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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.

[Illustration: ~Figure 1--Plan and Profile of Washington Aqueduct.~]

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.

[Illustration: ~Figure 2--General Plan of Washington Filtration Plant
Showing Finished Surfaces.~]


    ~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.]


[Illustration: ~Figure 3--Washington Aqueduct, D. C., Filteration
Plant. Sand Handling, System.~]

[Illustration: ~Figure 4--Washington Aqueduct, D. C., Filtration
Plant. Washer Sand-Handling, System.~]

[Illustration: ~Figure 5--Washington Aqueduct, D. C., Filtration
Plant. Ejector Sand-Handling, System.~]


     ~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.

[Illustration: ~Figure 6--Washington Aqueduct, D. C., Experimental
Filters Below Dalecarlia Reservoir Coagulating Basins and Apparatus.~]


         ~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.

[Illustration: ~Figure 7--Plan of Filter-House and Equipment.~]

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.

[Illustration: ~Figure 8--Diagrammatic Sketch Showing Arrangements for
Testing "Puech" System of Water Filtration at Washington D. C.,
U. S. A.~]

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.
  Apr. 26|50.00| O.97| 3.97| 0.14 | 46 |   2 |   1 | 1,200|    16|   16
  Apr. 27|50.00| 2.37| 4.00| 0.14 | 52 |   3 |   1 | 1,700|    25|   17
  Apr. 28|50.00| 5.33| 3.99| 0.14 | 45 |   4 |   1 |       Sunday.
         |Washed.
  Apr. 29|50.00| 0.81| 3.99| 0.14 | 44 |   5 |   1 |   600|    16|   17
  Apr. 30|50.00| 1.75| 3.99| 0.14 | 39 |   6 |   1 |   550|    27|   12
  -------+-----+-----+-----+-----+-----+-----+-----+------+------+------
  May   1|50.00| 0.80| 3.99| 0.14 | 31 |   5 |   1 |   500|    24|   11
         |Washed.
  May   2|50.00| 1.13| 4.00| 0.14 | 24 |   4 |   1 |   500|    12|   16
  May   3|50.00| 2.09| 4.00| 0.14 | 19 |   3 |   1 |   280|    30|   25
  May   4|50.00| 3.80| 4.00| 0.14 | 16 |   2 |   1 |   400|    20|   12
  May   5|50.00| 5.38| 4.00| 0.14 | 15 |   1 |   1 |       Sunday.
         |Washed.
  May   6|50.00| 0.91| 3.90| 0.14 | 13 |   1 |   1 |   390|    50|   40
  May   7|50.00| 1.56| 3.90| 0.14 | 12 |   1 |   1 |   190|    19|   80
  May   8|50.00| 2.25| 3.99| 0.14 | 10 |   1 |   1 |   ...|  ... |  ...
  May   9|50.00| 3.37| 4.00| 0.14 | 10 |   1 |   1 |   390|    21|   38
  May  10|50.00| 5.16| 4.00| 0.14 | 10 |   1 |   1 |   300|    14|   13
         |Washed.
  May  11|50.00| 1.03| 4.00| 0.14 | 12 |   1 |   1 |   390|    13|   12
  May  12|50.00| 1.89| 4.00| 0.14 | 17 |   1 |   1 |       Sunday.
  May  13|50.00| 3.82| 4.00| 0.14 | 35 |   2 |   1 |   600|    33|   15
  May  14|50.00| 6.31| 4.00| 0.14 | 39 |   3 |   1 |   500|    27|    7
         |Washed.
  May  15|50.00| 0.85| 4.00| 0.14 | 17 |   2 |   1 |   500|    20|   29
  May  16|50.00| 1.42| 3.99| 0.14 | 24 |   2 |   1 |   290|    19|   40
  May  17|50.00| 2.47| 3.99| 0.14 | 18 |   2 |   1 |   260|    19|   16
  May  18|50.00| 4.31| 4.00| 0.13 | 15 |   1 |   1 |   190|    16|   20
         |Washed.
  May  19|50.00| 0.83| 3.99| 0.13 | 12 |   1 |   1 |       Sunday.
  May  20|50.00| 1.66| 4.00| 0.13 | 12 |   1 |   1 |   260|    17|   41
  May  21|50.00| 3.83| 4.00| 0.13 | 16 |   1 |   1 |   260|    26|   25
         |Washed.
  May  22|50.00| 0.82| 3.99| 0.13 | 20 |   1 |   1 |   280|    16|   19
  May  23|50.00| 1.64| 4.00| 0.13 | 15 |   1 |   1 |   130|    20|   22
  May  24|50.00| 3.85| 4.00| 0.13 | 15 |   1 |   1 |   170|    17|   32
         |Washed.
  May  25|50.00| 0.84| 4.00| 0.13 | 15 |   1 |   1 |   340|    25|   55
  May  26|50.00| 1.67| 3.99| 0.13 | 18 |   1 |   1 |       Sunday.
  May  27|50.00| 3.03| 4.00| 0.13 | 13 |   1 |   1 |   210|    10|   40
         |Washed.
  May  28|50.00| 0.87| 4.01| 0.13 | 16 |   1 |   1 |   260|    26|   55
  May  29|50.00| 1.43| 4.01| 0.13 | 16 |   1 |   1 |   500|    19|   50
  May  30|50.00| 2.55| 4.00| 0.13 | 14 |   1 |   1 |       Holiday.
  May  31|50.00| 4.19| 4.00| 0.13 | 17 |   1 |   1 |   380|    22|   50
  -------+-----+-----+-----+-----+-----+-----+-----+------+------+------
  June  1|50.00| 6.26| 3.99| 0.13 | 15 |   1 |   1 |   900|    27|   50
         |Washed.
  June  2|50.00| 0.78| 3.98| 0.13 | 17 |   1 |   1 |       Sunday.
  June  3|50.00| 1.19| 4.00| 0.13 | 24 |   1 |   1 |   550|    41|   50
  June  4|50.00| 2.15| 4.00| 0.13 | 37 |   2 |   1 | 6,500|   150|   60
  June  5|50.00| 3.67| 4.01| 0.13 | 65 |   4 |   1 | 3,200|   150|   46
  June  6|50.00| 6.06| 4.00| 0.14 | 77 |  12 |   1 | 1,500|    60|   27
         |Washed.
  June  7|50.00| 0.86| 4.00| 0.14 | 64 |  19 |   1 | 2,100|    68|   45
  June  8|50.00| 1.41| 4.00| 0.14 | 46 |  16 |   1 |   600|    35|   44
  June  9|50.00| 2.62| 4.01| 0.14 | 44 |  12 |   1 |       Sunday.
  June 10|50.00| 4.79| 4.00| 0.14 | 36 |   8 |   1 |   240|    31|   35
         |Washed.
  June 11|50.00| 0.77| 4.00| 0.14 | 30 |   6 |   1 |   280|    47|   47
  June 12|50.00| 1.20| 4.01| 0.14 | 34 |   6 |   1 |   330|    70|   55
  June 13|50.00| 2.42| 4.00| 0.14 | 35 |   8 |   1 |   480|    43|   75
  June 14|50.00| 4.44| 4.00| 0.15 | 31 |   7 |   1 |   440|    55|   45
         |Washed.
  June 15|50.00| 0.80| 3.99| 0.15 | 32 |   6 |   1 |   420|    17|   34
  June 16|50.00| 1.15| 4.00| 0.15 | 26 |   5 |   1 |       Sunday.
  June 17|50.00| 2.15| 3.99| 0.14 | 26 |   5 |   1 |   340|    55|   37
  June 18|50.00| 4.36| 4.00| 0.14 | 31 |   6 |   1 |   440|    14|  140
         |Washed.
  June 19|50.00| 0.79| 4.01| 0.15 | 37 |   8 |   1 |   500|    70|   24
  June 20|50.00| 1.19| 4.00| 0.15 | 30 |   7 |   1 |   330|    49|   27
  June 21|50.00| 2.65| 3.98| 0.14 | 25 |   5 |   1 |   170|    30|   18
  June 22|50.00| 5.58| 4.00| 0.14 | 20 |   4 |   1 |   100|    18|   13
         |Washed.
  June 23|50.00| 0.85| 3.62| 0.13 | 26 |   3 |   1 |       Sunday.
  June 24|50.00| 2.02| 3.99| 0.13 |140 |  11 |   1 | 1,700|    27|   36
  June 25|50.00| 4.77| 3.99| 0.13 |130 |  26 |   1 |   400|    70|   23
         |Washed.
  June 26|50.00| 0.73| 4.01| 0.13 | 82 |  27 |   1 |   750|   200|   41
  June 27|50.00| 1.17| 4.01| 0.13 | 65 |  18 |   1 |   ...|  ... |  ...
  June 28|50.00| 3.10| 3.99| 0.13 | 47 |  16 |   1 |   ...|    20|  ...
         |Washed.
  June 29|50.00| 0.67| 3.99| 0.13 | 37 |   7 |   1 |   220|    35|   29
  June 30|50.00| 1.02| 4.00| 0.13 | 30 |   6 |   1 |       Sunday.
  -------+-----+-----+-----+-----+-----+-----+-----+------+------+------
  July  1|50.00| 2.70| 3.99| 0.13 | 30 |   6 |   1 |   400|    46|    3
         |Washed.
  July  2|50.00| 0.69| 4.00| 0.13 | 32 |   7 |   1 |  180 |    80|   38
  July  3|50.00| 1.21| 3.99| 0.13 | 36 |   8 |   1 |  350 |    70|   90
  July  4|50.00| 3.40| 3.99| 0.13 | 44 |  10 |   1 |       Holiday.
         |Washed.
  July  5|50.00| 0.77| 3.99| 0.13 | 44 |  11 |   1 |  550 |   180|   34
  July  6|50.00| 1.19| 4.01| 0.13 | 39 |  10 |   1 |  250 |    60|   26
  July  7|50.00| 3.72| 3.99| 0.13 | 34 |   8 |   1 |      Sunday.
         |Washed.
  July  8|50.00| 0.78| 3.97| 0.13 | 25 |   5 |   1 |  220 |    31|   21
  July  9|50.00| 1.27| 3.98| 0.13 | 22 |   4 |   1 |   50 |    10|    9
  July 10|50.00| 3.11| 4.09| 0.13 | 47 |   9 |   1 |        Lost.
         |Washed.
  July 11|50.00| 0.83| 3.99| 0.13 | 90 |  19 |   1 |  150 |    19|    8
  July 12|50.00| 1.47| 3.99| 0.13 | 97 |  25 |   1 |  300 |    40|   23
  July 13|50.00| 3.61| 4.00| 0.13 | 96 |  29 |   1 |  220 |    47|   16
         |Washed.
  July 14|50.00| 0.84| 3.99| 0.13 | 90 |  30 |   1 |       Sunday.
  July 15|50.00| 1.30| 4.00| 0.13 | 95 |  30 |   1 |  375 |    55|   21
  July 16|50.00| 2.72| 3.99| 0.14 |120 |  35 |   1 | Lost.|    90|   13
  July 17|50.00| 5.08| 3.99| 0.14 | 85 |  32 |   1 |  270 |     2|   11
         |Washed.
  July 18|50.00| 0.85| 3.99| 0.14 | 56 |  22 |   1 |1,675 |    70|   50
  July 19|50.00| 1.43| 4.00| 0.14 | 41 |  12 |   1 |  450 |    95|   22
  July 20|50.00| 3.23| 3.99| 0.14 | 62 |  19 |   1 |  300 |    38|   11
         |Washed.
  July 21|50.00| 0.80| 3.99| 0.14 | 62 |  21 |   1 |       Sunday.
  July 22|50.00| 1.06| 3.98| 0.14 | 80 |  26 |   1 |1,400 |   150|    7
  July 23|50.00| 2.18| 3.99| 0.14 |105 |  30 |   1 |3,700 | Lost.|   11
  July 24|50.00| 4.95| 3.98| 0.15 | 95 |  30 |   1 |  770 | Lost.|   22
         |Washed.
  July 25|50.00| 0.84| 3.98| 0.15 | 77 |  22 |   1 |  250 |    33|   11
  July 26|50.00| 1.22| 3.98| 0.15 | 67 |  19 |   1 |  140 |   100|    4
  July 27|50.00| 2.36| 4.00| 0.16 | 54 |  15 |   1 |  300 |    95|    7
  July 28|50.00| 4.74| 3.98| 0.16 | 46 |  12 |   1 |       Sunday.
         |Washed.
  July 29|50.00| 0.83| 3.99| 0.17 | 36 |  10 |   1 |  470 |  110 |   18
  July 30|50.00| 1.02| 4.00| 0.17 | 29 |   7 |   1 |    Plates lost.
  July 31|50.00| 1.66| 4.00| 0.17 | 21 |   5 |   1 |    Plates lost.
  -------+-----+-----+-----+-----+-----+-----+-----+------+------+------
  Aug.  1|48.20| 2.95| 4.00| 0.17 | 16 |   4 |   1 |    Plates lost.
  Aug.  2|46.40| 4.96| 4.00| 0.17 | 15 |   2 |   1 |  130 |    42|   13
         |Washed.
  Aug.  3|42.60| 0.79| 4.00| 0.17 | 16 |   1 |   1 |  120 |     4|   16
  Aug.  4|49.10| 0.91| 4.00| 0.17 | 21 |   1 |   1 |       Sunday.
  Aug.  5|49.10| 1.59| 4.00| 0.17 | 29 |   1 |   1 |  230 |   160|   11
  Aug.  6|48.20| 3.16| 4.00| 0.17 | 34 |   2 |   1 |   85 |   200|   12
  Aug.  7|45.60| 5.65| 3.99| 0.17 | 21 |   2 |   1 |  200 | Lost |    4
         |Washed.
  Aug.  8|50.00| 0.80| 3.99| 0.17 | 19 |   2 |   1 |  100 |    70|   11
  Aug.  9|49.10| 0.94| 4.00| 0.17 | 16 |   1 |   1 |   75 |    44|    9
  Aug. 10|48.20| 1.51| 4.00| 0.17|  24 |   1 |   1 |   60 |    13|    6
  Aug. 11|48.20| 3.32| 4.00| 0.17|  62 |   3 |   1 |       Sunday.
         |Washed.
  Aug. 12|41.90| 0.83| 3.99| 0.17| 120 |  14 |   1 |  620 |   110|    5
  Aug. 13|49.10| 1.14| 3.99| 0.17| 107 |  29 |   1 |  820 |    53|   36
  Aug. 14|49.10| 1.72| 4.00| 0.18|  82 |  30 |   1 |  850 |   160|  110
  Aug. 15|48.20| 3.30| 4.00| 0.18|  65 |  22 |   1 |  150 |    37|    4
  Aug. 16|46.40| 0.84| 4.00| 0.19|  45 |  15 |   1 |  270 |   110|   13
  Aug. 17|48.20| 1.05| 4.00| 0.19|  35 |  10 |   1 |  340 |   110|    6
  Aug. 18|50.00| 1.54| 4.00| 0.19|  21 |   5 |   1 |      Sunday.
  Aug. 19|49.10| 2.29| 4.00| 0.19|  18 |   4 |   1 |  180 |    85|   13
  Aug. 20|49.10| 3.74| 3.99| 0.19|  20 |   2 |   1 |  210 |    85|    8
         |Washed.
  Aug. 21|44.10| 1.01| 3.98| 0.19|  20 |   2 |   1 | 1300 |   115|    9
  Aug. 22|45.60| 1.86| 4.00| 0.19|  27 |   2 |   1 | 3800 |   265|    1
  Aug. 23|47.30| 4.08| 3.99| 0.19|  49 |   2 |   1 | 2500 |    70|   13
         |Washed.
  Aug. 24|41.30| 1.29| 3.97| 0.19|  36 |   6 |   1 | 3900 |    46|    6
  Aug. 25|44.10| 2.11| 3.98| 0.20|  34 |   7 |   1 |      Sunday.
  Aug. 26|48.20| 3.42| 3.99| 0.20|  21 |   5 |   1 |  700 |   140|    0
  Aug. 27|48.20| 5.10| 4.00| 0.20|  19 |   4 |   1 |  470 |   100|    4
         |Washed.
  Aug. 28|46.40| 1.28| 4.00| 0.20|  18 |   3 |   1 |  500 |    49|    3
  Aug. 29|41.90| 1.90| 4.02| 0.20|  17 |   2 |   1 |  360 |    80|    0
  Aug. 30|45.60| 3.23| 4.00| 0.20|  15 |   1 |   1 |  320 |   190|    1
  Aug. 31|46.40| 4.57| 4.00| 0.20|  13 |   1 |   1 |  200 |    20|    3
  -------+-----+-----+-----+-----+-----+-----+-----+------+------+------
  Sept. 1|50.00| 5.17| 3.65| 0.20|  14 |   1 |   1 |       Sunday.
  Sept. 2|48.20| 5.97| 4.00| 0.20|  12 |   1 |   1 |       Holiday.
         |Washed.
  Sept. 3|47.30| 1.13| 4.00| 0.20|  12 |   1 |   1 |  300 |     9|    1
  Sept. 4|48.20| 2.01| 4.00| 0.20|  16 |   1 |   1 |  600 |    60|    2
  Sept. 5|46.40| 5.41| 3.67| 0.20|  34 |   1 |   0 |  360 |    72|  ...
         |Washed.
  Sept. 6|40.60| 1.42| 3.98| 0.20| 160 |  12 |   0 |15000 |   140|    0
