Transcriber's Notes:

1. Tildes are used to denote text in small caps.



AMERICAN SOCIETY OF CIVIL ENGINEERS INSTITUTED 1852

TRANSACTIONS

Paper No. 1191

WATER PURIFICATION PLANT, WASHINGTON, D. C. RESULTS OF OPERATION.[1]

By E. D. Hardy, M. Am. Soc. C. E.

With Discussion by Messrs. Allen Hazen, George A. Johnson, Morris Knowles, George C. Whipple, F. F. Longley, and E. D. Hardy.

The Washington filtration plant has already been fully described.[2] At the time that paper was written (November, 1906), the filtration plant had been in operation for only about 1 year. It has now been in continuous operation for 5 years, and many data on the cost, efficiency, and methods of operation, have accumulated in the various records and books which have been kept. It is thought that a brief review of the results, and a summary of the records in tabular form, will be of interest to the members of the Society, and it is also hoped that the discussion of this paper will bring out the comparative results of operation of other filter plants. As a matter of convenience, the following general description of the plant is given.

Description of the Filtration Plant.—The Washington filtration plant was completed and put in operation in October, 1905. It consists of a pumping station for raising the water from the McMillan Park Reservoir to the filter beds; 29 filters of the slow sand type, having an effective area of 1 acre each; the filtered-water reservoir, having a capacity of about 15,000,000 gal.; and the necessary piping and valves for carrying water, controlling rates of filtration, etc.

[Footnote 1: Presented at the meeting of February 15th, 1911.]

[Footnote 2: "Works for the Purification of the Water Supply of Washington, D. C.," by Allen Hazen and E. D. Hardy, Members, Am. Soc. C. E., Transactions, Am. Soc. C. E., Vol. LVII, p. 307.]

In the pumping station, there are three centrifugal pumps, which are directly connected to tandem compound engines; two sand-washer pumps; three small electric generating sets for furnishing electric light; and four 200-h.p., water-tube boilers.

Each of the centrifugal pumps has a nominal capacity of 40,000,000 gal. per day when pumping against a head of 21 ft., and each sand-washer pump has a capacity of 2,500,000 gal. when pumping against a head of 250 ft. The electric light engines and generators supply the current for lighting the pumping station, the office and laboratory and other buildings, and also the courts and interior of the filter beds, and for operating a machine-shop.

The filters and filtered-water reservoir are built entirely of concrete masonry. The floors are of inverted groined arches on which rest the piers for supporting the groined arch vaulting. All this concrete work is similar to that in the Albany, Philadelphia, and Pittsburg filters.

The filters contain, on an average, 40 in. of filter sand and 12 in. of filter gravel. The gravel is graded from coarse to fine; the lower and coarser part acts as part of the under-drain system, and the upper and finest layer supports the filter sand. The raw water from the pumps is carried to the filters through riveted steel rising mains which have 20-in. cast-iron branches for supplying the individual filters. The filtered water is collected in the under-drainage system of the several filter beds, and is carried through 20-in., cast-iron pipes to the regulator-houses. These regulator-houses contain the necessary valves, registering apparatus, etc., for regulating the rate of filtration, showing the loss of head, shutting down a filter, filling a filter with filtered water from the under-drains, and for turning the water back into the raw-water reservoir, or wasting it into the sewer. From the regulator-houses, the filtered water flows directly to the filtered-water reservoir. Generally, five filters are controlled from one house, but there are two cases where the regulator-houses are smaller, and only two filters are controlled from each.

The dirty sand removed from the filters is carried by a portable ejector through one or more lengths of 3-in. hose and a fixed line of 4-in. pipe, to the sand washers. From the sand washers, the washed sand is carried to the reinforced concrete storage bins, each of which has a capacity of 250 cu. yd., and is at such an elevation that carts may be driven under it and loaded through a gate.

Until April, 1909, the sand was replaced in the filters by carts which were filled through the gates in the sand bins. It was then hauled to the top of the filter beds and dumped through the manholes on the chutes, which could be revolved in any direction. These chutes were used to prevent the sand from being unduly compacted in the vicinity of the manholes, and to facilitate spreading it in the filters. Since April, 1909, all the sand has been replaced by the hydraulic method. An ejector is placed under the gate in the sand bin, and the sand is carried in a reverse direction from the bin through the 4-in. piping and one or more lengths of hose to the filter bed. This process has lowered the cost of re-sanding considerably, and present indications are that it will prove entirely satisfactory in every way.

The average effective size and uniformity coefficient of the filters are shown in Table 1.

Table 1 Filter Sand as Originally Placed. ================================================== Filter Average Average Depth of Average No. effective size, uniformity sand, in turbidity. in millimeters. coefficient. inches. - - 1 0.32 1.88 35.3 2,600 2 0.30 1.78 37.7 2,200 3 0.32 1.77 40.2 3,000 4 0.29 1.80 42.5 1,800 5 0.34 1.74 44.9 2,700 6 0.31 1.78 37.7 2,300 7 0.29 1.72 40.1 2,300 8 0.32 1.75 40.2 2,800 9 0.32 1.78 42.5 2,900 10 0.30 1.69 39.5 2,500 11 0.34 1.93 37.1 2,600 12 0.29 1.66 34.7 2,100 13 0.32 1.83 33.6 3,500 14 0.29 1.66 33.6 2,600 15 0.33 1.75 39.0 2,400 16 0.33 1.78 42.3 3,000 17 0.33 1.86 45.5 3,300 18 0.34 1.80 48.7 3,100 19 0.34 1.80 52.0 ..... 20 0.34 1.87 39.0 2,700 21 0.32 1.82 42.3 2,400 22 0.33 1.74 45.5 2,200 23 0.33 1.81 48.7 2,300 24 0.35 1.80 52.0 2,600 25 0.29 1.64 39.5 2,400 26 0.31 1.71 37.1 2,100 27 0.31 1.71 34.7 1,900 28 0.33 1.93 33.6 2,300 29 0.34 1.93 33.6 3,000 - - Maximum 0.36 1.93 52.0 3,300 Minimum 0.29 1.64 33.6 1,800 Average 0.32 1.77 40.4 2,600 ==========================================

Description of Washington Aqueduct.—The water supply of Washington is taken from the Potomac River, at Great Falls, about 16 miles above the city. At that place, a dam has been built across the river, which holds the water at an elevation of 150.5 ft. above mean tide at Washington. From Great Falls the water flows by gravity for a distance of 16 miles through a 9-ft. conduit, three reservoirs, and a tunnel. From McMillan Park Reservoir, the last of the three, the water is lifted by centrifugal pumps about 21 ft. to the filters. After passing through the filters, it flows to the filtered-water reservoir, and later to the city mains. In its passage from Great Falls to the filters, the water flows through three settling reservoirs, which have already been referred to. These reservoirs are known as the Dalecarlia, the Georgetown, and the McMillan Park Reservoirs, and have available capacities of 141,000,000, 140,000,000, and 180,000,000 gal., respectively.

Turbidity.—The Potomac River water is rather turbid, the turbidity being caused by very fine particles of clay. The river is subject to sudden fluctuations, it being no uncommon thing to have a turbidity of 100 one day, and 1,000 the next. The high turbidity usually disappears about as rapidly as it comes, and is seldom higher than 500 for more than 5 days at a time. It is frequently the case, however, that a succession of waves of high turbidity will appear so close together that the effect of one has not disappeared before that of another is felt.

The clarification of the water supply begins at the dam at Great Falls. Here it is a clarification by exclusion, for when an excessive quantity of mud appears in the river water, the gates are closed, and the muddy water is allowed to flow over the dam and form mud-bars in the Lower Potomac, while the city is supplied from the water stored in the three settling reservoirs. Until a comparatively recent date, the excessively muddy water was never excluded, having been taken, like other decrees of Providence, as it came.

During the summer of 1907, the practice of shutting out water with a turbidity of 500 or more was established for the warm months. This practice was discontinued during the cold months, as it was feared that a very high consumption of water might occur at the time of low water in the reservoirs, and so cause a partial famine. During the winter of 1909-10, however, the gates were closed, as was the practice throughout the summer months.

When the reservoirs are well filled, and the consumption of water is less than 70,000,000 gal. per day, it is safe to close the gates at Great Falls for a period of about 4 days.



While a considerable reduction in turbidity is effected in each of the reservoirs, the bulk of the mud is deposited at the upper end of Dalecarlia Reservoir. This reservoir had become so completely filled, that, in 1905, it was necessary to dredge a channel through the deposit, in order to allow the water to pass it. During the summers of 1907 and 1908, a 10-in. hydraulic dredge removed more than 100,000 cu. yd. of mud which had been deposited in this reservoir. The mud deposited in Georgetown and McMillan Park Reservoirs is so fine that the accumulation of many years is not very noticeable in its effect on the depth of water.

The particles of clay which remain in the water after its passage through the three reservoirs, are so exceedingly small that they do not settle out in any reasonable length of time. Even the filtration of the water through one or more slow sand filters occasionally fails to remove the last trace of turbidity. This is especially true in the colder months, and not a winter has passed when the water supply has not been noticeably turbid at some time.

A general idea of the quantity of mud contained in the river water, the quantity excluded by closing the gates at Great Falls, and that removed by sedimentation and filtration, may be gained from Table 2, which is, of course, only a rough approximation.

Table 2 also shows that the gates were closed 10.50% of the time, thereby excluding 40.06% of the total suspended matter which otherwise would have entered the system.

The turbidities, bacterial counts, and chemical analyses of numerous samples of water are shown in Tables 3, 4, 5, and 6. The amount of work done in the pumping station, average consumption of water, death rate from typhoid fever, and filter runs are shown in Tables 7, 8, 9, and 10.

Raking.—At the time the filters were first put in service, the sand bins had not been completed, and, consequently, the work of cleaning the filters was carried on in the old-fashioned way of scraping by hand and wheeling out the sand in barrows. This method of cleaning was used from October, 1905, to April, 1906; then the regular sand-handling system was commenced.

At times, during the first two summers the filters were in operation, considerable difficulty was experienced in keeping them cleaned as fast as was necessary to provide an ample supply of filtered water. For a short period in each summer it was found necessary to organize night shifts, and keep the work of cleaning in progress for from 16 to 24 hours per day.



