section of an average city of 10,000 to 100,000 population. This gives P= 85. In many cities the maximum does not exceed 50 per acre. The population found times .00027 for residences and times .00003 for factories and office-buildings (on the basis of the previously assumed daily consumption) will give in cubic feet per second the maximum amount of house-sewage from buildings to be expected. To this must be added manufacturing wastes, which are to be allowed for in quantities which must be decided upon separately for each individual case. Also if the soil is inclined to be wet at a depth less than that of the proposed sewer (and this includes a larger proportion of localities than most persons realize) an additional allowance must be made for ground-water leaking through the joints (see Art. 35). With care this need not amount to more than one cubic foot per second for each 30 to 100 miles of sewer; but it has been known under most unusual conditions to more than equal the entire capacity of the system.* Where flush-tanks are used (see Chapter V) an additional allowance is frequently made for water from them. But this seems entirely unnecessary, since their very purpose is to temporarily gorge the sewer for as great a distance as possible; and the smaller the sewer the better is this mission fulfilled. The average discharge per minute of 100 tanks, each discharging 300 gallons once in 24 hours, would amount to only 1% of the capacity of a 15-inch sewer at minimum grade. ART. 15. DATA OF HOUSE-SEWAGE FLOW. Instead of using rates of water-consumption as equivalent to the sewage discharge it would undoubtedly be preferable to establish the actual relation between these, based upon the rate of flow of sewage itself in various towns already sewered. But very few such records exist-too few to enable us to deduce a definite law from them with certainty, although a Average leakage of 137 miles of 8 in. to 36 in. in Boston, .06 cu. ft. per sec. per mile. Double this in the spring. * study of even these few is instructive. Probably the most extended series of gaugings of sewage discharge made in America are those of the Providence, R. I., sewers by Samuel M. Gray. A condensed summary of them and of other gaugings is given in the following tables: TABLE NO. 3. SUMMARY OF RESULTS OF WEIR MEASUREMENTS OF SEWAGE FLOW IN PROVIDENCE, R. I. (Condensed from a Report by SAMUEL. M. GRAY on the Sewerage of Providence.) GAUGINGS MADE IN SCHENECTADY, N. Y., WEDNESDAY, FEBRUARY 5, AND THURSDAY, FEBRUARY 6, 1892-HOURLY FOR 24 HOURS. (Fifteen miles of sewers, about 1500 house-connections tributary to the point where gaugings were made. Before house-connections were made a seepage of 60,000 gallons per day was measured. There was also 50,000 gallons of water contributed daily by flush-tanks. These two, or 110,000 gallons per day, have been deducted from the total hourly flow in obtaining the quantities in the table.) Hour Total flow per hour WEDNESDAY, FEBRUARY 5, 1892. II 12 M. I P.M. 2 4 9 A. M. 10 7 8 10 II 12 P.M. 6 9 32,892 31,840| 31,840 31,840 29.301 29,301 29.301| 28,135 THURSDAY, FEBRUARY 6. 3 4 5 I AM.1 2 Average flow per hour, 31,213 gallons; minimum flow, 25,711 gallons; inaximum flow, 38,769 gallons, or 24% increase over the average. WATER-CONSUMPTION TABLE NO. 6. AND SEWAGE FLOW, ATLANTIC CITY, N. J., DECEMBER, 1891-NOVEMBER, 1892. (Average Daily Percentage of Excess of Water Consumed over Sewage Pumped-by Months.) The average daily percentage of excess to the year = 45%. TABLE NO. 7. RESULT OF A GAUGING BY WEIR MEASUREMENT OF THE FLOW OF THE MAIN OUTFALL SEWER OF THE STATE INSANE HOSPITAL AT WESTON, W. VA., IN JANUARY, 1891. (Made by GEO. W. RAFTER. Condensed from "Sewage Disposal in the United States." Self-closing fixtures were used in the building. 10,000 gallons per day, or 7 gallons per minute, of water of condensation from the steamheating apparatus was discharged into the sewer.) The flow of the Compton Avenue sewer, St. Louis, Mo., was gauged hourly from March 15 to 23, 1880. The minimum flow measured was 88 gallons per minute, the maximum 203 gallons, and the mean 132 gallons. A gauging of the College Street sewer, Burlington, Vt., taken at 15-minute intervals from 7.30 A.M. to 10.30 P.M. gave two maximums, one at 7.45 A.M., the other at 9 A.M.; these were each 140 gallons per minute. The minimum flow was 65 gallons, the mean 115 gallons. Fifty-four houses were connected; the tributary population was 325. Gaugings made at Memphis, Tenn., for one day gave a maximum of 80 gallons and a minimum of 35 gallons per minute. Gaugings made at Kalamazoo, Mich., in 1885, from I A.M to 12 midnight on Monday, March 9, gave a minimum |