  Sept. 7|42.60| 5.19| 3.99| 0.20|  64 |  18 |   1 | 2000 |   130|    1
         |Washed.
  Sept. 8|42.60| 1.25| 4.00| 0.20|  56 |  18 |   1 |      Sunday.
  Sept. 9|46.40| 3.07| 4.00| 0.22|  59 |  18 |   1 |  220 |    80|    4
         |Washed.
  Sept.10|45.60| 1.02| 3.99| 0.23|  57 |  16 |   1 |18000 |    57|    8
  Sept.11|48.20| 2.36| 4.00| 0.23|  65 |  18 |   1 | 2700 |    90|    1
         |Washed.
  Sept.12|44.10| 1.14| 3.99| 0.24|  72 |  18 |   1 | 1000 |    47|    4
  Sept.13|46.40| 3.61| 3.99| 0.25|  87 |  20 |   1 | 2300 |    77|    5
         |Washed.
  Sept.14|38.20| 1.42| 3.97| 0.26|  72 |  19 |   1 | 2400 |    80|    5
  Sept.15|45.60| 4.27| 4.00| 0.27|  65 |  18 |   1 |       Sunday.
         |Washed.
  Sept.16|40.00| 1.06| 3.99| 0.28|  65 |  18 |   1 | Lost.|    22|Lost.
  Sept.17|46.40| 2.48| 4.01| 0.28|  52 |  16 |   1 |  420 |    75|    1
         |Washed.
  Sept.18|46.40| 1.11| 4.00| 0.28|  60 |  13 |   1 |  900 |    37|    3
  Sept.19|46.40| 2.76| 4.00| 0.28|  85 |  16 |   1 | 2000 |   186|    0
         |Washed.
  Sept.20|44.10| 1.12| 4.00| 0.31| 100 |  19 |   1 | 4200 |   110|    7
  Sept.21|48.20| 2.07| 3.99| 0.33| 120 |  24 |   1 | 1100 |   110|    3
         |Washed.
  Sept.22|44.10| 1.30| 3.67| 0.34| 137 |  29 |   1 |      Sunday.
  Sept.23|45.60| 3.79| 3.99| 0.39| 112 |  25 |   1 | 2400 |    50|    2
         |Washed.
  Sept.24|45.60| 1.15| 3.97| 0.40| 100 |  25 |   1 | 4000 |    69|    4
  Sept.25|48.20| 2.06| 4.00| 0.42| 432 |  53 |   1 |56000 |   680|    0
  Sept.26|  Stopped, unable to wash preliminary.
  Sept.28|50.00| 1.74| 4.00| 0.71| 127 |  35 |   1 |  ... |  ... |   37
         |Washed.
  Sept.29|44.10| 2.85| 3.99| 0.82| 105 |  31 |   1 |       Sunday.
  Sept.30|44.90| 3.78| 3.97| 1.04| 115 |  32 |   1 | Lost.| Lost.|  160
         |Washed.
  -------+-----+-----+-----+-----+-----+-----+-----+------+------+------
  Oct.  1|44.10| 1.20| 3.98| 1.34|  82 |  26 |   1 |   600|   180|   55
  Oct.  2|49.10| 3.22| 3.97| 1.54|  65 |  19 |   1 | 4,400|   120|    5
         |Washed.
  Oct.  3|44.10| 1.31| 3.97| 1.56|  59 |  17 |   1 |   900|    55|   10
  Oct.  4|49.10| 2.97| 3.97| 1.65|  55 |  15 |   1 |   850|    60|    6
         |Washed.
  Oct.  5|44.90| 1.31| 3.98| 1.75|  59 |  16 |   1 | 2,000|   110|   38
  Oct.  6|46.40| 3.65| 3.99| 1.89|  59 |  17 |   1 |       Sunday.
         |Washed.
  Oct.  7|44.90| 1.34| 3.98| 1.99|  52 |  13 |   1 | 1,250|    70|   15
  Oct.  8|49.10| 3.49| 3.98| 2.17|  54 |  13 |   1 |11,000|    65|    6
         |Washed.
  Oct.  9|44.10| 1.20| 3.97| 2.33|  51 |  13 |   1 | 2,000|    85|    4
  Oct. 10|49.10| 2.22| 3.98| 2.55|  50 |  12 |   1 |   800|    36|   10
  Oct. 11|46.40| 4.59| 4.00| 2.51|  47 |  11 |   1 | 2,000|    57|   10
  Oct. 12|  Shut off to remove sand in preliminary filter in order to
         |                clean out the under-drains.
  -------+-----+-----+-----+-----+-----+-----+-----+------+------+------
  Nov.  5|50.00| 1.38| 3.97| 3.49| 185 |  50 |   1 |  ... |  ... |  ...
  Nov.  6|48.20| 3.25| 3.98| 3.79| 170 |  52 |   1 | 5,000| 1,500|  240
         |Washed.
  Nov.  7|45.60| 1.18| 3.98| 4.05| 100 |  35 |   1 |14,000| 1,000|  220
  Nov.  8|48.20| 4.08| 3.99| 4.37|  95 |  32 |   1 | 1,900|   270|  160
  Nov.  9|42.00| 6.58| 3.98| 4.39|  80 |  27 |   1 | 4,000|   500|  190
  Nov. 10|  Shut down for scraping. Removed 266,000 cu. cm. of sand.
  Nov. 12|50.00| 0.98| 3.99| 0.25|  40 |  10 |   1 |  ... |  ... |  ...
  Nov. 13|50.00| 1.51| 4.00| 0.22|  36 |   8 |   1 | 1,600|   750|   85
  Nov. 14|48.20| 2.60| 4.00| 0.21|  42 |  11 |   1 | 2,700|   700|  210
  Nov. 15|47.30| 3.80| 4.00| 0.20|  35 |   9 |   1 | 1,800|   350|  180
  Nov. 16|47.30| 4.87| 4.00| 0.19|  26 |   5 |   1 | 1,100|   200|   34
  Nov. 17|50.00| 5.75| 4.00| 0.19|  20 |   4 |   1 |       Sunday.
  Nov. 18|50.00| 6.41| 4.00| 0.19|  17 |   3 |   1 | 1,600|   290|   55
         |Washed.
  Nov. 19|48.20| 1.06| 3.99| 0.20|  16 |   2 |   1 | 1,300|   480|   60
  Nov. 20|48.20| 2.05| 3.99| 0.20|  45 |   3 |   1 | 6,500| 3,700|  800
  Nov. 21|48.20| 3.48| 3.99| 0.20|  52 |   9 |   1 | 9,900| 4,000|  300
  Nov. 22|47.30| 4.85| 3.99| 0.20|  65 |  17 |   1 |10,000| 1,000|  380
  Nov. 23|48.20| 6.11| 3.99| 0.20|  49 |  15 |   1 |18,000| 1,000|  320
         |Washed.
  Nov. 24|46.40| 3.71| 3.98| 0.20| 134 |  24 |   1 |       Sunday.
  Nov. 25|         Shut down for fear of washing preliminary
         |                    with such muddy water.
  Nov. 29|50.00| 1.55| 4.00| 0.21|  80 |  25 |   1 |  ... |  ... |  ...
  Nov. 30|47.30| 3.14| 3.98| 0.22|  54 |  16 |   1 | 3,800|   950|  160
  -------+-----+-----+-----+-----+-----+-----+-----+------+------+------
  Dec.  1|47.30| 4.48| 3.98| 0.23|  37 |  10 |   1 |       Sunday.
  Dec.  2|47.30| 5.63| 3.98| 0.25|  36 |   6 |   1 | 2,900|   550|   90
         |Washed.
  Dec.  3|46.40| 0.98| 3.99| 0.25|  29 |   6 |   1 | 2,900|   480|   75
  Dec.  4|50.00| 1.15| 3.99| 0.26|  20 |   4 |   1 | 2,000|   270|   70
  Dec.  5|50.00| 1.48| 4.00| 0.25|  18 |   3 |   1 | 1,100|   270|   50
  Dec.  6|48.20| 2.04| 3.63| 0.25|  16 |   2 |   1 | 3,000|  ... |  ...
  Dec.  7|48.20| 2.80| 4.00| 0.26|  14 |   1 |   1 | 2,400|   190|   10
  Dec.  8|50.00| 3.40| 3.72| 0.27|  12 |   1 |   1 |       Sunday.
  Dec.  9|49.10| 3.93| 4.00| 0.27|  11 |   1 |   1 | 1,200|   170|    7
  Dec. 10|49.10| 4.50| 4.00| 0.27|  12 |   1 |   1 |   800|    90|   55
  Dec. 11|48.20| 5.52| 4.00| 0.27| 255 |  44 |   1 | 6,500|  --- | ---
  Dec. 12|   Shut down 12/11 at 6 P. M. turbidity too high to wash.
  Dec. 15| --- | --- | --- | --- | --- | --- | --- |       Sunday.
  Dec. 16|50.00| 4.02| 3.99| 0.28|  90 |  35 |   2 |  --- |  --- | ---
         |Washed.
  Dec. 17|40.00| 1.90| 3.97| 0.30|  70 |  25 |   2 |21,000|10,000|1,200
         |Washed.
  Dec. 18|44.10| 1.08| 3.97| 0.31|  49 |  15 |   2 | 6,500| 4,200|  800
  Dec. 19|48.20| 1.88| 3.98| 0.31|  39 |  10 |   1 | Lost.| Lost.|Lost.
  Dec. 20|46.40| 4.77| 3.99| 0.31|  42 |  13 |   1 |   "  |   "  |  "
  Dec. 21|46.40| 6.68| 3.99| 0.32|  26 |   6 |   1 |   "  |   "  |  "
         |Washed.
  Dec. 22|49.10| 1.14| 3.99| 0.32|  20 |   4 |   1 |      Sunday.
  Dec. 23|49.10| 2.17| 4.00| 0.31|  34 |   7 |   1 | 1,400|   300|  100
  Dec. 24|49.10| 3.76| 4.00| 0.31| 195 |  56 |   1 | 9,000|   950|   70
  Dec. 25|Shut down 12/24 at 9 P.M. turbidity too high to wash. Holiday
  Dec. 30|50.00| 2.61| 3.97| 0.33|  56 |  19 |   2 |  --- |  --- | ---
  Dec. 31|44.80| 5.57| 3.98| 0.36|  39 |  12 |   1 |  --- |  --- | ---
         |Washed.
  -------+-----+-----+-----+-----+-----+-----+-----+------+------+------
  1908.
  -------+-----+-----+-----+-----+-----+-----+-----+------+------+------
  Jan.  1|46.40| 1.30| 3.98| 0.36|  31 |   6 |   1 |      Holiday.
  Jan.  2|48.20| 3.36| 4.00| 0.36|  39 |   9 |   1 |  --- |  --- | ---
  Jan.  3|47.30| 4.95| 3.99| 0.35|  36 |   9 |   1 | 3,100|   490|   90
  Jan.  4|50.00| 5.28| 3.99| 0.35|  32 |   7 |   1 | 2,400|   240|   43
  Jan.  5|49.10| 6.26| 4.00| 0.35|  26 |   5 |   1 |      Sunday.
         |Washed.
  Jan.  6|49.10| 0.99| 3.98| 0.35|  20 |   4 |   1 |   600|   200|   37
  Jan.  7|50.00| 1.15| 4.00| 0.35|  20 |   4 |   1 | 1,100|   150|   47
  Jan.  8|50.00| 1.41| 4.00| 0.35|  22 |   4 |   1 | 1,900|   160|   30
  Jan.  9|49.10| 1.92| 4.00| 0.35|  45 |  11 |   1 |13,000| 1,300|   70
  Jan. 10|49.10| 2.56| 4.00| 0.36|  70 |  25 |   1 |10,000| 3,500|  170
  Jan. 11|50.00| 3.17| 3.99| 0.37|  56 |  18 |   1 |16,000| 4,000|  240
  Jan. 12|49.10| 3.73| 4.00| 0.37|  40 |  10 |   1 |      Sunday.
  Jan. 13|50.00| 4.14| 4.00| 0.37| 110 |  45 |   2 | 8,500| 1,200|  840
  Jan. 14|49.10| 4.65| 3.99| 0.38| 210 |  95 |   3 |16,000| 3,900|  500
  Jan. 15|49.10| 5.23| 3.99| 0.41| 325 | 190 |  12 |24,000| 7,000|  550
  Jan. 16|50.00| 5.75| 3.99| 0.43| 360 | 210 |  37 |28,000| 8,500|1,200
  Jan. 17|49.10| 6.34| 4.00| 0.45| 242 | 122 |  24 |65,000|15,000|1,700
  Jan. 18| --- | --- | --- | --- | --- | --- | --- |  --- |  --- | ---
  Jan. 19|50.00| 1.17| 4.00| 0.46| 117 |  40 |  12 |      Sunday.
  Jan. 20|50.00| 1.38| 4.00| 0.46|  72 |  31 |   6 | 1,600| 1,800|  320
  Jan. 21|50.00| 1.68| 3.57| 0.37|  55 |  20 |   4 | 5,000|   450|
  Jan. 22|49.10| 2.04| 4.00| 0.44|  49 |  17 |   3 | 3,600|   600|  100
  Jan. 23|50.00| 2.47| 3.24| 0.33|  40 |  12 |   3 | 1,800|   290|  130
  Jan. 24|49.10| 3.03| 3.00| 0.34|  40 |  11 |   2 | 2,300|   270|   65
  Jan. 25|50.00| 3.61| 3.00| 0.35|  39 |  10 |   2 | 1,100|   180|   60
  Jan. 26|49.10| 4.18| 2.99| 0.35|  32 |   7 |   2 |      Sunday.
  Jan. 27|50.00| 4.81| 3.00| 0.35|  32 |   7 |   2 |   300|    40|   24
  Jan. 28|48.20| 5.45| 2.99| 0.35|  45 |  12 |   2 | 1,200|    90|   31
  Jan. 29|49.10| 6.01| 2.99| 0.35|  60 |  21 |   2 | 1,000|   230|   50
  Jan. 30|49.10| 6.62| 2.99| 0.36|  57 |  22 |   2 | 1,400|   170|   48
         |Washed.
  Jan. 31|50.00| 1.30| 2.99| 0.36|  42 |  15 |   2 | 1,100|   190|   23
  -------+-----+-----+-----+-----+-----+-----+-----+------+------+------
  Feb.  1|50.00| 1.51| 2.99| 0.37|   39|  11 |   2 |   750|    40|   31
  Feb.  2|50.00| 1.78| 3.00| 0.37|   27|   7 |   2 |      Sunday.
  Feb.  3|49.10| 2.13| 3.00| 0.37|   29|   6 |   2 | 1,300|   200|    7
  Feb.  4|50.00| 2.69| 3.00| 0.37|   25|   5 |   1 |   600|   160|   18
  Feb.  5|49.10| 3.31| 2.99| 0.37|   24|   5 |   1 |   750|   140|   41
  Feb.  6|50.00| 3.89| 2.99| 0.37|   20|   4 |   1 | 2,000|   180|   29
  Feb.  7|48.20| 4.50| 2.99| 0.37|   17|   3 |   1 |  ... |    38|   15
  Feb.  8|49.10| 5.11| 2.99| 0.37|   15|   3 |   1 |   900|    95|   24
  Feb.  9|49.10| 5.65| 3.00| 0.38|   14|   3 |   1 |      Sunday.
  Feb. 10|49.10| 6.43| 2.99| 0.38|   11|   3 |   1 |   850|    85|   21
  Feb. 11|50.00| 6.90| 3.00| 0.38|   10|   3 |   1 | 1,000|    70|   20
         |Washed.
  Feb. 12|49.10| 1.29| 2.99| 0.38|    8|   2 |   1 |   750|    20|   16
  Feb. 13|50.00| 1.50| 2.99| 0.39|    9|   2 |   1 |   700|    40|   11
  Feb. 14|50.00| 1.80| 2.99| 0.39|    9|   2 |   1 | 1,200|    39|    7
  Feb. 15|49.10| 2.35| 3.00| 0.39|   61|  13 |   1 | 5,500|   600|    7
  Feb. 16|49.10| 3.28| 2.99| 0.39|   80|  30 |   2 |      Sunday.
  Feb. 17|48.20| 4.85| 2.99| 0.39|   80|  29 |   3 |33,000| 3,800|  130
  Feb. 18|47.30| 6.39| 2.99| 0.39|  130|  44 |   3 |  --- | 2,600|  160
  Feb. 19|45.50| 7.32| 2.98| 0.40|  320| 143 |   6 |28,000| 6,000|  180
         |Washed.
  Feb. 22|50.00| 1.40| 3.00| 0.41|   85|  30 |   5 |      Holiday.
  Feb. 23|50.00| 1.77| 3.00| 0.41|   60|  21 |   4 |      Sunday.
  Feb. 24|49.10| 2.25| 2.99| 0.41|   46|  14 |   3 | 3,600| 2,800|   90
  Feb. 25|50.00| 2.61| 3.00| 0.41|   31|   7 |   2 | 2,300|   140|   47
  Feb. 26|50.00| 3.06| 3.00| 0.41|   30|   6 |   2 | 3,800|   140|   45
  Feb. 27|48.20| 3.65| 2.99| 0.41|   30|   5 |   1 | 1,300|   100|   22
  Feb. 28|50.00| 4.24| 3.00| 0.41|   37|   6 |   1 | 1,400|   100|   40
  Feb. 29|48.20| 5.28| 2.99| 0.41|  123|  52 |   2 |13,500|   420|   40
         |Washed.
  -------+-----+-----+-----+-----+-----+-----+-----+------+------+------
  Mar.  1|44.60| 1.56| 2.99| 0.42|   97|  39 |   5 |      Sunday.
  Mar.  2|48.20| 2.90| 2.99| 0.42|   82|  30 |   4 | 8,000|   320|   60
  Mar.  3|46.40| 4.69| 2.98| 0.42|   87|  33 |   4 |11,000|   750|   30
  Mar.  4|47.30| 6.13| 2.99| 0.42|   67|  24 |   3 | 6,000|   290|   34
  Mar.  5|48.20| 7.31| 2.99| 0.42|   59|  19 |   3 | 4,400|   220|   41
         |Washed.
  Mar.  6|49.10| 1.53| 2.99| 0.42|   72|  24 |   2 | 7,000|   170|   41
  Mar.  7|50.00| 1.95| 3.00| 0.43|   82|  30 |   2 | 9,500|   210|   34
  Mar.  8|49.10| 2.62| 2.99| 0.43|   92|  37 |   3 |      Sunday.
  Mar.  9|50.00| 3.19| 3.00| 0.43|  125|  56 |   4 |11,000|   700|   65
  Mar. 10|Preliminary filter discontinued and the Puech system started.
  =======+=====+=====+=====+=====+=====+=====+=====+======+======+======