Table 2—Tons of Suspended Matter Entering System, Etc.

Columns: A - Amount that would have entered the system if the gates had been left continuously open. B - Number of hours gates were closed. C - Amount shut out. D - Amount deposited in Dalecarlia Reservoir. E - Amount deposited in Georgetown Reservoir. F - Amount deposited in McMillan Park Reservoir. G - Amount entering filtration plant. ==================================================== Month. A B C D E F G Total. - - - - - - - - 1909. - - - - - - - - July 318 32.0 3 0 125 74 116 318 August 146 47.0 1 0 78 38 29 146 September 97 57.0 7 21 13 38 18 97 October 61 90.5 8 7 9 25 12 61 November 50 60.0 4 13 5 17 11 50 December 370 99.0 126 108 33 59 44 370 - - - - - - - - 1910. - - - - - - - - January 2,410 136.0 1,109 1,020 67 117 97 2,410 February 839 117.5 481 126 56 75 101 839 March 208 7.5 13 43 15 13 124 208 April 321 65.0 17 195 43 43 23 321 May 197 84.5 58 54 22 24 39 197 June 1,505 124.0 786 535 49 88 47 1,505 - - - - - - - - Total 6,522 920.0 2,613 2,122 515 611 661 6,522 ====================================================

In order to relieve the situation at such times, the expedient of raking was tried. This was first attempted with the filters filled with water; the effluent was first shut off in order to prevent a downward flow of water, and the filter was then raked or harrowed from boats. This method was not satisfactory, however, as the work was neither as uniform nor as thorough as necessary. Later, the filters were drained to the necessary depth, and the surface of the sand was thoroughly stirred with iron garden rakes. The filters were then filled with filtered water through the under-drains and put in service.

This latter method proved so satisfactory that it has been resorted to at all times when the work was at all pressing. When the runs were of short duration, and the depth to which the mud had penetrated the filter sand was slight, a raking seemed to be nearly as effective in restoring the filter capacity as a scraping; it could be done in 8 hours by 3 laborers, and there seemed to be no ill effects from lowered efficiency.

Table 3 Turbidities. Average by Months. (United States Geological Survey Standard.) =========================================================== Reservoirs: - - Month. Great Falls. Dalecarlia Georgetown McMillan Filtered Outlet. Outlet. Park. water. Outlet. - - - - - - - Max. Ave. Max. Ave. Max. Ave. Max. Ave. Max. Ave - - - - - - - 1905. - - - - - - - October 100 36 40 21 32 18 20 11 4 1 November 35 19 34 19 22 14 14 11 3 1 December 1,500 199 250 84 150 74 95 39 14 6 - - - - - - - 1906. - - - - - - - January 700 94 180 60 120 60 85 52 20 12 February 120 45 85 41 55 29 35 22 5 3 March 1,750 272 350 181 120 56 90 46 8 6 April 1,270 167 180 72 95 58 75 46 12 7 May 600 56 50 20 45 16 34 10 3 2 June 1,700 303 500 125 450 94 180 41 13 2 July 1,000 130 180 54 150 47 250 43 13 3 August 1,530 375 250 112 95 66 65 45 5 2 September 120 33 180 34 95 28 75 25 7 2 October 1,025 127 110 37 60 24 55 21 1 1 November 160 27 75 20 45 16 24 13 1 1 December 600 69 110 31 80 28 80 26 8 2 - - - - - - - 1907. - - - - - - - January 400 135 150 70 110 75 70 53 11 7 February 55 26 26 15 36 16 40 17 5 2 March 950 248 180 77 130 70 90 57 7 4 April 200 47 80 33 60 30 45 24 4 2 May 130 29 40 18 26 15 14 9 1 1 June 400 104 160 48 75 32 40 18 1 1 July 600 114 130 61 78 47 45 31 1 1 August 800 73 130 35 85 26 30 14 1 0 September 600 129 [1] [1] 150 51 70 28 1 0 October 75 32 [1] [1] 65 28 75 26 4 0 November 300 97 [1] [1] 100 45 45 23 2 1 December 680 135 [1] [1] 180 61 100 46 10 4 - - - - - - - 1908. - - - - - - - January 2,100 202 340 73 250 82 160 65 20 7 February 3,000 302 300 52 150 52 75 32 7 4 March 300 91 150 78 100 68 65 42 5 4 April 75 23 65 41 37 27 26 20 3 2 May 2,000 172 130 48 85 37 50 20 1 1 June 400 40 70 29 40 24 30 18 1 1 July 1,500 149 ... 74 170 44 75 15 0 0 August 900 129 200 [1] 150 56 85 39 2 1 September 75 24 [1] [1] 50 19 35 18 0 0 October 95 20 [1] [1] 55 18 28 15 0 0 November 24 11 [1] [1] 20 11 19 10 0 0 December 20 9 17 11 14 9 10 7 0 0 - - - - - - - 1909. - - - - - - - January 400 72 95 32 60 23 25 16 4 1 February 650 194 120 64 90 51 55 35 4 3 March 250 51 [1] [1] 90 44 60 37 8 4 April 750 98 [1] [1] 130 42 76 31 2 1 May 480 57 [1] [1] 30 19 30 12 2 1 June 650 141 [1] [1] 120 51 80 30 1 0 July 400 48 [1] [1] 215 46 120 35 2 1 August 180 23 [1] [1] 50 17 18 9 0 0 September 26 16 24 14 [1] [1] 25 6 0 0 October 14 10 15 10 11 9 8 4 0 0 November 11 9 11 8 10 8 6 4 0 0 December 600 63 110 31 80 28 50 15 3 0 - - - - - - - 1910. - - - - - - - January 3,000 357 200 58 150 53 115 30 5 2 February 3,000 143 150 55 120 50 100 36 7 4 March 210 36 100 35 95 38 100 43 9 5 April 350 55 100 25 55 18 25 8 1 0[2] May 300 33 55 19 50 17 28 13 1 0[2] June 1,500 246 180 42 110 37 50 16 1 0[2] - - - - - - - Fiscal years: - - - - - - - 1905-06[2] 1,750 133 500 70 450 47 180 31 20 5 1906-07 1,530 114 250 46 150 37 250 29 13 2 1907-08 3,000 117 340 53 250 45 160 31 20 2 1908-09 1,500 79 200 50 170 32 85 22 8 1 1909-10 2,100 86 200 30 215 29 120 18 9 1 =============================================

[Footnote 1: Reservoirs out of service.]

[Footnote 2: October to June 30th.]

Table 4 Bacteria. Averages by Months. ============+====================================================== Reservoirs: + + + + -+ Month. Dalecarlia Dalecarlia Georgetown McMillan Park Filtered Inlet. Outlet. Outlet. Outlet. water. -+ + + + -+ 1905. -+ + + + -+ October ... ... ... 210 80 November ... ... ... 150 27 December ... 15,500 ... 3,800 60 -+ + + + -+ 1906. -+ + + + -+ January ... 2,800 ... 1,500 39 February 2,900 4,100 1,800 550 16 March 1,800 1,100 900 650 19 April 3,300 1,700 700 400 22 May 425 210 95 65 17 June 7,900 4,600 325 220 17 July 13,500 600 475 160 26 August 8,700 1,100 1,200 190 14 September 425 250 140 135 14 October 2,300 950 650 270 16 November 1,800 1,100 1,200 220 12 December 6,900 3,800 3,600 700 45 -+ + + + -+ 1907. -+ + + + -+ January 4,400 2,400 2,200 950 70 February 1,000 950 1,000 700 45 March 11,500 8,300 7,200 3,600 65 April 3,700 2,100 1,400 475 21 May 750 350 325 130 26 June 2,300 1,000 600 100 18 July 2,700 575 350 160 17 August 3,000 275 425 80 17 September 6,200 [1] 1,900 230 32 October 1,400 [1] 950 275 27 November 8,900 [1] 6,600 1,500 27 December 16,000 [1] 9,600 4,300 190 -+ + + + -+ 1908. -+ + + + -+ January 11,000 8,700 9,400 3,700 190 February 11,500 6,000 5,000 2,800 75 March 4,600 4,000 2,900 1,300 30 April 700 450 250 120 13 May 9,500 1,100 650 325 17 June 750 120 110 95 12 July 4,900 ... 400 150 8 August 1,600 325 300 100 12 September 325 [1] 200 80 11 October 375 [1] 325 140 8 November 550 [1] 300 200 12 December 800 750 375 170 23 -+ + + + -+ 1909. -+ + + + -+ January 11,000 2,700 1,600 700 31 February 8,000 3,500 2,400 1,300 60 March 3,800 [1] 2,600 1,000 39 April 2,200 [1] 1,400 550 12 May 900 [1] 350 140 16 June 3,400 [1] 1,200 170 21 July 550 [1] 500 250 33 August 400 [1] 325 55 18 September 325 240 [1] 70 18 October 350 275 250 130 20 November 600 500 500 180 13 December 21,000 9,100 5,900 4,500 250 -+ + + + -+ 1910. -+ + + + -+ January 76,000 78,000 88,000 52,000 800 February 45,000 35,500 31,000 17,500 350 March 9,900 7,600 7,400 4,800 80 April 7,900 4,100 3,500 650 29 May 1,230 810 830 448 28 June 3,660 930 800 324 27 -+ + + + -+ Fiscal years: -+ + + + -+ 1905-06 3,300[2] 4,300[3] 750[4] 850[2] 33[2] 1906-07 4,900 1,900 1,700 650 31 1907-08 6,360 2,700 2,900 1,300 55 1908-09 3,400 2,000 950 400 21 1909-10 14,300 13,900 10,900 6,890 143 ============+========+======+======+============+========

[Footnote 1: Reservoirs out of service.]

[Footnote 2: October to June 30th.]

[Footnote 3: December to June 30th.]

[Footnote 4: February to June 30th.]

