MEMPHIS AND ITS WATER SUPPLY.
Engineers J. A. Omberg, jr., Arthur Hider, and A. T. Bell have in reporting as to the water question of Memphis, Tenn., stated that the water is obtained from a stratum of water-bearing sand 300 feet below the surface. Steel tubes are sunk through the upper clay to the sand stratum and the water is collected through them. Experience has shown that the system of wells has been adequate to the demands thus far presented, and chemical analysis and the marked reduction of the death rate accompanying the extension of the mains indicates the purity of the water. The permanence of the supply, depending on the rainfall, can be assured. Even under the worst conditions the maximum yield was 10,200,000 gallons a day, which by indicating the number of wells was brought up to 19,000,000—an increase not entirely permanent, and due to the deterioration in individual wells. Fifty wells during four years have averaged 14,900,000 gallons a day, which might be brought up some 5,000,000 by cleaning the strainers and sinking other wells. With the rapid growth of the city, 20,000,000 or 30,000,000 gallons a day will be called for. Flushing the wells—a merely temporary expedient at best—four times a year at a total cost of $70—will give 19,000,000 supply. Each new well sunk diminishes the flow from the other wells, and a limit is reached when no other wells in a certain area can be sunk profitably. The present area is about one-fourth of a square mile’in extent so that from 25,000,000 to 30,000,000 gallons a day, and the limit of supply will be reached in five years. The proposed additional pumping engine of 15,000,000 gallons will, with the limit of the number of wells, bring the present pumping station up ^to its ultimate capacity. If an auxiliary air-lift plant, with wells, some distance from the present one is installed, it would involve the following: A reservoir of 10,000,000 gallons capacity, lined with concrete and covered with concrete and expanded metal, with sewers, piping, etc., $87,500; twelve ten-inch wells and piping, $42,000; mains to wet wells and reservoir, $30,000; two air compressors, $25,000; a 15,000,ooo-gallon pump, $65,000; boilers, engines, motors, etc., $42,500; fifteen per cent, for engineering and contingencies, $43,800, giving a total of $335,800. If operated by steam, it would cost $15,000 less. For increasing the output of the present plant by a new pump, thirty wells, etc., the cost would approximate $225,112. This would bring the present plant up to its limit of capacity. Four miles from the present plant it would be safe to place the auxiliary, but a longer distance is preferred. Other stations could be installed as the needs of the city dictated, and, if separated considerably, could be almost unlimited in number. The estimated cost of subsequent stations is placed at $856,750. If the Mississippi supply is considered, to obtain that unpolluted an intake must be built four and one-half miles north of the city, with filter beds 4,000 feet back from the river—a point at which the nearest town to Memphis is 200 miles away. The water thus obtained would be in every way excellent. This location would, of course, add to the cost of the works, because of the long line of main that would be required. If a situation three miles below the city were selected, it would before long be rendered undesirable, because, with the growth of the city and the extension of the sewers, the water would be objectionable. If, however, it were passed through filters, the objection would be only sentimental, but it is held that even these should be respected. The Mississippi water settles rapidly, the suspended matter being principally fine sand and silt. Twenty-four hours is a safe length of time for clearing the water. The additional cost of filtration to be added to the cost of pumping into distributing mains, is estimated at $5 per million gallons, or one-half a cent per thousand. The intake necessary for either of these locations would be a cylinder thirty feet in diameter, the bottom to be five feet below the lowest water and the top to extend above high water. The sedimentation basin would have a capacity of 30,000,000 gallons. There would be eight filters, each with a capacity of over 3,250,000 gallons, and the pure water well would be located in the rear ot the filter beds and would be 100 feet by ten feet deep. The pumps would be operated by electric motors run by a current from a generator at the station. The approximate cost of this station is placed at $741,000, including two 15,000,000-gallon high duty pumping engines, generators, eight boilers, filter beds. etc. To this must be added $220,000 for a thirty-six-inch main to the city and $1,500,000 for distributing mains, making a total cost of $2,461,000. If the plant were placed below the city, the difference in cost of the thirty-six-inch main would be about $80,000. It has been shown that 25,000,000 gallons per day can he secured from one station, and that an indefinite supply can be had by increasing the stations. The chief expense of the artesian supply is in maintenance and depreciation of wells, or about $4 per million gallons on a basis of 300,000 gallons per day per well. The expense for slow sand filtration above ordinary pumping expense, which is higher than for the artesian system, is estimated at $5 per million gallons. The difference of $1 in cost and the excellent sanitary conditions brought about by the artesian water are infavor of that system. On the subject of the necessary water consumption: The average legitimate consumption of all the cities in the United States, allowing a small amount for leakage of fixtures, is about seventy gallons per capita. If the consumption of a city varies greatly with this average there is generally some well-defined local reason or excessive waste. In Memphis, taking into consideration all the local conditions, the average legitimate consumption per day per capita is about seventy gallons without waste. On account of the old iron service pipes, the leakage that is unavoidable amounts to about 7.5 gallons per capita a day. The remaining waste of thirty-seven gallons per capita is accounted for in flushing wells, flush-tanks in the sewers and on consumers’ premises. The greater part of this waste can and should be prevented. To do this it is recommended that meters be ordered, and all calculations are based on their installation. These meters form the most efficient method of preventing undue waste by the consumer. The value of the present plant of the water company is placed at $2,015,894, to which is added $60,000 for the company’s land. To duplicate the present plant would cost about $2,402,164.
Colonel H. L. Demoting, State geologist for Pennsylvania, has just investigated all the sand filtration plants in America, and will report upon them to the authorities at Washington, Philadelphia, and Harrisburg, where the plants are in course of construction. Among the largest plants visited by Col. Demming were those at Albany, N. Y.; Poughkeepsie, N. Y., which is the oldest plant in the world; -Mount Vernon, N. Y., and Lawrence, Mass. The best plant he found at Albany.