             ~Table 17--Record of Experimental Filter,
                   Puech system~.--(_Continued._)

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

  =======+===================+=========+============+===================
         |  ~Puech system~:  | ~Final  |~Turbidity.~|   ~Bacteria.~
         |                   | filter~.|            |
   Date. +-------------------+----+----+---+---+----+------+------+-----
         |         A         |  B |  C | D | E |  F |   G  |   H  |  I
  -------+---+---+---+---+---+----+----+---+---+----+------+------+-----
  1908.
  -------+---+---+---+---+---+----+----+---+---+----+------+------+-----
  Mar. 11|265|170| 90| 53| 18|2.99|0.53|155| 80|  7 | 6,500| 8,500| 490
  Mar. 12|265|170| 90| 53| 18|2.99|0.60|135| 70|  7 | 5,900| 6,000| 360
  Mar. 13|265|170| 90| 53| 18|3.00|0.60|122| 52|  6 | 1,900| 1,700| 140
  Mar. 14|265|170| 90| 53| 18|3.00|0.61| 97| 40|  5 | 1,800| 1,600| 130
  Mar. 15|265|170| 90| 53| 18|2.99|0.64| 77| 31|  4 |      Sunday.
  Mar. 16|265|170| 90| 53| 18|3.00|0.69| 65| 26|  3 | 1,400| 1,200|  50
  Mar. 17|241|155| 82| 48| 16|2.99|0.71| 59| 19|  3 |   900|   200|  45
  Mar. 18|252|162| 86| 50| 17|2.99|0.75| 67| 22|  2 | 1,000|   700|  33
  Mar. 19|241|155| 82| 48| 16|2.99|0.78| 60| 21|  2 |  ... |   800|  44
  Mar. 20|294|189|100| 59| 20|2.99|0.85| 57| 18|  2 | 1,300|   650|  37
  Mar. 21|279|179| 95| 56| 19|2.99|0.92| 67| 21|  2 |   800|   600|  34
  Mar. 22|265|170| 90| 53| 18|2.99|0.99| 80| 27|  2 |      Sunday.
  Mar. 23|265|170| 90| 53| 18|2.99|1.06| 90| 32|  2 | 4,600| 1,300|  33
  Mar. 24|265|170| 90| 53| 18|2.99|1.12| 82| 34|  3 | 2,500|   950|  38
  Mar. 25|265|170| 90| 53| 18|2.99|1.18| 67| 27|  3 | 1,600|  ... |  30
  Mar. 26|265|170| 90| 53| 18|2.99|1.22| 60| 20|  3 |   550|   400|  24
  Mar. 27|265|170| 90| 53| 18|3.00|1.23| 59| 18|  2 |   950|   360|  28
  Mar. 28|265|170| 90| 53| 18|3.00|1.25| 51| 14|  2 |   650|   230|  18
  Mar. 29|265|170| 90| 53| 18|2.99|1.28| 31|  6|  2 |      Sunday.
  Mar. 30|265|170| 90| 53| 18|2.99|1.36| 30|  5|  1 |   500|   160|  25
  Mar. 31|265|170| 90| 53| 18|2.99|1.43| 39|  7|  1 |   750|   140|  26
  -------+---+---+---+---+---+----+----+---+---+----+------+------+-----
  Apr.  1|265|170| 90| 53| 18|3.00|1.48| 44|  9|  1 |   750|    60|  41
  Apr.  2|265|170| 90| 53| 18|2.99|1.56| 42|  9|  1 | 1,100|   140|  26
  Apr.  3|318|204|108| 64| 22|2.99|1.63| 41|  8|  1 | 1,500|    47|  11
  Apr.  4|294|189|100| 59| 20|2.99|1.70| 54| 13|  1 |   700|    80|  35
  Apr.  5|279|179| 95| 56| 19|3.00|1.73| 50| 13|  1 |      Sunday.
  Apr.  6|279|179| 95| 56| 19|2.99|1.76| 41|  9|  1 |   440|    65|  17
  Apr.  7|265|170| 90| 53| 18|3.00|1.78| 35|  6|  1 |   650|    65|  34
  Apr.  8|265|170| 90| 53| 18|3.00|1.79| 39|  6|  1 |   550|    44|  10
  Apr.  9|265|170| 90| 53| 18|3.00|1.79| 40|  6|  1 |   390|    30|  25
  Apr. 10|265|170| 90| 53| 18|3.00|1.77| 40|  6|  1 |   500|    27|  16
  Apr. 11|265|170| 90| 53| 18|3.00|1.78| 45|  7|  1 |   430|    28|  28
  Apr. 12|265|170| 90| 53| 18|2.99|1.80| 52| 11|  1 |      Sunday.
  Apr. 13|265|170| 90| 53| 18| ...|1.81| 50| 10|  1 |   490|    17|  26
  Apr. 14|   Shut down on account of losing water when aqueduct was
         |drained; also cleaned coarse sand filter. Started April 22d.
  Apr. 23|241|155| 82| 48| 16| ...|1.82| 29|  4|  1 |   140|   600|  38
  Apr. 24|241|155| 82| 48| 16|3.00|1.87| 21|  3|  1 |   200| 1,000|  13
  Apr. 25|241|155| 82| 48| 16|2.99|1.95| 20|  3|  1 |    85|   180|  25
  Apr. 26|252|162| 86| 50| 17|3.00|1.95| 24|  3|  1 |      Sunday.
  Apr. 27|241|155| 82| 48| 16|3.00|1.93| 18|  2|  1 |    95|    35|  23
  Apr. 28|241|155| 82| 48| 16|3.00|1.96| 20|  2|  1 |    70|    24|  18
  Apr. 29|241|155| 82| 48| 16|2.99|1.97| 24|  3|  1 |   110|    21|  24
  Apr. 30|241|155| 82| 48| 16|2.99|2.03| 21|  2|  1 |    70|    25|   6
  -------+---+---+---+---+---+----+----+---+---+----+------+------+-----
  May   1|241|155| 82| 48| 16|3.00|2.07| 32|  4|  1 |   130|    20|  18
  May   2|241|155| 82| 48| 16|2.99|2.12| 26|  3|  1 |   140|    16|  12
  May   3|241|155| 82| 48| 16|2.99|2.17| 22|  3|  1 |      Sunday.
  May   4|241|155| 82| 48| 16|3.00|2.19| 19|  2|  1 |    85|    30|  17
  May   5|241|155| 82| 48| 16|3.00|2.20| 18|  2|  1 |   130|    33|   9
  May   6|241|155| 82| 48| 16|2.99|2.23| 18|  2|  1 |   230|    55|   6
  May   7|252|162| 86| 50| 17|3.00|2.24| 19|  2|  1 |   160|    75|  10
  May   8|241|155| 82| 48| 16|3.00|2.25| 19|  2|  1 |   375|    55|   8
  May   9|318|204|108| 64| 22|2.99|2.29| 18|  2|  1 | 1,200|    12|   9
  May  10|318|204|108| 64| 22|2.99|2.30| 30|  3|  1 |      Sunday.
  May  11|265|170| 90| 53| 18|2.99|2.33| 60| 10|  1 | 2,800|   130|  11
  May  12|252|162| 86| 50| 17|2.99|2.39| 70| 15|  1 | 2,900|   135|   9
  May  13|241|155| 82| 48| 16|3.00|2.41| 66| 14|  1 | 1,800|   110|  16
  May  14|265|170| 90| 53| 18|3.00|2.38| 45|  7|  1 | 2,700|    65|  18
  May  15|252|162| 86| 50| 17|3.00|2.41| 39|  5|  1 |   950|    45|  14
  May  16|241|155| 82| 48| 16|3.00|2.41| 49|  7|  1 |   800|    32|  10
  May  17|241|155| 82| 48| 16|3.01|2.34| 46|  7|  1 |      Sunday.
  May  18|241|155| 82| 48| 16|3.00|2.31| 31|  4|  1 |   700|    26|   6
  May  19|252|162| 86| 50| 17|3.00|2.26| 36|  4|  1 |   375|    28|  17
  May  20|252|162| 86| 50| 17|3.00|2.20| 41|  5|  1 |   425|    38|  11
  May  21|344|221|117| 69| 23|3.00|2.18| 30|  3|  1 |   300|    25|   9
  May  22|241|155| 82| 48| 16|3.01|2.17| 53|  7|  1 |   950|   220|  18
  May  23|265|170| 90| 53| 18|2.99|2.25|127| 38|  1 | 2,400|   600|  21
  May  24|331|212|112| 66| 22|3.00|2.19|110| 39|  3 |      Sunday.
  May  25|318|204|108| 64| 22|3.01|2.02| 90| 25|  3 |   600|   300|  40
  May  26|279|179| 95| 56| 19|3.02|1.87|135| 45|  3 | 3,200|   110|  34
  May  27|265|170| 90| 53| 18|3.01|1.63|110| 39|  3 |14,500|   320|  45
  May  28|252|162| 86| 50| 17|3.01|1.41| 90| 27|  3 | 1,000|    95|  28
  May  29|252|162| 86| 50| 17|3.01|1.24| 70| 17|  3 | 1,100|   150|  26
  May  30|252|162| 86| 50| 17|3.01|1.07| 50|  9|  2 |      Holiday.
  May  31|241|155| 82| 48| 16|3.01|1.03| 34|  4|  2 |      Sunday.
  -------+---+---+---+---+---+----+----+---+---+----+------+------+-----
  June  1|252|162| 86| 50| 17|3.00|0.83| 35|  4|  1 |  ... |  ... | ...
  June  2|241|155| 82| 48| 16|3.00|0.74| 39|  5|  1 |  ... |  ... | ...
  June  3|252|162| 86| 50| 17|3.00|0.68| 35|  4|  1 |  ... |  ... | ...
  June  4|241|155| 82| 48| 16|3.00|0.63| 30|  3|  1 |  ... |  ... | ...
  June  5|252|162| 86| 50| 17|2.99|0.60| 30|  3|  1 |  ... |  ... | ...
  June  6|241|155| 82| 48| 16|3.00|0.56| 27|  3|  1 |  ... |  ... | ...
  June  7|241|155| 82| 48| 16|2.99|0.53| 22|  2|  1 |  ... |  ... | ...
  June  8|241|155| 82| 48| 16|3.00|0.49| 20|  1|  1 |  ... |  ... | ...
  June  9|241|155| 82| 48| 16|2.99|0.46| 20|  1|  1 |  ... |  ... | ...
  June 10|241|155| 82| 48| 16|3.00|0.44| 17|  1|  1 |  ... |  ... | ...
  June 11|331|212|112| 66| 22|2.98|0.42| 12|  1|  1 |  ... |  ... | ...
  June 12|318|204|108| 64| 22|2.98|0.42| 11|  1|  1 |  ... |  ... | ...
  June 13|265|170| 90| 53| 18|3.00|0.40| 36|  3|  1 |  ... |  ... | ...
  June 14|252|162| 86| 50| 17|2.99|0.40| 39|  5|  1 |  ... |  ... | ...
  June 15|241|155| 82| 48| 16|2.99|0.39| 25|  3|  1 |  ... |  ... | ...
  June 16|241|155| 82| 48| 16|2.99|0.40| 34|  3|  1 |  ... |  ... | ...
  June 17|252|162| 86| 50| 17|2.99|0.41| 64| 11|  1 |  ... |  ... | ...
  June 18|241|155| 82| 48| 16|2.99|0.42| 57| 11|  1 |  ... |  ... | ...
  June 19|241|155| 82| 48| 16|2.99|0.42| 46|  8|  1 |  ... |  ... | ...
  June 20|241|155| 82| 48| 16|2.99|0.42| 40|  5|  1 |  ... |  ... | ...
  June 21|241|155| 82| 48| 16|3.00|0.43| 28|  4|  1 |  ... |  ... | ...
  June 22|241|155| 82| 48| 16|2.99|0.43| 25|  3|  1 |  ... |  ... | ...
  June 23|241|155| 82| 48| 16|2.99|0.43| 25|  3|  1 |  ... |  ... | ...
  June 24|241|155| 82| 48| 16|2.99|0.43| 29|  4|  1 |  ... |  ... | ...
  June 25|241|155| 82| 48| 16|2.99|0.43| 18|  2|  1 |  ... |  ... | ...
  June 26|241|155| 82| 48| 16|2.80|0.42| 15|  1|  1 |  ... |  ... | ...
  June 27|241|155| 82| 48| 16|2.99|0.44| 12|  1|  1 |  ... |  ... | ...
  June 28|241|155| 82| 48| 16|2.99|0.44|  9|  1|  1 |  ... |  ... | ...
  June 29|241|155| 82| 48| 16|2.99|0.44|  8|  1|  1 |  ... |  ... | ...
  June 30|241|155| 82| 48| 16|2.99|0.44| 10|  1|  1 |  ... |  ... | ...
  -------+---+---+---+---+---+----+----+---+---+----+------+------+-----
  July  1|241|155| 82| 48| 16|3.00|0.45|  8|  1|  1 |    80|    10|   4
  July  2|241|155| 82| 48| 16|3.00|0.46|  8|  1|  0 |   290|    24|   5
  July  3|241|155| 82| 48| 16|3.00|0.47|  8|  1|  0 |   350|    45|   6
  July  4|241|155| 82| 48| 16|2.99|0.49|  9|  1|  0 |  ... |  ... | ...
  July  5|305|195|103| 61| 21|3.00|0.51| 10|  1|  0 |  ... |  ... | ...
  July  6|241|155| 82| 48| 16|3.00|0.51|  9|  1|  0 |   300|    36|   7
  July  7|241|155| 82| 48| 16|2.99|0.53|  8|  1|  0 |   110|    10|   3
  July  8|252|162| 86| 50| 17|3.00|0.53|  9|  1|  0 |    85|    22|   2
  July  9|241|155| 82| 48| 16|3.00|0.54|  8|  1|  0 |    85|    26|   2
  July 10|...|...|...|...|...| ...| ...|   |   |    |   200|     3|   5
  July 11|305|195|103| 61| 21|3.00|0.56| 12|  1|  0 |   145|     7|   3
  July 12|241|155| 82| 48| 16|2.99|0.58| 11|  1|  0 |  ... |  ... | ...
  July 13|241|155| 82| 48| 16|3.00|0.60| 10|  1|  0 |   115|    34|  55
  July 14|241|155| 82| 48| 16|2.99|0.62| 16|  1|  0 |   300|    55|  30
  July 15|241|155| 82| 48| 16|2.99|0.64| 17|  1|  0 |   180|    32|  23
  July 16|241|155| 82| 48| 16|3.00|0.67| 13|  1|  0 |   100|   115|   3
  July 17|241|155| 82| 48| 16|2.99|0.71| 10|  1|  0 |    65|   275|   5
  July 18|241|155| 82| 48| 16|2.99|0.73| 11|  1|  0 |    38|   425|  10
  July 19|241|155| 82| 48| 16|3.00|0.76| 12|  1|  0 |  ... |  ... | ...
  July 20|241|155| 82| 48| 16|2.99|0.79| 10|  1|  0 |    95|    90|  70
  July 21|252|162| 86| 50| 17|2.99|0.83| 10|  1|  1 |    70|    17|   4
  July 22|241|155| 82| 48| 16|2.99|0.87| 13|  1|  1 |   440|     8|   5
  July 23|305|195|103| 61| 21|2.99|0.92| 54|  4|  1 |   650|    26|   5
  July 24|331|212|111| 66| 22|2.98|0.99|305| 61|  1 | 1,650|  ... | ...
  July 25|265|170| 90| 53| 18|2.98|1.08|330| 85|  1 | 2,600|   115|  15
  July 26|252|162| 86| 50| 17|2.98|1.21|290| 77|  2 |  ... |  ... | ...
  July 27|305|195|103| 61| 21|2.98|1.40|335| 87|  2 |35,000|   250| ...
  July 28|252|162| 86| 50| 17|2.98|1.68|170| 52|  2 | 1,200| 1,350|  15
  July 29|252|162| 86| 50| 17|2.97|2.14|180| 52|  2 | 2,000|   600|  13
  July 30|252|162| 86| 50| 17|2.97|2.65|237| 56|  2 |   800| 1,300|  12
  July 31|241|155| 82| 48| 16|2.95|3.01|250| 60|  2 | 1,000|   310|   7
  =======+===+===+===+===+===+====+====+===+===+====+======+======+=====