Table 5 Results of Tests for Bacillus Coli. Percentage Positive. ============+============+============+============== Great Falls, Dalecarlia or Dalecarlia Reservoir Georgetown Reservoir Outlet. Reservoir. Month. Inlet. + + + + + + + + + - 10 1 0.1 10 1 0.1 10 1 0.1 c.c. c.c. c.c. c.c. c.c. c.c. c.c. c.c. c.c. -+ + + + + + + + + - 1906. -+ + + + + + + + + - January[1] 55.6 38.9 22.2 69.2 23.1 7.7 56.0 40.0 8.0 February 33.3 26.7 6.7 26.1 17.4 8.7 30.4 13.0 4.4 March 50.0 12.5 0 45.5 18.2 0 20.8 8.3 0 April 72.2 33.3 16.7 95.5 50.0 4.6 59.1 22.7 4.6 May 20.0 8.0 4.0 20.0 12.0 0 7.8 0 0 June 57.7 38.5 19.2 40.0 32.0 8.0 50.0 34.6 0 July 65.0 50.0 5.0 60.0 25.0 10.0 15.0 5.0 5.0 August 84.6 69.2 61.5 88.5 65.4 34.6 80.0 57.7 23.1 September 50.0 10.0 0 30.0 10.0 10.0 40.0 10.0 0 October 60.0 30.0 10.0 55.5 33.3 0 80.0 60.0 20.0 November 37.5 0 0 25.0 12.5 12.5 37.5 25.0 0 December 55.5 44.5 0 66.7 44.5 22.2 66.7 22.2 0 -+ + + + + + + + + - 1907. -+ + + + + + + + + - January 77.8 33.3 22.2 66.7 33.3 0 55.5 55.5 22.2 February 37.5 25.0 0 12.5 0 0 37.5 12.5 0 March 87.5 50.0 0 75.0 37.5 0 50.0 25.0 0 April 44.5 11.1 11.1 66.7 22.2 11.1 77.8 11.1 11.1 May 91.3 65.2 17.4 88.9 33.3 0 87.5 50.0 12.5 June 80.0 68.0 24.0 87.5 62.5 0 66.7 44.5 11.1 July 42.3 30.8 19.2 25.0 12.5 0 22.2 22.2 0 August 48.1 29.6 3.7 33.3 16.7 16.7 36.4 18.2 0 September 62.5 54.1 25.0 ... ... ... 41.7 33.3 16.7 October 51.9 40.8 7.4 ... ... ... 53.3 40.0 6.7 November 80.0 64.0 24.0 ... ... ... 72.7 54.5 0 December 56.0 48.0 16.0 ... ... ... 46.2 38.5 7.7 -+ + + + + + + + + - 1908. -+ + + + + + + + + - January 46.2 30.8 15.4 50.0 12.5 0 33.3 0 0 February 12.5 0 0 25.0 0 0 12.5 0 0 March 38.5 19.2 7.7 44.4 11.1 0 11.1 0 0 April 15.4 7.7 0 0 0 0 0 0 0 May 76.0 52.0 40.0 87.5 50.0 12.5 33.3 22.2 0 June 7.7 0 0 0 0 0 11.1 0 0 July 26.9 15.4 11.5 22.2 22.2 0 11.1 0 0 August 46.2 26.9 3.9 44.4 33.3 0 62.5 25.0 12.5 September 20.0 8.0 4.0 42.9 28.6 1.4 22.2 11.1 0 October 18.4 3.7 0 0 0 0 9.1 0 0 November 13.0 0 0 28.6 0 0 11.1 0 0 December 11.5 7.7 3.8 0 0 0 12.5 0 0 -+ + + + + + + + + - 1909. -+ + + + + + + + + - January 12.0 8.0 0 30.0 10.0 0 0 0 0 February 52.1 47.8 47.8 28.6 14.3 0 37.5 0 0 March 69.4 34.6 3.8 50.0 25.0 0 44.5 11.1 0 April 42.3 15.4 3.9 33.3 22.2 11.1 44.4 22.2 11.1 May 88.4 26.1 4.3 50.0 12.5 0 33.3 0 0 June 85.0 60.0 25.0 60.0 40.0 10.0 44.4 33.3 11.1 July 34.8 8.7 4.4 ... ... ... 33.3 11.1 0 August 50.0 15.4 7.7 ... ... ... 40.0 10.0 0 September 43.5 21.8 8.7 25.0 25.0 12.5 0 0 0 October 36.4 13.6 0 18.2 0 0 0 0 0 November 4.5 0 0 10.0 0 0 0 0 0 December 38.5 23.1 7.7 36.4 36.4 18.2 33.3 22.2 11.1 -+ + + + + + + + + - 1910. -+ + + + + + + + + - January 72.0 48.0 24.0 44.5 33.3 11.1 75.0 25.0 0 February 47.8 43.5 17.4 63.2 21.1 5.3 40.0 30.0 5.0 March 33.3 14.8 0 30.8 11.1 3.7 29.6 22.2 7.4 April 41.7 33.3 20.8 40.0 32.0 16.0 38.5 23.1 15.4 May 47.8 17.4 0 52.0 20.0 0 36.0 16.0 4.0 June 95.5 86.4 31.8 80.8 46.2 19.2 64.0 28.0 8.0 -+ + + + + + + + + Fiscal years: -+ + + + + + + + + - 1905-06 35.2 19.4 9.3 0.0 3.2 5.2 6.4 4.9 1.7 1906-07 61.5 43.6 9.2 7.7 9.2 2.3 1.1 9.8 0.7 1907-08 44.6 31.3 3.0 2.3 2.3 3.1 4.4 2.1 4.1 1908-09 38.9 20.3 8.4 0.0 5.0 0 7.4 8.5 2.8 1909-10 45.5 26.9 0.1 5.3 4.0 8.8 7.9 9.8 6.2 ============+==+==+==+==+==+==+==+==+====

============+==========+======+========== McMillan Park Filtered- Tap water Reservoir water from var- (applied reser- ious parts Month. water). voir. of city. + + + + + + + - 10 1 0.1 10 1 10 1 c.c. c.c. c.c. c.c. c.c. c.c. c.c. -+ + + + + + + - 1906. -+ + + + + + + - January[1] 55.6 22.2 0 7.2 0 ... ... February 8.3 4.2 0 0 0 ... ... March 18.5 7.4 3.7 0 0 0 0 April 32.0 8.0 0 4.0 0 0 0 May 0 0 0 0 0 0 0 June 23.1 7.7 3.8 0 0 3.1 0 July 9.5 0 0 4.8 0 ... ... August 63.0 33.3 0 7.4 3.7 11.9 5.1 September 32.0 12.0 0 8.0 0 3.1 0 October 48.1 22.2 3.7 3.7 0 13.0 3.7 November 20.0 12.0 0 8.0 0 0 0 December 20.8 8.3 4.2 16.7 8.3 7.5 0 -+ + + + + + + - 1907. -+ + + + + + + - January 69.3 34.6 3.8 19.2 11.5 14.0 0 February 17.4 4.4 0 0 0 2.9 0 March 30.8 7.7 0 0 0 2.1 0 April 46.1 19.2 3.8 3.8 0 3.2 0 May 23.1 0 0 0 0 1.4 0 June 40.0 8.0 0 0 0 0 0 July 3.8 0 0 0 0 1.4 1.4 August 14.8 3.7 0 0 0 0 0 September 16.0 4.0 0 4.0 0 1.7 0 October 38.7 25.8 9.7 6.5 0 12.5 2.8 November 58.6 17.3 3.5 0 0 4.9 0 December 45.2 29.0 0 19.3 3.2 12.9 4.3 -+ + + + + + + - 1908. -+ + + + + + + - January 22.6 9.7 3.2 3.2 0 1.9 1.9 February 0 0 0 0 0 0 0 March 9.7 0 0 0 0 0 0 April 6.7 3.3 0 0 0 0 0 May 45.1 16.2 0 0 0 0 0 June 0 0 0 0 0 0 0 July 6.4 6.4 0 0 0 0 0 August 12.9 3.2 0 0 0 1.6 0 September 16.7 10.0 0 0 0 4.3 0 October 9.7 6.4 3.2 0 0 0 0 November 6.6 0 0 0 0 0 0 December 3.2 0 0 0 0 0 0 -+ + + + + + + - 1909. -+ + + + + + + - January 3.2 3.2 0 3.2 0 0 0 February 7.1 3.6 3.6 0 0 3.4 3.4 March 32.3 19.4 3.2 6.5 0 2.8 1.4 April 36.6 10.0 0 0 0 0 0 May 12.9 3.2 0 0 0 0 0 June 53.3 20.0 0 0 0 1.4 0 July 25.8 12.9 0 0 0 0 0 August 22.6 6.5 3.2 0 0 0 0 September 13.3 3.3 0 0 0 0 0 October 3.2 0 0 0 0 0 0 November 0 0 0 0 0 0 0 December 29.0 22.6 0 9.7 6.5 7.3 1.5 -+ + + + + + + - 1910. -+ + + + + + + - January 61.3 35.5 9.7 5.8 3.2 15.9 3.2 February 32.2 7.1 0 3.6 0 0 0 March 12.9 3.2 0 0 0 0 0 April 23.3 13.3 0 0 0 0 0 May 16.1 12.9 0 0 0 0 0 June 43.3 6.7 0 0 0 1.4 0 -+ + + + + + + - Fiscal years: -+ + + + + + + - 1905-06 4.3 8.3 .8 .3 1.8 1.3 0 1906-07 2.5 3.0 .4 .5 2.1 5.4 1.0 1907-08 2.2 9.4 .4 .8 0.3 3.1 0.9 1908-09 6.7 7.1 .8 .8 0 1.2 0.4 1909-10 3.6 0.4 .1 .3 0.8 2.2 0.4 ============+==+==+==+==+==+==+====

[Footnote 1: Presumptive tests.]

Table 6—Summary of Sanitary Chemicals Analyses of Weekly Samples, July 1st, 1909, to June 30th, 1910. (Results in Parts per Million.)

