Chapter I: Part 1

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
==============+====+====+=====+====+====+======