing rains or snows, see Waring's House," Second Edition. This book discusses other benefits to health and otherwise, conferred by a proper system of disposal for household wastes of the kind under discussion here. 15 way. Good engineering advice is needed from the very start in this or any Otherwise a chaotic similar enterprise. in this mass of opinions as to what should be done speedily develops, factions spring up and even political parties take sides on the questions involved. PRELIMINARY REPORTS AND PLANS. Such preliminary studies as are required need not be very expensive, but they are essential to a proper understanding of the Among the data which should be subject. determined as early as possible are: (1) The area to be served, with its topography and the general character of the soil. (2) Whether the separate or combined system of sewerage, or a compromise between to be adopted. (3) Whether subsoil drainage shall be attempted. (4) these two, The is best of the available means of final the sewage, often the most disposal difficult of the problems involved where of purification is necessary. (5) Population, water consumption and volume of sewage for which provision must be made, together 16 with rainfall data, if surface drainage is to be installed. (6) Extent and cost of the proposed system. (7) Method of meeting the cost of the sewerage system. (8) The needs for sewerage peculiar to the locality, with a study of the health and mortality of the town. These are the main points involved in sewering and draining a town. It may serve either as a mere outline, or the details suggested by the various heads may be so worked out as to form a complete design for the system. There is nothing like public confidence, and the quickest way to unsettle a community and to delay the introduction of public improvements, is to lay before the A people a number of conflicting plans. well-considered preliminary study is likely to at once commend taxpayers, and if itself to citizens and months or even years go by without further action it continues to be a rock upon which to build in the future. Succeeding engineers can but what has been commend so well put in the past, if they be possessed of sense and ability, and 17 the popular conception of done what should be strengthened with each endorsement of previous recommendations. The above being true, great care should is be taken on the part of local authorities to the right man for the preliminary and the fortunate engineer should exercise even greater care in fulfilling the select studies, trust confided in good regarding him. final The same holds plans and actual construction. Generally speaking, the smaller the com- munity or the amount of money available, the greater the need for the best obtainable advice, although of course the less intricate the tion, problem the cheaper its solueven by the most talented expert. It only a false economy that dispenses with engineering services, or employs the cheapest, because money is to be had only in small quantities. Experience is an ex- is pensive teacher, and the community that realizes this at the start will pay the engi- neer and secure the benefit of his training in the school of well-directed experience, instead of taking a more expensive course 18 of its own in the school of headstrong, blundering, haphazard experience, which municipalities have entered. now suppose that a village, town, or city has so far decided in favor of a sewerage system as to be ready to have so many Let us We will also preliminary studies made. that it has decided to have these suppose studies of a comprehensive character. authorities hesitate somewhat between The em- ploying a local engineer of good general standing in his profession, and with some experience in sewerage construction, and an engineer of national reputation in this line of work. Wishing the best they half decide to engage the latter, but inquiry develops the fact that his charges are high, although none too high con- sidering experience and knowledge, that he must be paid for time spent in his travelling, and that a comparatively large amount of ordinary surveying and simple compilation of facts and figures must be made, requiring a number of days from a principal arid assistants. Both the local man and the expert are finally engaged, 19 the latter to act principally in an advisory eapaeity throughout the study. Referring to the above outline for the preliminary study, it will be seen that the local engineer will the make the surveys, collect information regarding population, water consumption and rainfall and other merely local data upon which the design This for a sewerage system will depend. he will submit to the expert for use in preparing the report of the latter. It is not necessary to separate any further the The evolution of the two engineers. of the report and recommendations may therefore be considered as the work of one work engineer from start to finish. Indeed it is likely to be so to a very large extent in practice, the division of labor generally being carried far to one extreme or the other: That is, either the expert amend and approve the is called in to results of complete by an engineer with less experience than himself, or he employs his own as- studies sistants, local engineers or otherwise, to do the bulk of the routine work involved. 20 The various order (1) parts of the study in their may now be taken up, as follows: The area to be served, with its topog- raphy and the general character of the soil. A contour map of the whole municipality, showing the location of the several streets, streams, ponds, or lakes and contour lines for say each 5 ft. of change in elevation is essential to the best results and must be provided sooner or later if a sewerage system is to be carried out on intelligent lines. Such a map will be of service for other purposes and would be a good invest- ment for any municipality. The general character of the soil usually be ascertained without much can diffi- by more or less casual observation, and by inquiring among residents, builders and others who have dug wells and cellars, or observed the same while being culty dug. The kind of soil is important as affecting the cost of trenching, and its natural wetness or drynoss, together with the ground water level, will be a further indication of the difficulties likely to be met in construction, and of the necessity 21 or desirability of providing underdrains for removing ground water or lowering its which is further considered below. (2) Whether the separate or combined system of sewerage, or a compromise be- level, tween these two, is to be adopted. Obviously, these points depend almost wholly upon local conditions, including financial as well as natural factors. The and cost of combined sewers is truly enormous as compared with those on the size separate plan, since the surface drainage in times of heavy rainfall is many times as great as the flow of sanitary sewage. In the older towns and cities it is some- times the case that drains designed to remove only surface water were constructed long ago, before modern plumbing methods were introduced. Such drains were loosely built, may have been poor in grade from the start and were never designed to receive sewage. To-day, how- ever, they are serving as sewers ing much trouble and offense and givthrough Besides this, stoppages and stagnation. they are polluting the soil by means of numerous leaks. In designing a comprehensive sewerage system for such a city, it sometimes happens that these old drains can be relegated to their original purposes and sanitary sewers introduced to care for house wastes alone. Where a town or city is entirely or prac- tically without either sewers or drains, it often happens that it may consider itself fortunate if it can put in sanitary sewers on the strictly separate plan, leaving surface drainage for future generations, it may be. Here financial limitations govern, and this has been the experience of many American municipalities now possessed of first-class sanitary sewers. Many a town is so situated that street gutters and natural water courses alone make ample provision for surface drainage. may be insuffithrough various causes, and storm drains thus be necessary, but there may be Again, the street gutters cient, numerous natural outlets for these at fre- quent intervals, thus requiring only short lines and thus comparatively small storm drains. At the same time the only suita- 23 sewage may be at a point remote from the city, thus necessitating a ble outlet for and costly outlet sewer, if the combined system were to be employed, as against a comparatively small and inex- long, large pensive outlet for sewage alone. But strongest of all is the case for the when the sewage must be purified. simply out of the question for any city to build works large enough to treat the full flow of a combined system separate system It is at times of maximum the sewage treated, or must pass away entirely un- rainfall. Some of very inadequately purified. Generally speaking, each added drop of water is so much more burden, for while it is true that the sewage is thereby diluted, also true that the capacity of the works it is is taxed so much the more. If crops are being raised, or even simple intermittent filtration is in vogue, periods of heavy rainfall are just the times a smaller rather than a larger when volume of sewage ig desired, while at chemical precipitation works heavy increases in the sewage flow are always unwelcome. The volume to be treated in sewage is one of the greatest factors and the original and largely its cost, vary purification, size of .a plant, directly with the volume, while cost of more largely dependent volume than upon strength of sewage. The essential point is, that the combined system means great extremes and sudden fluctuations of flow, and whatever the is operation far character of the industry such conditions are consistent neither with economy nor the best results. Sometimes more or less limited areas of a town may require the combined system through lack of facilities for near-by disposal of surface water, and again roof water alone may need to be taken into the sewers. and As stated above, local conditions relative costs are the tors in deciding governing facbetween the separate and combined systems. An old fallacy concerning the combined system may be mentioned, although it has now well nigh disappeared: It is that the storm water will flush the sewers. Regard- ing this it must be remembered that the 25 sewage flow is continuous and likewise the dangers of and from stoppages, while rainare uncertain in frequency and falls amount. As a matter of fact special pains now taken by the best engineers to give combined sewers such a section that the are dry weather flow will be in a small channel as much as possible like that which might be employed for sanitary sewers.* Whether subsoil drainage shall be (3) attempted. As for providing underdrains for remov- ing ground water, this will also in most cases depend upon local conditions. It is always an advantage to lower the ground water level in places where to render the it is high enough ground wet at or near the sur- face through a large part of the year. As sewers are generally placed below the level of cellar bottoms and underdrains are most commonly put below or at least not higher than the sewers, it follows that when of ample size underdrains will lower the loiv i-; i-xtended discussions 01' the combined and separate may be found in Waring s "Sewerage and L :nd Dra.nage," Staley & Pierson's " Separate System of Sewerage," and the many reports of engineers on proposed sewerage systems. systems ground water level to a considerable depth below the surface and render house foundations practically dry. It may be neces- sary to supplement the street underdrains by branches running to the houses, and even extending through large lots. The advantage beneath and of rendering dry the soil around habitations need nut be enlarged upon here, as it is so generally well known. But it may not be known to all that underdrains are often such great good sewer construction as to war- aids to rant their introduction for the benefits caused during construction alone. This is the case where the trenches are so wet as to render the making and setting of cement joints difficult. By putting in underdrains advance of the sewer proper the trench may be kept dry and the work greatly facilitated, even where temporary pumps must be provided to remove the water coliii lected. Where it is desirable for any reason to keep down the sewage flow to the lowest possible point, underdraius are also of value without regard to sanitary condi- 27 This tions. may be the case where the to be purified, or simply to be sewage or where several municipalities pumped, is use a joint outlet sewer, each contributing towards the maintenance of the outlet in proportion to the amount of sewage from The latter condiits individual system. tions are found in a joint outlet in New Jersey, where Orange, Bloomfield and Montclair use the same trunk sewer to the Passaic River, and have as the only basis of dividing the cost of maintenance amount of sewage contributed by each. Of course the aim in good sewer work is the ground water engineers and contractors know that in very wet soils tight joints can be made only with difficulty and to reduce the infiltration of to a minimum, but all practically never with absolute certainty. of flow in the outlet of the The volume sanitary sewers at East Orange, N. J., was at one time fully half ground water, according to careful estimates, and that was after the sewerage system was well estab- lished. It must be remembered that with the 28 2-ft. lengths of vitrified sewer pipe now almost universally used, there are 2,640 These joints are made joints to the mile. of cement, and are not for a moment comparable with the joints of molten lead, with their subsequent heavy calking, used in water main construction. In view of the above it is evident that underdrains should be used where they expected to benefit the health of a may be community by lowering the ground water level; where they will be sufficient aids to sewer construction to warrant their introduction for this purpose, to which is also to be added their permanent benefit; and finally, where it is desirable to employ them to prevent an increase through infiltration of the volume carried by the sewage, in which case the benefit to health will also accrue. (4) The best of the available means the final disposal of the sewage. for Until recently this part of the problem, at America, meant only into which of the near-by streams or lakes or at what point in tide water could the crude sewage least in be discharged at the least cost and with the minimum of offence. Too often the matter was given only scant considerand sometimes none at all. Un- of offence ation, fortunately many cities are to-day facing the problem in the same manner, but the advance of modern sanitation more and more imposible. is rendering this The cardinal principle in the ultimate disposal of sewage is that no public water supply be should Strange to say, this endangered thereby. must be interpreted as meaning that no city should endanger the water supply of either itself or its neighbors. This is almost inconceivable, for while one can imagine a city mean or ignorant enough to endanger the lives of the citizens of an adjoining community, it seems incredible that any municipality should be sufficiently reckless to poison its water supply with its own excreta. But both conditions exist and must be combated. This deplorable state be may explained in part by the general ignorance of sanitary matters which has prevailed until of late, and in of affairs fact is seen still to exist when one com- pares what is with what should le. It does seem, though, that common sense and common decency combined ought to be prevent a city from drinking sewage or forcing it down the sufficient to its own throats of others. Coming back to the expressed above 3 constitutes it cardinal principle may be asked "what the endangering of a public water supply?" No very definite answer can be given at present, owing to our lack of knowledge regarding the exact length of time which disease germs from the human system will live in water. The Massachusetts legislature some time ago said that no excreta should be discharged into a stream within point where 20 miles of any used for a public water in the matter of new water but supply, and sewerage construction it has practiit is cally placed the subject in the hands of There are no its State Board of Health. data to-day which will warrant an engineer in saying that disease germs may not be conveyed more than 20 in les by the ; waters of a stream and afterwards cause 31 sickness and perhaps death. The engineer and sanitarian will consider the distance which must be traversed by the sewage dilution which it would receive before reaching a public water supply, to- and the gether with the minimum length of time which would elapse before a disease germ could pass from one human system to Unless another, a most important point. distance, dilution, and time are great, sewage should be purified or carried elsewhere for disposal. Of course there may be cases where sewage disposal seems to claim preference to water supply, in the use of a stream. Each of these must be adjusted on its own merits. The willful pollution of public water supplies, even, if it seems remote, should no longer be tolerated, and where new sewerage systems is unnecessary that Given a body of it are being should be. Avater, built, it not used, nor likely to be employee! for a public water supply, the case is far different. Knowing amount of water and the probable quantity and character of the sewage, it is the generally eay to determine whether all the crude sewage of the city can safely be discharged into the water in question. Averages are of no use here. The water available during a hot dry summer, when the stream, pond or lake is at its lowest, and banks and beds are exposed to the sun, is what must be considered. Partial purification may be sufficient through a few months or all of the year for some and works have been carBut most plants country have been built under concities, ried out on that basis. in this ditions that demand continuous operation at their utmost efficiency. Where sewage is discharged