Columns: A - Turbidity[1] B - Free C - Albuminoid D - Total E - Nitrites F - Nitrates G - Hardness H - Alkalinity I - Chlorine

(A) Maximum. ====================+=====+=================+===========+=====+=====+==== Ammonia. Nitrogen as: Reservoirs. A + -+ -+ -+ -+ G H I B C D E F + -+ -+ -+ -+ + + -+ -+ Dalecarlia inlet 2,100 0.034 0.264 0.280 0.0070 0.45 120.0 106.0 5.4 Dalecarlia outlet[2] 200 0.034 0.180 0.206 0.0050 0.70 115.0 105.8 5.7 Georgetown outlet[3] 215 0.030 0.182 0.182 0.0060 0.60 115.0 105.0 4.9 McMillan Park outlet 120 0.028 0.126 0.154 0.0060 0.65 118.0 104.4 4.2 Filtered water 9 0.016 0.078 0.086 0.0010 0.70 119.5 106.3 4.5 + -+ -+ -+ -+ + + -+ -+ -

Table 6 (Continued.) (B) Minimum. ====================+=====+=================+===========+=====+=====+==== Ammonia. Nitrogen as: Reservoirs. A + -+ -+ -+ -+ G H I B C D E F + -+ -+ -+ -+ + + -+ -+ Dalecarlia inlet 7 0.000 0.016 0.016 0.0000 0.00 52.9 39.5 1.0 Dalecarlia outlet[2] 7 0.000 0.040 0.040 0.0000 0.00 54.3 38.2 0.9 Georgetown outlet[3] 7 0.000 0.044 0.044 0.0000 0.00 51.4 40.6 0.7 McMillan Park outlet 2 0.000 0.010 0.010 0.0010 0.00 51.4 38.5 0.2 Filtered water 0 0.000 0.000 0.000 0.0000 0.00 52.9 40.3 0.4 + -+ -+ -+ -+ + + -+ -+

Table 6 (Continued.) (C) Average. ====================+=====+=================+===========+=====+=====+==== Ammonia. Nitrogen as: Reservoirs. A + -+ -+ -+ -+ G H I B C D E F + -+ -+ -+ -+ + + -+ -+ Dalecarlia inlet 86 0.006 0.167 0.113 0.0027 0.19 93.2 81.4 2.9 Dalecarlia outlet[2] 30 0.008 0.106 0.114 0.0023 0.18 95.5 79.5 3.4 Georgetown outlet[3] 29 0.005 0.101 0.106 0.0027 0.18 93.4 80.9 2.9 McMillan Park outlet 18 0.004 0.077 0.081 0.0027 0.17 94.0 83.0 2.7 Filtered water 1 0.002 0.027 0.029 0.0000 0.19 94.9 84.0 2.8 ==================+===+=====+=====+=====+======+====+=====+=====+====

[Footnote 1: Summary of daily samples of water.]

[Footnote 2: Reservoir out of service from July 1st to September 13th, 1909.]

[Footnote 3: Reservoir out of service from September 10th to October 4th, 1909.]

No chemical determinations were made during February, March, April, and May, 1910, on account of the rearrangement of the laboratory and equipment.

Table 7 Daily Results at Pumping Station. (A) ============+==================================+======+======== Million gallons pumped: Pressure + -+ -+ at sand- Lift washer To filters. To sand washers. to pumps, Month. filters. per -+ -+ -+ -+ -+ - square Max. Min. Ave. Max. Min. Ave. inch. -+ -+ -+ -+ -+ -+ -+ + 1909. -+ -+ -+ -+ -+ -+ -+ + July 76.16 57.65 64.05 1.140 0.298 0.730 24.18 110.0 August 69.31 54.44 61.42 0.629 0.157 0.441 22.18 110.0 September 66.02 52.82 69.32 0.831 0.207 0.572 22.26 110.0 October 78.50 48.12 59.18 0.761 0.060 0.467 21.84 110.0 November 64.92 49.83 55.25 0.468 0.141 0.272 20.49 110.0 December 67.83 48.32 56.77 0.307 0.039 0.174 20.54 110.0 -+ -+ -+ -+ -+ -+ -+ + 1910. -+ -+ -+ -+ -+ -+ -+ + January 70.04 51.02 62.49 0.499 0.008 0.156 22.43 110.0 February 70.79 55.19 60.28 0.284 0.041 0.173 21.44 112.3 March 59.11 51.64 56.04 0.409 0.063 0.171 19.76 120.0 April 66.53 53.79 58.32 0.715 0.167 0.474 20.78 120.0 May 61.93 54.55 57.76 0.525 0.059 0.251 20.30 120.0 June 70.49 50.42 58.37 0.281 0.124 0.207 21.19 117.3 -+ -+ -+ -+ -+ -+ -+ + Fiscal years: -+ -+ -+ -+ -+ -+ -+ + 1909-10 78.50 48.12 59.19 1.140 0.008 0.373 21.45 113.3 -+ -+ -+ -+ -+ -+ -+ + 1905-06[1] 80.59 57.18 66.07 2.062 0.089 0.747 21.71 107.4 1906-07 80.29 57.44 66.89 2.120 0.023 0.580 21.60 120.8 1907-08 80.38 54.35 64.91 0.735 0.017 0.347 22.20 125.0 1908-09 78.93 47.83 61.47 0.875 0.060 0.453 22.52 122.3 -+ -+ -+ -+ -+ -+ -+ +

============+==========+============ Coal consumed Station duty, per day in per 100 lb. of Month. tons.~ coal consumed.~ + + + + + - Max. Min. Ave. Max. Min. Ave. -+ + + + + + - 1909. -+ + + + + + - July 13.4 8.4 10.8 67.8 52.3 61.4 August 12.4 8.0 10.1 64.2 49.5 56.6 September 12.7 8.7 10.5 61.0 48.9 55.1 October 13.4 8.0 10.3 59.6 49.1 53.6 November 11.3 7.9 9.2 55.6 45.7 51.1 December 10.3 8.5 9.5 61.0 45.4 50.4 -+ + + + + + - 1910. -+ + + + + + - January 12.7 9.1 10.4 59.6 49.8 54.9 February 12.3 8.7 10.2 57.4 44.8 51.5 March 10.5 7.8 9.2 53.2 45.2 49.8 April 11.1 8.1 9.7 58.7 47.2 53.7 May 10.1 7.4 8.8 60.7 48.1 54.9 June 12.3 7.4 9.1 60.1 49.9 54.4 -+ + + + + + - Fiscal years: -+ + + + + + - 1909-10 13.4 7.4 9.8 67.8 44.8 54.0 -+ + + + + + 1905-06[1] 14.8 6.4 8.9 79.6 48.2 62.8 1906-07 15.0 7.0 10.0 71.6 46.5 58.6 1907-08 12.0 7.2 9.6 70.7 51.3 60.3 1908-09 13.2 7.0 10.0 74.0 45.7 57.7 -+ + + + + +

[Footnote 1: Raw water shut off from city supply on October 5th.]

Table 7 (Continued.) (B) ============================================================= Duty per Cost of 100 lb. coal per Fiscal Name of coal used. Cost per of coal 1,000,000 ft- Year. ton. consumed. lb. of work performed - - - 1905-06 George's Creek Big Vein $3.34 62.8 $0.00238 1906-07 George's Creek Big Vein 3.43 58.6 0.00261 1907-08 George's Creek Big Vein 3.75 60.3 0.00278 1908-09 Orenda 3.47 57.7 0.00268 1909-10 Orenda [1]3.15 54.0 0.00255 =========================================================

[Footnote 1: Corrected for increase or decrease in ash and British thermal units, as determined by United States Geological Survey.]

Table 8 Average Consumption of Water for Twenty-four Hours, Per Million Gallons. ==========+================================================ Fiscal years. Month. + -+ -+ -+ -+ -+ -+ -+ 1903. 1904. 1905. 1906. 1907. 1908. 1909. 1910. + -+ -+ -+ -+ -+ -+ -+ July 59.80 61.50 63.20 69.80 69.18 68.64 71.08 64.05 August 59.00 59.70 67.70 71.40 68.03 67.74 68.14 61.42 September 56.50 61.10 67.90 71.30 69.82 68.93 65.83 60.32 October 58.70 59.10 63.90 68.40 69.14 66.46 65.89 59.18 November 54.70 58.60 62.10 66.10 65.51 61.54 60.06 55.25 December 60.70 60.10 70.30 67.20 65.71 62.29 57.99 56.77 January 60.10 65.30 75.10 65.30 67.62 63.36 57.72 62.49 February 59.30 67.80 86.00 68.70 74.68 68.17 55.42 60.28 March 55.30 60.00 67.60 64.30 64.23 59.63 55.31 56.04 April 55.10 57.20 63.10 62.70 63.45 61.51 58.19 58.32 May 57.70 60.80 66.30 65.60 62.47 62.96 59.25 57.76 June 59.50 62.30 70.60 67.80 63.53 67.96 60.12 58.37 + -+ -+ -+ -+ -+ -+ -+ Average 58.03 61.10 68.70 67.40 66.90 64.91 61.47 59.19 ==========+=====+=====+=====+=====+=====+=====+=====+======

The length of runs, depth of scraping, etc., after the scraping or raking, are shown in Tables 10 and 11.

Sand Handling.—For the first three years of operation, the sand was carried from the sand bins in carts and dumped through the numerous manholes of the filters on chutes which could be revolved in various directions, in order to facilitate the spreading of the sand evenly over the surface of the filter.

About a year ago, however, this method was changed, by substituting sand ejectors for the carts. By this method, an ejector is either attached to, or placed directly under, the outlet gate of the sand bin, the gate is opened, and the ejector is started. From this ejector, the sand is carried back through the line of 4-in. fixed pipe, and one or more lengths of 3-in. hose, to the point of discharge in the filter bed which is being re-sanded.

Table 9.

Columns: A - July. B - August. C - September. D - October. E - November. F - December. G - January. H - February. I - March. J - April. K - May. L - June.

(A) Number of Deaths from Typhoid Fever, by Months, in the District of Columbia for the Last Fourteen Fiscal Years. ============================ Fiscal year. A B C D E F G H I J K L Total. - - - - - - 1896-97 8 15 25 25 18 16 13 4 4 4 6 9 147 1897-98 10 16 18 10 9 18 8 4 2 9 6 20 130 1898-99 24 22 22 28 21 16 10 4 7 6 3 6 169 1899-1900 9 38 30 28 27 26 17 6 8 10 5 12 193 1901-02 16 33 28 21 22 16 19 8 12 9 13 9 206 1902-03 21 39 25 32 19 20 9 5 9 6 6 3 194 1903-04 17 26 18 19 8 14 5 5 6 10 8 8 144 1904-05 16 22 25 14 11 9 11 1 5 7 1 3 125 1905-06[1] 15 30 23 26 14 6 6 4 5 4 10 9 152 1906-07 21 32 21 25 17 4 7 6 4 6 7 2 152 1907-08 10 18 17 19 11 7 4 1 1 8 8 3 107 1908-09 15 13 23 17 16 13 16 8 3 8 7 7 146 1909-10 12 12 17 12 12 2 3 4 7 5 5 4 95 - - - - - - Average 15.3 25.5 22.9 21.5 16.6 13.1 9.6 4.4 5.8 6.7 6.4 7.5 155.4 - - - - - -

Table 9—(Continued.)