  ~Table 18--Record of Experimental Filter Plant No. 2.~
  ========+=====================+=====================
          |~Preliminary Filter.~|   ~Final Filter.~
          +-----------+---------+-----------+---------
    Date. |   Rate,   |         |   Rate,   |
          |millions of| Loss of |millions of| Loss of
          |gallons per|  head.  |gallons per|  head.
          |acre daily.|         |acre daily.|
  --------+-----------+---------+-----------+---------
  1907.
  --------+-----------+---------+-----------+---------
  Feb.   8|    21.50  |   0.04  |    2.81   |   0.17
  Feb.   9|    21.60  |   0.04  |    1.09   |   0.06
  Feb.  10|    20.90  |   0.05  |    1.59   |   0.08
  Feb.  11|    19.80  |   0.05  |    3.01   |   0.15
  Feb.  12|    19.70  |   0.06  |    3.01   |   0.14
  Feb.  13|    19.60  |   0.06  |    3.01   |   0.12
  Feb.  14|    24.70  |   0.07  |    2.65   |   0.13
  Feb.  15|    37.20  |    ...  |    3.40   |   0.12
  Feb.  16|    37.30  |    ...  |    3.40   |   0.11
  Feb.  17|Shut down for changes in meters and piping.
  Feb.  18|     ...   |    ...  |     ...   |    ...
  Feb.  21|    44.50  |    ...  |    4.36   |   0.19
  Feb.  22|    48.60  |    ...  |    4.37   |   0.16
  Feb.  23|    48.40  |    ...  |    4.20   |   0.15
  Feb.  24|    48.30  |    ...  |    4.02   |   0.13
  Feb.  25| Shut down several hours.        |   0.14
  Feb.  26|    48.60  |   0.04  |    4.12   |   0.14
  Feb.  27|    53.20  |   0.04  |    4.08   |   0.15
  Feb.  28|    52.80  |   0.04  |    4.09   |   0.15
  --------+-----------+---------+-----------+---------
  Mar.   1|    53.00  |   0.04  |    4.10   |   0.16
  Mar.   2|    53.30  |   0.04  |    4.11   |   0.16
  Mar.   3|    50.60  |   0.05  |    4.11   |   0.16
  Mar.   4|    42.40  |   0.05  |    4.12   |   0.17
  Mar.   5|    42.70  |   0.05  |    4.11   |   0.17
  Mar.   6|    48.60  |   0.07  |    4.13   |   0.17
  Mar.   7|    50.50  |   0.08  |    4.12   |   0.18
  Mar.   8|    51.80  |   0.09  |    4.12   |   0.18
  Mar.   9|    53.00  |   0.10  |    4.12   |   0.18
  Mar.  10|    54.40  |   0.12  |    4.11   |   0.19
  Mar.  11|    51.00  |   0.12  |    4.12   |   0.19
  Mar.  12|    51.20  |   0.12  |    4.07   |   0.19
  Mar.  13|    50.50  |   0.12  |    4.00   |   0.19
  Mar.  14|    46.50  |   0.12  |     ...   |   0.20
  Mar.  15|    45.80  |   0.12  |    3.98   |   0.20
  Mar.  16|    42.50  |   0.12  |    3.97   |   0.19
  Mar.  17|    49.30  |   0.14  |    3.98   |   0.19
  Mar.  18|    52.60  |   0.16  |    3.98   |   0.20
  Mar.  19|    53.50  |   0.17  |    4.01   |   0.19
  Mar.  20|    52.90  |   0.17  |    3.99   |   0.18
  Mar.  21|    48.20  |   0.16  |    4.00   |   0.19
  Mar.  22|    51.80  |   0.18  |    4.01   |   0.20
  Mar.  23|    51.60  |   0.19  |    4.01   |   0.20
  Mar.  24|    48.20  |   0.17  |    4.01   |   0.20
  Mar.  25|    48.50  |   0.18  |    4.01   |   0.20
  Mar.  26|    45.90  |   0.18  |    3.98   |   0.20
  Mar.  27|    50.50  |   0.20  |    4.04   |   0.20
  Mar.  28|    49.60  |   0.20  |    3.92   |   0.19
  Mar.  29|    42.20  |   0.17  |    3.98   |   0.19
  Mar.  30|    48.00  |   0.22  |    4.01   |   0.19
  Mar.  31|    49.10  |   0.22  |    3.99   |   0.20
  --------+-----------+---------+-----------+---------
  Apr.   1|    49.10  |   0.24  |    4.00   |   0.20
  Apr.   2|    49.70  |   0.25  |    4.00   |   0.20
  Apr.   3|    51.40  |   0.27  |    4.00   |   0.21
  Apr.   4|    48.70  |   0.27  |    4.00   |   0.22
  Apr.   5|    48.10  |   0.27  |    4.00   |   0.22
  Apr.   6|       Shut down awaiting Mr. Maiguen
          |          to apply bone-charcoal.
  Apr.   7|         Removed 1.06 in. of sand.
  Apr.   8|    52.20  |   0.33  |    4.05   |   0.27
  Apr.   9|    46.90  |   0.29  |    4.02   |   0.29
  Apr.  10|    47.60  |   0.31  |    4.03   |   0.28
  Apr.  11|    46.00  |   0.30  |    4.04   |   0.28
  Apr.  12|    45.40  |   0.31  |    4.03   |   0.29
  Apr.  13|    45.10  |   0.32  |    3.99   |   0.32
  Apr.  14|    49.00  |   0.34  |    4.00   |   0.32
  Apr.  15|    47.80  |   0.35  |    3.99   |   0.33
  Apr.  16|    47.40  |   0.36  |    3.99   |   0.34
  Apr.  17|    45.60  |   0.36  |    4.00   |   0.34
  Apr.  18|    45.70  |   0.36  |    4.00   |   0.34
  Apr.  19|    45.60  |   0.37  |    4.00   |   0.34
  Apr.  20|    45.30  |   0.40  |    4.00   |   0.36
  Apr.  21|    47.20  |   0.44  |    3.99   |   0.38
  Apr.  22|    45.20  |   0.42  |    3.99   |   0.38
  Apr.  23|    44.90  |   0.44  |    4.05   |   0.40
  Apr.  24|    40.50  |   0.41  |    4.02   |   0.44
  Apr.  25|    39.60  |   0.41  |    4.03   |   0.45
  Apr.  26|    40.70  |   0.44  |    4.05   |   0.45
  Apr.  27|    39.30  |   0.44  |    4.00   |   0.44
  Apr.  28|    34.70  |   0.43  |    4.05   |   0.44
  Apr.  29|    37.20  |   0.45  |    4.00   |   0.42
  Apr.  30|    43.00  |   0.49  |    4.00   |   0.41
  --------+-----------+---------+-----------+---------
  May    1|    41.30  |   0.49  |    4.00   |   0.41
  May    2|    42.40  |   0.49  |    4.00   |   0.41
  May    3|    40.70  |   0.48  |    4.00   |   0.40
  May    4|    33.80  |   0.47  |    4.00   |   0.39
  May    5|    26.20  |   0.43  |    4.00   |   0.39
  May    6|    29.00  |   0.38  |    3.99   |   0.37
  May    7|    27.60  |   0.36  |     ...   |   0.37
  May    8|    24.70  |   0.31  |    3.99   |   0.37
          |Washed.    |         |           |
  May    9|    24.40  |   0.03  |    3.98   |   0.39
  May   10|    24.80  |   0.04  |    4.00   |   0.42
  May   11|    50.00  |   0.06  |    4.00   |   0.44
  May   12|    50.00  |   0.08  |    4.00   |   0.48
  May   13|    50.00  |   0.09  |    4.00   |   0.47
  May   14|    50.00  |   0.10  |    4.00   |   0.46
  May   15|    48.50  |   0.15  |    4.00   |   0.45
  May   16|    47.00  |   0.16  |    4.00   |   0.46
  May   17|    47.00  |   0.16  |    3.99   |   0.47
  May   18|    47.00  |   0.19  |    4.00   |   0.48
  May   19|    47.00  |   0.21  |    3.99   |   0.51
  May   20|    46.60  |   0.24  |    4.00   |   0.53
  May   21|    46.40  |   0.24  |    4.00   |   0.55
  May   22|    46.40  |   0.27  |    4.00   |   0.58
  May   23|    46.40  |   0.29  |    4.00   |   0.61
  May   24|    46.40  |   0.30  |    4.00   |   0.63
  May   25|    46.40  |   0.32  |    4.00   |   0.66
  May   26|    46.40  |   0.34  |    3.99   |   0.70
  May   27|    46.40  |   0.86  |    3.99   |   0.74
  May   28|    46.40  |   0.38  |    3.15   |   0.76
  May   29|    46.00  |   0.44  |    3.88   |   0.78
  May   30|    45.60  |   0.46  |    3.99   |   0.86
  May   31|    45.60  |   0.46  |    4.00   |   0.92
  --------+-----------+---------+-----------+---------
  June   1|    45.60  |   0.46  |    4.00   |   0.98
  June   2|    45.60  |   0.48  |    4.00   |   1.09
  June   3|    45.60  |   0.51  |    4.00   |   1.20
  June   4|    45.60  |   0.54  |    4.00   |   1.32
  June   5|    45.60  |   0.55  |    4.00   |   1.48
  June   6|    45.60  |   0.56  |    4.01   |   3.66
  June   7|    45.00  |   0.57  |    4.00   |   1.80
  June   8|    45.00  |   0.57  |    4.00   |   1.90
  June   9|    45.00  |   0.55  |    4.01   |   2.00
  June  10|    45.00  |   0.56  |    4.00   |   2.09
  June  11|    45.00  |   0.58  |    4.00   |   2.17
  June  12|    45.00  |   0.60  |    4.01   |   2.27
  June  13|    45.00  |   0.62  |    4.00   |   2.36
  June  14|    45.00  |   0.63  |    3.99   |   2.49
  June  15|    45.00  |   0.64  |    3.99   |   2.56
  June  16|    44.70  |   0.65  |    4.00   |   2.63
  June  17|    44.40  |   0.64  |    4.00   |   2.67
  June  18|    45.00  |   0.63  |    3.98   |   2.69
  June  19|    45.00  |   0.63  |    4.00   |   2.73
  June  20|    45.00  |   0.62  |    4.01   |   2.72
  June  21|    45.00  |   0.61  |    4.01   |   2.68
  June  22|  Shut down to scrape and apply asbestos
          |    and coke; removed 0.79 in. of sand.
  June  23|      Applied 8 lb. of asbestos and
          |         10 lb. of bone-charcoal.
  June  25|   50.00   |   0.54  |    4.00   |   0.27
  June  26|   50.00   |   0.57  |    4.01   |   0.46
  June  27|   50.00   |   0.63  |    4.01   |   0.55
  June  28|   50.00   |   0.65  |    3.99   |   0.63
  June  29|   50.00   |   0.70  |    4.00   |   0.73
  June  30|   50.00   |   0.77  |    3.99   |   0.82
  --------+-----------+---------+-----------+---------
  July   1|   50.00   |   0.87  |    4.00   |   0.80
  July   2|   50.00   |   0.95  |    4.01   |   0.73
  July   3|   50.00   |   1.01  |    4.00   |   0.66
  July   4|   50.00   |   1.03  |    4.00   |   0.58
  July   5|   50.00   |   1.07  |    3.99   |   0.54
  July   6|   50.00   |   1.10  |    4.00   |   0.52
  July   7|   50.00   |   1.14  |    4.00   |   0.50
  July   8|   50.00   |   1.16  |    4.00   |   0.48
  July   9|   50.00   |   1.18  |    4.00   |   0.46
  July  10|   50.00   |   1.20  |    3.99   |   0.45
  July  11|   50.00   |   1.20  |    3.99   |   0.45
  July  12|   50.00   |   1.20  |    4.01   |   0.44
  July  13|   50.00   |   1.15  |    4.00   |   0.47
  July  14|   50.00   |   1.15  |    4.00   |   0.48
  July  15|   50.00   |   1.14  |    3.99   |   0.48
  July  16|   50.00   |   1.19  |    4.00   |   0.48
  July  17|   50.00   |   1.21  |    4.00   |   0.48
  July  18|   50.00   |   1.19  |    3.99   |   0.50
  July  19|   50.00   |   1.16  |    3.99   |   0.52
  July  20|   50.00   |   1.16  |    3.99   |   0.56
  July  21|   50.00   |   1.19  |    3.99   |   0.63
  July  22|   50.00   |   1.20  |    3.99   |   0.77
  July  23|   50.00   |   1.21  |    3.99   |   0.93
  July  24|   50.00   |   1.38  |    3.99   |   1.07
  July  25|   50.00   |   1.17  |    3.99   |   1.22
  July  26|   50.00   |   1.07  |    4.00   |   1.37
  July  27|   50.00   |   1.11  |    4.00   |
  July  28|   50.00   |   1.22  |    3.98   |   1.65
  July  29|   50.00   |   1.21  |    4.00   |   1.82
  July  30|   50.00   |   1.20  |    3.99   |   1.98
  July  31|   50.00   |   1.20  |    3.99   |   2.11
  --------+-----------+---------+-----------+---------
  Aug.   1|   51.00   |   1.21  |    3.99   |   2.27
  Aug.   2|   51.00   |   1.21  |    3.99   |   2.43
  Aug.   3|   51.00   |   1.21  |    4.00   |   2.66
  Aug.   4|   50.00   |   1.21  |    3.99   |   2.95
  Aug.   5|   50.00   |   1.21  |    3.98   |   3.22
  Aug.   6|   50.00   |   1.22  |    3.98   |   3.50
  Aug.   7|   50.00   |   1.21  |    3.99   |   3.74
  Aug.   8|   48.20   |   1.20  |     ...   |   4.09
  Aug.   9|   50.00   |   1.18  |     ...   |   4.45
  Aug.  10|   47.30   |   1.16  |     ...   |   4.67
  Aug.  11| Shut down to drain and scrape sand filter;
          |          O.9 in. depth over all.
  Aug.  16|Out of service all the rest of month washing
          |               sponge and asbestos.
  --------+-----------+---------+-----------+---------
  Sept.  3|   50.00   |   0.02  |    4.00   |   0.16
  Sept.  4|   50.00   |   0.02  |    3.99   |   0.14
  Sept.  5|   50.00   |   0.02  |    4.01   |   0.13
  Sept.  6|   46.40   |   0.02  |    4.00   |   0.12
  Sept.  7|   50.00   |   0.03  |    4.00   |   0.11
  Sept.  8|   46.40   |   0.04  |    3.99   |   0.11
  Sept.  9|   50.00   |   0.05  |    4.90   |   0.11
  Sept. 10|   50.00   |   0.05  |    4.00   |   0.11
  Sept. 11|   50.00   |   0.06  |    4.00   |   0.11
  Sept. 12|   50.00   |   0.07  |    4.00   |   0.12
  Sept. 13|   50.00   |   0.08  |    4.00   |   0.12
  Sept. 14|   50.00   |   0.09  |    4.01   |   0.12
  Sept. 15|   48.20   |   0.11  |    4.00   |   0.12
  Sept. 16|   51.00   |   0.13  |    4.00   |   0.12
  Sept. 17|   50.00   |   0.14  |    4.00   |   0.12
  Sept. 18|   49.10   |   0.14  |    4.00   |   0.13
  Sept. 19|   50.00   |   0.15  |    4.00   |   0.13
  Sept. 20|   49.10   |   0.17  |    4.00   |   0.13
  Sept. 21|   49.10   |   0.18  |    4.00   |   0.13
  Sept. 22|   48.20   |   0.20  |    4.00   |   0.13
  Sept. 23|   49.10   |   0.19  |    4.00   |   0.13
  Sept. 24|   46.40   |   0.19  |    3.99   |   0.14
  Sept. 25|   46.40   |   0.20  |    4.00   |   0.14
  Sept. 26|   45.60   |   0.24  |    4.00   |   0.15
  Sept. 27|   44.80   |   0.27  |    4.00   |   0.16
  Sept. 28|   46.40   |   0.30  |    3.99   |   0.16
  Sept. 29|   46.40   |   0.31  |    3.99   |   0.16
  Sept. 30|   46.40   |   0.31  |    4.00   |   0.17
  --------+-----------+---------+-----------+---------
  Oct.   1|   48.20   |   0.33  |    4.00   |   0.18
  Oct.   2|   50.00   |   0.33  |    4.01   |   0.19
  Oct.   3|   48.20   |   0.33  |    4.00   |   0.19
  Oct.   4|   48.20   |   0.34  |    4.00   |   0.19
  Oct.   5|   50.00   |   0.38  |    4.00   |   0.19
  Oct.   6|   48.20   |   0.41  |    4.00   |   0.19
  Oct.   7|   48.20   |   0.42  |    4.00   |   0.19
  Oct.   8|   50.00   |   0.42  |    4.00   |   0.19
  Oct.   9|   44.80   |   0.40  |    4.00   |   0.19
  Oct.  10|   48.20   |   0.42  |    4.00   |   0.19
  Oct.  11|   48.20   |   0.43  |    4.00   |   0.20
          |Washed.    |         |           |
  Oct.  12|   50.00   |   0.14  |    4.00   |   0.20
  Oct.  13|   47.30   |   0.15  |    4.00   |   0.21
  Oct.  14|   50.00   |   0.18  |    4.00   |   0.22
  Oct.  15|   53.00   |   0.20  |    4.00   |   0.23
  Oct.  16|   50.00   |   0.20  |    4.00   |   0.24
  Oct.  17|   50.00   |   0.21  |    4.00   |   0.25
  Oct.  18|   50.00   |   0.21  |    4.00   |   0.25
  Oct.  19|   50.00   |   0.21  |    4.00   |   0.25
  Oct.  20|   50.00   |   0.22  |    4.00   |   0.25
  Oct.  21|   50.00   |   0.23  |    4.00   |   0.25
  Oct.  22|   50.00   |   0.24  |    4.00   |   0.26
  Oct.  23|   50.00   |   0.25  |    4.00   |   0.26
  Oct.  24|   50.00   |   0.26  |    4.00   |   0.26
  Oct.  25|   50.00   |   0.27  |    4.00   |   0.27
  Oct.  26|   50.00   |   0.28  |    4.00   |   0.27
  Oct.  27|   50.00   |   0.29  |    4.00   |   0.27
  Oct.  28|   50.00   |   0.30  |    4.00   |   0.27
  Oct.  29|   50.00   |   0.31  |    4.00   |   0.27
  Oct.  30|   50.00   |   0.32  |    4.00   |   0.27
  Oct.  31|Out of commission. 4-in supply pipe stopped up.
  --------+-----------+---------+-----------+---------
  Nov.   4|   50.00   |   0.16  |    4.00   |   0.28
  Nov.   5|   50.00   |   0.17  |    4.00   |   0.28
  Nov.   6|   50.00   |   0.18  |    4.00   |   0.29
  Nov.   7|   50.00   |   0.20  |    4.00   |   0.30
  Nov.   8|   50.00   |   0.21  |    4.00   |   0.32
  Nov.   9|   50.00   |   0.22  |    4.00   |   0.34
  Nov.  10|   50.00   |   0.23  |    4.00   |   0.36
  Nov.  11|   50.00   |   0.24  |    3.46   |   0.38
  Nov.  12|   50.00   |   0.26  |    3.99   |   0.40
  Nov.  13|   50.00   |   0.27  |    4.00   |   0.44
  Nov.  14|   50.00   |   0.28  |    4.00   |   0.49
  Nov.  15|   50.00   |   0.29  |    4.00   |   0.55
  Nov.  16|   50.00   |   0.30  |    4.00   |   0.65
  Nov.  17|   50.00   |   0.31  |    3.98   |   0.80
  Nov.  18|   50.00   |   0.32  |    3.99   |   0.98
  Nov.  19|   50.00   |   0.34  |    3.99   |   1.26
  Nov.  20|   50.00   |   0.35  |    3.98   |   1.64
  Nov.  21|   50.00   |   0.36  |    3.99   |   2.03
  Nov.  22|   50.00   |   0.37  |    3.98   |   2.33
  Nov.  23|   50.00   |   0.38  |    3.99   |   2.60
  Nov.  24|   50.00   |   0.40  |    3.98   |   2.85
  Nov.  25|   48.20   |   0.45  |    3.98   |   3.10
  Nov.  26|   50.00   |   0.49  |    3.98   |   3.62
  Nov.  27|   50.00   |   0.51  |    3.99   |   4.15
  Nov.  28|   50.00   |   0.54  |    3.84   |   4.44
  Nov.  29|   50.00   |   0.55  |    3.67   |   4.55
  Nov.  30|   50.00   |   0.56  |    3.44   |   4.65
  --------+-----------+---------+-----------+---------
  Dec.   2|       Shut down to scrape sand filter.    |
  Dec.   6|   50.00   |   0.64  |    4.00   |   0.46
  Dec.   7|   50.00   |   0.64  |    4.00   |   0.39
  Dec.   8|   50.00   |   0.64  |    4.01   |   0.35
  Dec.   9|   50.00   |   0.65  |    4.01   |   0.33
  Dec.  10|   50.00   |   0.65  |    4.00   |   0.33
  Dec.  11|   47.30   |   0.64  |    4.00   |   0.35
  Dec.  12|   46.40   |   0.70  |    3.98   |   0.39
  Dec.  13|   50.00   |   0.79  |    3.98   |   0.49
  Dec.  14|   52.00   |   0.84  |    3.97   |   0.65
  Dec.  15|   49.10   |   0.84  |    3.98   |   0.77
  Dec.  16|   49.10   |   0.86  |    3.97   |   0.84
  Dec.  17|   49.10   |   0.88  |    3.98   |   0.91
  Dec.  18|   48.20   |   0.89  |    3.98   |   0.94
  Dec.  19|   50.00   |   0.91  |    3.98   |   0.97
  Dec.  20|   49.10   |   0.92  |    3.98   |   1.03
  Dec.  21|   50.00   |   0.94  |    3.98   |   1.08
  Dec.  22|   50.00   |   0.97  |    3.98   |   1.13
  Dec.  23|   50.00   |   0.95  |    3.98   |   1.19
  Dec.  24|   47.30   |   0.93  |    3.98   |   1.28
  Dec.  25|   44.10   |   0.91  |    3.97   |   1.47
  Dec.  26|   46.40   |   1.01  |    3.97   |   1.63
  Dec.  27|   50.00   |   1.11  |    3.98   |   1.81
  Dec.  28|   48.20   |   1.12  |    3.99   |   1.87
  Dec.  29|   50.00   |   1.14  |    3.99   |   1.85
  Dec.  30|   49.10   |   1.15  |    3.98   |   1.86
  Dec.  31|   50.00   |   1.17  |    4.00   |   1.87
  --------+-----------+---------+-----------+---------
  1908.
  --------+-----------+---------+-----------+---------
  Jan.   1|   50.00   |   1.18  |    3.98   |   1.90
  Jan.   2|   50.00   |   1.18  |    3.99   |   1.94
  Jan.   3|   50.00   |   1.19  |    3.98   |   1.98
          |Washed.    |         |           |
  Jan.   4|   50.00   |   0.17  |    3.97   |   2.09
  Jan.   5|   50.00   |   0.18  |    3.98   |   2.22
  Jan.   6|   50.00   |   0.19  |    3.98   |   2.28
  Jan.   7|   50.00   |   0.20  |    3.98   |   2.37
  Jan.   8|   50.00   |   0.21  |    3.99   |   2.43
  Jan.   9|   50.00   |   0.23  |    3.98   |   2.52
  Jan.  10|   50.00   |   0.24  |    3.99   |   2.66
  Jan.  11|   50.00   |   0.27  |    3.98   |   2.74
  Jan.  12|   50.00   |   0.28  |    3.98   |   2.83
  Jan.  13|   49.10   |   0.30  |    3.98   |   2.93
  Jan.  14|   48.20   |   0.33  |    3.99   |   3.04
  Jan.  15|   46.40   |   0.35  |    3.98   |   3.21
  Jan.  16|   50.00   |   0.40  |    3.98   |   3.49
  Jan.  17|   50.00   |   0.43  |    3.98   |   3.86
  Jan.  18|   50.00   |   0.46  |    3.91   |   3.99
  Jan.  19|     ...   |   ...   |     ...   |    ...
  Jan.  20|  Scraped. |         |           |
  Jan.  21|   50.00   |   0.48  |    3.00   |   0.76
  Jan.  22|   50.00   |   0.48  |    3.01   |   0.60
  Jan.  23|   50.00   |   0.49  |    3.00   |   0.57
  Jan.  24|   50.00   |   0.49  |    2.99   |   0.60
  Jan.  25|   50.00   |   0.50  |    2.99   |   0.65
  Jan.  26|   50.00   |   0.50  |    2.98   |   0.69
  Jan.  27|   50.00   |   0.51  |    2.99   |   0.76
  Jan.  28|   50.00   |   0.52  |    2.99   |   0.82
  Jan.  29|   50.00   |   0.55  |    2.99   |   0.90
  Jan.  30|   50.00   |   0.57  |    2.98   |   0.98
  Jan.  31|   50.00   |   0.58  |    2.98   |   1.08
  --------+-----------+---------+-----------+---------
  Feb.   1|   50.00   |   0.59  |    2.99   |   1.16
  Feb.   2|   49.10   |   0.60  |    2.99   |   1.22
  Feb.   3|   49.10   |   0.61  |    2.98   |   1.30
  Feb.   4|   50.00   |   0.64  |    2.99   |   1.40
  Feb.   5|   50.00   |   0.66  |    2.99   |   1.50
  Feb.   6|   50.00   |   0.67  |    2.99   |   1.55
  Feb.   7|   50.00   |   0.68  |    3.00   |   1.56
  Feb.   8|   50.00   |   0.69  |    3.00   |   1.53
  Feb.   9|   50.00   |   0.71  |    3.00   |   1.54
  Feb.  10|   50.00   |   0.72  |    2.99   |   1.60
  Feb.  11|   50.00   |   0.74  |    2.99   |   1.62
  Feb.  12|   50.00   |   0.75  |    2.98   |   1.68
  Feb.  13|   50.00   |   0.76  |    2.99   |   1.74
  Feb.  14|   48.20   |   0.76  |    2.99   |   1.77
  Feb.  15|   51.80   |   0.79  |    2.99   |   1.89
  Feb.  16|   48.20   |   0.79  |    2.99   |   2.08
  Feb.  17|   48.20   |   0.81  |    2.99   |   2.24
  Feb.  18|   47.30   |   0.82  |    2.99   |   2.31
  Feb.  19|   51.80   |   0.92  |    2.99   |   2.45
  Feb.  20|   52.70   |   0.99  |    2.99   |   2.61
  Feb.  21|   51.80   |   1.03  |    2.99   |   2.68
  Feb.  22|   50.90   |   1.07  |    2.99   |   2.72
  Feb.  23|   50.00   |   1.09  |    2.99   |   2.76
  Feb.  24|   51.80   |   1.12  |    2.99   |   2.80
  Feb.  25|   50.00   |   1.14  |    2.99   |   2.84
  Feb.  26|   50.00   |   1.17  |    3.00   |   2.87
  Feb.  27|   48.20   |   1.18  |    2.99   |   2.90
  Feb.  28|   47.30   |   1.19  |    2.99   |   2.94
  Feb.  29|   51.80   |   1.23  |    2.99   |   3.01
  --------+-----------+---------+-----------+---------
  Mar.   1|   48.20   |   1.20  |    2.98   |   2.99
  Mar.   2|   50.00   |   1.28  |    2.99   |   3.12
  Mar.   3|   50.90   |   1.32  |    2.98   |   3.22
  Mar.   4|   50.00   |   1.33  |    2.99   |   3.28
  Mar.   5|   50.00   |   1.35  |    2.99   |   3.32
  Mar.   6|   Discontinued; sand filter being used
          |       for sedimentation experiments.
  ========+===========+=========+===========+=========


