sewage purification is chiefly to get rid of the one one-thousandth part of organic matter.1

Comparing several series of analyses, both American and English, it becomes apparent that ordinary town sewage in England is usually considerably more concentrated than that of the American towns. It is very important to bear this in mind in applying English data to American conditions. The elaborate experiments conducted by the Massachusetts State Board of Health at Lawrence, and which have been reported from year to year in the annual reports of that board from 1888 to the present time, indicate that there is a relation between the purifying capacity of different filtrating materials and the amount of impurity which can be removed from sewage of a given strength. This point is strongly brought out by the experiments conducted by the Massachusetts board. It follows, then, that if we prepare special areas of sewage purification in accordance with the indications of the Massachusetts experiments we may expect to apply somewhat larger volumes of average American dilute town sewage per unit of area than has usually been found expedient in English practice. If, therefore, we use English data without reference to the quality of the soil to which the sewage is to be applied, or of the sewage itself, we shall be likely to arrive, at times, at more or less erroneous conclusions.

As a summation of this part of the discussion, we may say that the chief object of sewage purification is to rid the sewage of the one onethousandth part of organic matter which it contains, and that all of the appliances for sewage purification and utilization may be considered as directed toward this one point.

QUANTITY OF SEWAGE.

In considering processes for the utilization of sewage, either in agriculture or for its direct purification by chemical methods or by intermittent filtration, it becomes necessary to learn, first of all, what quantity of sewage may be expected from a given population, and, inasmuch as the flow of sewage will vary with the quantity of water supply, our first inquiry may be properly directed toward ascertaining the amount of water used in American towns. It may be pointed out, however, and, indeed, strongly insisted upon, that general discussion of this phase of the question can only be of use as indicating tested and approved methods of procedure. The conditions vary so greatly in different towns that each case must be taken by itself as a problem for special solution.

If we examine statistics of the average consumption of water per inhabitant in the various cities of the United States, as given in the Manual of American Water Works and in other publications, we

'See table in the Twenty-Sixth Annual Report of the State Board of Health of Massachusetts, 1894, page 457, for the average composition of the sewage used in the experiments conducted at Lawrence by that board from 1888 to 1894, inclusive.

learn that there are wide variations. Without attempting to show their extent here, we may cite the statistics of a few cities of the United States by way of illustration:

Average use of water in various cities of the United States.

Many other cases could be cited from a vast mass of statistics bearing upon this subject now in existence, but the foregoing are sufficient to show that the use of water in towns, both large and small, does not follow any special law, and that the only way to proceed will be to consider each case on its merits. On this point we may say that usually the use is smaller in towns provided with meter systems than in those without, and, further, that in those towns where meters are being gradually introduced the tendency seems to be, on the whole, toward a reduction per capita of consumption; all of which again emphasizes the importance of studying each case on its merits.

In making arrangements for utilizing sewage in agriculture, or even for the purpose of purifying it in order to comply with sanitary requirements, it is very important to take into account the future growth of the town. The tendency of the last few decades has clearly been in the direction of great increase in urban population, as illustrated by the reports of the last census.

In addition to variations in quantity of sewage due to varying uses of water in public supplies, we may frequently expect to find variations due to infiltration of drainage water into the sewers themselves, which will of course increase the flow of sewage over and above that due to the water supply, and to leakage from the sewers through gravel and other porous material and through the seams of rocks, which tends to decrease the flow below the amount due to the water supply. Both of these sources of variation will frequently operate to modify conclusions based upon water supply purely.

According to Frederick P. Stearns, M. Am. Soc. C. E.,1 the amount of ground water finding its way into the sewers of the main drainage system of the city of Boston is about 45 gallons per capita per day. This large filtration is due chiefly to the fact that many of the older sewers of Boston are built of either dry or relatively open rubble masonry, while some of them follow the threads of old water courses, both of these circumstances leading to relatively large contributions of ground water.

At East Orange, New Jersey, a separate system of sewers was carried out in 1886 and 1888. The infiltration as measured before any house connections were in use was, for 25 miles of vitrified tile sewers, about 2.5 gallons per second. For the main brick sewer, 4,000 feet in length, the infiltration was 5 gallons per second. The total infiltration from the whole system amounted at these rates to 650,000 gallons per day. The flush-tank flow was taken at 30,000 gallons per day, and after the house connections were made the house-sewage flow from the contributing population of about 15,000 was taken at 620,000 per day; hence the infiltration was 50 per cent of the total quantity. The remedy for a leakage into the sewers of this character may be found in improved methods of laying the sewers themselves. In any case it may be pointed out that an addition to the sewage flow proper of 50 per cent in the way of ground water is an unnecessary addition to the expense of sewage purification, should any be required.

We will assume, as regards the present argument, that the sewers of a separate system may, with careful workmanship, be made practically impervious, and that the sewage flow will therefore be about represented by the amount of the public water supply. We will further assume that there is no good reason why, in a properly managed municipality, there should be used more than from 60 to 80 gallons of water per capita per day. At this rate the sewage flow of a population of 10,000 would amount to from 600,000 to 800,000 gallons per day. In combined systems where the sewers receive the rainfall as well as the sewage proper it will be necessary to provide, in any purification project, for taking care of and properly purifying a considerable portion of the storm water at each rainfall.

Special Report upon the Sewerage of the Mystic and Charles River Valleys, as made to the State Board of Health of Massachusetts.

2See Inland sewage disposal, with special reference to the East Orange (New Jersey) works, by Carroll Phillips Bassett, M. Am. Soc. C. E.: Trans. Am. Soc. Civil Eng., Vol. XXV, p. 125.

IRR 3-2

STREAM POLLUTION.