Columns: A - July. B - August. C - September. D - October. E - November. F - December. G - January. H - February. I - March. J - April. K - May. L - June. M - Annual death rate.

(B) Number of Deaths from Typhoid Fever Reduced to Death Rates per 100,000 Inhabitants per Year. ====================================== Fiscal year. A B C D E F G H I J K L M - - - - - - - - - - - - 1896-97 35 65 109 109 78 70 56 17 17 17 26 39 53 1897-98 43 69 78 43 39 78 31 17 8 38 25 85 46 1898-99 102 93 93 119 89 68 42 17 29 25 12 26 59 1899-1900 37 158 125 116 112 108 69 24 33 41 20 49 74 1900-01 82 167 118 102 114 69 28 8 32 8 16 40 65 1901-02 64 132 112 84 88 64 75 31 47 35 51 35 68 1902-03 83 153 98 126 75 79 35 19 35 23 23 12 63 1903-04 66 100 69 73 31 54 19 19 23 38 30 30 46 1904-05 61 83 95 53 42 34 41 4 19 26 4 11 39 1905-06 56 111 85 97 52 22 22 15 18 15 36 33 47 1906-07 69 105 69 82 56 13 24 20 13 20 24 7 42 1907-08 35 64 60 67 39 25 14 4 4 28 28 11 32 1908-09 53 45 80 60 56 45 56 28 10 28 24 24 43 1909-10 42 42 60 42 42 7 11 14 24 17 17 14 28 - - - - - - - - - - - - Average monthly 59 99 89 84 65 53 38 24 22 26 24 30 ... death rate. ======================================

[Footnote 1: Filtered water supplied since October, 1905.]



Table 10 Periods of Operation, and Quantities Filtered. ==================================================================== Number of Number of days since previous: filter runs - ended after: Scraping. Raking. Month. - - - Scrap- Rak- Max. Min. Ave. Max. Min. Ave. ing. ing. - - - - 1909. - - - - July 14 0 89 44 67.4 0 0 0 August 8 0 74 51 60.4 0 0 0 September 13 0 98 53 68.3 0 0 0 October 18 5 81 32 59.9 43 33 39.4 November 8 2 79 44 53.4 47 37 42.0 December 3 4 62 61 61.3 63 50 57.3 - - - - 1910. - - - - January 9 4 95 79 88.0 88 72 77.0 February 1 4 99 99 99.0 93 51 71.0 March 3 4 120 110 113.7 108 101 104.3 April 10 12 126 62 84.8 129 21 65.3 May 3 2 86 38 69.7 55 32 43.5 June 13 2 100 61 79.7 129 78 103.5 - - - Year 1909-10 103 39 126 32 71.1 129 21 66.6 - - - Fiscal years: - - - - 1905-06 71 0 195 38 91.1 0 0 0 1906-07 101 4 199 24 77.0 32 14 21.7 1907-08 143 77 180 11 54.9 63 7 28.6 1908-09 128 50 135 11 49.9 93 13 34.2 ======================================

============+======================================================= Million gallons filtered since previous: + Month. Scraping. Raking. - Max. Min. Ave. Max. Min. Ave. - - 1909. - - July 229.01 106.27 163.289 0 0 0 August 175.54 124.94 152.581 0 0 0 September 237.52 114.37 161.702 0 0 0 October 206.09 78.78 132.359 96.50 71.51 82.708 November 168.19 82.32 112.603 99.00 90.23 94.615 December 135.77 128.33 132.647 144.35 106.11 125.940 - - 1910. - - January 204.38 146.58 178.461 189.48 152.33 170.735 February 205.73 205.73 205.730 192.98 118.85 158.890 March 275.96 257.36 265.493 249.68 224.49 238.993 April 295.96 104.13 181.972 307.57 45.22 142.448 May 186.64 81.66 150.230 102.15 69.79 85.978 June 213.70 130.85 171.059 181.25 167.84 174.540 - - Year 1909-10 295.96 81.66 159.151 307.57 45.22 143.832 - - Fiscal years: - - 1905-06 497.45 116.66 240.379 0 0 0 1906-07 466.12 69.76 220.693 103.28 32.13 76.870 1907-08 477.19 28.20 146.912 165.25 17.08 75.775 1908-09 298.08 39.26 125.617 244.19 41.41 88.439 ===========================================================

In re-sanding a filter, it is first filled with water to the proposed depth of the sand layer. The outlet end of the hose is connected to a 3-in. pipe which is supported on a boat, and the sand is discharged through this pipe at the point required. Work is first begun at the far end of the filter, and it is gradually filled by swinging the boat from side to side and backing it by degrees to the front end.

At first it was feared that a small quantity of mud would be deposited on the surface of the old sand, and that this mud would ultimately cause subsurface clogging. For this reason, when this method was first adopted, a man was required to rake the sand very thoroughly in front of the discharge. Later, it was found that by giving the end of the discharge pipe a slope of about 45 degrees downward from the horizontal, the force of the current of sand and water could be depended on to cut the old surface of sand to any required depth, and move it ahead together with the new sand, thus completely breaking up the possible mud layer between the old and new sand layers. After having used this method almost exclusively for 15 months, in which time eleven filters have been re-sanded, and 24,531 cu. yd. of sand have been replaced, there seems to be no indication of an increased initial loss of head. The sand is very compact, and has no apparent tendency to separate into different sizes. The general appearance is similar to that of very fine sand on the seashore. The filters re-sanded in this way have been considerably more efficient than those in which the sand was replaced with carts, and as yet, no harmful results have been noted. The rate at which the sand is replaced is shown in Table 12, and the cost of labor for sand handling is given in detail in Table 14, which shows that quite a perceptible saving has been effected by the hydraulic method.

The figures showing the cost for sand handling do not include any charge for the quantity of water used, that item having been carried on the pumping-station account.

Table 11 Quantities of Sand Removed. ============+==============+=============================== ~No. of filters ~Cubic yards when last scraped when last treatment was:~ treatment was:~ Month. + -+ -+ -+ Scraping. Raking. Scraping. Raking. + + -+ + + Max. Min. Ave. Max. Min. Ave. + -+ -+ + + -+ + + 1909. + -+ -+ + + -+ + + July 14 0 338 121 190.6 0 0 0 August 8 0 356 149 218.5 0 0 0 September 8 0 524 97 178.6 0 0 0 October 9 5 150 93 115.8 301 121 169.0 November 2 2 134 88 111.0 132 81 106.5 December 0 2 0 0 0 133 126 129.5 + -+ -+ + + -+ + + 1910. + -+ -+ + + -+ + + January 2 4 155 112 133.5 195 121 147.8 February 0 4 0 0 0 390 160 225.8 March 1 4 489 489 489.0 262 179 214.3 April 4 12 172 84 119.3 230 146 178.8 May 1 2 320 320 320.0 249 241 245.0 June 0 2 0 0 0 203 190 196.5 + -+ -+ + + -+ + + Year 1909-10 49 37 524 84 176.7 390 81 181.0 + -+ -+ + + -+ + + Fiscal Years: + -+ -+ + + -+ + + 1905-06 71 0 600 71 250.0 0 0 0 1906-07 94 2 536 52 259.0 398 276 337.0 1907-08 81 53 527 46 190.2 411 35 118.4 1908-09 92 50 580 55 169.5 472 81 177.5 =============+========+======+++==+==++====

==============+================================ Depth, in inches, when last treatment was: + -+ Month. Scraping. Raking. + + + -+ + + Max. Min. Ave. Max. Min. Ave. + + + -+ + + 1909. + + + -+ + + July 2.51 0.90 1.415 0 0 0 August 2.65 1.11 1.631 0 0 0 September 3.90 0.72 1.330 0 0 0 October 1.12 0.69 0.862 2.24 0.90 1.256 November 1.00 0.65 0.825 0.98 0.60 0.790 December 0 0 0 0.99 0.94 0.965 + + + -+ + + 1910. + + + -+ + + January 1.15 0.83 0.990 1.45 0.90 1.100 February 0 0 0 2.90 1.19 1.678 March 3.64 3.64 3.640 1.95 1.33 1.593 April 1.28 0.62 0.885 1.71 1.09 1.331 May 2.38 2.38 2.380 1.85 1.79 1.820 June 0 0 0 1.51 1.41 1.460 + + + -+ + + Year 1909-10 3.90 0.62 1.314 2.90 0.60 1.373 + + + -+ + + Fiscal Years: + + + -+ + + 1905-06 4.47 0.53 1.799 0 0 0 1906-07 4.00 0.56 1.931 2.95 2.05 2.500 1907-08 3.92 0.21 1.507 3.06 0.21 0.881 1908-09 4.31 0.41 1.259 3.51 0.60 1.317 ==============+====+====+=====+====+====+======