                  ~Table 18~--(_Continued._)
  ========+===========================+===========================
          |       ~Turbidity.~        |       ~Bacteria.~
          +-------+---------+---------+-------+---------+---------
   Date.  |Applied|Effluent,|Effluent,|Applied|Effluent,|Effluent,
          | water.|  pre-   |  final  | water.|  pre-   | final
          |       |liminary | filter. |       |liminary | filter.
                  | filter  |         |       | filter. |
  --------+-------+---------+---------+-------+---------+---------
  1907.
  --------+-------+---------+---------+-------+---------+---------
  Feb.   8|  ...  |   ...   |   ...   | 1,100 |  2,100  |   ...
  Feb.   9|  ...  |   ...   |   ...   |   200 |    550  | 2,100
  Feb.  10|  ...  |   ...   |   ...   |   ... |    ...  |   ...
  Feb.  11|   12  |     6   |     2   |   600 |  1,160  | 1,100
  Feb.  12|   12  |     5   |     2   |   650 |    400  |   700
  Feb.  13|   15  |     5   |     2   |   660 |    900  |   700
  Feb.  14|   15  |     6   |     2   |   650 |  1,100  |   900
  Feb.  15|   12  |     5   |     2   |   600 |    800  |   850
  Feb.  16|   14  |     4   |     2   |   850 |    950  |   600
  Feb.  17|     Shut down for changes in meters and piping.
  Feb.  18|  ...  |   ...   |   ...   | 1,200 |    ...  |   600
  Feb.  21|   20  |     6   |     2   | 1,800 |  1,400  |   800
  Feb.  22|   15  |     4   |     2   |        Holiday.
  Feb.  23|   20  |     7   |     2   | 1,600 |    750  |   380
  Feb.  24|   20  |    10   |     3   |         Sunday.
  Feb.  25|   20  |    10   |     3   | 1,400 |  1,000  |   450
  Feb.  26|   20  |    10   |     3   |   700 |    800  |   260
  Feb.  27|   17  |     8   |     3   |   700 |    700  |   290
  Feb.  28|   15  |     8   |     3   |   800 |    650  |   500
  --------+-------+---------+---------+-------+---------+---------
  Mar.   1|   15  |     8   |     3   |   650 |    550  |   200
  Mar.   2|   15  |     7   |     3   | 1,000 |    800  |   300
  Mar.   3|   31  |    11   |     3   |         Sunday.
  Mar.   4|   35  |    15   |     6   | 1,200 |  1,500  |   360
  Mar.   5|  135  |    52   |    10   |13,000 |    850  |   ...
  Mar.   6|  135  |    54   |    12   |18,000 |  8,000  |   ...
  Mar.   7|  102  |    46   |     8   |24,000 |  6,500  | 1,800
  Mar.   8|  100  |    40   |     6   |22,000 |  6,000  | 1,600
  Mar.   9|   90  |    40   |     5   |24,000 |  6,000  |   800
  Mar.  10|   82  |    39   |     6   |         Sunday.
  Mar.  11|   68  |    32   |     7   |18,000 |  4,300  |   240
  Mar.  12|   46  |    25   |     5   |11,000 |  4,600  |   210
  Mar.  13|   40  |    20   |     5   | 9,000 |  1,500  |   200
  Mar.  14|   39  |    20   |     4   | 5,500 |  1,200  |    90
  Mar.  15|   35  |    18   |     4   | 6,500 |  1,100  |   150
  Mar.  16|   60  |    24   |     4   | 5,000 |    800  |   160
  Mar.  17|  135  |    45   |     5   |         Sunday.
  Mar.  18|  170  |    59   |     9   | 9,000 |  1,700  |   100
  Mar.  19|  125  |    51   |     8   | 7,000 |  1,000  |   120
  Mar.  20|  102  |    40   |     6   | 4,800 |    700  |    75
  Mar.  21|  125  |    42   |     5   | 8,500 |  1,100  |    90
  Mar.  22|  190  |    82   |     5   | 7,500 |  1,100  |    55
  Mar.  23|  180  |    75   |     6   | 7,500 |  1,300  |    90
  Mar.  24|  140  |    68   |     7   |         Sunday.
  Mar.  25|   88  |    40   |     5   | 4,400 |    900  |    75
  Mar.  26|   62  |    32   |     4   | 3,600 |    750  |    90
  Mar.  27|   47  |    25   |     4   | 2,200 |    400  |    60
  Mar.  28|   35  |    16   |     3   | 1,300 |    350  |    55
  Mar.  29|   26  |    12   |     3   |   700 |    180  |    20
  Mar.  30|   25  |     7   |     3   |   310 |    220  |    39
  Mar.  31|   21  |     6   |     2   |         Sunday.
  --------+-------+---------+---------+-------+---------+---------
  Apr.   1|   20  |     6   |     2   |   600 |    110  |    38
  Apr.   2|   24  |     6   |     2   |   270 |    110  |    29
  Apr.   3|   24  |     6   |     2   |   460 |     85  |    31
  Apr.   4|   20  |     6   |     2   |   280 |     60  |    22
  Apr.   5|   20  |     5   |     2   |   450 |     70  |    40
  Apr.   6|Shut down awaiting Mr. Maiguen to apply bone-charcoal.
  Apr.   7|Removed 1.06 in. of sand.            Sunday.
  Apr.   8|   18  |     4   |     3   |   330 |    ...  |   ...
  Apr.   9|   18  |     4   |     2   |   140 |     60  |    32
  Apr.  10|   30  |     4   |     1   |   750 |    120  |    28
  Apr.  11|   66  |     7   |     2   | 4,000 |    ...  |    32
  Apr.  12|   72  |    20   |     3   |14,000 |  2,900  |    85
  Apr.  13|   80  |    30   |     3   |13,000 |  2,500  |    95
  Apr.  14|   77  |    35   |     4   |         Sunday.
  Apr.  15|   62  |    31   |     4   | 7,000 |  1,100  |    60
  Apr.  16|   47  |    27   |     4   | 3,600 |    650  |    31
  Apr.  17|   39  |    21   |     3   | 1,600 |    160  |    38
  Apr.  18|   30  |    13   |     2   | 1,810 |    210  |    42
  Apr.  19|   25  |     9   |     2   |   790 |    190  |    34
  Apr.  20|   20  |     6   |     2   |   540 |     87  |    23
  Apr.  21|   20  |     4   |     2   |         Sunday.
  Apr.  22|   18  |     3   |     1   |   235 |     55  |    22
  Apr.  23|   15  |     3   |     1   |   170 |     45  |    16
  Apr.  24|   19  |     2   |     1   |   150 |     14  |    14
  Apr.  25|   34  |     3   |     1   |   700 |     12  |    23
  Apr.  26|   46  |     4   |     1   | 1,200 |     80  |    16
  Apr.  27|   52  |     4   |     1   | 1,700 |    160  |    23
  Apr.  28|   45  |     5   |     1   |         Sunday.
  Apr.  29|   44  |     6   |     1   |   600 |     60  |    10
  Apr.  30|   39  |     7   |     1   |   550 |     55  |    15
  --------+-------+---------+---------+-------+---------+---------
  May    1|   31  |     6   |     1   |   500 |     80  |    17
  May    2|   24  |     5   |     1   |   500 |     80  |    19
  May    3|   19  |     4   |     1   |   280 |     75  |    48
  May    4|   16  |     3   |     1   |   400 |     80  |     9
  May    5|   15  |     1   |     1   |         Sunday.
  May    6|   13  |     2   |     1   |   390 |    100  |    65
  May    7|   12  |     2   |     1   |   190 |     60  |    19
  May    8|   10  |     2   |     1   |   ... |    ...  |   ...
          |Washed.          |         |       |         |
  May    9|   10  |     2   |     1   |   390 |     65  |    10
  May   10|   10  |     2   |     1   |   300 |     80  |    18
  May   11|   12  |     2   |     1   |   390 |    110  |    12
  May   12|   17  |     2   |     1   |         Sunday.
  May   13|   35  |     3   |     1   |   600 |    100  |    18
  May   14|   39  |     4   |     1   |   500 |     65  |    15
  May   15|   17  |     3   |     1   |   500 |     70  |    16
  May   16|   24  |     3   |     1   |   290 |     70  |    16
  May   17|   18  |     3   |     1   |   260 |     40  |     9
  May   18|   15  |     2   |     1   |   190 |    ...  |    17
  May   19|   12  |     2   |     1   |         Sunday.
  May   20|   12  |     2   |     1   |   260 |     40  |    13
  May   21|   16  |     2   |     1   |   260 |     65  |     9
  May   22|   20  |     2   |     1   |   280 |     35  |    12
  May   23|   15  |     2   |     1   |   130 |     35  |    10
  May   24|   15  |     2   |     1   |   170 |     26  |     6
  May   25|   15  |     2   |     1   |   340 |     80  |    13
  May   26|   18  |     2   |     1   |         Sunday.
  May   27|   13  |     2   |     1   |   210 |     80  |     7
  May   28|   16  |     2   |     1   |   260 |     70  |    10
  May   29|   16  |     2   |     1   |   500 |     55  |    12
  May   30|   14  |     2   |     1   |         Holiday.
  May   31|   17  |     2   |     1   |   380 |     65  |    11
  --------+-------+---------+---------+-------+---------+---------
  June   1|   15  |     2   |     1   |   900 |     48  |    10
  June   2|   17  |     2   |     1   |         Sunday.
  June   3|   24  |     2   |     1   |   550 |     75  |    16
  June   4|   37  |     3   |     1   | 6,500 |    ...  |    22
  June   5|   65  |     5   |     1   | 3,200 |    140  |    19
  June   6|   77  |    16   |     1   | 1,500 |    210  |    14
  June   7|   64  |    27   |     1   | 2,100 |    230  |    20
  June   8|   46  |    22   |     1   |   600 |    240  |    33
  June   9|   44  |    18   |     1   |         Sunday.
  June  10|   36  |    12   |     1   |   240 |    110  |    43
  June  11|   30  |     8   |     1   |   280 |    130  |    60
  June  12|   34  |     8   |     1   |   330 |    150  |    60
  June  13|   35  |    10   |     1   |   480 |    ...  |   120
  June  14|   31  |     9   |     1   |   440 |    ...  |    65
  June  15|   32  |     8   |     1   |   420 |    ...  |    49
  June  16|   26  |     7   |     1   |         Sunday.
  June  17|   26  |     6   |     1   |   340 |    270  |    55
  June  18|   31  |     7   |     1   |   440 |    140  |    65
  June  19|   37  |    10   |     1   |   500 |    110  |    24
  June  20|   30  |     9   |     1   |   330 |     70  |    34
  June  21|   25  |     7   |     1   |   170 |    130  |    60
  June  22|   Shut down to scrape and apply asbestos and coke;
          |                removed 0.79 in. of sand.
  June  23|Applied 8 lb. of asbestos and 10 lb. of bone-charcoal.
  June  25|  130  |    45   |     1   |   400 |    ...  |  ...
  June  26|   82  |    37   |     1   |   750 |    550  |    35
  June  27|   65  |    26   |     1   |   ... |  1,200  |   140
  June  28|   47  |    21   |     1   |   ... |  1,200  |    26
  June  29|   37  |     9   |     1   |   220 |    800  |    22
  June  30|   30  |     8   |     1   |         Sunday.
  --------+-------+---------+---------+-------+---------+---------
  July   1|   30  |     8   |     1   |   400 |     90  |    37
  July   2|   32  |     9   |     1   |   180 |    230  |    25
  July   3|   36  |    10   |     1   |   350 |     80  |    58
  July   4|   44  |    12   |     1   |         Holiday.
  July   5|   24  |    14   |     1   |   550 |    130  |    47
  July   6|   39  |    12   |     1   |   250 |    110  |    33
  July   7|   34  |    10   |     1   |         Sunday.
  July   8|   25  |     7   |     1   |   220 |    190  |    14
  July   9|   22  |     5   |     1   |    50 |     30  |     3
  July  10|   47  |    11   |     1   | Lost. |  Lost.  | Lost.
  July  11|   90  |    30   |     1   |   150 |    140  |    12
  July  12|   97  |    35   |     1   |   300 |    110  |    20
  July  13|   90  |    39   |     1   |   220 |    120  |    14
  July  14|   90  |    40   |     1   |         Sunday.
  July  15|   95  |    40   |     1   |   375 |    320  |    19
  July  16|  120  |    45   |     1   | Lost. |    150  |    12
  July  17|   85  |    42   |     1   |   270 |     60  |     5
  July  18|   56  |    32   |     1   | 1,675 |     23  |    39
  July  19|   41  |    20   |     1   |   450 |    200  |    13
  July  20|   62  |    29   |     1   |   300 |    220  |     8
  July  21|   62  |    31   |     1   |         Sunday.
  July  22|   80  |    36   |     1   | 1,400 |    700  |     9
  July  23|  105  |    40   |     1   | 3,700 |    370  |    25
  July  24|   95  |    40   |     1   |   770 |    260  |    31
  July  25|   77  |    32   |     1   |   250 |    230  |     3
  July  26|   67  |    29   |     1   |   140 |     90  |    12
  July  27|   54  |    25   |     1   |   300 |    180  |     6
  July  28|   46  |    19   |     1   |         Sunday.
  July  29|   36  |    16   |     1   |   470 |    230  |    18
  July  30|   29  |    11   |     1   |       Plates lost.
  July  31|   21  |     9   |     1   |        July    "
  --------+-------+---------+---------+-------+---------+---------
  Aug.   1|   16  |     6   |     1   |       Plates lost.
  Aug.   2|   15  |     4   |     1   |   130 |    130  |     4
  Aug.   3|   16  |     3   |     1   |   120 |     80  |     4
  Aug.   4|   21  |     3   |     1   |         Sunday.
  Aug.   5|   29  |     3   |     1   |   230 |    210  |     4
  Aug.   6|   34  |     4   |     1   |    85 |    320  |    19
  Aug.   7|   21  |     4   |     1   |   200 |  Lost.  |    19
  Aug.   8|   19  |     4   |     1   |   100 |    150  |    17
  Aug.   9|   16  |     3   |     1   |    75 |    220  |     9
  Aug.  10|   24  |     3   |     1   |    60 |    250  |    10
  Aug.  11|        Shut down to drain and scrape sand filter;
          |                O.9 in. depth over all.
  Aug.  16|       Out of service all the rest of month washing
          |                  sponge and asbestos.
  --------+-------+---------+---------+-------+---------+---------
  Sept.  3|   12  |     5   |     1   |   300 |    ...  |   ...
  Sept.  4|   16  |     6   |     1   |   600 |    260  |   370
  Sept.  5|   34  |     6   |     1   |   360 |     71  |   165
  Sept.  6|  160  |    52   |     1   |15,000 |  1,900  |   120
  Sept.  7|   64  |    26   |     1   | 2,000 |    170  |    62
  Sept.  8|   56  |    25   |     1   |         Sunday.
  Sept.  9|   59  |    25   |     1   |   220 |     13  |    19
  Sept. 10|   57  |    21   |     1   |18,000 |    100  |    24
  Sept. 11|   65  |    25   |     1   | 2,700 |    150  |    25
  Sept. 12|   72  |    26   |     1   | 1,000 |    190  |    36
  Sept. 13|   87  |    30   |     1   | 2,300 |    ...  |    35
  Sept. 14|   72  |    27   |     1   | 2,400 |    130  |   230
  Sept. 15|   65  |    25   |     1   |         Sunday.
  Sept. 16|   65  |    25   |     1   | Lost. |  Lost.  |    27
  Sept. 17|   52  |    21   |     1   |   420 |     60  |    29
  Sept. 18|   60  |    18   |     1   |   900 |     80  |    41
  Sept. 19|   85  |    22   |     1   | 2,000 |    ...  |    19
  Sept. 20|  100  |    29   |     1   | 4,200 |    300  |    28
  Sept. 21|  120  |    34   |     1   | 1,100 |    160  |    30
  Sept. 22|  137  |    41   |     1   |         Sunday.
  Sept. 23|  112  |    37   |     1   | 2,400 |     90  |    34
  Sept. 24|  100  |    35   |     1   | 4,000 |    210  |    12
  Sept. 25|  432  |    80   |     1   |56,000 |    510  |    27
  Sept. 26|  385  |    80   |     4   | 1,300 |    450  |    55
  Sept. 27|  245  |    70   |     3   | 4,000 |    240  |    41
  Sept. 28|  127  |    46   |     2   |15,000 |    430  |    37
  Sept. 29|  105  |    41   |     2   |         Sunday.
  Sept. 30|  115  |    42   |     1   | Lost. |  1,600  |   110
  --------+-------+---------+---------+-------+---------+---------
  Oct.   1|   82  |    36   |     1   |   600 |    600  |   120
  Oct.   2|   65  |    27   |     1   | 4,400 |    170  |    47
  Oct.   3|   59  |    34   |     1   |   900 |    210  |    44
  Oct.   4|   55  |    20   |     1   |   850 |    200  |    37
  Oct.   5|    9  |    21   |     1   | 2,000 |    150  |    34
  Oct.   6|   59  |    24   |     1   |         Sunday.
  Oct.   7|  552  |    17   |     1   | 1,250 |    200  |    28
  Oct.   8|   54  |    16   |     1   |11,000 |    210  |    28
  Oct.   9|   51  |    16   |     1   | 2,000 |    310  |    29
  Oct.  10|   50  |    15   |     1   |   800 |    220  |    16
  Oct.  11|   47  |    13   |     1   | 2,000 |    310  |    46
          |Washed.|         |         |       |         |
  Oct.  12|   36  |    11   |     1   | 1,200 |    370  |    25
  Oct.  13|   40  |    15   |     1   |         Sunday.
  Oct.  14|   47  |    19   |     1   | 1,200 |    390  |    22
  Oct.  15|   41  |    16   |     1   |   900 |    140  |    16
  Oct.  16|   35  |    12   |     1   | Lost. |    310  |    18
  Oct.  17|   30  |     8   |     1   |   550 |    180  |     7
  Oct.  18|   25  |     6   |     1   |   260 |    100  |    33
  Oct.  19|   25  |     6   |     1   |   750 |    220  |    15
  Oct.  20|   20  |     5   |     1   |         Sunday.
  Oct.  21|   19  |     5   |     1   |   480 |    120  |    11
  Oct.  22|   18  |     4   |     1   |   230 |     70  |     7
  Oct.  23|   15  |     3   |     1   |   250 |    120  |    12
  Oct.  24|   15  |     3   |     1   |   300 |     80  |    12
  Oct.  25|   15  |     2   |     1   |   450 |     60  |    15
  Oct.  26|   15  |     2   |     1   |   450 |  Lost.  |    14
  Oct.  27|   13  |     2   |     0   |         Sunday.
  Oct.  28|   13  |     2   |     0   |   190 |    110  |     9
  Oct.  29|   25  |     2   |     0   |   380 |    ...  |   ...
  Oct.  30|   21  |     3   |     0   |   ... |    ...  |   ...
  Oct.  31|  Out of commission. 4-in. supply pipe stopped up.
  --------+-------+---------+---------+-------+---------+---------
  Nov.   4|  125  |    11   |     1   |   ... |    ...  |   ...
  Nov.   5|  185  |    61   |     1   | 6,000 |  3,000  |   220
  Nov.   6|  170  |    66   |     1   | 5,000 |  1,100  |   150
  Nov.   7|  100  |    45   |     1   |14,000 |  1,600  |   120
  Nov.   8|   95  |    42   |     1   | 1,900 |  2,000  |    29
  Nov.   9|   80  |    36   |     1   | 4,000 |  2,000  |   110
  Nov.  10|   67  |    29   |     1   |         Sunday.
  Nov.  11|   52  |    20   |     1   | 1,900 |    460  |   160
  Nov.  12|   40  |    13   |     1   | 7,500 |  1,100  |   110
  Nov.  13|   36  |    10   |     1   | 1,600 |    550  |    50
  Nov.  14|   42  |    13   |     1   | 2,700 |    950  |    48
  Nov.  15|   35  |    11   |     1   | 1,800 |    900  |    49
  Nov.  16|   26  |     7   |     1   | 1,100 |    360  |    35
  Nov.  17|   20  |     5   |     1   |         Sunday.
  Nov.  18|   17  |     4   |     1   | 1,600 |    200  |    35
  Nov.  19|   16  |     3   |     1   | 1,300 |    400  |    55
  Nov.  20|   45  |     4   |     1   | 6,500 |  3,500  |   200
  Nov.  21|   52  |    12   |     1   | 9,900 |  4,500  |   130
  Nov.  22|   65  |    24   |     1   |10,000 |  5,500  |   220
  Nov.  23|   49  |    19   |     1   |18,000 |  3,500  |   100
  Nov.  24|  134  |    32   |     1   |         Sunday.
  Nov.  25|  225  |    87   |     2   |50,000 | 19,000  |   340
  Nov.  26|  237  |    90   |     2   |40,000 | 11,000  |   220
  Nov.  27|  185  |    77   |     2   |16,000 |  7,500  |   310
  Nov.  28|  130  |    57   |     2             Holiday.
  Nov.  29|   80  |    36   |     1   |10,000 |  2,200  |    80
  Nov.  30|   54  |    25   |     1   | 3,800 |  2,200  |    55
  --------+-------+---------+---------+-------+---------+---------
  Dec.   2|Shut down to scrape sand filter.
  Dec.   6|   16  |     3   |     1   |       |         |
  Dec.   7|   14  |     3   |     1   | 2,400 |  1,200  |   490
  Dec.   8|   12  |     2   |     1   |         Sunday.
  Dec.   9|   11  |     2   |     1   | 1,200 |    420  |    60
  Dec.  10|   12  |     2   |     1   |   800 |    950  |    66
  Dec.  11|  255  |    84   |     3   | 6,500 |  1,600  |   140
  Dec.  12|  212  |   100   |     6   |48,000 | 15,000  | 1,800
  Dec.  13|  495  |   217   |     9   |42,000 | 20,000  | 1,600
  Dec.  14|  357  |   167   |     9   |49,000 |  9,500  | 1,200
  Dec.  15|  157  |    76   |     6   |         Sunday.
  Dec.  16|   90  |    42   |     4   |19,000 |    800  |   700
  Dec.  17|   70  |    31   |     2   |21,000 | 18,000  | 1,600
  Dec.  18|   49  |    21   |     2   | 6,500 |  7,000  |   600
  Dec.  19|   39  |    13   |     1   | Lost. |  Lost.  | Lost.
  Dec.  20|   42  |    16   |     1   |  Dec. |   Dec.  |   "
  Dec.  21|   26  |     7   |     1   |  Dec. |   Dec.  |   "
  Dec.  22|   20  |     5   |     1   |         Sunday.
  Dec.  23|   34  |     9   |     1   | 1,400 |    500  |   160
  Dec.  24|  195  |    75   |     2   | 9,000 |  1,700  |   130
  Dec.  25|  445  |   210   |     9   |         Holiday.
  Dec.  26|  370  |   172   |     7   |51,000 |  8,000  |   250
  Dec.  27|  245  |   110   |     5   |55,000 |  5,600  |   210
  Dec.  28|  102  |    46   |     3   |10,000 |  4,500  |   140
  Dec.  29|   75  |    32   |     2   |         Sunday.
  Dec.  30|   56  |    24   |     2   | 4,400 |  1,900  |   190
  Dec.  31|   39  |    15   |     1   |14,000 |  1,300  |    60
  --------+-------+---------+---------+-------+---------+---------
  1908.
  --------+-------+---------+---------+-------+---------+---------
  Jan.   1|   31  |     8   |     1   |   ... |    ...  |   ...
  Jan.   2|   39  |    11   |     1   | 4,400 |    750  |    45
  Jan.   3|   36  |    11   |     1   | 3,100 |  1,600  |    70
          |Washed.|         |         |       |         |
  Jan.   4|   32  |     9   |     1   | 2,400 |  1,200  |    43
  Jan.   5|   26  |     6   |     1   |         Sunday.
  Jan.   6|   20  |     5   |     1   |   600 |    600  |    49
  Jan.   7|   20  |     5   |     1   | 1,100 |    330  |    49
  Jan.   8|   22  |     5   |     1   | 1,900 |    900  |    43
  Jan.   9|   45  |    13   |     1   |13,000 |  3,400  |    50
  Jan.  10|   70  |    30   |     1   |10,000 |  8,000  |    50
  Jan.  11|   56  |    22   |     1   |16,000 |    220  |   200
  Jan.  12|   40  |    12   |     1   |         Sunday.
  Jan.  13|  110  |    51   |     2   | 8,500 |  1,200  |    43
  Jan.  14|  210  |   113   |     4   |16,000 |  6,000  |   280
  Jan.  15|  325  |   222   |    15   |24,000 |  9,500  |   700
  Jan.  16|  360  |   247   |    42   |28,000 | 14,000  |   900
  Jan.  17|  242  |   147   |    26   |65,000 | 20,000  | 1,200
  Jan.  18|  137  |    73   |     7   | 7,000 |  6,500  |   400
  Jan.  19| ...   |   ...   |   ...   |         Sunday.
  Jan.  20|Scraped.         |         |       |         |
  Jan.  21|   55  |    25   |     4   |   ... |    ...  |   ...
  Jan.  22|   49  |    21   |     4   | 3,600 |  1,900  |   150
  Jan.  23|   40  |    15   |     3   | 1,800 |    700  |   170
  Jan.  24|   40  |    13   |     3   | 2,300 |    950  |    90
  Jan.  25|   39  |    12   |     3   | 1,100 |    800  |    95
  Jan.  26|   32  |     9   |     2   |         Sunday.
  Jan.  27|   32  |     9   |     2   |   300 |    700  |    70
  Jan.  28|   45  |    15   |     2   | 1,200 |    900  |    70
  Jan.  29|   60  |    26   |     2   | 1,000 |  1,400  |    95
  Jan.  30|   57  |    27   |     2   | 1,400 |    210  |    33
  Jan.  31|   42  |    18   |     2   | 1,100 |    750  |    45
  --------+-------+---------+---------+-------+---------+---------
  Feb.   1|   39  |    14   |     2   |   750 |  1,000  |    70
  Feb.   2|   27  |     9   |     2   |         Sunday.
  Feb.   3|   29  |     8   |     2   | 1,300 |    750  |    20
  Feb.   4|   25  |     6   |     2   |   600 |    900  |    60
  Feb.   5|   24  |     6   |     2   |   750 |    200  |    75
  Feb.   6|   20  |     5   |     2   | 2,000 |    800  |    60
  Feb.   7|   17  |     4   |     1   |   ... |    600  |    34
  Feb.   8|   15  |     4   |     1   |   900 |    220  |    35
  Feb.   9|   14  |     4   |     1   |         Sunday.
  Feb.  10|   11  |     4   |     1   |   850 |    500  |    28
  Feb.  11|   10  |     4   |     1   | 1,000 |    500  |    23
  Feb.  12|    8  |     4   |     1   |   750 |    290  |    18
  Feb.  13|    9  |     4   |     1   |   700 |    260  |    10
  Feb.  14|    9  |     4   |     1   | 1,200 |    250  |    27
  Feb.  15|   61  |    18   |     1   | 5,500 |  4,800  |    13
  Feb.  16|   80  |    40   |     2   |         Sunday.
  Feb.  17|   80  |    40   |     3   |33,000 |  1,300  |    60
  Feb.  18|  130  |    65   |     3   |   ... |    950  |   120
  Feb.  19|  320  |   200   |     7   |28,000 | 22,000  |   360
  Feb.  20|  177  |    97   |     9   |22,000 | 16,300  |   350
  Feb.  21|  105  |    52   |     6   |10,600 |  3,800  |   270
  Feb.  22|   85  |    42   |     5   |         Holiday.
  Feb.  23|   60  |    30   |     4   |         Sunday.
  Feb.  24|   46  |    19   |     3   | 3,600 |  1,700  |   120
  Feb.  25|   31  |     9   |     2   | 2,300 |  1,300  |    60
  Feb.  26|   30  |     8   |     2   | 3,800 |  1,300  |    43
  Feb.  27|   30  |     7   |     1   | 1,300 |    900  |    42
  Feb.  28|   37  |     7   |     1   | 1,400 |    800  |    31
  Feb.  29|  123  |    49   |     2   |13,500 |    750  |    35
  --------+-------+---------+---------+-------+---------+---------
  Mar.   1|   97  |    44   |     5   |         Sunday.
  Mar.   2|   82  |    35   |     4   | 8,000 |  2,500  |    70
  Mar.   3|   87  |    38   |     4   |11,000 |  6,000  |    55
  Mar.   4|   67  |    29   |     3   | 6,000 |  1,400  |    38
  Mar.   5|   59  |    23   |     3   | 4,400 |  2,500  |    37
  Mar.   6|          Discontinued; sand filter being used
          |            for sedimentation experiments.
  ========+=======+=========+=========+=======+=========+==========