into large bodies of water, either lakes or the ocean, generally necessary to make a careful study of the prevailing currents in order it is most available point or points of discharge in order to prevent the sewage becoming stagnant in bays or the to determine the washing ashore of its lighter portions. Such studies are commonly made by floats, as direction of current is factor of prime importance. generally the 33 When it is decided that purification must be employed, it becomes necessary to select the method best suited to local needs and conditions. This matter can better be discussed after the subject of purification has been taken up in detail, further on, and so will be dropped for the present. In concluding this phase of the subject, or postponing its further consideration, it may be said that until new advances have been made in the recovery of fertilizing matter from sewage, no compunction need be felt in discharging such into any body of water which can receive it without harm. Where such water is available it is often a mere question of the relative cost of an outfall to it and a shorter outfall with purification works to a nearer point of discharge where purification is necesOf course treatment of the sewage sary. is sometimes the only course which has a shadow of practicability. Again all conof such a procedure is often sideration unnecessary by an especially available point for the discharge of un- rendered 34 sewage. purified Where there is uncer- best to keep on the safe side and tainty Uncerprovide purification at the start. in these matters means tainty to-day it is certainty in favor of purification to-morwe advancing in sanitation row, so fast are and so rapid is the increase of population and also of the pollution of our streams. (5) Population, water consumption, and volume of sewage for which provision should be made, together with rainfall data if surface drainage is to be installed- The basis for population studies will generally be the United States census for a number of decades past, with figures for as intermediate years as possible local numerations. these figures percentages of growth many filled in From from State and for decades or shorter intervals may be computed and population curves plotted, and from one or both of these, coupled with present local conditions and future prospects, the 30 to 50 years population for the next may be forecast by decades or half decades. In small and rapidly 35 growing communities it must be remem- bered that the percentage of increase generally less as the greater. It is desirable to is population becomes design a sewerage number system large enough of years to come, say 30, though parts of the work need not be made so large, as to serve for a pumping or purification works where either or both of these are necessary. It is rarely the case that the whole population of smaller communities is connected with the sewers until years have elapsed after the construction of a system. This is due to lack of sewers on some streets and to that strange perversity of human nature which leads many people to put off the making of sewer connections as long as possible, notwithstanding the fact that the soil of their premises is daily becoming more and more polluted with excrementitious matter, and that the yearly expense of properly cleaning privies and cesspools is greater than the interest on the investment necessary for making sewer connec- 3G tions. In some communities allowances for these delays may be made in designing pumping or purification works, but the pipe system should be large enough at the start to serve each street and district for an indefinitely long period. The advan- tages of the use of city sewers are so great that all property is bound to be connected with them sooner or later, leased property without these conveniences soon dropping in market value. In view of these facts the population figures are sometimes based on an estimatad number of people per acre, or per lineal foot of sewer, more especially where a separate system of sanitary sewers being constructed. Safe figures of the cannot be laid down for general application, but must be decided on is latter class after a careful study of the question, the character of community its in residence property and general population. Often it is necessary to divide a city into districts its population and rate of flow studies. Thus the residence sections occupied by the for wealthiest classes will be comprised of a 37 comparatively small population per acre, duo to the large size of the lots. The grow more dense population will in the passage through the sections occupied by the less wealthy, the well-to-do and finally the tenement sections. city devoted to The portions of a manufacturing will in some sewage and manufacturing cities contribute wastes in pretty close proportion to the number of employers, while in others, or in different lines of industry, the sewage yield will vary more especially with the character of the goods being produced. The total water consumption is of course mainly dependent upon the population, and these two factors together enter largely into the amount of sewage requiring re- moval and disposal. No fixed rule can be down for water consumption, except that in general it is on the increase in all laid American cities, and in many places has reached immense and sometimes alarming proportions. It may be kept down by proper inspection and the use of meters for the prevention of waste, as it is absolute 38 waste and not beneficial use which is re- sponsible for high water consumption. The instances are rare where it is safe to less than 60 gallons per capita as the average water consumption per day of a town, if most of the people patronize allow for the public water supply. were to be laid If a general rule down 100 gallons would be a safer figure. Obviously not all the water which passes through a water- works system reaches the sewers. is for In summer much lawn and of it street sprinkling employed and similar purposes, very little of which reaches the sewers even where the combined system is in use, and practically none where a separate system of sanitary sewers is employed. But while all this tends to diminish the sewage yield the infiltration of ground water, already discussed, increases it, and average daily figures have been discussed above, while works must be built on the basis of maximum daily, or even hourly, yields. Altogether, then, 100 gallons per capita will be none too large except in particular cases or possibly for the immediate present, where 39 a portion of the works can be built for future enlargement.* The total daily flow of sewage is not distributed evenly through the 24 hours. The actual percentages at different hours day vary widely, according to the nature and occupations of the contributory populations. In most towns there should of the be scarcely any sewage, enough tween say 10 period of from tight if to prevent P. M. the sewers are infiltration, be- and 4 to 6 A. M., a six to eight hours. As a matter of fact few sewerage systems exist where the flow during these hours is not considerable. From two-thirds to three- fourths of the daily flow generally occurs during from say nine to twelve hours of the day, the particular hours varying some- what in different communities and having or no significance in designing the smaller portions of most pipe systems, but affecting the outlets and being of great little * For an extended study of vater consumption, with large number of American municipalities and with much other data on tlie relation of this subject and of population to amount of sewage, see Rafter & Baker's "Sewage Disposal in the United States." figures for a 40 importance where the sewage must be lifted or treated before its final discharge. Moreover, there are generally from one to three hours in the day when the flow is considerably above the average for the The heaviest ten hours. actual amount of sewage for these hours must be taken into consideration in the separate system and the plant designed accordingly. For ordinary laterals, these fluctuations need not be taken into account, for in the best practice these are for their duty. generally more than ample As the sewers increase in and territory served, and as disposal works are reached, the flow during maximum hours becomes of more importance. size Roughly speaking, total daily flow in 10 per cent, of the may be con- one hour sidered a perfectly safe limit.* When the sewers are being proportioned for their respective streets and districts, density of population must be considered. It is generally necessary to arrive at this " * Staley & Pierson, in the Separate System of Sewerage," givtt ihu maximum hourly flow as twice the mean hotirly flow, which would be about 8 3 per cent, of the total daily flow. 41 an arbitrary way, as actual figures, except for the whole town, are seldom available except in communities long since sewered, or that may be considered as in having reached their full growth. The proper figures must be reached for each community separately, so no attempt will be made to give them here. Rainfall data are liable to be very scarce in all but the larger cities and towns, and at points where the national and state weather bureaus have stations or observers. Such defects in the records as exthrough lack of observations, simply, cannot be remedied, but it sometimes hap- ist pens that figures for near-by towns will do But even when records are very well. available they may not be sufficiently detailed for the purposes under discussion. Monthly or weekly totals are of scarcely any use, and even daily records do not completely meet the case. What is necessities of the where storm sewers the duration and rate desired are to be provided is of precipitation of the heaviest rains. very heavy shower of 15 minutes A may 42 cause more inconvenience and damage, if the sewers are inadequate, than a steady There rain extending over a day or two. of course, a limit to the size of sewers* imposed by financial, and in some cases by is, physical conditions. Oftentimes, where sharp, heavy rainfalls occur, their complete speedy removal is impossible, and the surface water simply must be allowed to Sewers may generally stand for awhile. be so designed that they will speedily re the total rainfall except at long in tervals when an unusual precipitation oc^ move curs. After a careful study of all the rainfall records available and a consideration of the slope and character of tha area, especially with paved in forest drainage whether closely built up, streets, many roofs, small areas and under cultivation, or the the rate of rainfall per hour furnish the basis of calculashall which contrary, tions may readily be decided upon by any A maximum rate of competent engineer. 1 in. per hour may be considered as a liberal figure in some localities. The pro- 43 portion of this which will reach the sewers during a given time will depend upon such factors local surface its slope of land, as whether covered with houses and is paved streets, cultivated fields, or forests, and the permeability of such soil as is exposed. Extent and cost of the proposed (6) system. This is a matter largely dependent local treasury, or the willingness of the people to incur indebtedness, upon the levy general taxes, or pay special assessments for benefits, as the case may be. The to afford every buildcommunity an opportunity to ideal plan ing in the is connect with the sewerage system. This cannot often be done at the start, and in most instances sparsely settled outlying districts must wait long and weary years before the sewers reach them, although their taxpayers may be called upon year after year to pay taxes to redeem i,he bonds, meet interest, maintenance and repairs. The and most thickly settled community naturally will oldest portions of the 44 be sewered first, after which the system should be carried as far out in various Directions as the funds available will perThe exact course followed will de- mit. pend largely upon the legislative authority conferred upon a given municipality to raise money for sewerage construction. Practice in the several States, and often in the various cities and towns of one State, Somevaries widely in these particulars. times the city authorities have full power to lay out as complete a system as they deem best, either issuing bonds for its construction or levying assessments for benefits upon abutting property owners for a part or the whole of the work. Again, there is authority only for the construction of trunk sewers and other works for final disposal, the building of laterals depending entirely upon the initiative of property owners. All the local conditions, legal and otherwise, must be ascertained before the extent of the system can be settled. All work should be planned and carried out with the future in view and should be complete and adequate in itself and in re- 45 lation to other parts of the system, so that reconstruction will not be necessary for years to come, if ever. appears from the above, and from a simple common-sense view of the subject without regard to what has been written, It the system will be governed very largely by the local pocketbook and existing statutes, and that it that the extent of should be made to suit the most pressing needs of the community and be capable of easy extension as soon as possible. The cost of the system will be a matter for estimate in each case. Most sewer work, especially for sanitary sewers, is so simple, and there is now so much of it being esti- mated upon and carried out by engineers and contractors, that it is comparatively easy to figure up the approximate cost of a sewerage system. Local prices of labor and freight rates on sewer pipe, cement and brick, where the latter is used, are the main factors, and must be decided upon by each engineer in making up his cost The technical papers now pubestimates. lish exhaustive detailed lists of bids for 46 sewer work all over the country, and the reports of city engineers, superintendents of sewers, sewerage committees and boards of public works often abound in work figures or quantities and cost of actually done. (7) Method of meeting system. As stated down by this above, so law, that the is cost laid often there is the of little choice to be had, except in the details. But ample latitude is sometimes left and generally the details of carrying out even fairly definite laws afford a chance for a considerable amount of variation, together with much study. Broadly speaking there are two methods of raising money sewerage system a charge upon raising the isssue; and : to defray the cost of a (1) By making the work the whole municipality, taxation or a bond money by (2) assessing the cost upon the A combinaproperty specially benefited. The tion of these plans is very common. first one is sometimes put into effect and the second with comparative infrequency, 47 except for single streets or drainage districts of a city with independent outlets. The trouble with the second plan is that it not easy to determine the proportionate amount of benefit which each property is owner receives, unless it be in the most simple cises. The cost of constructing and operating a water- works system is met by the yearly rentals charged for water furnished the users of the same, but the general aim in the case of sewers is to make their use as popular as possible. Therefore, the most common practice in this country has been to charge nothing for using the sewer. An entrance fee, sometimes designed to repay the city the cost of supervising the work, and sometimes intended to help pay for or maintain the system, is often charged for connecting with the sewers and paid once for all. The actual cost of house connections is always, so far as the writer knows, borne by the house owner. Where the general public and the property especially benefited, that is, actually 48 or potentially served by the system as conshare the cost, it is divided in various proportions, seemingly without structed, rhyme may many instances. It may be the property all the way from one pays or reason, in be the city or benefited that to three-fourths it of the cost, or perhaps through a wider range. With the separate system of sanitary sewers a popular plan and an apparently cost is simply to fair be one, where the divided as stated above, is to assess upon abutting property the cost of the smallest-sized lateral sewer, or in other words of a just sewer just large enough to serve the houses on one street of moderate length. The further cost tensions, system or exbe raised in the of the would then general tax levy or by a sale of bonds. The assessments for benefits are levied upon the frontage bordering on the streets in which the sewers are laid, or upon the area of th'e lots, or are divided between these methods. The whole subject under discussion is a complicated one and has 49 never received the consideration it deserves from municipal But to one such an officers.* official, great credit should be given for having made a very exhaustive investigation of the problem and presented a solution which aims to be conducive to the rapid extension and use of his particular sewerage system, and in many points admirably adapted to other fair, localities. This study was made by Mr. F. H. Snow, City Engineer of Brockton, Mass., and the plan recommended was A adopted by that city. summary of Mr. Snow's report is given below, the importance of the subject, the lack of both popular and technical information regarding it, and the value of the report itself, seeming to warrant the devotion of a few pages to this purpose. f The population of Brockton is about The sewerage system includes a 30,000. * A monograph, entitled "Special Assessments," by Victor Kosewater. (Columbia College Studies in History, Economics and Public Law) will be of interest and value to those who wish to pursue the general subject further. t This summary is condensed from an editorial digest and discussion by the writer which appeared in " Engineering iVeutt" of Ju y 19, 1894. 