Filtration as a Solution of Lake Michigan Sewage Pollution
In the course of their report to the board of trustees, of the North Shore Sanitary District of Illinois upon the disposal of the sewage, the board of engineers, comprised of John W. Alvord, Harrison P. Eddy and George W. Fuller, devote an interesting chapter to the “Relation of Public Water Supplies to the Problem.” In it they say: All of the communities in this district except Lake Bluff take their public water supply from Lake Michigan. Each community has its own intake, which is located in fairly shallow water at distances ranging from 300 feet at North Chicago to 4,000 feet at Lake Waukegan, where, however, there is an emergency intake quite near to the shore. The lake water as drawn through these short intakes is in no case above suspicion hygienically. This is due primarily to the discharge of raw sewage into the lake from the various sewer outlets within the district. Mention is also to be made of the general trend of the lake currents to the south, which brings from the north pollution to the various intakes. Still another point which is worthy of consideration is that at times of storm accumulations of polluting matters, which have been gradually deposited during long periods of time upon the lake bottom, are stirred up and transported to the intakes. Another feature of the lake waters is that the shallow depth permits storms to make the water distinctly muddy for some considerable distances from the shore. In consequence of these natural conditions the appearance of the public water supplies of this district is not fully satisfactory from a modern standpoint for periods ranging from ten to twenty per cent, of the time, depending upon the frequency and intensity of lake storms. The hygienic requirements of the water supply of the district are usually met fairly well by the careful application of sterilizing agents, but this is not entirely satisfactory in that it requires rapid changes in the rate of application of chemicals at times of severe storms, when it is not always feasible to make such changes promptly and accurately. Filtration in connection with sterilizing agents alone will make the public water supplies of this district thoroughly satisfactory, and it is with this viewpoint in mind that we deal with the problem of sewage disposal. In further explanation of our viewpoint, it is to be said that if all the dry weather flow of sewage were to be purified perfectly, there would still remain serious obstacles in obtaining a satisfactory water supply at all times without filtration. Reference is made, singly and collectively, to the influence of polluting matters brought by the lake currents from points without the district, to the polluting substances forming a carpet upon the lake bottom. and which are stirred up by lake storms, to the soil wash brought by heavy rains into the lake by surface streams at each ravine, and also to the discharges of combined sewers which, in several instances, especially at Waukegan, carry sewage mixed with the storm flow. While we recognize the advantages of diverting all sewage from the lake, both for hygienic and sentimental reasons, we consider that from an engineering standpoint the problem, in relation to the public water supply of the district, is essentially one of restricting the pollution to such small limits as will clearly prevent the pollution of the lake water from overloading or overtaxing the reasonable performance of carefully operated modern water filtration plants. 1 his is the viewpoint which has been developed by the International Joint Commission, which, in accordance with the treaty in 1910 between the United States and Great Britain, is proceeding to eliminate excessive pollution from the international boundary waters between this country and Canada. And we understand that this is the basis upon which this International Commission is proceeding in its dealings with the restriction of pollution of the lake and river waters in the Detroit and Buffalo districts. While it is true that Lake Michigan is not an international boundary water, yet we attach importance to the viewpoint above expressed by virtue of the consensus of opinion. which this commission has sought as a result of several years’ effort through inquiry, inspection, laboratory and field investigation, as well as through various public hearings. In stating the above views as to restricting pollution to such limits as will not overtax modern water filters for the public water supplies of the district, it is only fair to state that we have been guided in part by the motive of seeking to recommend engineering works, which, for a given aggregate expenditure within the district, will give the residents the best return. By no means do we object to the removal from the lake of all sewage or the complete purification of all sewage, or the extension of the water works intakes far into the lake beyond the shallow depths where the water is more or less frequently polluted and objectionably turbid. As the district grows and as additional funds become available, we assume that some or all of these refinements, accruing to the benefit of the public water supplies, may be added to the fundamental and basic requirements herein stated.