[Illustration: ~Figure 9--Detail of Strainer System.~]


~Table 19--Record of Experimental Filter Plant. No. 3.~
  ========+===============+============================
          | ~Sand Filter.~|        ~Turbidity.~
          +---------------+-------+----------+---------
    Date. | Rate. |Loss of|Applied| Effluent,|Effluent,
          |       | head. | water.|coagulant.|  sand.
  --------+-------+-------+-------+----------+---------
  1907.
  --------+-------+-------+-------+----------+---------
  Feb.  12|  2.99 |  0.18 |   14  |    ...   |     2
  Feb.  13|  3.00 |  0.17 |   15  |    ...   |     2
  Feb.  14|  3.19 |  0.18 |   15  |    ...   |     2
  Feb.  15|  3.86 |  0.22 |   12  |    ...   |     2
  Feb.  16|  3.84 |  0.29 |   14  |    ...   |     2
  Feb.  17|   ... |   ... |  ...  |    ...   |   ...
  Feb.  18|   ... |   ... |  ...  |    ...   |   ...
  Feb.  21|  3.91 |  0.32 |   20  |    ...   |     2
  Feb.  22|  3.95 |  0.39 |   15  |    ...   |     2
  Feb.  23|  3.94 |  0.43 |   20  |    ...   |     3
  Feb.  24|  3.89 |  0.47 |   20  |    ...   |     3
  Feb.  25|  4.19 |  0.52 |   20  |    ...   |     3
  Feb.  26|  4.13 |  0.57 |   20  |    ...   |     3
  Feb.  27|  3.32 |  0.62 |   17  |    ...   |     3
  Feb.  28|  4.41 |  0.67 |   15  |    ...   |     3
  --------+-------+-------+-------+----------+---------
  Mar.   1|  3.91 |  0.72 |   15  |    ...   |     3
  Mar.   2|  3.93 |  0.79 |   15  |    ...   |     3
  Mar.   3|  3.90 |  0.82 |   31  |    ...   |     3
  Mar.   4|  3.92 |  0.80 |   35  |    ...   |     3
  Mar.   5|  3.96 |  0.98 |  135  |    ...   |     4
  Mar.   6|  4.05 |  1.25 |  135  |     29   |     2
  Mar.   7|  3.95 |  1.52 |  102  |     15   |     1
  Mar.   8|  3.90 |  1.67 |  100  |     15   |     1
  Mar.   9|  3.93 |  1.80 |   90  |     15   |     1
  Mar.  10|  3.95 |  1.91 |   82  |     16   |     1
  Mar.  11|  3.96 |  2.08 |   68  |     18   |     1
  Mar.  12|  4.02 |  2.19 |   46  |     18   |     1
  Mar.  13|  4.02 |  2.31 |   40  |     15   |     1
  Mar.  14|  3.96 |  2.44 |   39  |     16   |     1
  Mar.  15|  4.07 |  2.42 |   35  |     20   |     1
  Mar.  16|  3.85 |  2.20 |   60  |     29   |     1
  Mar.  17|  3.95 |  2.21 |  135  |     25   |     1
  Mar.  18|  3.88 |  2.86 |  170  |     25   |     1
  Mar.  19|  3.82 |  3.31 |  125  |     21   |     1
  Mar.  20|  3.78 |  3.47 |  102  |     20   |     1
  Mar.  21|  3.71 |  3.70 |  125  |     20   |     1
  Mar.  22|  3.64 |  3.81 |  190  |     25   |     1
  Mar.  23|  3.58 |  3.95 |  180  |     26   |     1
  Mar.  24|  3.46 |  4.18 |  140  |     19   |     1
  Mar.  25|Scraped, 1.03 in. of sand removed.
  Mar.  27|  4.06 |  0.22 |   47  |      8   |     1
  Mar.  28|  4.02 |  0.37 |   35  |    ...   |     0
  Mar.  29|  4.02 |  0.46 |   26  |    ...   |   ...
  Mar.  30|Shut down to fill coagulant basin.
          |   ... |   ... |   25  |    ...   |   ...
  Mar.  31|  4.00 |  0.45 |   21  |     15   |     1
  --------+-------+-------+-------+----------+---------
  Apr.   1|  3.39 |  0.42 |   20  |     15   |     1
  Apr.   2|  3.06 |  0.46 |   24  |     17   |     1
  Apr.   3|  3.01 |  0.49 |   24  |     17   |     1
  Apr.   4|  2.95 |  0.50 |   20  |     15   |     1
  Apr.   5|  2.95 |  0.51 |   20  |     13   |     1
  Apr.   6|  2.96 |  0.49 |   20  |     12   |     1
  Apr.   7|  2.99 |  0.48 |   20  |     12   |     1
  Apr.   8|  3.01 |  0.49 |   18  |     12   |     1
  Apr.   9|  3.01 |  0.55 |   18  |     12   |     1
  Apr.  10|  3.02 |  0.57 |   30  |     15   |     0
  Apr.  11|  3.04 |  0.61 |   66  |     16   |     0
  Apr.  12|  3.09 |  0.72 |   72  |     13   |     0
  Apr.  13|  3.07 |  0.88 |   80  |     19   |     0
  Apr.  14|  2.98 |  1.04 |   77  |     18   |     1
  Apr.  15|  2.97 |  1.20 |   62  |     18   |     1
  Apr.  16|  3.01 |  1.32 |   47  |     17   |     1
  Apr.  17|  3.05 |  1.44 |   39  |     19   |     0
  Apr.  18|  3.04 |  1.41 |   30  |     20   |     1
  Apr.  19|  3.04 |  1.35 |   25  |     18   |     1
  Apr.  20|  3.07 |  1.30 |   20  |     15   |     1
  Apr.  21|  3.07 |  1.26 |   20  |     15   |     1
  Apr.  22|  3.04 |  1.21 |   18  |     12   |     0
  Apr.  23|  3.06 |  1.22 |   15  |     10   |     0
  Apr.  24|  2.99 |  1.26 |   19  |     10   |     0
  Apr.  25|  3.04 |  1.27 |   34  |     12   |     0
  Apr.  26|  3.07 |  1.28 |   46  |     12   |     0
  Apr.  27|  2.94 |  1.49 |   52  |    ...   |     0
  Apr.  28|  2.96 |  1.88 |   45  |    ...   |     1
  Apr.  29|  2.99 |  2.40 |   44  |     33   |     1
  Apr.  30|  3.00 |  2.83 |   39  |     29   |     1
  --------+-------+-------+-------+----------+---------
  May    1|  3.01 |  2.71 |   31  |     21   |     1
  May    2|  3.01 |  2.51 |   24  |     15   |     1
  May    3|  3.00 |  2.36 |   19  |     12   |     1
  May    4|  3.01 |  2.29 |   16  |     10   |     0
  May    5|  3.01 |  2.25 |   15  |      9   |     0
  May    6|  3.06 |  2.32 |   13  |      8   |     0
  May    7|  2.96 |  2.46 |   12  |      7   |     0
  May    8|  3.00 |  2.51 |   10  |      5   |     0
  May    9|  3.00 |  2.77 |   10  |      5   |     0
  May   10|  3.01 |  2.87 |   10  |      5   |     0
  May   11|  2.99 |  3.16 |   12  |      6   |     0
  May   12|  3.00 |  3.34 |   17  |      7   |     0
  May   13|  3.00 |  3.44 |   35  |      9   |     0
  May   14|  3.01 |  3.46 |   39  |     12   |     0
  May   15|  3.01 |  3.56 |   17  |    ...   |     0
  May   16|  2.93 |  4.07 |   24  |    ...   |     0
  May   17|  3.01 |  4.34 |   18  |    ...   |     0
  May   18|  2.93 |  4.25 |   15  |      8   |     0
  May   19|  2.97 |  4.36 |   12  |      8   |     0
  May   20|  3.01 |  4.64 |   12  |      8   |     0
  May   21|  2.99 |  4.55 |   16  |      8   |     0
  May   22|  3.01 |  4.57 |   20  |      8   |     0
  May   23|  3.00 |  4.51 |   15  |      8   |     0
  May   24|  2.98 |  4.44 |   15  |      8   |     0
  May   25|  3.00 |  4.38 |   15  |      8   |     0
  May   26|  3.00 |  4.38 |   18  |      8   |     0
  May   27|      Shut down to scrape sand filter;
          |        1.09 in. of sand removed.
  May   28|      Cleaning coagulant basin and
          |      treating coagulant basin with
          | 1:2,000,000 solution of copper sulphate.
  May   29|       |       |   16  |    ...   |   ...
  May   30|  3.00 |  0.11 |   14  |      8   |     1
  May   31|  3.01 |  0.10 |   17  |      8   |     1
  --------+-------+-------+-------+----------+---------
  June   1|  3.01 |  0.09 |   15  |      8   |     1
  June   2|  3.01 |  0.10 |   17  |      8   |     1
  June   3|  3.01 |  0.10 |   24  |     10   |     1
  June   4|  3.04 |  0.11 |   37  |     13   |     1
  June   5|  3.00 |  0.11 |   65  |     29   |     1
  June   6|  3.00 |  0.11 |   77  |     46   |     1
  June   7|  2.99 |  0.12 |   64  |     21   |     1
  June   8|  2.98 |  0.17 |   46  |     22   |     1
  June   9|  3.00 |  0.18 |   44  |     30   |     1
  June  10|  3.01 |  0.18 |   36  |     26   |     1
  June  11|  3.00 |  0.17 |   30  |     20   |     1
  June  12|  3.00 |  0.17 |   34  |     22   |     1
  June  13|  2.99 |  0.17 |   35  |     25   |     1
  June  14|  2.98 |  0.17 |   31  |     22   |     1
  June  15|  2.99 |  0.19 |   32  |     22   |     1
  June  16|  3.02 |  0.21 |   26  |     18   |     1
  June  17|  2.99 |  0.23 |   26  |     16   |     1
  June  18|  3.02 |  0.25 |   31  |     20   |     1
  June  19|  3.02 |  0.29 |   37  |     27   |     1
  June  20|  3.00 |  0.32 |   30  |     21   |     1
  June  21|  3.01 |  0.36 |   25  |     16   |     1
  June  22|  3.00 |  0.40 |   20  |     12   |     1
  June  23|  2.97 |  0.43 |   26  |     11   |     1
  June  24|  2.97 |  0.44 |  140  |     36   |     1
  June  25|  3.02 |  0.45 |  130  |     27   |     1
  June  26|       Interrupted, defective meter.
  June  27|  3.00 |  0.43 |   65  |     15   |     0
  June  28|  3.00 |  0.44 |   47  |     19   |     0
  June  29|  2.99 |  0.44 |   37  |     20   |     0
  June  30|  2.97 |  0.42 |   30  |     19   |     0
  --------+-------+-------+-------+----------+---------
  July   1|  2.99 |  0.37 |   30  |     18   |     0
  July   2|  3.01 |  0.33 |   32  |     19   |     0
  July   3|  3.00 |  0.31 |   36  |     21   |     0
  July   4|  3.00 |  0.30 |   44  |     30   |     0
  July   5|  3.00 |  0.29 |   44  |     35   |     0
  July   6|  3.00 |  0.28 |   39  |     30   |     0
  July   7|  3.00 |  0.28 |   34  |     24   |     0
  July   8|  3.00 |  0.28 |   25  |     16   |     0
  July   9|  3.00 |  0.27 |   22  |     13   |     0
  July  10|  2.98 |  0.27 |   47  |     27   |     1
  July  11|  3.00 |  0.27 |   90  |     41   |     1
  July  12|  3.00 |  0.29 |   97  |     21   |     1
  July  13|  3.00 |  0.34 |   90  |     20   |     0
  July  14|  3.00 |  0.40 |   90  |     19   |     0
  July  15|  3.00 |  0.54 |   95  |     18   |     0
  July  16|  3.00 |  0.59 |  120  |     20   |     0
  July  17|  3.00 |  0.58 |   85  |     16   |     0
  July  18|  2.99 |  0.61 |   56  |     13   |     0
  July  19|  3.01 |  0.61 |   41  |     18   |     0
  July  20|  2.99 |  0.51 |   62  |     27   |     0
  July  21|  3.00 |  0.47 |   62  |     32   |     0
  July  22|  3.00 |  0.47 |   80  |     34   |     0
  July  23|  3.01 |  0.49 |  105  |     21   |     0
  July  24|  3.01 |  0.60 |   95  |     19   |     0
  July  25|  3.00 |  0.68 |   77  |     16   |     0
  July  26|  2.99 |  0.68 |   67  |     17   |     0
  July  27|  3.00 |  0.69 |   54  |     20   |     0
  July  28|  3.00 |  0.72 |   46  |     27   |     0
  July  29|  3.00 |  0.74 |   36  |     26   |     0
  July  30|  2.99 |  0.76 |   29  |     19   |     0
  July  31|  2.99 |  0.77 |   21  |     12   |     0
  --------+-------+-------+-------+----------+---------
  Aug.   1|  3.00 |  0.75 |   16  |      9   |     0
  Aug.   2|  3.00 |  0.74 |   15  |      8   |     0
  Aug.   3|  3.00 |  0.74 |   16  |      7   |     0
  Aug.   4|  3.00 |  0.75 |   21  |      6   |     0
  Aug.   5|  3.00 |  0.76 |   29  |      8   |     0
  Aug.   6|  3.00 |  0.79 |   34  |     12   |     0
  Aug.   7|  2.99 |  1.01 |   21  |     12   |     0
  Aug.   8|  3.00 |  1.31 |   19  |     11   |     0
  Aug.   9|  2.98 |  1.44 |   16  |      9   |     0
  Aug.  10|  3.00 |  1.44 |   24  |      9   |     0
  Aug.  11|  3.00 |  1.49 |   62  |     22   |     0
  Aug.  12|  3.00 |  1.62 |  120  |     39   |     0
  Aug.  13|  2.97 |  2.06 |  107  |     22   |     0
  Aug.  14|  2.97 |  3.06 |   82  |     19   |     0
  Aug.  15|  2.81 |  3.91 |   65  |     15   |     0
  Aug.  16|  3.00 |  4.29 |   45  |     18   |     0
  Aug.  17|  3.00 |  3.86 |   35  |     22   |     0
  Aug.  18|  3.00 |  3.47 |   21  |     13   |     0
  Aug.  19|  3.00 |  3.49 |   18  |     10   |     0
  Aug.  20|  3.00 |  3.56 |   20  |      8   |     0
  Aug.  21|  3.00 |  3.58 |   20  |     10   |     0
  Aug.  22|  2.99 |  3.73 |   27  |     13   |     0
  Aug.  23|  3.00 |  4.00 |   49  |     34   |     0
  Aug.  24|  3.00 |  4.05 |   36  |     26   |     0
  Aug.  25|  2.98 |  4.06 |   34  |     24   |     0
  Aug.  26|  3.00 |  4.20 |   21  |     13   |     0
  Aug.  27|  3.00 |  4.31 |   19  |     11   |     0
  Aug.  28|  2.99 |  4.40 |   18  |     10   |     0
  Aug.  29|  3.01 |  4.41 |   17  |      9   |     0
  Aug.  30|  2.98 |  4.46 |   15  |      8   |     0
  Aug.  31|    Scraped.   |   13  |    ...   |   ...
          |  1.88 in. of  |       |          |
          | sand removed. |       |          |
  --------+-------+-------+-------+----------+---------
  Sept.  5|  3.00 |  0.10 |   34  |      4   |     0
  Sept.  6|  3.00 |  0.10 |  160  |      3   |     0
  Sept.  7|  3.00 |  0.09 |   64  |      3   |     0
  Sept.  8|  3.00 |  0.08 |   56  |      4   |     0
  Sept.  9|  3.00 |  0.08 |   59  |      3   |     0
  Sept. 10|  2.97 |  0.07 |   57  |      3   |     0
  Sept. 11|  2.98 |  0.07 |   65  |      2   |     0
  Sept. 12|  2.98 |  0.08 |   72  |      2   |     0
  Sept. 13|  3.00 |  0.08 |   87  |      3   |     0
  Sept. 14|  3.00 |  0.08 |   72  |      3   |     0
  Sept. 15|  3.00 |  0.08 |   65  |      3   |     0
  Sept. 16|  3.00 |  0.08 |   65  |      2   |     0
  Sept. 17|  3.00 |  0.08 |   52  |      2   |     0
  Sept. 18|  3.00 |  0.08 |   60  |      2   |     0
  Sept. 19|  2.98 |  0.08 |   85  |      2   |     0
  Sept. 20|  2.98 |  0.09 |  100  |      2   |     0
  Sept. 21|  2.99 |  0.09 |  120  |      3   |     0
  Sept. 22|  3.00 |  0.09 |  137  |      3   |     0
  Sept. 23|  3.02 |  0.09 |  112  |      4   |     0
  Sept. 24|  3.00 |  0.10 |  100  |      4   |     0
  Sept. 25|  3.00 |  0.11 |  432  |      3   |     0
  Sept. 26|  2.99 |  0.11 |  385  |      2   |     0
  Sept. 27|  3.00 |  0.12 |  245  |      4   |     0
  Sept. 28|  2.98 |  0.13 |  127  |      4   |     0
  Sept. 29|  2.98 |  0.14 |  105  |      4   |     0
  Sept. 30|  2.99 |  0.15 |  115  |      3   |     0
  --------+-------+-------+-------+----------+---------
  Oct.   1|  3.00 |  0.15 |   82  |      3   |     0
  Oct.   2|  2.98 |  0.16 |   65  |      3   |     0
  Oct.   3|  3.00 |  0.17 |   59  |      2   |     0
  Oct.   4|  2.99 |  0.17 |   55  |      2   |     0
  Oct.   5|  2.99 |  0.19 |   59  |      2   |     0
  Oct.   6|  2.98 |  0.20 |   59  |      2   |     0
  Oct.   7|  2.98 |  0.21 |   52  |      2   |     0
  Oct.   8|  2.97 |  0.21 |   54  |      2   |     0
  Oct.   9|  2.98 |  0.22 |   51  |      2   |     0
  Oct.  10|  2.98 |  0.24 |   50  |      2   |     0
  Oct.  11|  2.98 |  0.25 |   47  |      2   |     0
  Oct.  12|  2.97 |  0.26 |   36  |      3   |     0
  Oct.  13|  2.98 |  0.27 |   40  |      4   |     0
  Oct.  14|  2.98 |  0.29 |   47  |      5   |     0
  Oct.  15|  2.99 |  0.31 |   41  |      5   |     0
  Oct.  16|  2.99 |  0.32 |   35  |      4   |     0
  Oct.  17|  2.98 |  0.34 |   30  |      4   |     0
  Oct.  18|  3.00 |  0.35 |   25  |      4   |     0
  Oct.  19|  3.00 |  0.35 |   25  |      4   |     0
  Oct.  20|  3.00 |  0.35 |   20  |      3   |     0
  Oct.  21|  3.00 |  0.35 |   19  |      3   |     0