50 receiving reservoir, pumping station, force main and filter beds. The first cost of the system, so far as constructed, was raised by an issue of bonds. The summary is as follows : In arriving at the proper plan for Brockton, Mr. studied with great care the various methods Snow of assessments already in use, after first having shown that the benefits of a sewerage system were partly public and partly private, and should be borne accordingly. Public benefits are, of course, to be met by general taxation. The proportion to be paid by the public has been fixed by the Massachusetts legislature at not less than one-fourth nor more than two-thirds of the total cost of the sewer- For private benefits a variety of methods are permitted by the statutes, such as frontage and area assessments, yearly rentals, age system. ****** entrance fees, or a combination of these. Either the frontage or the area plan alone is shown by Mr. Snow to be inequitable, diagrams being used to illustrate how by either plan differences in the shape of lots may allow several houses on one lot and only one or two on another, each having the same area or frontage, as the case may be. The entrance fee is also shown to be unjust, unless it is graded in accordance with bene- lot fits received, while, in addition, a large fee would 51 be required at the start, when there were but few connections, or else reliance on the general tax levy would be necessary The method finally . recommended by Mr. Snow given in his report as follows It is recommended that one-fourth of the total cost of the sewerage system be raised by first assessment, one-half by rental, and the remainder is : by general tax. It is also recommended that first assessmant be based on area and frontage of land adjacent to sewers 0.6 on area within 125 ft. of 4 on frontage that the first the street line and assessment be collected in one payment and credited to construction account that the unit of rental be 1,000 gallons of water reaching the sewer, this to be ascertained from meter gagings of the water department, and to be corrected for water finding another outlet than the sewer by a system of discounts 70 per cent, to be deducted from water supply of shops and 20 per cent, from water supply of houses having sill-cocks. And it is further recommended that abuttors be not compelled to enter the sewer as soon as completed that no one be allowed to enter without a permit that no rent be charged users before January 1, 189.5, rents starting from that date that such rents be charged from the first of the month following that in which the permit is dated and that all deficiencies be made up in the early years by general tax levy. It is further recommended that the following For first assessment, prices be assessed per unit 0.3 cents per square foot, and 15 cents per front foot; for rental, 28 cents per 1,000 gallons entering the sewer and that $8.40 be charged for unmetered connections, subject to a discount of 20 ; ; ; ; ; ; ; : ; per cent, for sill-cocks. These first assessments represent the value of the sewerage system to land, in enhancing its price without regard to whether the sewers are used by the owners of the land. The amount raised by general taxation will likewise represent the benefit to the community as a whole, without regard to the locat'on of the sewers. Benefits from actual use of the sewers are to be paid by rental, acsording to the amount of sewage contributed, and the sums so raised will be applied to paying off the bonds, meeting interest and to maintenance. The rentals will pay two-thirds of the total yearly charges, leaving the balance to be taxation. met by general It is eminently fitting that rental should be based on the amount of sewage contributed, since upon the latter depends the size of the sewers, and notably the cost of constructing and operating the pumping plant and filter beds. Fortunately at Brockton G5 per cent, rf the water connections are metered and the records of the water department are well kept, so that the sewer rentals can Obvieasily be based on the water consumption. ously on many premises some of the water used does not find its way to the sewers, hence the proposed deduction of 20 per cent, of the consumpand of tion for houses having sill-cocks for hose 70 per cent for shops. 53 The unit of 28 cts. per 1,000 gallons of water was arrived at by computing the probable yearly expenses of the sewerage system until 1900 and the probable water comsumption for the same period. It should be stated that the water consumption in Brockton is phenomenally low, only 25 gallons p( r The yearly rate of $8.40 for unmetered capita. houses was chosen because the minimum rates for metered water are such as to make it an object to when the water consumption goes above a point that would call for water users to have a meter such a rental. Coming to the amount to be raised yearly in the tax levy, the problem is simple, the amount being the difference between the total amount to be and that provided for as outlined above. Although this system has been worked out to meet the situation of Brockton, which is in a numraised ber of respects unique, the general principles involved may be applicable in other places. The special conditions at Brockton are as follows; (1) No sewers are yet in use, although the city has a population of about 30,000; this renders possible the adoption of any desirable system without the unfairness, real or fancied, which follows a change in the case of old systems. (2) It is expected that the whole city will be sewered in a comparatively few years, so that the total cost of the system can be readily estimated, which plan. (3) The is essential to this large percentage of metered water 54 taps and the fact that the city owns the water- works, so that water and sewer departments can co-operate, while each desires to keep the water consumption down, are favorable to a yearly Modirental plan, based on water consumption. fications of these conditions might make the system tion difficult when of application or might cause fricNevertheless- the principles at applied. the bottom of it seem correct, and this general distribution of the burden of a sewerage system, whether in these or other proportions, seems fair and likely to be popular. General public and individual private benefit are each recognized and the latter is divided into two classes, (1) potential benefit through increased value of a certain piece of property because the sewer passes by it and may be used, and (2) the actual benefit through use. Two dangers which beset the extremes of the two methods most usually employed to raise money for sewers seem likely to be counteracted to a large extent by this plan: (l) When the whole cost is put in the general tax levy or is met by bonds, the interest and principal of which must be met by taxes, it is difficult to secure money for extentensions, every taxpayer wishing to keep the rate down, and those living on sewered streets having no direct interest in extensions. In the Brockton plan the t~x levy is increased by only one-fourth the total cost of the sewers, the bulk of the expenditure being put upon those whose land is 55 improved or those who, by use of the sewers, are saved the expense of cleaning cesspools or privy vaults. system The taxpayer is, to feels that the sewerage large extent, self-sustaining, like a (2) The other municipal water-works plant. danger is that where property benefited bears the whole expense of sewers it will, in case of assess- ments for frontage or area, try to keep the sewer out of the street. But in Brockton a given property owner will be paying towards one-fourth the whether the sewers are in his and once in his street he need pay cost of the system street or not, only an additional one-fourth for property benefit, unless he wishes to connect with the sewer. The sewer once in, however, he will already be paying towards one-half of the total cost of the system and the additional expense for the use of the sewer will small. Moreover, by economy in the use of seem rental may be kept low, and most people do not consider themselves extravagant water users. water his (8) The needs of sewerage peculiar to of the health and the locality^ with a study mortality, of the town. Little need be said on these phases of the subject. The adoption of a scheme and the raising of money for its realization may be greatly aided by showing that demand the local conditions imperatively -56 A study of the health and mortality of the town, and comparisons of the results with like studies of communi- improvement. ties enjoying good sewerage systems is often helpful in enlisting popular enthusiasm for sanitary progress. But such work must be done wisely and false state- ments and impressions regarding the relation between unsanitary conditions and disease avoided as one would shun poison. There has been so much ranting of late regarding deadly disease germs lurking here, there and everywhere that many persons on reflecting that they and most of their neighbors still live, grow suspicious feel inclined to discredit the and germ theory of disease and the advantage of cleanliness in all the departments of life. It must be remembered that just as there are thou- sands of visible forms of plant life, of which only a very small percentage are poisonous, so among the many invisible forms of plant life known as bacteria or microbes there are only a few harmful germs. These few, it must be taught, , give rise to dire results when allowed 57 access to private water supplies, like house- through leaching privies and cesspools, or to public water supplies by discharging crude sewage into streams or lakes from which such supplies are drawn. Furthermore, unsanitary conditions, while not giving rise to certain forms of disease, wells, may render the human system unfit to ward off attacks of the same. reasonably presented, Facts like these, a may sometimes do world of good in an engineer's report, while the too common exaggerations would disarm instead of assure the people. ADOPTION OF THE ENGINEER'S REPORT. The report of the engineer having been completed and submitted to the proper officials its assumed. adoption by them them may be Sometimes the plan recommended has to be submitted to a popular vote, but more often where a vote is taken it is only indirectly upon the specific plans proposed, the real question being whether bonds shall or shall not be issued for the execution of the scheme. ral report is After the gene- adopted the next step is to 58 select an engineer to prepare detailed and specifications preparatory to contractors. advertising for bids from plans Frequently the engineer who made the engaged as designing engineer and sometimes to supervise preliminary studies is construction as well. This course has the advantage of continuing the services of one more or less familiar with local conditions, and with the plan for seweralready partially worked ing the town out. DESIGN AND CONSTRUCTION OF THE CONDUIT SYSTEM. The first work of the engineer will be to design his pipe or conduit system. For this task the topographical map already mentioned will be a help, but this should be supplemented by a profiles of all the streets in which sewers are to be laid, in order that the proper grades may be deter- mined and the accessories of the systems designed. Numerous diagrams and tables are avail- able for use in designing conduit systems, 59 rendering separate computations with the aid of complicated formulae altogether unnecessary, unless the engineer wishes to his own figures.* In the separate sys- make tem it is the minimum generally best to use 8-in. pipe as size, in order to lessen the risk of stoppages, for the although 6 ins. is ample volume of sanitary sewage from an ordinary residence street of medium length. Pipe sewers are generally made of vitrified clay, with a salt-glazed surface. Cement pipe (cement and sand) is also used 'in some cities. The size* of pipe sewer was for many years limited to a diameter of 24 ins. but some of the manufacturers now make pipe 36 ins. in diamThe 24 in. limit was eter for general use. in force because of the difficulty and expense of making the larger pipe and the comparative ease of laying brick sewers of any size from 24 ins. up. Monolithic sewers * Mathematical dipcussions of sewer formulae are beyond the bcope of this work. See Baumeister's "Cleaning and " Sewerage of Cities for a brief but able presentation of the subject, illustrated by diagrams, and Flynn's "Flow of Water in Open Channels, Pipers Sewers, Conduits, etc.," for " tables. Staley & Piersou's Separate Systems of Sewerage " may also be "consulted. More recent books are Ogden's Sewer Design and FolwelTs Sewerage." ' ' 60 have been used for a limited extent, the conduits being built in place from cement mortar.* In very wet ground cast iron pipe with lead joints is used, either because it is specially desirable to prevent because of fear of damage infiltration or through settlements. The pipe should be laid to grade with great care, and a good alignment should be secured. Holes should be dug for the bells of the pipe so that each length of the latter will have a solid bearing throughout. When the material is such as to make uncertain a solid support for the pipe, sand, gravel, concrete, plank or piles should be employed for the purpose. countered in trenching, If rock is en- will Le necessary for the pipe which will it to provide a bed not be washed into fissures of sub-soil water the eewer which is when the ground Little Falls, N. by the stream likely to follow is saturated. At Y., in the case of a vitri- a water supply conduit, such a washing-out of material occurred, fied pipe line for * Concrete, both plain and reinlomd vith steel, has bt-en into n*e since the lit t ed.tion c f this book was \N rit(it>U5;, but u.ore puniculaily for large fcew<,is. coming uu 61 causing settlements and the pulling apart of joints. The trench was opened through the rock portion and the pipe embedded in concrete. SUBSOIL DRAINS, OR UNDERDRAINS. Where sewers are in wet sand or gravel, subsoil drains, or, as they are more usually called, underdrains may be laid beneath or alongside the sewer to advantage, as discussed above. These are generally simple from have agricultural tiles 3 ins. in diameter no joints, being They upward. hollow cylinders, and are laid with simply their ends a fraction of an inch apart, wrapped with a cheap so-called muslin cloth, or other suitable material to keep out the dirt until the matter in the trench becomes thoroughly packed about them. These underdrains may almost always be emptied into the nearest stream, provided it is not used as a public water supply. This qualification is on account of the fact that the sewers may leak and sewage thus Such was con- flow directly into the underdrains. danger may seem remote, but it 62 sidered sufficient to cause the city of Boston to refuse to pay a promised sum toward the cost of the" sewers of South Framing- ham, Mass., so long as the sewer underdrainge discharged into a stream tributary to one of the sources of the Boston water supply. Boston had agreed to make this contribution in order to induce the town of Framingham to remove from the Boston water works. purification necessary, which manded pumped -its sewage This made de- in turn that all the sewage should be to the- filter beds and irrigation Naturally the town did not wish pump and purify the underdrainage, but area. to some years of delay and an offer of an additional sum from the city of Boston the town constructed reservoirs and filter beds for the purification of the underdrainage, all of which must be pumped a small after lift. Perhaps one of the best examples of subsoil drains beneath sanitary sewers, or at least the best example which has been described and illustrated in detail, is at 63 Newton, Mass., where drains were placed below many miles of sewers.* MANHOLES. Manholes should be placed at all changes of grade and at all junctions between two or more street sewers. These are built of brick and afford access to the sewer for In addition they are someinspection. times used for flushing. They are pro- vided with iron covers, the latter often being pierced with holes to afford ventilation to the sewers. When the covers are perforated pails are often suspended beneath to catch the dirt from the street so surface, especially in when the manholes are macadamized gravel or dirt streets. On long stretches of straight sewers lampholes are somtimes put in between manholes, consisting generally of a vertical piece of pipe extending from the sewer nearly to the surface and provided with a cover. These are valuable aids to inspection. * See Engineering News, January description of this system. 2, 1896, for illustrated 64 SEWER GRADES. The grades where of sewers should be sufficent, possible, to give them a self-cleans- ing velocity, thus rendering stoppages from ordinary suspended matters impossible. " Baumeister, in his Cleaning and Sewerage of Cities," makes the following state- ments on this subject: Practical experiments show that sewers of the usual sections will remain clean with the follow- ing minimum 2 tions, separate house conneccases, 1 per cent. grades: per cent. extreme ; Small street sewers, 1 per cent. ; extreme cases, Main sewers, 0.7 per cent. ex0.7 percent. treme cases, 0.5 per cent. The extreme cases are ; for sewers carrying only rain or quite pure water. The following empirical formula will give the minimum grade for a sewer of clear diameter equal to d inches and either circular or oval in section : Minimum grade, in per cent ~r 100 >_i_ro FLUSHING DEVICES. Where very low and grades are unavoidable branch sewers where at the heads of the volume of flow is small, flushing may In some cases a be used with advantage. 