Table 12 Rates of Sand Handling. ===================================================================== Sand removed from filters. Sand replaced in filters. - - - - Ejector Cubic Average Ejector Cubic Average Date. hours. yards of rate in hours. yards of rate in sand cubic yards sand cubic removed per hour removed yards per hour - - - - - 1906. - - - - - April 49 253 5.2 ... ... ... May 380 2,511 6.6 ... ... ... June 567 3,280 5.8 ... ... ... July 931 5,376 5.8 ... ... ... August 105 533 5.1 ... ... ... September 315 1,892 6.0 ... ... ... October 1,067 5,173 5.8 ... ... ... November 168 935 5.6 ... ... ... December 203 1,073 5.3 ... ... ... - - - - - 1907. - - - - - January 399 2,974 7.3 ... ... ... February 140 1,139 8.1 ... ... ... March 115 878 7.6 ... ... ... April 427 3,103 7.3 ... ... ... May 133 939 7.0 ... ... ... June 105 674 6.4 ... ... ... July 7 46 6.6 ... ... ... August 90 574 6.4 ... ... ... September 306 1,396 6.5 ... ... ... October 273 1,701 6.2 ... ... ... November 202 1,258 6.8 ... ... ... December 304 2,138 5.9 ... ... ... - - - - - 1908. - - - - - January 546 3,708 6.8 ... ... ... February 98 776 7.9 ... ... ... March 315 2,832 9.0 ... ... ... April 469 3,775 8.1 ... ... ... May 182 1,414 7.8 ... ... ... June 280 2,057 7.4 ... ... ... July 280-1/2 2,683 9.6 ... ... ... August 327-1/2 2,808 8.6 ... ... ... September 402 3,371 8.4 ... ... ... October 308 2,696 8.7 ... ... ... November 47-1/2 333 7.0 ... ... ... December 153-3/4 1,268 8.3 ... ... ... - - - - - 1909. - - - - - January 119-1/2 1,055 8.8 ... ... ... February 161-1/2 1,479 9.2 ... ... ... March 144 1,465 10.2 ... ... ... April 214-3/4 2,260 10.5 188 2,405 12.8 May 219-3/4 2,223 10.1 190 2,196 11.5 June 355 3,096 8.7 243 3,054 12.6 July 312-1/4 2,707 8.7 425-1/2 4,050 9.5 August 218-3/4 1,955 9.0 64-1/2 620 9.6 September 172-1/2 1,360 7.9 408 2,842 7.0 October 203 1,870 9.2 261-1/4 2,350 9.0 November 54 397 7.4 0 0 ... December 62 382 6.2 0 0 ... - - - - - 1910. - - - - - January 104 703 6.8 0 0 ... February 106-1/2 1,058 9.9 28-1/4 371 13.1 March 98 985 10.0 72 1,008 14.0 April 268-3/4 2,852 10.7 134-1/4 2,159 16.1 May 58-3/4 693 11.8 171-3/4 3,042 17.7 June 58-3/4 642 10.9 9-3/4 166 17.0 ============================================================

The cost for pumping water for sand handling, including all labor, materials, and repairs, amounts to $0.06 per cu. yd. of sand ejected and washed, and $0.03 per cu. yd. for replacing.

In addition to the water used for carrying the sand which is being replaced, it is customary to keep a slight upward flow in the filter, thus using about 500,000 gal. of filtered water per day for this purpose. Assuming the value of this water to be the total cost for pumping, filtering, etc., or $3.80 per 1,000,000 gal., the cost per cubic yard of sand replaced would be about $0.02 when one ejector is used, and $0.01 when two are in operation.

It is not considered absolutely necessary to have an upward flow of water in the filter which is being re-sanded, and it is not always done. It was used, however, as an additional safeguard against the formation of a stratum of mud between the old and new layers of sand while the hydraulic method was in an experimental stage.

The quantities of sand removed from the filters per scraping and the rates of sand handling are shown in Tables 11 and 12.

Cost of Operation.—It is frequently difficult to compare the relative cost of corresponding items for different plants, because of the different methods of dividing the cost and the varying opinions of the officials as to what should properly be charged to each item.

In order that the data may be in sufficient detail to permit it to be rearranged to compare with other plants, a list of employees and charges for supplies is given in Table 13. This list accounts for the entire appropriation for the care and maintenance of the filtration plant, including pumping the water to the filters, parking and caring for the grounds, buildings, roads, sidewalks, etc. The cost for the various items per million gallons pumped to the filters is shown in Table 14, and the cost per cubic yard of sand handled in Table 15.

Preliminary Treatment.—Before the present filtration plant was designed, Rudolph Hering, George W. Fuller, and Allen Hazen, Members, Am. Soc. C. E., made an investigation and report. This report was dated February 18th, 1901, and contained the following paragraph:

"In consideration of the full evidence, we recommend the construction of a complete system of slow or sand filters, with such auxiliary works as may be necessary for preliminary sedimentation, and the use of a coagulant for part of the time. There is no reason to believe that the use of this coagulant will in any degree affect the wholesomeness of the water."

Notwithstanding this opinion, considerable prejudice existed among the citizens of Washington against the use of a coagulant, and, as finally passed, the bill providing for the construction of the filters did not include an appropriation for the coagulant.

Table 13 List of Employees, Rates of Pay, and Approximate Cost for Supplies. ========================================================+=========== 1 Superintendent $3,000.00 1 Chief Chemist and Assistant Superintendent 2,100.00 1 First Assistant Chemist 1,500.00 1 Second Assistant Chemist 1,000.00 1 Stenographer and Clerk 1,200.00 1 Surveyor 1,200.00 1 Laboratory Helper 720.00 1 Janitor 600.00 1 Chief Steam Engineer 1,800.00 1 First Assistant Steam Engineer 1,440.00 1 Second Assistant Steam Engineer 1,080.00 3 Oilers, at $900 each 2,700.00 3 Firemen, at $900 each 2,700.00 3 Laborers, at $540 each 1,620.00 1 Filter Foreman 1,200.00 2 Foremen, at $900 each 1,800.00 1 Timekeeper 900.00 3 Watchmen and Gauge Tenders, at $900 each 2,700.00 1 Machinist 1,140.00 1 Blacksmith 900.00 1 Storekeeper 900.00 1 Painter 900.00 1 Mechanic 900.00 1 Electrician 900.00 4 Skilled Laborers at $600 each 2,400.00 1 Watchman and Special Officer 900.00 1 Recorder 720.00 27 Laborers, at $1.50 per day for 300 days 12,150.00 3 Teams, at $2.00 per day for 200 days 1,200.00 Laboratory and office supplies 2,700.00 Filter supplies, tools, hose, repair of roads, parks, shrubs, etc. 8,820.00 Pumping station supplies, oil, waste, packing, repairs, etc. 3,570.00 3,600 tons of coal, at $3.15 per ton 11,340.00 Charges in U. S. Engineer Office, labor 2,900.00 Charges in U. S. Engineer Office, materials 400.00 + - Total $82,000.00 =====================================================+========

The results obtained from operating the filters being such as to justify the conclusions in the report referred to, an experimental plant was constructed for the purpose of studying the efficiency of various methods of preliminary treatment of the water. This plant consisted of three cylindrical concrete filter tanks, each 10 ft. in diameter. These tanks were filled with the layers of gravel and sand necessary to make them represent as accurately as possible the large slow sand units of the main filtration plant. Means were also provided for giving a preliminary treatment to the water supplying each of these experimental slow sand filters. In two cases, the preliminary treatment was rapid filtration, while the third consisted of sedimentation and coagulation. The sedimentation tank was of sufficient size, when compared with the area of the experimental slow sand filter, to represent the Georgetown and McMillan Park Reservoirs when used in connection with the large filters. The first preliminary filter was very similar in construction and operation to a mechanical filter. The sand for this filter was taken from the main filters, and, consequently, was finer than is generally used in mechanical filters. The second preliminary filter was a Maignen scrubber. It consisted of a cylindrical concrete tank, 4 ft. in diameter and 8-1/2 ft. deep, which contained 12 in. of cobble-stones on the bottom, then, successively, 12 in. of egg-size coke, 12 in. of stove-size coke, 24 in. of nut-size coke, and 24 in. of sponge clippings as the final or top layer.

Table 14 Cost Per Million Gallons Filtered. (A) Labor. ================================+================== Office Filter and Pumping operations: Month. laboratory. station. + Sand Repairs handling. etc. - - - 1909. - - - July $0.73 $0.57 $0.86 ... August 0.75 0.64 0.59 ... September 0.83 0.67 0.80 ... October 0.72 0.66 0.73 ... November 0.87 0.76 0.42 ... December 0.90 0.69 0.27 ... - - - 1910. - - - January 0.81 0.63 0.33 ... February 0.94 0.74 0.35 $0.07 March 0.92 0.81 0.30 0.07 April 0.93 0.83 0.49 0.03 May 0.86 0.72 0.36 0.03 June 0.88 0.67 0.38 ... - - - Average 0.84 0.70 0.27 [1]0.25 - - - Fiscal years: - - - 1905-1906 0.45 0.45 0.47 0.02 1906-1907 0.57 0.57 0.58 0.21 1907-1908 0.70 0.56 0.42 0.32 1908-1909 0.72 0.61 0.41 0.34 - - -

========================================================= Parking Month. (care of Experimental Main Total. grounds). filters. Office. - - - 1909. - - - July $0.31 ... $0.15 $2.62 August 0.71 ... 0.14 2.83 September 0.51 ... 0.17 2.98 October 0.34 ... 0.08 2.53 November 0.38 ... 0.18 2.61 December 0.40 ... 0.12 2.38 - - - 1910. - - - January 0.14 ... 0.10 2.01 February 0.11 ... 0.16 2.37 March 0.18 ... 0.13 2.41 April 0.36 ... 0.13 2.77 May 0.55 ... 0.18 2.70 June 0.38 ... 0.12 2.43 - - Average 0.36 ... 0.14 2.56 - - Fiscal years: - - - 1905-1906 0.01 ... 0.09 1.49 1906-1907 0.07 $0.03 0.04 2.07 1907-1908 0.15 0.09 0.09 2.36 1908-1909 0.22 0.01 0.13 2.44 - -

Table 14 (Continued.) (B) Materials. ================================+================== Office Filter and Pumping operations: Month. laboratory. station. + Sand Repairs handling. etc. - - - 1909. - - - July ... ... $0.01 ... August $0.01 ... ... ... September 0.05 $0.31 0.04 ... October 0.08 0.11 0.13 ... November 0.13 0.78 0.10 ... December 0.03 0.17 0.05 ... - - - 1910. - - - January 0.12 0.74 0.14 ... February 0.07 1.88 0.18 ... March 0.26 0.28 0.01 ... April 0.18 1.22 0.10 ... May 0.06 0.72 0.02 ... June 0.54 2.23 ... $[2]2.16 - - - Average 0.13 0.69 0.02 [3]0.21 - - - Fiscal years: - - - 1905-1906 0.04 0.59 0.02 ... 1906-1907 0.03 0.67 0.08 0.20 1907-1908 0.05 0.54 0.04 0.07 1908-1909 0.10 0.69 0.05 0.18 - - -

========================================================= Parking Month. (care of Experimental Main Total. grounds), filters. Office. - - - 1909. - - - July ... ... ... $0.01 August $0.07 ... $0.01 0.09 September 0.01 ... 0.03 0.44 October 0.46 ... 0.02 0.80 November 0.34 ... 0.02 1.37 December 0.01 ... 0.05 0.31 - - - 1910. - - - January 0.01 ... ... 1.01 February 0.01 ... 0.01 2.15 March ... ... ... 0.55 April 0.29 ... 0.02 1.81 May 0.11 ... 0.02 0.98 June 0.46 ... 0.04 5.43 - - Average 0.17 ... 0.02 1.24 - - Fiscal years: - - - 1905-1906 ... ... ... 0.65 1906-1907 0.02 ... 1.00 1907-1908 0.06 ... 0.01 0.77 1908-1909 0.18 ... 0.02 1.22 - -

[Footnote 1: $0.02 for new sand-handling system.]