  Oct.  22|  2.99 |  0.36 |   18  |      3   |     0
  Oct.  23|  2.99 |  0.37 |   15  |      3   |     0
  Oct.  24|  2.98 |  0.38 |   15  |      3   |     0
  Oct.  25|  2.99 |  0.39 |   15  |      3   |     0
  Oct.  26|  2.99 |  0.40 |   15  |      3   |     0
  Oct.  27|  2.99 |  0.41 |   13  |      2   |     0
  Oct.  28|  2.99 |  0.43 |   13  |      2   |     0
  Oct.  29|  2.98 |  0.44 |   25  |      2   |     0
  Oct.  30|  2.99 |  0.46 |   21  |      2   |     0
  Oct.  31|  2.96 |  0.48 |   25  |      3   |     0
  --------+-------+-------+-------+----------+---------
  Nov.   4|  3.00 |  0.51 |  125  |      2   |     0
  Nov.   5|  3.00 |  0.53 |  185  |      2   |     0
  Nov.   6|  2.99 |  0.56 |  170  |      2   |     0
  Nov.   7|  2.99 |  0.60 |  100  |      3   |     0
  Nov.   8|  2.99 |  0.64 |   95  |      3   |     0
  Nov.   9|  2.99 |  0.70 |   80  |      4   |     0
  Nov.  10|  2.99 |  0.79 |   67  |      4   |     0
  Nov.  11|  2.99 |  1.00 |   52  |      6   |     0
  Nov.  12|  2.99 |  1.46 |   40  |      9   |     0
  Nov.  13|  2.98 |  2.09 |   36  |     10   |     0
  Nov.  14|  2.99 |  2.74 |   42  |      9   |     0
  Nov.  15|  2.99 |  2.98 |   35  |      8   |     0
  Nov.  16|  2.99 |  3.03 |   26  |      8   |     0
  Nov.  17|  3.00 |  3.07 |   20  |      6   |     0
  Nov.  18|  3.00 |  3.09 |   17  |      5   |     0
  Nov.  20|  2.99 |  3.17 |   45  |      3   |     0
  Nov.  21|  2.99 |  3.22 |   52  |      3   |     0
  Nov.  22|  2.99 |  3.27 |   65  |      5   |     0
  Nov.  23|  2.99 |  3.33 |   49  |      8   |     0
  Nov.  24|  2.99 |  3.41 |  134  |     11   |     0
  Nov.  25|  2.98 |  3.54 |  225  |     12   |     1
  Nov.  26|  2.98 |  3.68 |  237  |     13   |     1
  Nov.  27|  2.99 |  3.96 |  185  |     16   |     1
  Nov.  28|  2.98 |  4.29 |  130  |     18   |     1
  Nov.  29|  2.97 |  4.48 |   80  |     19   |     1
  Nov.  30|  2.97 |  4.54 |   54  |     15   |     1
  --------+-------+-------+-------+----------+---------
  Dec.   6|      Scraped, 1.62 in. of sand removed.
  Dec.   8|  2.97 |  0.16 |   12  |      3   |     0
  Dec.   9|  2.98 |  0.16 |   11  |      3   |     0
  Dec.  10|  2.98 |  0.15 |   12  |      3   |     0
  Dec.  11|  2.99 |  0.15 |  255  |      3   |     0
  Dec.  12|  3.00 |  0.13 |  212  |      2   |     0
  Dec.  13|  2.98 |  0.13 |  495  |      4   |     0
  Dec.  14|  2.99 |  0.14 |  357  |      5   |     0
  Dec.  15|  2.99 |  0.15 |  157  |      6   |     0
  Dec.  16|  2.98 |  0.16 |   90  |      9   |     0
  Dec.  17|  2.98 |  0.20 |   70  |     12   |     0
  Dec.  18|  2.98 |  0.24 |   49  |     12   |     1
  Dec.  19|  2.98 |  0.29 |   39  |      9   |     1
  Dec.  20|  2.98 |  0.36 |   42  |      7   |     1
  Dec.  21|  2.97 |  0.45 |   26  |      5   |     0
  Dec.  22|  2.98 |  0.57 |   20  |      4   |     0
  Dec.  23|  2.98 |  0.71 |   34  |      3   |     0
  Dec.  24|  2.98 |  0.83 |  195  |      2   |     0
  Dec.  25|  2.98 |  0.97 |  445  |      2   |     0
  Dec.  26|  2.98 |  1.11 |  370  |      2   |     0
  Dec.  27|  2.98 |  1.27 |  245  |      3   |     0
  Dec.  28|  2.98 |  1.40 |  102  |      4   |     0
  Dec.  29|  2.98 |  1.60 |   75  |      3   |     0
  Dec.  30|  2.97 |  1.85 |   56  |      3   |     0
  Dec.  31|  2.98 |  2.07 |   39  |      2   |     0
  --------+-------+-------+-------+----------+---------
  1908.
  --------+-------+-------+-------+----------+---------
  Jan.   1|  2.99 |  2.11 |   31  |      2   |     0
  Jan.   2|  2.98 |  2.17 |   39  |      2   |     0
  Jan.   3|  2.98 |  2.26 |   36  |      2   |     0
  Jan.   4|  2.98 |  2.34 |   32  |      2   |     0
  Jan.   5|  2.98 |  2.41 |   26  |      2   |     0
  Jan.   6|  2.98 |  2.49 |   20  |      2   |     0
  Jan.   7|  2.98 |  2.58 |   20  |      2   |     0
  Jan.   8|  2.99 |  2.61 |   22  |      2   |     0
  Jan.   9|  2.99 |  2.63 |   45  |      2   |     0
  Jan.  10|  2.98 |  2.67 |   70  |      2   |     0
  Jan.  11|  2.98 |  2.72 |   56  |      2   |     0
  Jan.  12|  2.98 |  2.78 |   40  |      2   |     0
  Jan.  13|  2.98 |  2.84 |  110  |      2   |     0
  Jan.  14|  2.98 |  2.95 |  210  |      2   |     0
  Jan.  15|  2.98 |  3.07 |  325  |      3   |     0
  Jan.  16|  2.98 |  3.23 |  360  |      5   |     6
  Jan.  17|  2.97 |  3.73 |  242  |      6   |     0
  Jan.  18|  2.98 |  4.42 |  137  |      6   |     0
  Jan.  19|  2.99 |  4.75 |  117  |      5   |     0
  Jan.  21|        Scrape, 1.45 in. of sand removed.
  Jan.  23|  3.00 |  0.14 |   40  |      3   |     0
  Jan.  24|  3.00 |  0.14 |   40  |      3   |     0
  Jan.  25|  3.00 |  0.13 |   39  |      3   |     0
  Jan.  26|  3.00 |  0.13 |   32  |      3   |     0
  Jan.  27|  3.00 |  0.13 |   32  |      2   |     0
  Jan.  28|  2.99 |  0.15 |   45  |      3   |     0
  Jan.  29|  2.99 |  0.20 |   69  |      6   |     1
  Jan.  30|  2.99 |  0.24 |   57  |      8   |     1
  Jan.  31|  2.99 |  0.30 |   42  |      6   |     1
  --------+-------+-------+-------+----------+---------
  Feb.   1|  2.99 |  0.34 |   39  |      5   |     1
  Feb.   2|  2.99 |  0.41 |   27  |      4   |     1
  Feb.   3|  2.99 |  0.51 |   29  |      3   |     0
  Feb.   4|  2.99 |  0.56 |   25  |      3   |     0
  Feb.   5|  2.99 |  0.58 |   24  |      4   |     0
  Feb.   6|  2.99 |  0.61 |   20  |      6   |     0
  Feb.   7|  3.00 |  0.64 |   17  |      8   |     1
  Feb.   8|  2.99 |  0.66 |   15  |      8   |     1
  Feb.   9|  3.00 |  0.67 |   14  |      8   |     1
  Feb.  10|  2.99 |  0.67 |   11  |      8   |     1
  Feb.  11|  3.00 |  0.66 |   10  |      7   |     1
  Feb.  12|  3.01 |  0.64 |    8  |      6   |     1
  Feb.  13|  3.00 |  0.62 |    9  |      5   |     1
  Feb.  14|  3.00 |  0.61 |    9  |      5   |     1
  Feb.  15|  3.00 |  0.60 |   61  |      5   |     1
  Feb.  16|  3.00 |  0.60 |   80  |      6   |     1
  Feb.  17|  3.00 |  0.62 |   80  |     14   |     1
  Feb.  18|  2.99 |  0.67 |  130  |     20   |     1
  Feb.  19|  2.99 |  0.76 |  320  |     18   |     2
  Feb.  20|  2.99 |  0.83 |  177  |     15   |     2
  Feb.  29|  3.00 |  0.85 |  123  |      8   |     1
  --------+-------+-------+-------+----------+---------
  Mar.   1|  3.00 |  0.87 |   97  |      9   |     1
  Mar.   2|  2.99 |  0.92 |   82  |     13   |     1
  Mar.   3|  2.98 |  0.96 |   87  |     19   |     1
  Mar.   4|  2.99 |  1.02 |   67  |     21   |     1
  Mar.   5|  2.99 |  1.08 |   59  |     25   |     1
  Mar.   6|  2.99 |  1.15 |   72  |     25   |     2
  Mar.   7|  2.98 |  1.21 |   82  |     25   |     2
  Mar.   8|  2.99 |  1.25 |   92  |     29   |     2
  Mar.   9|  2.99 |  1.30 |  125  |     34   |     2
  Mar.  10|  2.99 |  1.35 |  142  |     39   |     2
  Mar.  11|  2.99 |  1.39 |  155  |     35   |     2
  Mar.  12|  2.99 |  1.42 |  135  |     29   |     2
  Mar.  13|  2.99 |  1.46 |  122  |     19   |     2
  Mar.  14|  2.99 |  1.47 |   97  |     12   |     1
  Mar.  15|  2.99 |  1.48 |   77  |      8   |     1
  Mar.  16|  3.00 |  1.52 |   65  |      9   |     0
  Mar.  17|  2.99 |  1.66 |   59  |      7   |     0
  Mar.  18|  2.99 |  1.72 |   67  |     11   |     1
  Mar.  19|  2.99 |  1.75 |   60  |     24   |     1
  Mar.  20|  2.99 |  1.81 |   57  |     25   |     1
  Mar.  21|  2.99 |  1.89 |   67  |     22   |     1
  Mar.  22|  2.99 |  1.95 |   80  |     21   |     1
  Mar.  23|  3.00 |  2.00 |   90  |     26   |     1
  Mar.  24|  2.98 |  2.06 |   82  |     32   |     1
  Mar.  25|  2.99 |  2.17 |   67  |     39   |     1
  Mar.  26|  2.99 |  2.24 |   60  |     36   |     1
  Mar.  27|  2.99 |  2.29 |   59  |     30   |     1
  Mar.  28|  3.00 |  2.32 |   51  |     21   |     1
  Mar.  29|  2.99 |  2.35 |   31  |     18   |     1
  Mar.  30|  3.00 |  2.38 |   30  |     14   |     1
  Mar.  31|  2.99 |  2.43 |   39  |      9   |     1
  --------+-------+-------+-------+----------+---------
  Apr.   1|  2.99 |  2.50 |   44  |      7   |     1
  Apr.   2|  2.99 |  2.58 |   42  |      8   |     1
  Apr.   3|  2.99 |  2.65 |   41  |     11   |     1
  Apr.   4|  2.99 |  2.74 |   54  |     12   |     1
  Apr.   5|  3.00 |  2.82 |   50  |     12   |     1
  Apr.   6|  2.99 |  2.88 |   41  |     14   |     1
  Apr.   7|  2.99 |  2.98 |   35  |     13   |     1
  Apr.   8|  2.98 |  3.15 |   39  |     11   |     1
  Apr.   9|  2.99 |  3.35 |   40  |      8   |     1
  Apr.  10|  2.98 |  3.50 |   40  |      8   |     1
  Apr.  11|  2.99 |  3.65 |   45  |      7   |     0
  Apr.  12|  2.99 |  3.79 |   52  |      5   |     0
  Apr.  13|  2.99 |  3.92 |   50  |      4   |     0
  Apr.  14|  2.99 |  4.05 |   45  |      4   |     0
  Apr.  15|  2.99 |  4.16 |   45  |      3   |     0
  Apr.  16|   ... |  4.24 |   45  |      3   |     0
  Apr.  21|     Scraped, 0.12 in. of sand removed.
  Apr.  23|   ... |  0.13 |   25  |      2   |     0
  Apr.  24|  3.00 |  0.12 |   21  |      2   |     0
  Apr.  25|  3.00 |  0.10 |   20  |      2   |     0
  Apr.  26|  3.00 |  0.10 |   21  |      3   |     0
  Apr.  27|  3.00 |  0.10 |   18  |      3   |     0
  Apr.  28|  3.00 |  0.10 |   20  |      3   |     0
  Apr.  29|  3.00 |  0.09 |   24  |      3   |     0
  Apr.  30|  3.00 |  0.09 |   21  |      3   |     0
  --------+-------+-------+-------+----------+---------
  May    1|  3.00 |  0.09 |   32  |      3   |     0
  May    2|  3.00 |  0.09 |   26  |      3   |     0
  May    3|  3.00 |  0.11 |   22  |      5   |     0
  May    4|  3.00 |  0.11 |   19  |      4   |     0
  May    5|  3.00 |  0.11 |   18  |      4   |     0
  May    6|  2.99 |  0.12 |   18  |      3   |     0
  May    7|  3.00 |  0.13 |   19  |      3   |     0
  May    8|  3.00 |  0.14 |   19  |      3   |     0
  May    9|  2.99 |  0.14 |   18  |      3   |     0
  May   10|  3.00 |  0.14 |   30  |      3   |     0
  May   11|  3.00 |  0.13 |   60  |      3   |     0
  May   12|  3.00 |  0.13 |   70  |      3   |     0
  May   13|  3.00 |  0.13 |   66  |      7   |     0
  May   14|  3.00 |  0.14 |   45  |      9   |     0
  May   15|  2.99 |  0.14 |   39  |      7   |     0
  May   16|  2.99 |  0.22 |   49  |      6   |     0
  May   17|  2.99 |  0.33 |   46  |      4   |     0
  May   18|  2.99 |  0.44 |   31  |      3   |     0
  May   19|  2.98 |  0.62 |   36  |      3   |     0
  May   20|  2.99 |  0.75 |   41  |      3   |     0
  May   21|  2.99 |  0.89 |   31  |      4   |     0
  May   22|  2.99 |  1.01 |   50  |      5   |     0
  May   23|  2.99 |  1.12 |  127  |      5   |     0
  May   24|  2.99 |  1.20 |  110  |      6   |     0
  May   25|  2.99 |  1.24 |   90  |      9   |     0
  May   26|  2.98 |  1.31 |  135  |     11   |     0
  May   27|  2.97 |  1.54 |  110  |     12   |     0
  May   28|  2.97 |  1.81 |   90  |     10   |     0
  May   29|  2.97 |  2.08 |   70  |      7   |     0
  May   30|  2.97 |  2.36 |   50  |      5   |     0
  May   31|  2.98 |  2.63 |   34  |      4   |     0
  --------+-------+-------+-------+----------+---------
  June   1|  2.98 |  2.77 |   35  |      2   |     0
  June   2|  2.98 |  2.84 |   39  |      2   |     0
  June   3|  2.98 |  3.02 |   35  |      3   |     0
  June   4|  3.00 |  3.01 |   30  |      4   |     0
  June   5|  3.00 |  2.97 |   30  |      5   |     0
  June   6|  3.01 |  2.81 |   27  |      5   |     0
  June   7|  3.01 |  2.62 |   22  |      5   |     0
  June   8|  3.01 |  2.38 |   20  |      4   |     0
  June   9|  3.00 |  2.19 |   20  |      3   |     0
  June  10|  3.01 |  2.02 |   17  |      3   |     0
  June  11|  2.99 |  1.89 |   12  |      3   |     0
  June  12|  2.98 |  1.92 |   11  |      2   |     0
  June  13|  2.98 |  1.99 |   36  |      2   |     0
  June  14|  2.98 |  2.08 |   39  |      2   |     0
  June  15|  2.98 |  2.25 |   25  |      4   |     0
  June  16|  2.98 |  2.54 |   34  |      5   |     0
  June  17|  2.97 |  2.85 |   64  |      5   |     0
  June  18|  2.97 |  3.20 |   57  |      5   |     0
  June  19|  2.98 |  3.47 |   46  |      7   |     0
  June  20|  2.99 |  3.73 |   37  |      8   |     0
  June  21|  2.99 |  4.10 |   29  |      8   |     0
  June  22|  2.99 |  4.44 |   25  |      6   |     0
  June  23|  2.99 |  4.61 |   25  |      5   |     0
  June  26|  3.01 |  0.09 |   15  |      2   |     0
  June  27|  3.00 |  0.09 |   12  |      2   |     0
  June  28|  3.00 |  0.09 |    9  |      2   |     0
  June  29|  3.00 |  0.08 |    8  |      2   |     0
  June  30|  3.00 |  0.07 |   10  |      2   |     0
  --------+-------+-------+-------+----------+---------
  July   1|  3.00 |  0.07 |    6  |      2   |     0
  July   2|  3.00 |  0.07 |    8  |      2   |     0
  July   3|  3.00 |  0.07 |    8  |      2   |     0
  July   4|  3.00 |  0.07 |    9  |      2   |     0
  July   5|  3.00 |  0.07 |   10  |      2   |     0
  July   6|  3.00 |  0.07 |    9  |      2   |     0
  July   7|  3.00 |  0.07 |    8  |      2   |     0
  July   8|  3.00 |  0.07 |    9  |      2   |     0
  July   9|  3.00 |  0.07 |    8  |      2   |     0
  July  10|   ... |   ... |   ... |    ...   |   ...
  July  11|  3.00 |  0.08 |   12  |      2   |     0
  July  12|  3.00 |  0.08 |   11  |      2   |     0
  July  13|  3.00 |  0.08 |   10  |      2   |     0
  July  14|  3.00 |  0.09 |   16  |      2   |     0
  July  15|  3.00 |  0.09 |   17  |      2   |     0
  July  16|  3.00 |  0.10 |   14  |      2   |     6
  July  17|  3.00 |  0.10 |   10  |      2   |     0
  July  18|  3.00 |  0.11 |   11  |      2   |     0
  July  19|  3.00 |  0.11 |   12  |      2   |     0
  July  20|  3.00 |  0.12 |   10  |      2   |     0
  July  21|  3.00 |  0.12 |   10  |      2   |     0
  July  22|  3.00 |  0.13 |   13  |      2   |     0
  July  23|  2.99 |  0.13 |   54  |      2   |     0
  July  24|  2.99 |  0.14 |  305  |      2   |     0
  July  25|  3.00 |  0.15 |  330  |      4   |     0
  July  26|  3.00 |  0.15 |  290  |      9   |     0
  July  27|  3.00 |  0.16 |  335  |     11   |     0
  July  28|  2.99 |  0.17 |  170  |     10   |     0
  July  29|  3.00 |  0.17 |  180  |      8   |     0
  July  30|  2.99 |  0.18 |  237  |      7   |     0
  July  31|  3.00 |  0.19 |  250  |      6   |     0
  ========+=======+=======+=======+==========+=========