65 copious supply of water is turned into the sewer through a manhole from some stream, pond or lake, or from the public water works system. Generally, however, the water introduced is allowed to accumulate before discharge, being held back, for instance, by plugging up the lower side of a lates in manhole it, until the water accumu- then suddenly withdrawing the plug and releasing the water, upon which rushes down the sewer carrying before practically all treme it it obstructions, except in ex- cases. Instead of relying upon clear water, as described above, it may l,e sufficient at some points on the system to simply back up the sewage by plugging the manhole outlet, thus sewage flushing the sewer with the itself. The necessity of frequent and regular flushing has given rise to automatic flushing tanks. These generally make use of the siphon for self-discharge, although there is on the market a purely gravity flush tank, when full. which tips by its own weight Whatever the means of dis- charge the feed to the tank is regulated by a valve or cock on the supply pipe, so the tank will fill and empty once in a given number of hours. Y-BKANCHES FOR HOUSE CONNECTIONS. Provision for house connections should be made when laying sewers, avoid as much as may in order to be tearing up the streets after the pipe system is in breaking of holes into the sewer. and the It is a wise plan to lay the house connections from the street sewer to the curb, or even across the sidewalk, while the street is dug At the least Y-branches for house up. connections should be put in at frequent intervals, say from 25 ft. apart upwards, according to the character of the street. When the sewer is put down deep quarter bends are sometimes provided and the house connection pipe carried vertically upwards until within a few face to avoid deep digging. house connection may join feet of the sur- However the the sewer, or any two sewers join each other, the direction of flow in connection and street sewer 67 should be as nearly the same as possible, and the entering sewer should be at a little higher level than the sewer entered in order to increase the velocity of the influent sewage and thus lessen the tendency retardation and stoppage which naturally results where two confined streams to with matters in suspension unite. DEPTH OF SEWERS BELOW SURFACE OF GROUND. No general rule can be laid down for the depth of sewers further than that they must be deep enough to :idmit of house connections with a proper fall, and on the other hand should be p.s near the surface as possible to save the expense of deep trenching. Of course they must be kept below the point at which clanger from freezing might arise, but the natural usually sufficient to make such a consideration unnecessary, especially as the depth is temperature of sewage is generally a number of degrees above that of the atmosphere at the street surface. 68 VENTILATION OF SEWEKS. The ventilation of sewers is a subject fraught with many fears and perIn the early days of sewers the plexities. still conduits were faulty in the design of their cross-sections, in their grades construction. and all of in their these con- Practically duits originally carried surface water, and large quantities of Many of these conduits, infiltration through ground water. as stated at the beginning, were built to carry storm water alone, in other words were simply drains. With the advent of ample public water supplies and modern plumbing, which, with its many fixtures providing hot and cold water at every hand led to high water consumption, houses were connected with the drains, Still thus converting them into sewers. this the of convenience later, practice being recognized, conduits were designed and built to carry both drainage and sewage, but these sewers on what we now call the combined system were little or no better in design and construction than the old 69 drains. The consequence of all was that the uneven bottoms made surface this long stretches of sewer little or no better than cesspools, and this cause, with poor construction, gave rise to stoppages which still further aggravated the stagnation. Decomposition, without the presence of a plentiful supply of oxygen, evolved offensive gases, which sought the upper air all possible channels. Street infor surface water and manholes for through lets cleaning belched forth gases whose malo- dorous presence was easily recognized. Too often these odors were noticeable in houses. To prevent such a state of affairs various methods of sewer- ventilation were tried, which it is unnecessary to describe here. In modern work of good design sewers are built with the intention of removing all sewage immediately before offensive de- The has time to begin. are as as grades possible, nearly perfect the interiors are reasonably smooth to composition prevent adhesion of putrescible matter, and the manholes have perforated covers to aid in ventilation. In some cities ven- 70 tilating shafts are provided to supplement the manholes, these sometimes being the soil pipes of the houses, the main trap being omitted for this purpose. The latter practice is recommended by some of the best engineers and sanitarians of the day, the theory being that by such means well constructed sewers are kept so filled with from bad gases, that no harm can arise if occasionally a trap to some wash bowl or water closet fails and the sewer air reaches a dwelling room. fresh air, and so free But notwithstanding these opinions the majority of sanitarians still object to ventilating sewers through houses and insist upon the main trap. It seems obvious that system of sewers, with 4-in. ventilating 50 or 100 ft. pipe the separate small laterals, a not needed every in its is on both sides of the street to change the air in a 10, 8, or even, as is sometimes the case, a G-in. street sewer. The most common practice is to assess the whole or a considerable portion of the cost of such small sewers ; property owners. Where upon abutting done it this is 71 difficult to say to one man out of perhaps five, "you must for the general good omit the usual main trap from your may be pipe in order that the street sewer may be ventilated ; or if you object to that you may run a separate ventilating soil pipe from your house sewer at a point just outside your main trap to the top of ,ypur Naturally, most roof." men would object an alternative, preferring not to might think, with ample from support engineers and others supto the lives of themselves know, posed to such risk, as they ana their families, nor to spend money to avoid such a risk while four of their neighbors were not called upon for either To be sure some means risk or sacrifice. might be devised to ventilation this through their would give the cost of assess these extra pipes upon the where the people refused rise to town to at large, allow the soil pipes, some the best, so that the wisest course be to provide extra ventilation, perience showed but trouble, at might if ex- necessary, entirely at town expense, and independently f dwellit ings. The matter of ventilation is further discussed at the end of the next section. MISAPPREHENSIONS REGARDING SO-CALLED SEWER GAS. Before leaving this subject a few words seem necessary regarding misapprehensions on the question of so-called sewer gas and the conveying of disease germs thereby. And first, there is no specific and defin- sewer gas for which a chemical formula or combination of symbols can be laid ite down. The air in sewers contains in greater or less degree some of the gaseous products of chemical decomposition whenever changes are taking place in the organic matter conveyed by or deposited in the sewers. This air is harmful if breathed, same as any other foul air, and to no greater extent, except for the slight possibility that it may contain harmful bacteria. The disease germs which may be just the expected in sewage are essentially waterborne instead of air-borne, and develop in the human intestines rather than in the 73 throat, nose or lungs, and therefore gain access to man chiefly tli rough food and drink. The germs carried by so-called sewer gas must obviously be air-borne and from their origin are not likely to be found in sewage, or if found they would be in small quantities but while all this is true it does not make sewer air any more de; sirable for breathing. impure The air give rise are evils to which invidious, attack- ing the weak and undermining the physical system of both weak and strong, ren- dering them more susceptible to various forms of sickness, notably the zymotic or Thus it is evident that no filth diseases. matter how much the nature of the dan- gers from this source may have been misunderstood in the past they are sufficiently grave to demand ward them off. all The reasonable efforts to first aim should be to prevent, as far as possible, the formation of foul air within the sewers, and the second to keep such air as may form away from mankind. After good design and construction of the sewer conduits, as such, have been secured ventilation should be called 74 upon for the introduction of a plentiful supply of fresh air and the removal of 'foul air to points where it will be diffused throughout the atmosphere without offense. Stagnation of air within the sewers must be avoided. DR. BILLINGS' OPINIONS ON SEWER AIR AND VENTILATION. Before leaving this subject some quotamay be introduced to advantage from tions the exhaustive work entitled "Ventilation Heating," by. Dr. John and formerly Siirgeon^General U. S. Billings, S. A., recognized sanitary authority. other things Dr. Billing's says and a Among : The structed an ordinary modern, fairly well conand ventilated sewer appears to differ from the street air chiefly in air of having a higher pro- portion of carbonic acid. * * * 1C * * Specific pathogenic micro-organisms have not been found in the air of sewers * * * * As and soil pipes, the condition regards house drains them in air greatly upon whether depends cf the So long as ventilated or not. "are they properly 75 them are in daily use these pipes are lined with a moist slimy layer of organic matter, in which bacteria of various kinds the fixtures connected with in immense numbers. If the supply of air abundant, these bacteria are mostly aerobic and the substances produced by their action are, as a grow is and are rapidly carried away, by the ****** rule, odorless next flush of liquid, if soluble. In hospitals, before the introduction of antisepmethods of treatment of wounds, the pyogenic tic organisms were of course very numerous in the hospital drains, and there are several cases in which localized outbreaks of erysipelas and unhealthy wound action appeared to be connected with the passage of the house drain air into the ward. ****** Distinguished English sanitarians believe that typhoid fever has been spread through the gases coming from foul sewers, but I know of no satisfactory evidence of such an occurrence. Diph- and typhoid fever are diseases which premore extensively where there are no sewers than in the sewered part of the cities, even where theria vail the sewers are badly constructed. While I do not attach much importance to sewer means of transmission of specific disease, I believe that its continuous inhalation is dangerous, air as a owing to the large amount of volatile organic mat- 76 which it contains, and for that reason, as well as to prevent the formation of explosive mixtures and of unpleasant odors, continuous ventilation ter should be provided for and all sewers, house drains cesspools. In well constructed sewers Dr. Billings considers ventilation an easy matter, which can generally be effected by frequent openings to the outer air, and always at each dead end of a sewer. Special tall ventilating shafts, or ventilation through factory furnaces or chimneys he considers as of little value, stating that the influence of such shafts or chimneys extends only to the nearest air inlet. Ventilation through house soil pipes is approved where the sewers and house connections are properly designed, constructed and operated, and all are under the control of the municipal engineer, provided also the houses uniform on a given street are nearly in height. Where opposite condi- tions prevail, so that the air in the sewers is bad, and the tops of the soil pipes of one house would end under the windows of another, the Doctor thinks that main traps 77 should be placed on all soil pipes and air inlets and outlets be placed on the sewers at intervals of 300 to 400 ft. FEATURES PECULIAR TO THE COMBINED SYSTEM. Coming now system their to sewers of the most notable combined differences from separate sanitary sewers are their greater size and the use of catch basins or inlets for the admission of surface water. are generally of brick, stone, or concrete, or a combination of two or more of these, instead of being chiefly of vitrified They pipe. Still another distinctive feature is the provision of storm overflows, by means of which the main sewers, when overcharged at times of heavy rainfall, may empty a part of their contents through a some water course. At short conduit into such times the sewage is diluted by the rain-water, while the stream which receives the overflow large vplume. The is also of an unusually relief thus afforded ren- ders possible smaller conduits than could 78 otherwise be used without backing up sewage into houses or flooding streets and cellars SIZE, on the lower levels of the city. SHAPE AND MATERIAL OF COMBINED SEWERS. The actual size of the sewer of course depends upon local conditions, as to a large extent does its shape and material. Where the depth of flow varies greatly it is de- sirable to give the sewer a cross-section designed to suit all flows as fully as possible. Experience has shown this to be an approx- imation to the cross-section of an egg placed upright on its smaller end. With this maximum section a sewage is depth and velocity of secured for a minimum flow, rendering deposits and stoppages far less With sewers having a flow more liable. nearly constant and equal to their full capof acity the form may be modified to that an ellipse, a horse shoe with an arc of a circle or for some an invert, or bottom, a circle, combinaor modification tion of these, according to circumstances. sewers brick is by far the For the larger most common material, both because of cheapness and of its adaptability to any Stone inverts are sometimes emshape. on ployed heavy grades, notably where its much sand is carried in suspension, in or- der to present a more lasting surface to the scouring and wearing effect of gritty maConcrete is sometimes used for in- terial. verts, where leakage may be expected, or movement, but more in material liable to commonly it affords a foundation for the The concrete is also sometimes extended up the sides of the sewer, and sometimes completely around it.* If the brickwork. material is liable to much settlement, as in marshes and bogs, the sewer may be constructed on a timber platform, the latter sometimes being supported by piles, generally having at least a thin layer of concrete between it and the invert. It not infrequently occurs that sewers rock. In com- must be constructed through paratively rare cases this is sufficiently solid to warrant the use of an unlined tunnel, where grades are * See foot note, i>age CO. sufficient to permit a 80 rough surface. But generally stones and uneven walls left after blasting make lining necessary, which is commonly composed of brick, with any spaces behind the filled with brick or stone masonry, or concrete. ring or rings CATCH BASINS OB RAINWATER INLETS. A catch basin is generally placed at each with a grated opening, or otherwise, giving the surface water access to a chamber or basin beneath the sidewalk, from which a pipe or other conduit leads to the sewer. Catch basins may be provided street corner, with water traps to prevent the sewer air from reaching the street, but these traps are liable to lose their seal through evaporation in dry weather, unless they are re- newed by manual labor from the public water supply system. To prevent the carrying of street washings into the sewers catch basins should be provided with silt chambers of considerable depth with overflow pipes leading to the sewers, and thus lessen the bulk of the heavy suspended matters in the silt chamber to be removed " 81 by buckets and carted away at proper inIn the case of long street blocks basins may be placed in the centers tervals. catcli of the blocks, as well as at street corners. STOEM OVERFLOWS. Storm overflows are simple in theory, and often so in construction, the main point being to ensure an overflow into another conduit when the flow reaches a certain elevation in the sewer. main and intercepting sewers are Where at right angles to each other the connection is sometimes so made that the dry weather flow drops into the intercepting sewer, but the flood flow, with its greater volume and velocity, shoots over the interceptor, in part, and into and through the overflow sewers. The lower portions of main sewers formerly discharging at many points into a stream or lake are sometimes utilized in this manner when intercepting sewers are added. The junction of large sewers, and other complications in combined sewerage systems, sometimes afford ample opportunity 82 and contractor in designand ing building masonry suitable for such for the engineer places. Sewers designed to remove surface drain^ age alone are practically the same as combined sewers, without house connections, and need no discussion here. PUMPING STATIONS, RECEIVING RESERVOIRS AND FORCE MAINS. A large percentage of the sewerage systems of the United States and Canada operate wholly by gravity, but it is sometimes necessary to pump a part or all of the sewage of a city. The lifts involved are usually quite low, so that high-priced pumping machinery may is not required. It be necessary to thoroughly screen the sewage before it passes to the pumps, or to provide these with valves not likely to be injured by the miscellaneous bulky substances in the sewage. The Shone hydro-pneumatic system, used at the World's Columbian and elsewhere in this country Exposition and abroad, may sometimes be used to lift successfully 83 sewage to higher levels. In this system compressed air from a central station is automatically discharged into a receiving chamber with which the sewers are connected, whenever the chamber fills to a The air under pressure certain point. forces the sewage through the outlet pipe. Where pumping is necessary receiving reservoirs with more or less storage cap- may sometimes be provided with advantage, to equalize the work demanded acity pumps and perhaps down the pumping of the to permit shut- ting plant at night. Such reservoirs are generally covered, unless in very isolated localties, and may be ventilated by connecting with the smokestack, or the gases from the ventimay be conveyed to the furnace fire. lator Force mains are generally required in pumping plants, but some- connection with times the latter are so near the point of outlet, serving as mere vertical lifts, that the discharge pipes from the pumps cut no When employed the force main figure. will naturally be of cast iron, similar to that for a water supply system. 