[Footnote 2: $2.02 for new sand-handling system.]

[Footnote 3: $0.16 for new sand-handling system.]

Table 14 (Continued.) (C) Totals. ==================================+=================== Office Filter and Pumping operations: Month. laboratory. station. + - Sand Repairs handling. etc. - - - - 1909. - - - - July $0.73 $0.57 $0.87 ... August 0.76 0.64 0.59 ... September 0.88 0.98 0.84 ... October 0.80 0.77 0.86 ... November 1.00 1.54 0.52 ... December 0.93 0.86 0.32 ... - - - - 1910. - - - - January 0.93 1.37 0.47 ... February 1.01 2.62 0.53 $0.07 March 1.18 1.09 0.31 0.07 April 1.11 2.05 0.59 0.03 May 0.92 1.44 0.38 0.03 June 1.42 2.90 0.38 2.16 - - - - Average. 0.97 1.39 0.29 0.46 - - - - Fiscal years: - - - - 1905-1906 0.49 1.04 0.49 0.02 1906-1907 0.60 1.24 0.66 0.41 1907-1908 0.75 1.13 0.46 0.39 1908-1909 0.82 1.30 0.46 0.52 ====================================================

=================================================== Parking Month. (care of Experimental Main Total. grounds), filters. Office. - - - 1909. - - - Jul $0.31 ... $0.15 $2.63 August 0.78 ... 0.15 2.92 September 0.52 ... 0.20 3.42 October 0.80 ... 0.10 3.33 November 0.72 ... 0.20 3.98 December 0.41 ... 0.17 2.69 - - - 1910. - - - January 0.15 ... 0.10 3.02 February 0.12 ... 0.17 4.52 March 0.18 ... 0.13 2.96 April 0.65 ... 0.15 4.58 May 0.66 ... 0.20 3.63 June 0.84 ... 0.16 7.86 - - - Average. 0.58 ... 0.16 3.80 - - - Fiscal years: - - - 1905-1906 0.01 ... 0.09 2.14 1906-1907 0.09 $0.03 0.04 3.07 1907-1908 0.21 0.09 0.10 3.13 1908-1909 0.40 0.01 0.15 3.66 ===============================================

The two preliminary filters were operated at a rate of about 50,000,000 gal. per acre per day, and the three slow sand filters at rates of from 3,000,000 to 4,000,000 gal. per day.

This plant was put in service during the early part of February, 1907, and was kept in practically continuous operation until the end of July, 1908.



Table 15 Average Cost for Labor for Sand Handling. (A) Per Million Gallons Pumped To Filter. ============+======+======+======+======+======+========+======== Month. Scrap- Eject- Wash- Smooth- Raking. Re- Total. ing. ing. ing. ing. sanding. -+ -+ -+ -+ -+ -+ + 1909. -+ -+ -+ -+ -+ -+ + July $0.10 $0.21 $0.03 $0.02 ... $0.21 $0.57 August 0.07 0.16 0.03 0.01 ... 0.04 0.31 September 0.05 0.13 0.02 0.01 $0.01 0.27 0.49 October 0.06 0.15 0.03 0.01 0.02 0.12 0.39 November 0.02 0.06 ... ... 0.02 ... 0.70 December 0.02 0.04 0.01 ... 0.01 0.01 0.09 -+ -+ -+ -+ -+ -+ + 1910. -+ -+ -+ -+ -+ -+ + January 0.04 0.07 ... 0.01 0.02 ... 0.14 February 0.04 0.10 ... 0.01 ... 0.02 0.17 March 0.04 0.06 ... 0.01 0.01 0.05 0.17 April 0.10 0.15 0.04 0.01 0.02 0.06 0.38 May 0.02 0.03 0.01 ... 0.01 0.11 0.18 June 0.02 0.04 ... ... 0.02 0.01 0.09 -+ -+ -+ -+ -+ -+ + Average 0.05 0.10 0.01 0.01 0.01 0.08 0.26 -+ -+ -+ -+ -+ -+ + Fiscal years: -+ -+ -+ -+ -+ -+ + 1905-06 0.06 0.29 0.02 0.06 ... 0.04 0.47 1906-07 0.07 0.20 0.05 0.02 ... 0.24 0.58 1907-08 0.09 0.14 0.03 0.01 0.02 0.13 0.42 1908-09 0.07 0.15 0.03 0.01 0.01 0.14 0.41 -+ -+ -+ -+ -+ -+ +

Table 15 (Continued.) (B) Per Cubic Yard of Sand. ============+======+======+======+======+======+======+======== Month. Scrap- Eject- Wash- Smooth- Raking. Re- Total. ing. ing. ing. ing. sanding. -+ -+ -+ -+ -+ -+ + 1909. -+ -+ -+ -+ -+ -+ + July $0.08 $0.15 $0.03 $0.01 ... $0.10 $0.37 August 0.07 0.15 0.03 0.01 ... 0.11 0.37 September 0.07 0.17 0.03 0.01 ... 0.17 0.45 October 0.06 0.15 0.03 0.01 ... 0.09 0.34 November 0.10 0.23 0.02 0.02 ... ... 0.37 December 0.12 0.25 0.04 0.02 ... 0.08 0.51 -+ -+ -+ -+ -+ -+ + 1910. -+ -+ -+ -+ -+ -+ + January 0.10 0.19 ... 0.02 ... ... 0.31 February 0.07 0.15 ... 0.01 ... 0.09 0.32 March 0.06 0.11 ... 0.02 ... 0.08 0.27 April 0.07 0.09 0.03 0.01 ... 0.05 0.25 May 0.06 0.09 0.03 0.01 ... 0.06 0.25 June 0.06 0.12 ... 0.01 ... 0.10 0.29 -+ -+ -+ -+ -+ -+ + Average 0.07 0.14 0.02 0.01 ... 0.10 0.34 -+ -+ -+ -+ -+ -+ + Fiscal years: -+ -+ -+ -+ -+ -+ + 1905-06 0.07 0.35 0.04 0.07 ... 0.14 0.67 1906-07 0.06 0.19 0.03 0.02 ... 0.17 0.47 1907-08 0.09 0.15 0.03 0.01 ... 0.14 0.42 1908-09 0.06 0.14 0.03 0.01 ... 0.13 0.37 ============+======+======+======+======+======+======+========

For convenience in referring to the different systems, the combined rapid and slow sand filter will be designated as Filter Plant No. 1, the combined Maignen scrubber and slow sand filter as Filter Plant No. 2, and the combined coagulating basin and slow sand basin as Filter Plant No. 3.

The length of run of Filter Plant No. 1 was relatively long at first. The rapid rate of filtration, however, tended to carry the clay, which was suspended in the applied water, to a considerable depth in the filtering material, so that the runs gradually decreased in length until they were reduced to about three days. Unfortunately, it was necessary to use unfiltered water for washing, which, together with the great penetration from the applied water, finally made it necessary to remove all the filtering materials, and wash them.

Although this preliminary filter was operated at a high rate, its efficiency was quite satisfactory. In fact, at times when the applied water was comparatively good, very little work was left for the slow sand filter. At times of high turbidity, however, some of the exceedingly fine mud in the applied water passed through this filter, as well as the slow sand filter connected with it, and it proved to be absolutely impossible to produce a clear effluent at all times with this combination.

Filter Plant No. 2 proved more economical and convenient in operation, but somewhat less efficient than Filter Plant No. 1. Neither filter could be depended on to give a clear effluent when the applied water was turbid.

In the operation of Filter Plant No. 3, sulphate of alumina was used when the applied water contained too much turbidity to be treated satisfactorily by slow sand filters.

When the water was comparatively clear, either one of the three systems, or slow sand filtration alone, was entirely satisfactory. At times of high turbidity, however, Filter Plant No. 3 was the only one which could be depended on to produce a clear effluent.

A fair comparison between the results of the three systems when treating turbid water in January, 1908, is given in Table 16.

Table 16 shows very clearly that neither Filter Plant No. 1 nor No. 2 would prove at all satisfactory when treating turbid water, while No. 3 could be depended on under all conditions. The results of operation are shown in detail in Tables 17, 18, and 19. It will be noticed in Table 17, that on March 10th, 1908, Filter Plant No. 1 was put out of service and a Puech system of preliminary filters was substituted for it.

The Puech preliminary filters consisted of five units containing gravel of varying sizes through which the water was filtered successively before it was finally applied to the final slow sand filter. A general idea of this system may be obtained by referring to Figure 8.

Table 16—Turbidity Results with Experimental Filters, During Period of High Turbidity, January, 1908.

Columns: A - Effluent preliminary filter. B - Effluent sand filter. C - Effluent preliminary filter. D - Effluent sand filter. E - Effluent coagulant basin. F - Effluent sand filter.

============+======+=============+=============+============== Raw Filter No. 1. Filter No. 2. Filter No. 3. Date. water. + + + + + - A B C D E F + + + + + + + - January 12th 40 10 1 12 1 2 0 January 13th 110 45 2 51 2 2 0 January 14th 210 95 3 113 4 2 0 January 15th 325 190 12 222 15 3 0 January 16th 360 210 37 247 42 5 0 January 17th 242 122 24 147 26 6 0 January 18th 137 ... ... 73 7 6 0 January 19th 117 40 12 clean- ... 5 0 ing January 20th 72 31 6 sand ... clean- 0 filter ing January 21st 55 20 4 25 4 sand ... January 22d 49 17 3 21 4 filter ... January 23d 40 12 3 15 3 3 0 January 24th 40 11 3 13 3 3 0 ============+======+======+======+======+======+======+=======

It is unfortunate that this system was not in operation in January, 1908, when the water was cold and turbid. The results, however, indicate that it would be no more successful than either Filter Plant No. 1 or No. 2.