It is a well-established principle of law that every riparian proprietor is entitled to have a stream of water flow by his realty as it is wont to flow by nature. From this principle we have derived the old and well-settled doctrine that to pollute a public stream is to maintain a common nuisance. The necessities and conditions of modern society have, however, tended to some modification of this principle as thus strictly announced, so that at the present time there are certain reasonable pollutions of streams, or, rather, there are certain specific cases in which a stream may be polluted to some extent without abrogating the essential force of the fundamental proposition. At the same time it must be remembered that the broad proposition that streams ought not to be polluted is on the whole sound.1 Admitting such premise, we are forced to the conclusion that some form of sewage purification is necessary wherever an aggregation of human beings in thickly settled communities leads to the production of any considerable amount of sewage.

If, however, towns or manufacturing establishments are situated on tide water, there is no reason why the sewage may not be disposed of by discharging it into the ocean, provided such a discharge can be made without creating a nuisance along inhabited beaches, and also provided it is clear that such discharge is, on the whole, financially to the advantage of the community furnishing the sewage. But if on examining all the attendant circumstances it appears that the sewage can be profitably utilized in agriculture, then there is no reason why such utilization may not be made, even in the case of towns situated on tide water. We need, therefore, as a necessary part of our subject, to discuss the general question of purification of streams. This question has been the subject of a large amount of discussion in England, where interest in it may be considered as dating from the first report of the Health of Towns Commission, made in 1844.2

1 The legal aspects of stream pollution as the matter stands to-day are discussed in Sewage Disposal in the United States, Chapter VI. The attention of the reader is specially directed to the views of the Massachusetts Drainage Commission as there given. The report of that commission may also be referred to, though, as it has long been out of print, it is now difficult to obtain.

2 This commission made two reports: The first, in 1844, published in two octavo volumes; the second, in 1845, also in two octavo volumes. These two reports may be taken as the beginning of sanitary science in England and in the civilized world generally. Previous to and at that time the condition of the English towns, especially in the manufacturing districts, as shown by the information contained in these two reports, was such that the present generation can only with difficulty realize it. These reports should be studied by any person wishing to compass the whole subject of sewage utilization, by way of showing the magnitude of the evil which has been combated and greatly mitigated since 1844.

Among the subjects which this commission was especially charged with investigating were the causes of disease among the inhabitants as well as the best means of promoting and securing the public health. The commission pointed out a large number of cases where stream pollution was undoubtedly the cause of insanitary conditions, and the notable sanitary reforms which have placed England as regards sanitary improvements easily in the front rank of nations have all been perfected since that date. During the same period the literature of sanitation has been enriched by a number of valuable reports in which every possible phase of stream pollution has been discussed.

Without referring here to all of the various commissions in detail, we may cite the Royal Sanitary Commission of 1869, and the Rivers Pollution Commission. The former recommended that any stream from which drinking water is taken should be effectually protected from sewage pollution. The principle laid down at that time has been gradually extended until we now formulate it by the statement that streams which are even likely to be a source of water supply ought not to receive sewage pollution, or, if they do, only under such regulations as will admit of immediate discontinuance of the pollution whenever the water is required for domestic purposes.

The Rivers Pollution Commission' in their report point out not only the evils of pollution by sewage proper, but also those produced by pollution from manufacturing refuse. As regards this second class of pollutions, from manufacturing refuse, the following classification can be made: Pollution by dye, print, and bleach works; chemical works; tanneries; paper making; woolen works; silk works. The reports of the Royal Commission on Metropolitan Sewage Discharge and of the Royal Commission on Metropolitan Water Supply also contain much information relating to stream pollution.

In this country stream pollution has been generally discussed by the State boards of health of Massachusetts, Connecticut, Illinois, and some of the other States. In Massachusetts the State Board of Health made the following recommendations many years ago:2

(1) That no city or town shall be allowed to discharge sewage into any water course or pond without first purifying it according to the best process at present known, which is irrigation; provided, that this regulation does not apply to a discharge from sewers already built, unless water supplies be thereby polluted; and

1 Rivers Pollution Commission (first commission). This commission made three reports. The first report deals generally with the best methods of preventing the pollution of rivers, with special reference to the conditions prevailing at that time on the River Thames. The second report deals with the River Lea. The third report deals with the rivers Ayr and Calder. Five volumes in all, 4°, London, 1866-67.

Rivers Pollution Commission (second commission). Report of the commissioners appointed in 1868 to inquire into the best means of preventing the pollution of rivers. This commission made six reports in all. The first report (2 volumes) treats of the pollution of the basin of the rivers Mersey and Ribble and of the best means of preventing pollution therein. The second report is taken up with a description of the A B C process of treating sewage. The third report (2 volumes) discusses the pollution arising from the woolen manufacture and processes connected therewith. Whoever would understand this division cf stream pollution in all its phases should study this report. The fourth report treats of the pollution of the rivers of Scotland, and gives special consideration, among other subjects, to the pollution arising from papermill wastes, etc. The fifth report (2 volumes) treats of the pollution arising from mining operations and metal manufactures. The sixth report treats of the general subject of domestic water supply of Great Britain. A large amount of information about water supplies from cultivated and uncultivated areas and the contamination of water from manured and unmanured, cropped and uncropped land, is given, the whole forming a vast body of sanitary information pertinent to present conditions. Ten volumes, 4°, London, 1870-71-72-74.

'Seventh Annual Report, 1876, p. 12. To illustrate the pollution to which a single stream is subject, reference should be made to the Eighth Annual Report of the Massachusetts State Board of Health. In this it is stated that on the Nashua River are 92 mills, employing 5,543 perThis stream drains an area of 437 square miles, with an average population of 106.5 to square mile.

sons. the

The reports of the Philadelphia water department, from the eighty-third to the eighty-sixth, inclusive, may be referred to for information in regard to stream pollution.