84 TIDAL CHAMBERS. Besides receiving and storage reservoirs at pumping stations these may be required where the disposal of sewage is into tide water under such conditions that it is necessary to discharge it on ebb tides. The main distinguishing features of such compared with these desan arrangement of gates which will permit of emptying the reservoir in a brief period. These gates should be easily handled in order to reduce the cost of attendance. This may sometimes reservoirs, as cribed above, is be effected by mechanical power provided by the outflowing sewage. FINAL PLANS AND SPECIFICATIONS. Before bids for construction are invited and specifications should be prepared by the engineer. The plans should be in sufficient detail to make the general full plans design and all the accessories of the sys^ to bidders, and the tern perfectly plain specifications should be explicit upon every 85 comes within their scope. Blue prints of the plans and printed copies of the specifications should be ready for all inquiring bidders in advance of the point which date fixed for opening bids. The specifi- cations are usually accompanied with the form of contract to be executed between the city and the successful bidder. In the matter of specifications and forms of contract the engineer should generally work in conjunction with an able lawyer, the city's permanent legal representative, or circumstances. otherwise, according to Years of experience on sewer work in a may fit an engineer to cope all the legal questions with single-handed involved, but in the long run co-operation with members of the legal profession will particular city When difficulties prove advantageous. with contractors arise the city's legal adviser is pretty sure to be called in, so it is well that he should be consulted at the start. Outside of his the engineer may own particular city be practically helpless in legal matters, owing to the wide divergence of laws relating to public im- 86 provements in cities of the same and of different states.* SECURING BIDS AND AWARDING CONTRACTS. In no department of the engineer's work money be saved his employers can more than in the securing of numerous truly competitive bids from able contractors and deciding to whom the contract should in be awarded. On the proper performance depends not only the first cost of the improvements, but the interest and maintenance account and to a large extent the successful operation of of these duties the undertaking. It is more essential to secure an able and honest contractor than a low bid; more important that the work be done well than that it be done cheaply. The number and character of the bidders on a given job will depend upon the importance of the work, the publicity given to the proposed letting and the character * A form of specification and contract is given in Staley & Pierson's ''Sepatate System of Sewerage" Prof. J. B. " Johnson's " Engineering Contracts ai d Specifications is a valuable book devoted exclusively to the subjects named in its title. 8? of the plans, specifications In these days of contract. and foi-ms of numerous con- tractors eager for work at a fair price it is only necessary to present a clear idea of the for work to be done and just conditions execution to secure an abundance of its proposals on almost any job, provided only the opportunity to bid be brought to the attention of the possible bidders. Most cities and towns are obliged by law where advertise all contract lettings more than a small cost is involved. to It is generally required that the advertisements shall appear in one or more local news- papers and permissible that in others. The the large cities, it be inserted local newspapers, even in reach only a small propossible bidders, almost ex- portion of clusively those of the city in which the papers are published. For this reason, and because of the better results which ex- perience teaches are to be secured thereby, thv3 practice of advertising engineering contracts in growing course is engineering journals in favor of late. is When rapidly such a pursued the work in hand is brought to the attention of the contractors of a great section of the country, or of the if of sufficient importance, whole country, instead of to those of one city, and the number of bids received is in like propor- But this is not the only advantage. The wider competition renders far more tion. difficult, yes, practically impossible, except under the most corrupt city governments, the growth of a ring of local con- who through combinations, personal favoritisms and even worse, maintain prices at a high point, at the same time tractors generally doing poor work. The. bids having been received, they should be referred to the engineer for tabulation and recommendation. From his estimates of quantities he can determine the relative aggregate prices of the several and from his knowledge, through acquaintance and inquiry, of the bidders, and of the probable cost of the work in bidders, upon and report the most favorable bid. As stated above this is by no means always the lowest bidder, and it should net be obligatory upon the question, he can decide 89 award the contract to the parties do the work for the least city to who offer to money. many Unfortunately the experience of cities in having their officials award contracts to favored bidders has led to leg- enactments affecting some localwhich make it imperative that con- islative ities tracts shall be given to the lowest bidder, although often the privilege of rejecting all bids and readvertising is given. This is a long step in advance, but where the can be trusted time and expense officials can be saved both city and contractor by allowing an award to other than the lowest bidder, if demanded by the best interests of the city, based on past records of contractors and the danger of poor work at ex- Such a course, aside cessively low prices. from obliging a city to accept an undesirable bid, discourages designing contractand those who, in their eagerness for work, figure too low, and does not call ors upon responsible men, of good judgment, to be to the trouble and expense of putting in bids the second time. 90 THE PROPER EXECUTION OF THE CON- TRACT. The contract having been awarded and construction started, it devolves upon the engineer to give the contractor all necessary lines and grades, and any information needed and not provided in the plans and specifications. It is also his duty, both personally and through his inspectors, to see work is done according to the This requires the and plans specifications. most careful and conscientious attention on the part of able men. Every detail of construction must be watched with an eagle eye and no work not subject to complete examination after it has been executed that the should be allowed to proceed in the absence of the inspectors. On pipe work or conduit construction, especially, one inspector should never be called upon to look after work in more than one street at the same time. Pipe and brick must be examined with the greatest care, the former Cement should be subpiece by piece. to test to show its fitness for jected proper 01 the use to which it is to bo put. This re- quires at least a simple testing laboratory, and the provision of a fully-equipped one is money well spent where naich work is to be done. After the sewers are completed they should be tested for obstructions, the small sewers by passing a ball through, or otherwise, and large ones by having a man go through them. REGULATIONS FOK THE USE OF SEWERS. These include all necessary precautions for the prevention of obstructions, chief of which, perhaps, is the proper laying and joining to the street sewer of house conThis work is often, if not gennections. done by plumbers, but all such should work under a license, revokable for erally, non-compliance with city and town ordinances, and should be under the supervision engineering, sewer or health department. The size, grade and material of house connections should be specified in the of the above regulations, and in order that prosecutions and punishments may be possible for offenses against these and other rules 92 necessary to have an ordinance or or. dinances passed, embodying all the neces- it is sary rules and regulations and providing penalties-.* OPERATING THE SYSTEM. The sewers completed their operation is nearly always very simple, especially where pumping or purification is not necessary. A superintendent of in sewers, in fact if to not have name, generally employed general charge of the sewerage system. This official often oversees house connecis and frequently has charge of minor, and sometimes of important extensions of the system. He removes stoppages and looks after flush tanks and other devices tions for keeping the sewers clean. If pumps are used these are likely to be in sole charge of the pumping engineer> although he may be under the superintendent. Where purification is employed a man independent of the superintendent may or may not have charge. All purification * A model tem ordinance will be found in the of Sewerage. " ' ' Separate Sys- 93 plants should be under the immediate direction of the most competent men attainable, within reasonable limits, as intelli- gence and knowledge are absolutely essential to their continued, and often to their temporary success. Politics and political berths should be kept clear of this depart- ment of the sewerage system, other it should be from if from no all parts. SEWERAGE COMMITTEE, BOARD OF PUBLIC WORKS OR CITY The above COUNCIL. considerations suggest the question, should the construction and operation of a sewerage system be entrusted to a sewerage committee entirely independent of other departments of to city government, a board of public works charged with other municipal improvements of an engineering The character, or to the city council ? answer to this, like that to so many otln-r questions already raised in this volume, is that local conditions often determine what is best. It is cities interesting and towns, as to note that ck-arly English in Dr. shown Albert Shaw's " Municipal Government in Great Britain," manage in an admirable practically all their public works through their city councils and committees of the same, always relying, however, upon able and experienced engineers and others for technical advice and the details manner In this country the mistrust of operation. of city councils has been, and largely is PO great that the first thought of tax-payers on undertaking the installation or ex- tension of to entrust some important public work is it to a special and independent body of men. The English system has the advantage *- that all public improvements are thereby carried out with due consideration to their r relation to eSeh other and to the finances A of the^ity as a whole. board of public works entrusted with streets, sewers, water . and lighting plants, if the two latter be operated by the city, would be a close approach to the English plan, and would in many instances have its advantages over that plan under American conditions. Generally speaking independent sewer 95 commissions, right men if only and it is composed of the which counts have built and are this more than any system managing sewerage systems with good results in this country. But from the nature of the case they cannot always so plan their work, for instance, as to interfere as as possible with good street pavebecause have no control over ments, they the time and place of laying such. Whatlittle ever the system, an able city engineer, or engineer of the sewer department, should be given the practical settlement of all en- gineering questions. SEWAGE PURIFICATION IN ITS GENERAL ASPECTS. Having treated the other phases of the subject as fully as the space available will permit, there remains for consideration the important matter of sewage purification. This has been reserved to the last, except for the incidental references to it already made, because it is quite complete in itself and demands independent handling. The main principles of sewerage construction, 96 from disposal works, have been established for many years, but the best aside means of rendering sewage fit to discharge into water courses or other bodies of water not suitable for the reception of crude sew- age are problems of yesterday, to-day and even of the future. Enough has been settled, however, to render no longer valid the plea that sewage purification is as yet in too experimental a stage to forbid efforts We know to a certainty how sewage may be rendered harmless. in that direction. Further knowledge will probably be in the line of making present processes do more work without additional cost. The facts are, that the two older systems of sewage purification and chemical for now in use, precipitation, land treatment were practised years in a blind rule o'thumb way, and often with good results, before many their fundamental covered. Since principles were dis- the discovery of these principles, or natural laws, we can do nearly always what formerly was done only occasionally. Blood pulsed through man's veins for 97 countless centuries before Harvey dis- covered the law of circulation, and many maladies incident to blood and circulation were helped or healed in utter ignorance of the law, but since and by means of the discovery what a revolution there has been in medicine and hygiene ! We look for- more progress in these particulars, but we do not for this reason hesitate to ward to avail ourselves of all that has been accom- But this is exactly what some plished. do in the matter of sewage would people purification, or at least they offer as an excuse that the science in too tentative a is stage to warrant the adoption of any plan as yet, their real motive too often being a desire to keep the municipal purse strings pulled tight. What is most needed now is not new processes, but the careful carrying out of well-known methods, with observations on the results obtained under all the varying which naturally arise in and under varying conditions at the same works. We have a host of suggestive and many conclusive circumstances different localities deductions drawn from careful and longcontinued experiments, both at home and abroad, but we need, particularly in Amerto have more of the scientific spirit and method which have made the laboraica, work tory so successful applied to the daily operation and study of actual sew- Instead of caviling at the age works. uncertainties of sewage purification those who raise questions might better take their turn at efforts to perfect, simplify and cheapen the already admirable processes now available. They may rest assured that the worst yet attained by intelligent effort along the new lines of work is infinitely better tion than the shameful prostituand lakes now going on of streams throughout this broad land, a marring of beautiful face of nature, rendering limpid waters black and repugnant, chang- the ing their refreshing breezes to sickening odors, while life-giving water is made a death-dealing poison, and all through sewage pollution. Before taking up sewage purification in it will be well to consider what sew- detail age from the standpoint of the chemist bacteriologist, and what should be is, and expected or purification. it appears at way of its and as when fresh, Sewage, the mouth of an outlet sewer, desired in the a cloudy, opaque grey with some large particles of suspended matter not easily broken up in is generally liquid, transit, as orange peels, rags, paper and various nondescript articles too numerous It very often has a faint, to mention. musty odor, and in both looks and .smell sometimes quite comparable with the of suds-water family laundry work. of the is all sewage Nearly simply water, the total solids in supsension averaging is perhaps 2 per 1,000, of which a half may be organic matter. It is this 1 part in 1,000 which is to be removed or so changed in character as ttfW 'rendered harmless. These facts regarding the composition sewage are far different from the popular conception, which pictures a vile mass, indescribable in appearance and odor. Such ideas are gained in part from the of 100 contents of cesspools and from improperly constructed and neglected sewers, known but they arise largely in vivid imaginations. They would be applicable in many sewage allowed to stagnate and take on putrescible decomposition, as happens in cesspools and obstructed sewers, or where the sewage stands on the surface of respects to poorly graded land disposal areas, or accumulates in any similar manner before being purified. The greatest danger from sewage is in the harmful bacteria which it conveys, but even these are not to be feared if kept out of the human system, to which they rarely gain access except through water used for domestic purposes or in connection with milk supplies. Generally speaking, sewage swarms with bacteria, engaged, when sufficient oxygen is present, in the laudible occupation of converting unstable organic matter which might become offensive into fixed mineral compounds of a wholly unobjectionable These plants may millions to the teaspoonful, and character. number yet be 101 wholly invisible, so minute are the organisms and so hidden is the mighty work in which they are engaged. To isolate the harmful from the harmless with certainty, if at all, is an achievment for some future Pasteur. The organic matter and the bacteria always accompany each other. If all the bacteria should be removed or killed, but some of the organic matter remain, another crop of microbes would develop as if by magic as soon as seed was sown, although the renewal of disease germs in their orginal quantities would rarely, if ever, occur except from a source the same as or similar to the original. But, remove all the organic matter and all the bacteria food is gone and without food death comes swiftly, even though the bacteria be legions. From the above it may be inferred that sewage purification processes are valuable in so far as they remove or change the composition of organic matter. Mechanical straining, sedimentation and chemical precipitation are largely removal processes, all 102 while septic tanks, broad irrigation, intermittcnt filtration, contact beds and percolating filters change the putrescible organic matter into stable compounds. Either form of land treatment may be employed where practically complete purification is desired. Straining or sedimen- remove only a small portion of the organic matter. Chemical precipitation and the use of septic tanks will do more, but must be supplemented by irrigation or intermittent filtration where a high degree of purity is required. Contact beds and percolating filters, generally tation will preceded by septic tanks, but sometimes by sedimentation or chemical precipitation instead, may be relied upon to pro- duce a non -putrescible effluent relatively free from suspended matter, but generally high in bacteria. Aeration may also be be called in to supplement other processes, but the part which it can perform is far more limited than is supposed by many. The object of sewage purification, then, being the removal of organic matter, and certain modes being available for the 103 partial or complete this end, the question accomplishment of which is the most is, Like nearly all the other queswhich have arisen in the course of tions this book, and like most other questions in desirable ? engineering, other sciences or the arts, The degree of there is no one answer. purification required and the local conditions which make one system cheaper than another in construction and operation all have their weight in selecting a system of disposal. It sometimes happens that a partial removal of the organic matter contained in sewage is ample, in which case the 20 to 30 per cent., more or less, that can be accomplished by either sedimentation or straining will be sufficient. If better results are wanted and some 50 per slightly more, of the sedimentation may cent., or is needed, be accelerated by purification the use of certain chemicals, which constitutes chemical precipitation, or the septic tank may be employed. If neither of these will suffice, the effluent from either process, or in fact from sedimentation or 104 straining, may be applied to a sewage intermittent lating filters farm, contact beds or percoor where plenty of hii'd is filters, ; available, all previous treatment dispensed with and intermittent may be filtration or irrigation, commonly known as sewage farming, or a combination of these two land processes, may be brought into requido all the work. Obviously where sition to only partial purification is required there be a wide range of choice between may the methods named.