Experimental Rate Studies.—In September, 1908, an experimental plant consisting of six small filters was put in operation. The object of these experiments was to study the relative efficiencies and cost for the operation of slow sand filters when operated at different rates.

The units of the plant consisted of cylindrical galvanized-iron tanks 4 ft. in diameter and 9 ft. high. The filter sand in these tanks was taken from the supply for the main filters. It was supported on gravel layers and supplied with under-drains of suitable sizes for the proposed rate of flow in each case.

The units of the experimental plant were designated as Nos. 1, 2, 3, 4, 5, and 6, and it was the original intention to operate them at rates of 1,000,000, 3,000,000, 6,000,000, 10,000,000, 30,000,000, and 100,000,000 gal. per acre daily, respectively.

This schedule of rates was carried out in a general way with all the filters, with the exception of Nos. 5 and 6. For these, the rates were found to be higher than could be maintained for any great length of time, owing to the deeper penetration of the mud in the filter sand, which caused high initial losses of head, short runs, and deep scrapings. A rate of about 30,000,000 gal. was maintained in the case of Filter No. 5 from the time it was started on September 9th, 1908, until November 8th, 1909, when it was reduced to about 17,000,000 gal., which rate was maintained thereafter until the filter was shut down in February, 1910.



In the case of Filter No. 6, it was found impossible to maintain a rate of 100,000,000 gal. for more than a very few days at a time. It was started at about this rate, however, at the beginning of each run, and kept as high as possible for the remainder of the time during the first seven runs. At the end of the seventh run, on October 17th, 1908, the filter was given a very deep scraping and re-sanded.



The layer of clean sand restored the original capacity, and the filter was operated as before, but with gradually decreasing rates until December, 1908, when the rate was reduced to about 40,000,000 gal. Even this lower rate was too high to be maintained without removing and replacing a large part of the sand. The rates, therefore, gradually decreased to about 23,000,000 gal. on March 13th, 1909, when the filter was again re-sanded. After this re-sanding the rate was reduced to about 20,000,000 gal., and the filter was operated at approximately that rate until it was again re-sanded on November 13th, 1909, when the rate was again reduced to about 14,000,000 gal., which was maintained until the filter was put out of service on February 28th, 1910.

This experimental plant was in service from September, 1908, to the latter part of February, 1910, or for about 1-1/2 years, and the leading results are summarized in Table 20.

Table 17—Record of Experimental Filter Plant No. 1.

Columns: A - Rate, millions of gallons per acre daily. B - Loss of head. C - Rate, millions of gallons per acre daily. D - Loss of head. E - Applied water. F - Effluent preliminary filter. G - Effluent final filter. H - Applied water. I - Effluent preliminary filter. J - Effluent final filter.

======+==========+==========+================+==================== Preliminary Final Turbidity. Bacteria. Filter. Filter. Date. -+ -+ -+ -+ -+ -+ -+ + + A B C D E F G H I J -+ -+ -+ -+ -+ -+ -+ -+ + + 1907. -+ -+ -+ -+ -+ -+ -+ -+ + + Feb. 8 19.40 0.71 3.10 0.17 ... ... ... 1,100 2,000 2,500 Feb. 9 21.50 0.81 3.11 0.16 ... ... ... 200 950 500 Feb. 10 20.60 0.95 3.04 0.14 ... ... ... ... ... ... Feb. 11 20.10 1.08 3.03 0.12 12 3 2 600 900 1,300 Feb. 12 19.80 1.23 3.02 0.13 14 4 2 650 650 650 Feb. 13 19.50 1.38 2.96 0.12 15 6 2 600 600 950 Feb. 14 21.20 1.67 3.21 0.11 15 4 2 650 700 800 Feb. 15 25.40 2.03 3.90 0.13 12 4 2 600 550 800 Feb. 16 25.00 2.23 3.89 0.12 14 3 2 850 550 500 Feb. 17 Shut down for changes in size of meter and piping. Feb. 18 ... ... ... ... ... ... ... 1,200 ... 650 Feb. 21 38.60 1.59 3.93 0.18 20 4 2 1,800 1,100 700 Feb. 22 38.00 1.84 3.92 0.15 15 3 2 Holiday. Feb. 23 42.10 2.36 3.95 0.14 20 5 2 1,600 600 220 Feb. 24 47.90 3.04 3.93 0.13 20 6 3 Sunday. Feb. 25 Shut down change meter 1,400 800 450 from outlet to inlet. Feb. 27 ... 2.24 ... 0.13 17 6 3 700 550 280 Feb. 28 49.80 2.55 3.90 0.13 15 6 3 800 470 230 -+ -+ -+ -+ -+ -+ -+ -+ + + Mar. 1 50.00 2.90 3.93 0.13 15 5 3 650 450 140 Mar. 2 50.20 3.21 3.93 0.13 15 5 3 1,000 650 200 Mar. 3 38.80 3.09 3.89 0.13 31 8 3 Sunday. Mar. 4 50.00 3.54 3.93 0.12 35 10 5 1,200 ... ... Mar. 5 50.00 4.01 3.90 0.13 135 39 8 13,000 3,700 600 Mar. 6 50.00 4.82 3.90 0.13 135 39 8 18,000 4,500 ... Mar. 7 50.00 5.89 3.90 0.13 102 34 6 24,000 5,000 2,000 Mar. 8 50.00 6.58 3.90 0.13 100 25 4 22,000 5,000 1,400 Mar. 9 50.00 7.21 3.93 0.13 90 25 4 24,000 4,000 650 Mar. 10 50.00 7.52 3.90 0.13 82 22 5 Sunday. Washed. Mar. 11 50.00 0.84 3.90 0.13 68 19 6 18,000 2,100 350 Mar. 12 50.00 0.95 3.96 0.13 46 19 4 11,000 6,000 310 Mar. 13 50.00 1.17 3.99 0.13 40 19 4 9,000 4,900 300 Mar. 14 50.00 1.53 4.01 0.13 39 17 4 5,500 1,300 130 Mar. 15 50.00 2.27 4.05 0.13 35 15 4 6,500 1,500 60 Mar. 16 50.00 3.08 4.03 0.13 60 20 4 5,000 1,200 100 Mar. 17 50.00 4.26 4.03 0.13 135 35 4 Sunday. Mar. 18 50.00 5.65 4.00 0.13 170 49 7 9,000 1,200 95 Mar. 19 50.00 7.02 4.01 0.13 125 37 6 7,000 600 100 Washed. Mar. 20 50.00 1.08 3.98 0.13 102 30 5 4,800 300 75 Mar. 21 50.00 1.23 3.98 0.12 125 32 4 8,500 1,000 85 Mar. 22 50.00 1.46 4.00 0.13 190 65 4 7,500 1,100 45 Mar. 23 50.00 1.76 3.99 0.13 180 65 6 7,500 600 55 Mar. 24 50.00 2.11 3.99 0.12 140 52 7 Sunday. Mar. 25 50.00 2.46 4.00 0.11 88 30 5 4,400 500 85 Mar. 26 50.00 2.75 4.00 0.12 62 22 4 3,600 300 65 Mar. 27 50.00 3.04 4.08 0.13 47 18 4 2,200 160 60 Mar. 28 50.00 3.38 3.94 0.11 35 10 3 1,300 100 55 Mar. 29 50.00 3.70 4.00 0.11 26 8 3 700 80 29 Mar. 30 50.00 4.42 4.00 0.11 25 6 3 310 70 35 Mar. 31 50.00 5.25 3.99 0.11 21 5 2 Sunday. -+ -+ -+ -+ -+ -+ -+ -+ + + Apr. 1 50.00 6.14 4.00 0.12 20 5 2 600 25 30 Washed. Apr. 2 50.00 2.10 4.00 0.12 24 5 2 270 28 32 Apr. 3 50.00 3.00 4.00 0.12 24 5 2 460 26 43 Apr. 4 50.00 4.01 4.00 0.12 20 5 2 280 20 26 Apr. 5 50.00 5.15 4.00 0.12 20 4 2 450 37 41 Washed. Apr. 6 50.00 O.76 3.59 0.12 20 4 2 320 6 34 Apr. 7 50.00 O.99 3.47 0.12 20 4 2 Sunday. Apr. 8 50.00 1.39 4.03 0.14 18 3 2 330 10 20 Apr. 9 50.00 2.04 4.01 0.13 18 3 2 140 9 35 Apr. 10 50.00 3.03 4.02 0.13 30 2 1 750 43 29 Apr. 11 50.00 4.45 4.02 0.14 66 1 1 4,000 900 26 Apr. 12 50.00 6.14 4.01 0.13 72 11 2 14,000 1 700 41 Washed. Apr. 13 50.00 0.95 4.00 0.14 80 21 2 13,000 1 300 70 Apr. 14 50.00 1.18 4.00 0.13 77 25 3 Sunday. Apr. 15 50.00 1.57 4.00 0.14 62 21 3 7,000 380 55 Apr. 16 50.00 2.33 4.00 0.15 47 20 3 3,600 160 33 Apr. 17 50.00 3.33 4.00 0.15 39 15 2 1,600 70 39 Apr. 18 50.00 4.81 4.00 0.16 30 10 2 1,810 130 34 Apr. 19 50.00 6.29 3.99 0.16 25 7 2 790 50 32 Washed. Apr. 20 50.00 0.93 4.01 0.16 20 5 2 540 24 28 Apr. 21 50.00 1.36 3.97 0.16 20 3 2 Sunday. Apr. 22 50.00 2.22 4.02 0.16 18 2 1 235 15 28 Apr. 23 50.00 3.33 3.99 0.14 15 2 1 170 14 16 Apr. 24 50.00 4.78 3.97 0.15 19 1 1 150 32 14 Apr. 25 50.00 6.43 3.90 0.15 34 1 1 700 20 18 Washed.