* Although the object of sewage treatment may sometimes be the removal of bacteria, the chief aspect of most of the sewage works now in operation is to prevent nuisances in the nature of foul sights or odors. Where public water supplies are involved the aim is to keep the sewage out, or to purify the water, or both. SEDIMENTATION. This is effected by allowing the sus- See " The Partial Purification cf Sev age," by C< 1. Geo. E Waring, Jr., Ewjin- ering Aevsof Jau. 4. 1894, for an eit<-ndt d d.scussion of the subject named in the title just quoted. * 105 pended matters to settle tanks. in The partially clarified liquid is drawn off, leaving the solid matter, called sludge, at the bottom for subsequent disposal. This proas has been intimated, is akin to cess, chemical precipitation, so the shape of the tanks, the relative merits of continuous and intermittent settlement and the treatment of the sludge will be taken up later on. Experiments with sedimentation at Lawrence, Mass., during the last three months of 1893, indicated a subsidence of 18.2 per cent, of the albuminoid ammonia and 12 per cent, of the bacteria in the crude during a period of four hours. experiments in 1894 showed a sewage The same much better average for organic matter, as measured by the albuminoid ammonia, but about the same results for bacteria, the respective figures being 30 and 14.6 per cent. In 1895, there were removed 48 percent, of the total albuminoid ammonia, and 31 percent, bacabout 35 per cent, of each.* teria; in 1897, * Reports of the Massachusetts State Board of Health, 1893, p. 41,6, f^r 1894, p. 454, 1805, p. 451, and 1897, p. 416. 106 These experiments were discontinued early tinned early in 1898. It is hard to imagine conditions in actual practice which would warrant the construction of tanks of sufficient capacity to admit of four hours settlement where only a 30 to 40 per cent, removal of the organic matter could be expected. With smaller tanks the work done would of course be so sedimentation is not likely to be employed except where a small amount of less, purification at a slight expense is all that is needed. MECHANICAL STRAINING. This admits of a great variety of practice, ranging from attempts to remove and other large substances to an approximation to intermittent filtration. rags, paper Wire screens or filters of various materials may be employed. Generally little is accomplished, but in well-constructed and operated plants screening or straining may be an important factor in the purification effected. filtration, As a preliminary to intermittent coke strainers, or thin filter 107 were used at Lawrence during the last seven months of 1894, removing 52.4 per cent, of the albuminoid ammonia in the original sewage.* These beds ranged from IK to 8 ins. in thickness during the experi- ments, and the sewage passed them at an average rate of about 345,000 gallons a day for six days in the week. A depth of is given as desirable and it estimated that when straining ordinary sewage from 5 to 8 cu. yds. of coke would 6 ins. of coke is have to be removed per 1,000,000 gallons filtered. Mechanical straining through coke or sand at the rates named might perhaps more properly be termed continuous rapid filtration. Some of the better of the re- sults given are about the same as those secured in the same experiments by means of chemical precipitation, using 1,000 Ibs. of sulphate of alumina per 1 ,000,000 gal* Keport of the Massachusetts State Board of Health for The rep rts of the Massachusetts State Board 1894, p. 455. of Health from 189t to 19u2, inclusive, contain accounts of various further experiments with coke, anthracite and bituminous coal as screens. From 3 to 15 ins. of these materials, working at rates of 1,000,000 gallons a day and upvards, r< moved from 32 to 62 per cent, of the total albumincid aii iiionia. 108 Ions of sewage, or 7 grains per gallon, allowing four hours for precipitation. and The mechanical straining usually employed is insignificant in results compared with the above. The same may said of sedimen- Both processes in these experias well as the chemical tests carried ments, on simultaneously, were intended to facili- tation. tate and relieve the work of filter beds. CHEMICAL PRECIPITATION. Sedimentation alone removes only such suspended matter as will sink by its own weight during the comparatively brief time which can be allowed for the purpose. Some of the lighter matters may of course be carried down by the heavier particles,but the total results are comparatively small. If the process could be continued long enough, practically all matters in suspension might be removed, but those in solution would remain and putrefaction might begin in the sludge, if not in the sewage By adding cer- tain substances chemical action sets in and undergoing clarification. precipitation occurs. Some of the organic 109 substances are brought together by the formation of new compounds, and as they masses they carry with them other suspended matter. As in sedimentation or straining, a part of the bacteria fall in flaky removed by mere entanglement, while every grain of organic matter removed are decreases supplies, by so much the bacterial food and thus the potential number of bacteria, A great number and variety of chemhave been employed as precipitants, but years of experience have resulted in icals the general adoption of lime, sulphate of alumina and some of the salts of iron, more especially ferrous sulphate or copperas, or a combination of two of these, as best suited for the chemical precipitation of sewage. The character of the sewage and the relative cost of the several chemicals in a given locality should be deterLime is cheap almost mining factors. everywhere, but the comparatively large quantities required increase greatly the amount of sludge. Sulphate of alumina is not so readily obtained, and often must 110 be transported such a distance as to make freight rates quite a factor in its cost. It often used in conjunction with lime, is less amount of sludge than lime alone and in some cases doing more effective work. Where either an acid producing a sewage or one containing iron salts is to be treated, lime may be used without the sulphate of alumina and a considerable saving effected. If the acid or iron salts are discharged at intervals the sewage must be tested from time to time to determine when to modify the amount of chemicals A very interesting example of this sort is found at Worcester, Mass., where large quantities of acid and artificially applied. iron are discharged into the city sewers from manufacturing establishments.* In buying chemicals of any kind great care should be exercised in determining the available amount of the active agent, as the amount of calcium oxide in lime, or of alumina in sulphate of alumina, different products varying greatly in this respect, See Engineering Xeu-ss, No. 15. 1F90, and July 28, 1892 and Baker's " Sewage Disposal in the United ; also Rafter States." Ill notably the lime from different quarries and kilns.* The chemicals should be added to and thoroughly mixed with the sewage before the latter reaches the settling tank. The be effected in nearly all cases by projections into the channel leading to mixing may the tank, called baffle plates. Experience has demonstrated that the tanks should be long and narrow and that they should be operated on the continuous j The rather than the intermittent plan. width of the tank may be, say one-fourth its length. In the continnous plan the sewage is constantly flowing into one part of the tank and discharging from another more or in a less clarified state. In the intermittent system a tank is filled and then the flow turned elsewhere, allowing the sewage in the first tank to come to Where the continuous plan is used rest. 'the sewage generally flows through a set * For tl e theory of the actions of the various re-agents, the qiiHulities employed and their costs, both in experimental and practical work, see Rafter and Baker's "Sewage Disposal i:i the United States." Tl>e brief limits rf tl.i-v lume render! possible much more than a discuhsion of g. neral principles; detailed ninires, UDHCCOII pam d by ihn data upon \Nhieh they are based, am apt to be misleading. i 112 of tanks without change of gates or other interruption until one compartment needs cleaning. This compartment being cut out and left to itself for a while, the clarified then drawn off gradually from sewage the top through a hinged pipe, the upper and open end of which takes sewage from the surface on opening a valve in the horis izontal portion of the drain pipe beyond When the effluent is the hinged joint. decanted to the top of the deposited sludge the valve just mentioned is closed and another one, in the sludge pipe, opened, allowing the sludge to flow out, or to be pumped out for final disposition. The tank should then be thoroughly cleaned, after which it may be treated with disinfectants or deodorants, if desired, before being again put in use. The disposition of sludge is one of the most vexed problems connected with sewage disposal. It is a pasty, semi-liquid mass, ordinarily containing from 90 to 95 per cent, of water and 10 to 5 per cent, of solid matter. The most common method of disposal, and perhaps the one most gen- 113 erally available and satisfactory, is to much as as is possible out water squeeze of the sludge by means of presses designed This greatly reduces the bulk of the material. The liquid from the press goes back to the tank for further for the work. treatment. The sludge cake, as it is called, may be handled easily. It is sometimes burned and sometimes hauled away by farmers for use as a fertilizer. There have been great expectations on the part of projectors of chemical precipitation works that the farmers would vie with each other in securing the sludge, and even pay good money for it. The general experience, both in this country and abroad, has been that a city is lucky if it is able to induce anyone to haul the sludge away for it. In some cases peat or some other absoris mixed with the sludge to render it more easily handled and removed in, bulk. Again, it is run out on the surface of coarse sand and gravel beds and its liquid parts reduced by draining and drying. Some of the difficulties connected with this last bent method are : 114 In wet weather little drying takes the colder mouths the place, and during in considerable quanaccumulates sludge labor must be emManual tities. (2) (1) ployed to remove the sludge from the draining and drying beds. (3) Where chemical precipitation is employed suitable land, in character and extent, is often not to be had. At Birmingham, England, large volumes of sludge are pumped through force mains distributed through portable pipes to and covered with earth. There remains another method available for some seaside cities, and that is dumping in the ocean by means of large steam sludge ships. Thousands upon thousands of tons are so disposed of from the sewage works of London and Manchester, England, and Glasgow, Scotland. The capacity of the settling tanks is often the chief factor in determining the cost of installing precipitation works. As- suming that the sewage should be one hour in passage through the tanks, and that the maximum flow is twice the average, pro- 115 vision must be made for one-twelfth the to- tal daily flow, where house sewage only is treated. This makes no allowance for throw- ing out a portion of the tanks for cleaning or repairs. It would certainly be erring on the safe side, if at all, to provide a tank capacity equal to one-eighth the total maximum daily flow. Where sewage from a combined system is treated, it is of course practically impossible to provide a tank capacity sufficiently large to treat all the sewage. Either the excess of storm water must be discharged into natural water courses along the lines of the sewers or by the works without treatment. If pass ample tank capacity is available it may be possible to treat all the sewage during the first part of a moderate rain. This would mean the purification of the foulest portion and other washings, after which many localities it might be admissible of street in to forego all attempts at purifying the sewage, as the results which could be ob- tained would be comparatively insignificant. During such a heavy rainfall the sewage of a combined system would be 116 times diluted, and where the effluent from the works discharges into a stream many the latter ume. is also greatly increased in vol- where purification in connection with a new sewproposed the erage system separate plan will pracIt is evident that is tically always be adopted. tion plants in this country Most purificahave been built same time as the collecting system, such cases the separate plan has used. Worcester, Mass., was forced to adopt purification after many miles of combined sewers had been built, and after at the and been it in had converted a brook with a consider- able drainage area into an outlet sewer. Its later sewers have been built for house wastes only, and hundreds of thousands of dollars have been spent since the sewage works were built in excluding water from the sewers. THE The surface SEPTIC TANK. septic tank, as we now know it, has been developed since 1894. In effect, it is a sedimentation basin, so designed and operated as to lessen the sludge deposit by II 1 dissolving a portion of it and by reducing another portion to gaseous form. This re- duction or hydrolysis of the sludge is brought about by anaerobic bacteria, which work in the absence of air, and are thus directly opposed in character to the aerobic bacteria or nitrifying organism of sew- age farms, intermittent and percolating filters, contact beds Since inorganic matter is not acted upon by the bacteria, its exclusion from the septic tank is desir- To filters. chambers are which the sewage passes provided, through on its way to the septic tank. The high specific gravity of the sand and other min- able. this end, small grit eral matter in the sewage causes much of to sink in a brief period of time, while the remainder of the suspended matter, init cluding the lighter organic sludge, passes into the septic tank. Since the admission of air to the septic tank would tend to displace the anaerobic bacteria by aerobic, the tank inlets and outlets are generally submerged a foot or so beneath the normal sewage level. The tanks are made long and narrow, thus affording time for sedi- 118 mentation, and have a sewage depth of 6 For convenience in removing to 9 feet. sludge, their bottoms slope to one or more sumps or gates. Whether or not septic tanks should be covered has not been universally agreed. It is held by some that a roof, excluding light and cessity, air, is a great help, if not a neto the highest efficiency; while others argue that roofing is unnecessary to full bacterial action, except in very cold climates, and that a roof need be provided, at all, only for such tanks as are near if dwellings or much-traveled highways, and which on that account might give offense to residents or passers by. Any fairly water-tight material may be used in constructing septic tanks ; probably concrete, either plain or reinforced, is now used more commonly than any other material. The roof, as well as the walls and bottom, may be of concrete, or where low first cost is an object, wood may be used for roofing. Since the action of the septic tank is due tc anaerobic bacteria, while further purifi- 119 cation is effected by aerobic germs, and since the septic effluent is not only high in germ contents, and nearly if not available oxygen, the septic without quite anaerobic effluent is sometimes aerated before being passed to filter beds. Weirs over which the effluent flows in a very shallow stream or a series of overflow steps are used for purposes of aeration. The amount of sludge removed by septic tanks cannot yet be safely predicted for a given sewage works until actual tests have been made. show wide Such figures as are available variations at different localities. No one should be deluded by observations amount of sludge remaining in a septic tank, since large volumes of sludge of the in a finely divided state may pass off in the effluent. Volume for volume, however, this finely divided suspended matter will make far less trouble than the sludge from ordinary settling tanks or from chemical Some of it is already a mineral ash, subject to no further organic change, and the balance is partly reduced precipitation works. 120 to mineral matter and also to food for the low forms of organic life. Such sludge as remains in septic tanks may be disposed of by the means already described. In some cases, probably due to the charsewage or to improper opera- acter of the tion, when sludge from septic tanks is offensive first exposed to the air. Under such a condition the sludge disposal should be carried on at a remote point, or the sludge should be buried quickly a few inches beneath the earth. Investigations should made to determine whether the odors cannot be prevented by a change in the design or operation of the tank. also be Were it within the scope of this book, and less free from conflicting claims, it would be interesting to attempt to trace the history of the septic tank. The subject involves claimants in Great Britain, the United States, and Germany and France; early tanks installed and used with success, though with little or no also many understanding of the principles involved, long before the name septic tank came into 121 use. the It is now generally recognized that man who gave the septic tank its name and brought it into scientific prominence was Donald Cameron, of Exeter, England, but up to early in the year 1905 it was not generally conceded that Cameron's work entitled him to patent control of the septic tank process. The question was then in the courts of the United States for trial, but had never been legally raised in Great Britain, so far as the author of this book could learn. " ELECTRICAL " AERATION. PROCESSES. ARTIFICIAL While the oxygen of the atmosphere be made one of the may greatest agents in some and others writers purifying sewage, have laid too much stress upon the value of artificial aeration. Mountain streams, which tumble over rocky beds, are noted for their purity, and this has been attributed largely to the aeration which the water receives. It should be remembered that 122 the waters of such streams are generally of a high degree of purity to start with, often being little different from rainwater just from the clouds, and that the aerating It is quite commonly a long one. has been further observed that even badly process polluted streams show greatly improved chemical analyses at points a number of miles below the source of contamination. But here, sedimentation, and the action of both animal and vegetable life in their more minute forms, play a notable part in the purification process, and the timeelement is also important. It has been well established by the Massachusetts State Board of Health in its Lawrence work that the two essentials for the removal or transformation of the organic matter in sewage are oxygen and time, where dependence is placed on a nitrifying or oxidizing process. The time-' element has been largely ignored by some theorists, a few of whom have put their theories into practice. Purification plants have been built, and more have been projected, in which the great reliance has been put 123 upon artificial aeration, either by forcing the sewage or by causing the latter to fall through the air in drops or air into This has been accompanied streamlets. by rapid sand. filtration, generally through Now aeration of the sewage, or of the filtering material, may be employed as an aid to sewage purification, but like all things else it has its limits. It can maintain a supply of oxygen which is of use up and this will be of value. All in excess of this amount is of no to a certain point value, and unless time even is oxygen and The this is not of use given for the action of the of the nitrifying organism. latter develops rapidly in the presence oxygen and organic matter, transforming the latter into mineral compounds. These facts are overlooked by some of the of promoters o.f aerating processes,the assumpseeming to be that given a plenty of the desired work will be accomplished tion air The facts are that sewsoon loses all the available oxygen age taken up by it during aeration and needs to be aerated again and again until all .almost instantly. 124 The the organic matter is transformed. time-element can best be secured, almost invariably in some form of filter bed. Perhaps there is an even greater so-called regarding misunderstanding methods of electrical sewage purifiThese processes, which have cation. met with but little favor, simply prepare by electrical means some chemical agent which performs all the work accomplished and might be obtained in some other manner, although possibly at greater expense. In the Woolf and Hermite processes either sea common water or a solution of according to the readiness of one or the other, is partially deobtaining an electric current, and sodium composed by salt, hypochlorite is formed. The mixed with the sewage and dorizer and germicide, its solution is acts as a deoefficiency de- pending on its strength. The organic matter remains in the sewage and is subject to secondary decomposition later on. The product obtained by this process might be of value under certain conditions, 125 the same as other good disinfectants are, but there seems to be no reliable inform- show that anything further be can expected of it. The direct treatment of sewage by electricity has been talked of for some time but it still remains a dream. ation to BROAD IRRIGATION OR SEWAGE FARMING. Where sewage is applied to the surface ground upon which crops are raised the process is called broad irrigation, or sewage farming. The practice is in most of the respects similar to the ordinary irrigation of crops with clean water, the sewage being applied by a variety of methods, ac- cording to topographical and other natural conditions and the kind of crops under cultivation. The land employed for this method of purification should preferably be composed of a fairly light, porous soil. The crops should be such as require, or at least develop best under a large amount of 126 Where the soil is heavy and and the crops cannot stand much water, the sewage must be applied sparingly, and so a large amount of land As and much labor must be provided. moisture. wc-t, may be prepared at small expense it is somecomparatively times feasible to make use of land not so broad irrigation areas well suited to the purpose as might be it can be obtained desired, provided cheaply enough and too much stress is not laid upon the raising of crops. The less the attention paid to cropping, gene- rally speaking, the greater the amount of sewage which can be put on a given area of land. Wet, clayey soils can take but under any circumstances, little sewage but sometimes improve with cultivation and the application of sewage. The application of an average of from to 5,000 10,000 gallons of sewage per day to one acre of land is considered by many On the basis liberal allowance. 100 gallons of sewage per head of population this means that one acre of as a of 127 land sufficient for a population of is, 50 to 100 persons. the crops kind there if More could be from purified would stand it, but for each if is a limit which passed means the destruction of the crop. Allowing even 10,000 gallons of sewage, or 100 persons, to an acre in a city of 20,000 inhabitants would require 200 acres. To find suitable land at a low price near not always easy. The larger the the city greater the difficulty. Labor, too, is a big item in sewage farming on this cities is side the Atlantic, especially near cities. As a partial offset to this, great cities afford excellent and never-failing markets. Another great obstacle to adequate finanreturns from sewage farming in America is the deplorable fact that political ends and not business principles govern in large numbers of our cities, cial though there is good reason to predict a great change in this respect ere Where such conditions do prevail, long. however, the positions of both superintendents and laborers on sewage farms are ulinost sure to be considered rewards for 128 and encouragements to party service, with results most unfavorable to the enterprise in hand. Sewage farming means the selling as well as the raising of crops, and perhaps of live stock, and so requires business ability and agricultural skill. The latter must be accompanied with the faculty of handling considerable bodies of men. These apparently discouraging ments are meant rather as warnings. state- They are necessary because of the glowing representations which have been made regard- ing the profits of sewage farming by those who have not looked at all sides of the am not unmindful of the resewage farming abroad, but Euro- question. sults of I pean conditions are far different from ours. Many of the European farms are most admiral ly managed, both from an agricultural and business standpoint, and not a few of them have to contend far less favorable than with soil could be found United States. American I do not say that an city could in many sections of the not conduct so great an enterprise in a 129 creditable manner, for we have many well-conceived and well-operated municipal works of great magnitude. I do say that high prices for land near large cities, costly labor, a constant warfare against corruption with too frequent surrenders, and our sudden and complete changes in government all make sewage farming more difficult here than abroad. For the present, sewage disposal cannot be accomplished in this country at a profit. It is sometimes possible to regain through the raising of crops a part of the expense entailed in removing and purifying sewage, and this is the only method by which any considerable portion of the expense has yet We been recovered here or elsewhere. should be thankful for the day of small things, and wherever a revenue can be obtained from irrigation area or filtration beds our efforts should be to secure it. But the logic of figures will often show that some method of disposal that carries with no financial returns is the cheapest, in which case instead of crying over spilt and wasted sewage, we may laugh over a sav- it 130 ing in capital, interest and maintenance. Wherever irrigation, pure and simple, the application of water to crops for the sake of moisture, can be practiced that is to advantage, sewage farming should receive serious consideration, for in such localities every drop of water is valua- As ordinary irrigation may yet be used in the East as well as in the West, ble. (it is already practiced to some extent in the South) the use of sewage for mere watering as well as fertilizing may some day be seen -here and there throughout the length and breadth of the land. This is a subject which demands careful investigation and perhaps might be taken up with advantage by some of our agricultural experiment stations and by any live official in a position to do so.* * For an article on "The Use of Sewage for' Iriigation in the \\ est " ste Angineei ing iYew for .Nov. 3, Ife9j the substance of the article is a.so given in Kafter and Baker's " Sewage Disposal in the United States. A later treatment of the subject may be found in "Sewage Irrigation," Nos. 3 and 22 of Water Supply und Irrigation Papers of the U. fc. Geological Survey, by Gto W. Rafter, M. Am. Soc. C. E. In March, 1905, the author cf this book visited the sewage farm of Pasadena, Cal., and also land to which some of the sewage of Los Angeles is applied. As a result, he is more than even convinced of the wisdom of using sewage for ir; 1 ' rigation wherever water is scarce. 131 SUB-SURFACE IRRIGATION. Before passing on to intermittent fila word should be said regarding tration sub-surface irrigation. The system is capable of use on a small scale, chiefly for private dwellings, various public institutions and small communities where for any reason surface disposal would be objectionable. Tiie sewage agricultural drain joints, is distributed through laid with open tiles, and placed only a few inches below Provision should be made the surface. for changing the disposal area as often as the soil may require by turning the sewage into sub-divisions of the distributing pipes. The sewage is generally discharged auto- matically at intervals on the filling of a tank to a certain height. Where surface application can be practiced erally, if it would gennot always, be preferable to this system. INTERMITTENT FILTRATION. This method of sewage purification is capable of producing the highest results 132 under favorable conditions, and those conditions prevail perhaps more widely in this country than like ones for any other system. The process is a most simple one. With a competent man in charge large areas of beds can be operated with cheap labor. The construction of the beds is nearly as simple as their operation, only common labor being required, except putting down pipe and accessories. The for essential features of filter beds are some 4 to 5 feet of medium-sized sand, located above the natural ground water level; a pipe system for distributing the sewage to one or more points on each bed, and another beneath the bed, for collecting the purified liquid. In operation, the sewage is turned on to one bed for a given length of time, and then to another, in order to give the first a rest, or literally a breathing spell. When the beds become clogged with the matter retained on their surface and in their uppermost part, they may be raked over, or the sludge, and with it a thin layer of sand, may be scraped off. 133 If the beds are scraped, it will eventually be necessary to make good the sand re- moved, although this will not be required until perhaps a foot has been taken off, which should not result for a long time. Intermittent filtration is a nitrifying process effected through the agency of oxygen and bacteria, and requiring time for these two factors to act. A more complete perhaps that given in the Massachusetts State Board of the Report of Health for 1893, as follows: definition is The process * * * consists of intermingling the sewage in the pores of the filtering material, with sufficient air for a sufficient time, in the presence of micro-organisms which quickly establish themselves there. Experience has taught that a good filtering material is one composed of clean, sharp sand with grains of uniform size, and having interstices forming about onethird the total volume. The interstices serve as air spaces. When the sewage is admitted to the sand not all the air is driven out, and hence thtre is a store of oxygen to be drawn upon by the bacteria* 134 As more and more sewage is added the exhausted, the nitrifying bacoxygen teria diminish in numbers, as they cannot is live without air, and the efficiency of the purification process diminishes. If the application of sewage ceases, the beds grad- ually become drained as the sewage goes air is drawn into the pores of the down, bed, until finally a new supply is secured and the operation can be repeated. The sewage in filter beds spreads itself in thin films over the sand grains, thus giving bacteria an opportunity to develop, feed upon the organic matter, and so break it up as to cause the formation of new compounds, until the organic matter is trans- formed into inorganic. If intermittent filtration were a mere straining process, then the finer the sand used the higher the degree of purification. As already pointed out, it is a nitrifying rather than a straining process, so the aim must be to select a material of the size best suited to that end, and which will same time give the highest rate of at the filtra- tion with the least expenditure of labor. 135 The luw rate of filand a high degree of purity. The sewage not only enters the sand slowly, finer materials give a tration but a long time is required to drain it out and renew the air. If crowded, poor reWith sults and ultimate clogging follow. coarse material the sewage passes through too rapidly for nitrification to take place. The drainage and air renewal can therefore be effected quickly. It is thus evident that with very fine material the sewage must be applied slowly, with long intervals of rest, while with very coarse material the rate of application must be yet slower and the rests far more frequent, though short. As compared with material of a medium the fine does not give sufficiently better results, in actual practice, to warrant its adoption, nor does the higher rate possize, sible with the coarse material. The slow and the tendency to clog, on the one hand, and the very frequent manipulation of gates to throw the beds into and out of use, on the other, are rate of filtration against the extremes. Moreover, the very coarse materials are not so certain in their 136 removal of bacteria as fine ones. Here, as elsewhere, a happy mean is to be sought. R( jecting the extremes, the Massachusetts State Board of Health, in its report for 1891, gives as the range of available masand having 10 percent, of its weight terial finer than 0.03 to 0.98 millinuUTS (0.0012 to 0.0392 ins.). All material in filter sands finer than composed of grains O.C1 mm. matter. (O.C004 ins.) is classed as The maximum size of organic the coarser materials included in the above range was about 0.5 in. in diameter, and the mini- mum size of the finest material was 0.01 in. in diameter. As the work done by a filter is largely determined by smalltr particles of sand, and as a sand of uniform size is desired, the Massachusetts State Board of Health has adopted two standards for comparing different materials. The sand is subjected to mechanical analysis to determine the per- by weight, of the total which have grains below a certain diameter. The diameter at the 10 per cent, point is taken as the effective size, and the uniformity centages, 137 coefficient is the ratio between the diameter of the grains at the 60 and 10 per cent, points. Although a range sand in the size of the may be allowed, the coarse and finer particles should be fairly well intermingled. Or, in other words, there should not be strata of fine and coarse material in grains a filter The bed. effect of stratification is well expressed in the report of the MaspaQhusetts State Board of Health for 1892, as follows: We have thus found that with a coarse material above a fine one in the same filter thsre is a chance of trouble from a clogging of tlio fine material below the coarse ; and this is far wo.se than surface clogging, for the latter can be completely remedied have by disturbing the surface or by scraping. We found that a fine sand supported by a coarse sand will keep its lower layer saturated and act as a also water allowing the passage of water, but not and may in this way prevent tha necessary circulation of air, and reduce the action of the filter to mere straining. of seal, air, ******* * The above examples are perhaps extreme cases. With less marked differences in sand sizes, or with gradual instead of abrupt transitions from ccarse 138 to fine, the causes of failure might be reduced, or even in some cases entirely eliminated. In the many cases where the fields available for sewage filtration contain layers of various materials, the must be separately studied, in order different sands to detormine the probabla action of existing combinations; and in case the natural conditiors are unfavorable, changes may be made which will improve the action of the filter. Not all communities are so fortunate as have ideal filtering material conveniently located for sand filter beds. If net, then the choice may be between extending the outfall sewer to a distance, with or without pumping, and the adoption of a site giving poor material and thus requiring a larger area, or an inferior sand may be the only kind available far or near. The Lawrence experiments, to which reference has freely been made, have now been carried on for about seventeen years, to and the results of fifteen years' studies of a great variety of material under widely different conditions are on record in the published reports of the Massachusetts State Board of Health. Actual results obtained at city filter beds are also available, 139 so that with expert advice any community may ascertain the approximate possibilities While and gravels may be good results, under of such materials as are at hand. a wide range of sands counted on for giving proper conditions, it is necessary to determine those conditions in order to know to provide, and how to the after the disposal grounds sewage apply are ready. The area and volume of sand what area of beds or gravel required for the intermittent sewage are so large that the transportation of material any great disfiltration of is out of the question. Generally speaking, the beds are constructed in ma- tance and loam of course being removed, together with any pockets of other unsuitable material as naturally deposited, top soil terial. The sewage is carried to the several beds through open or closed channels built in the embankments, with distributing chambers where two or more beds join together. Ordinary sewer pipe, half pipe, brick, concrete or even wood conduits may be used. The distributing chambers may be of any 140 of the above materials, excepting sewer Wood of masonry. pipe, but are generally are to be avoided, if or accessories carriers on account of becoming sewageand thus liable to give off bad soaked, possible, odors. The sewage should be brought onto the beds so as to disturb their surface as little as possible, and great pains should be taken to distribute it evenly over the whole bed. The underdrains should rarely, if ever, be placed more than 50 feet apart, and should be provided with manholes, or inspection chambers at all intersections. Underdrains are sometimes put much nearer together than this. Their size and depth will be governed by the amount of effluent they are expected to remove, the ground water level and possibly other local conditions. Before admitting sewage to the beds it generally advisable to screen it, at least sufficiently to take out paper, rags and large floating matter. The screening cham- is bers often serve to some extent as settling size to tanks, but must be of pretty large 141 remove any considerable proportion of the total matters in suspension. Crops are beds, which sometimes is raised on filter equivalent to practicing broad irrigation in summer and filtration the remainder of the year. The beds generally being thoroughly underdrained, and the soil often more permeable than that of a broad irrigation area, larger doses of sewage may probably be applied to crops on filter beds than those growing on ordinary sewage farms. The size of each bed should be such as to permit an easy and equable distribution of sewage over it. Where the total filtration area is small it must be divided so as to permit of intermittent operation; that is, if a bed is to be in use and at rest for equal periods, then at least two beds would be necessary, and so on according to the relative periods of use and rest. Some additional area should also be provided for use while beds are being scraped or in case of an emergency. If a large area is laid out so that the size of the beds is lim- 142 ited only by convenience in use, then an acre may be a very acceptable size. As to degree of purification which may be expected, and the rate of filtration, it may be said, without going into details, that practically all of the organic matter may be removed from sewage by intermittent filtration at rates approximating 100,000 gallons per acre per day, with the best material and all conditions favorable. With unfavorable conditions the rate may be as low as 30,000 gallons per acre per day or even less. CONTACT BEDS. To make possible an increase in the low rates feasible with intermittent filtration under even the best conditions, and also to lessen the clogging of such beds (the two efforts being largely identical), the Massachusetts State Board of Health early began to experiment with various preliminary processes of sewage treatment, including rapid filtration of various sorts and sedi- mentation. A little later than these exper- 143 iments, and in some instances coincident with them, a number of men began experiments on their own account. These included the late Colonel George E. Waring in America, and Scott-Moncrieff, Dibdin and others in Great Britain. In the latter country intermittent filtration has almost always been supplemental to broad irrigation or sewage farming. The clayey na- ture of most of the available land density of population, and the made imperative some change in sewage treatment in Great Britain, and from about 1892 on gave rise to a multiplicity of new schemes. Except for details these schemes may be narrowed down ters, to contact beds and percolating fil- with the septic tank, which has been described already, available as preliminary to either of these, and also to broad irrigation and sewage farming. Although, as a rule, it is dangerous to credit these newer processes to a single man, the contact bed may be ascribed to W. J. Dibdin, for some years Chemist to the cil. The London County Coun- percolating filter, as described in subsequent pages, cannot be so readily 144 credited to a single individual, since the Massachusetts State Board of Health, Col- onel Waring, Scott Honor off and several others had a hand in its development. i Both the contact bed and the percolating filter, in their working form and the extent of their use, are essentially British. It may also be stated here that the septic tank was combined with contact beds almost if not quite from the beginning of the development of the former by Donald Cameron. The contact bed differs can type of intermittent composed of much erally enclosed floor, by from the Amerifilter in being coarser material, genwater-tight walls and the basin thus formed being pro- vided with inlet and outlet gates. It also differs from the intermittent filter in that when in use the outlet gates are closed, the bed filled quickly and held full for two hours or so, then emptied quickly and kept empty for two to four or five hours. The series of operations is called a cycle, and there are from two to four cycles in each 24.hours. The filling and emptying gates 145 are frequently worked automatically means of specially designed apparatus. Contact beds are singly, in by built -for operation pairs and in groups of three; the sewage in the last two cases passing through two or three beds in succession. When built in pairs a coarse and a fine bed are provided. The coarse material is approximately from 3-4 to 2 ins. in greatest diameter, and the fine material from 1-4 to 1 in. The material now most commonly used in contact beds abroad is hard clinker from soft coal or from refuse destructors, but coke, broken stone a gravel and other substances may be employed. Care should be taken to select a material which does not readily disintegrate. The coarse beds are sometimes called primary, and the fine ones secondary, and sometimes the terms single and double contact beds are used. The relatively large size of the material composing these beds, and of the intersti- permits quick filling and empfacilitates also a rapid renewal of the air supply in the free spaces or pores tial spaces, tying, and 146 The latter, in turn, favors an enormous bacterial development and a corlespondingly speedy breaking down and of the bed. transformation of the organic matter of the sewage. As can be understood, holding the sewage in the bed in contact with the bacterial agents gives the beds their name. Some form of preliminary treatment, most commonly septic or sedimentation tanks, has been found advisable before applying sewage to contact beds, particularly where only a single contact is pro- A high degree of bacterial removal commonly effected by contact beds, unless very fine material is employed, but vided. is not the organic matter in the sewage may nevertheless be so transformed as to prevent from subsequent putrefaction, usually the main object of sewage treatment. With such an object it is renuisance which is ported that satisfactory results have been obtained when passing settled or septic sewage through double contact beds at from 500,000 to ], 000,000 gallons an acre of total surface area. rates of 147 PERCOLATING FILTERS. Trickling, continuous streaming and intermittent filters are some of the names that have been applied to the last class of awaiting consideration, but both reason and usage are on the side of the filters term percolating The filters. features of percolating are the use of large-sized material, with the freest possible aeration and drainessential filters age, and a uniform distribution of the sewage over the filter in drops, small streams or spray. The sewage has an un- interrupted passage through the drainage system of percolating filters, just as through intermittent filters, but tLe sewage is ap- plied continuously, or with numerous brief interruptions that break the continuity but a little, in the case of percolating filters, and the distribution is so even and rapid, and the pores of the filters are so large, that no sewage stands oa the percolating whereas the surface of intermittent often flooded hours at a time. Percolating filters are generally built on filters, filters is 148 a solid floor of concrete or other water- tight material, and enclosed by openjointed walls, the latter consisting of large fragments of the medium, laid up with joints, or regular sized moulded or cut pieces, laid pigeon-hole fashion. Tne body of percolating filters is composed of open clinker, stone or other fairly cohesive terial, in particles egg or a man's from the fist up ma- size of a hen's to that of a man's head, the larger pieces being placed at the bottom. Distributors for percolating filters may be revolving radial arms of wrought-iron pipe, perforated, or revolving radial weirs, or fixed pipes provided with mere perforations or with spray nozzles. Drains, formed in the concrete or other solid floor, or con- sisting of specially moulded tiles, are used to ensure thorough drainage. The effluent from percolating filters, even when the original sewage is given a usually high in preliminary treatment, divided suspended matter, and also finely in bacteria, but, as a rule, the effluent is is non-putrefactive and, being largely min- 149 eral matter, is easily removed or reduced in quantity by a brief period of sedimenThe rates claimed for percolating tation. filters, dosed with septic sewage, range from 1,000,000 to 10,000,000 gallons an but in the present state of the art 2,000,000 to 3,000,000 gallons seems high. acre, SEWAGE PLANTS PURIFICATION NOT NUISANCES. There much opposition to sewage purification plants by those living or owning property near by on the ground is often that such works must of necessity be a From experience gained by nuisance. visiting many such plants, both in this country and abroad, and from studying the subject in other ways for years, I know that well conducted plants are entirely inoffensive, either within The or without their employees about such works are as healthy as similar classes of men in other occupations, and the same holds true of the families of these men living on the European sewage farms. enclosures. 150 The crops raised on sewage farms are as safe eating as those of the same kind raised elsewhere. There are objections, however, to applying sewage to crops for hu- man consumption which are to be eaten without being cooked, but meat and milk from sewage farms is usually as good as when produced under other conditions. Good design and construction, followed by proper methods of operation, are all make sewage purifica- that are needed to when once the right system has been adopted and put into use. No one system can be said to be the best for tion a success, The special problems of all localities. each community must be met and solved case by case and out of several systems and combinations of systems the best for the conditions at hand must be chosen. THE PRESENT STATUS or SEWAGE PURIFICATION. In the United States, chemical precipitation is no longer being adopted for new The septic tank has come more plants. rapidly into favor than contact beds or 151 filters, but some men of pracexperience seem strongly inclined to plain sedimentation rather than the septic percolating tical tank. Comparatively few percolating filbuilt, but small contact Uis have been beds are in use in a number of cases. In- termittent filtration has for years been the system most in use in America, and seems likely to continue to lead for filter beds is where sandy land available at a reasonable In our Far West, sewage irrigation price. frequently practiced, but as a rule the sewage is merely a substitute for water in is sections where irrigation is a necessity. be the most successful to appears farm in the United States treats sewage What the sewage of Pasadena, Cal. Large and paying crops of walnuts are raised each year. farm On in a visit to the Pasadena sewage March, 1905, the author was told number of orange trees would be set out soon, and that sewage would be put on these in the summer and on the that a large walnut trees in the winter. Early in 1904 the author visited twentyfour sewage works in Great Britain and 152 three on the continent of Europe. lie numerous chemical precipitation plants and sewage farms still in use, at the works visited and elsewhere, but many of these were being converted to, or supplemented by, the newer processes. The septic tank was widely used. Contact beds were numerous and percolating filters were found fast becoming so. In America the septic tank, contact beds and percolating filters are far less often compared with other processes, than Great Britain. Local conditions abroad, should be remembered, are widely dif- used, in it ferent from local conditions here. The streams of Great Britain are small and the population dense, requiring more sewage works than are yet felt to be necessary in the United States, and the clayey soil and good natural filtering maEngland and Scotland compels the adoption of clinker, coke and other absence of terial in substitutes. All these things should be remembered in selecting a mode of treatment and filter bed material for American sewage works. 153 If it seem to any that the newer pro- sewage treatment have been but briefly discussed, the author would point out the fact that in 1904 there was pubcesses of lished a tled, whole volume in this series, enti- " The Treatment of Septic Sewage," by George W. Rafter, M. Am. Soc. C. E. Later in 1904, the author of the book now being brought to a close, embodied his recent observations in Great Britain and at in " BritFrankfort and Wiesbaden, Paris, Sewage Works." Present day sewage treatment, from the viewpoint of British " The authorities, is set forth in Barwise's ish Purification of Sewage," Rideal's " Sewage and the Bacterial Purification of Sewage," and Dibdin's "The Purification of Sewage and Water." The first American book on " sewage was Rafter and Baker's Sewage in the United States," a large Disposal treatise on the subject published early in 1894, before the septic tank, contact beds and percolating filters had come into public view. A revision under consideration. of this treatise is THE VAN NOSTRAND SCIENCE SERIES No. 47. LINKAGES: THE DIFFERENT FORMS and Uses No. 48. By of Articulated Links. J. D. C. De Roos. THEORY OF SOLID AND BRACED Elastic Arches. tion, revised By William Second edi- Cain, C.E. and enlarged. No. 49. MOTION OF A SOLID IN A FLUID. By Thomas Craig, Ph.D. No. 50. DWELLING-HOUSES; THEIR SANIBy Prof. W. H. tary Conduction and Arrangements. Corfield. No. 51. THE TELESCOPE: OPTICAL PRINCI- ples Involved in the Construction of Refracting and Telescopes, with a new chapter on the Evolution of the Modern Telescope, and a Bibliography With diagrams and folding plates. By to date. Thomas Nolan. Second edition, revised and enlarged. Reflecting No. 52. 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Mechanical Engineering, Purdue University, La Fayette, Ind. Fourteenth Ed. I2mo,cloth, illus.$2.oo. Elements of Mechanics Including- Kinematics, Ki locations. ;:itics. By With of Union =r, College, Eighth Ed., revised. 8v O> cloth, illus.$2. 50. Elements of Mechanics of Materials. A Text-Book for Stud ByC. n^ Courses. E, HOUGHTON, A.B. Svo, cloth, 186 pages. Illustr.. N'ork University. $2.00! . , i Elementary Mechanics, including Hydrostatics and Pneumatics. By Professor OLIVER J. LODGE. Revised Edition. I2mo, cloth, illu $1.50 Applied Mechanics. Use of Students who have time id Graphical ExExperimental, Nut A Treatise for the to Work ercises, Illustrating the Subject. M.E..D.Sc.,F.R.S. Svo, cloth . i By JOHN PFRRY, . . . .$2.50.
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