                 ~Table 19~--(_Continued._)
  ========+==============================+============
          |         ~Bacteria.~          |~Coagulant.~
          +---------+----------+---------+------------
   Date.  | Applied | Effluent,|Effluent,|Grains, per
          |  water. |coagulant.|  sand.  |  gallon.
  --------+---------+----------+---------+------------
  1907.
  --------+---------+----------+---------+------------
  Feb.  12|    ...  |     ...  |    ...  |     ...
  Feb.  13|     600 |     ...  |    ...  |     ...
  Feb.  14|     650 |     ...  |    ...  |     ...
  Feb.  15|     600 |     ...  |  2,500  |     ...
  Feb.  16|     850 |     ...  |  1,600  |     ...
  Feb.  17|     ... |     ...  |    ...  |     ...
  Feb.  18|   1,200 |     ...  |    300  |     ...
  Feb.  21|   1,800 |     ...  |    550  |     ...
  Feb.  22|       2 |          | Holiday.|
  Feb.  23|   1,600 |     ...  |  1,100  |     ...
  Feb.  24|       3 |          | Sunday. |
  Feb.  25|   1,400 |     ...  |    600  |     ...
  Feb.  26|     700 |     ...  |    650  |     ...
  Feb.  27|     700 |     ...  |  2,300  |     ...
  Feb.  28|     800 |     ...  |    550  |     ...
  --------+---------+----------+---------+------------
  Mar.   1|     650 |     ...  |    300  |     ...
  Mar.   2|   1,000 |     ...  |    270  |     ...
  Mar.   3|         |  Sunday. |         |
  Mar.   4|   1,200 |     ...  |    140  |    1.45
  Mar.   5|  13,000 |     ...  |    190  |    1.94
  Mar.   6|  18,000 |   2,100  |    160  |    2.03
  Mar.   7|  24,000 |   3,500  |    160  |    1.50
  Mar.   8|  22,000 |   1,800  |    130  |    1.38
  Mar.   9|  24,000 |   3,500  |    130  |    1.37
  Mar.  10|         |  Sunday. |         |    1.26
  Mar.  11|  18,000 |   6,000  |    120  |    1.24
  Mar.  12|  11,000 |   9,000  |    140  |    1.08
  Mar.  13|   9,000 |   5,000  |    120  |    0.94
  Mar.  14|   5,500 |   3,600  |     90  |       0
  Mar.  15|   6,500 |   3,800  |     85  |       0
  Mar.  16|   5,000 |   3,500  |    100  |    1.26
  Mar.  17|         |  Sunday. |         |    1.52
  Mar.  18|   9,000 |   1,900  |     85  |    1.75
  Mar.  19|   7,000 |     700  |     65  |    1.57
  Mar.  20|   4,800 |   1,500  |     60  |    1.31
  Mar.  21|   8,500 |   1,500  |     70  |    1.38
  Mar.  22|   7,500 |   1,100  |     35  |    1.57
  Mar.  23|   7,500 |     470  |     55  |    1.68
  Mar.  24|         |  Sunday. |         |    1.52
  Mar.  25|Scraped, 1.03 in. of sand removed.
  Mar.  27|   2,200 |     480  |     60  |    1.08
  Mar.  28|   1,300 |     250  |     80  |    1.00
  Mar.  29|     700 |     240  |     65  |       0
  Mar.  30|{Shut down to fill coagulant basin.
          |{    310 |     ...  |    ...  |       0
  Mar.  31|         |  Sunday. |         |       0
  --------+---------+----------+---------+------------
  Apr.   1|     600 |   1,000  |     43  |       0
  Apr.   2|     270 |   Lost.  |     35  |       0
  Apr.   3|     460 |    Apr.  |     41  |       0
  Apr.   4|     280 |     550  |     27  |       0
  Apr.   5|     450 |   1,000  |     60  |       0
  Apr.   6|     320 |      50  |     35  |       0
  Apr.   7|  Sunday.|       0  |         |
  Apr.   8|     330 |     650  |     22  |       0
  Apr.   9|     140 |     750  |     21  |       0
  Apr.  10|     750 |   5,000  |     29  |       0
  Apr.  11|   4,000 |     550  |     25  |    1.11
  Apr.  12|  14,000 |   2,200  |     17  |    1.15
  Apr.  13|  13,000 |   3,900  |     25  |    1.14
  Apr.  14|         |  Sunday. |         |    1.17
  Apr.  15|   7,060 |   2,200  |     19  |    1.09
  Apr.  16|   3,600 |     900  |     22  |    1.08
  Apr.  17|   1,600 |   1,100  |     12  |       0
  Apr.  18|   1,810 |   1,870  |     14  |       0
  Apr.  19|     790 |     910  |     14  |       0
  Apr.  20|     540 |     480  |     15  |       0
  Apr.  21|         |  Sunday. |         |     ...
  Apr.  22|     235 |     420  |     21  |       0
  Apr.  23|     170 |     420  |      8  |       0
  Apr.  24|     150 |     250  |     17  |       0
  Apr.  25|     700 |     260  |     19  |       0
  Apr.  26|   1,200 |     320  |     80  |       0
  Apr.  27|   1,700 |   1,500  |     70  |       0
  Apr.  28|         |  Sunday. |         |       0
  Apr.  29|     600 |   1,400  |     19  |       0
  Apr.  30|     550 |   1,200  |     14  |       0
  --------+---------+----------+---------+------------
  May    1|     500 |   1,300  |     20  |       0
  May    2|     500 |     850  |     16  |       0
  May    3|     280 |     650  |     34  |       0
  May    4|     400 |     550  |     24  |       0
  May    5|         |  Sunday. |         |       0
  May    6|     390 |     460  |     80  |       0
  May    7|     190 |     ...  |     18  |       0
  May    8|     ... |     ...  |    ...  |       0
  May    9|     390 |   1,100  |     14  |       0
  May   10|     300 |     500  |     21  |       0
  May   11|     390 |     650  |     16  |       0
  May   12|         |  Sunday. |         |       0
  May   13|     600 |     470  |     27  |       0
  May   14|     500 |     550  |     25  |       0
  May   15|     500 |     900  |     23  |       0
  May   16|     290 |   2,500  |     25  |       0
  May   17|     260 |   2,000  |     16  |       0
  May   18|     190 |     600  |     19  |       0
  May   19|         |  Sunday. |         |       0
  May   20|     260 |     450  |     15  |       0
  May   21|     260 |     330  |     14  |       0
  May   22|     280 |     390  |     22  |       0
  May   23|     130 |     240  |     19  |       0
  May   24|     170 |     240  |     30  |       0
  May   25|     340 |     400  |     41  |       0
  May   26|         |  Sunday. |         |       0
  May   27|     Shut down to scrape sand filter;
          |    1.09 in. of sand removed. Cleaning
  May   28|  coagulant basin and treating coagulant
          |         basin with 1:2,000,000
  May   29|      solution of copper sulphate.
  May   30|         | Holiday. |         |       0
  May   31|     380 |  18,000  |    150  |       0
  --------+---------+----------+---------+------------
  June   1|     900 |   7,000  |    150  |       0
  June   2|         |  Sunday. |         |       0
  June   3|     550 |   8,000  |    130  |       0
  June   4|   6,500 |   7,500  |    140  |       0
  June   5|   3,200 |   3,600  |    110  |       0
  June   6|   1,500 |     800  |     60  |    1.17
  June   7|   2,100 |   1,500  |     90  |    1.18
  June   8|     660 |   1,000  |     60  |       0
  June   9|         |  Sunday. |         |       0
  June  10|     240 |     400  |     32  |       0
  June  11|     280 |     300  |     31  |       0
  June  12|     330 |    ...   |     28  |       0
  June  13|     480 |     480  |     39  |       0
  June  14|     440 |     550  |     32  |       0
  June  15|     420 |     450  |     27  |       0
  June  16|         |  Sunday. |         |       0
  June  17|     340 |     750  |     14  |       0
  June  18|     440 |     750  |     21  |       0
  June  19|     500 |     460  |     35  |       0
  June  20|     330 |     440  |     88  |       0
  June  21|     170 |     370  |     23  |       0
  June  22|     100 |     300  |     17  |       0
  June  23|         |  Sunday. |         |       0
  June  24|   1,700 |     350  |     22  |    1.59
  June  25|     400 |     250  |     16  |    1.55
  June  26|     750 |     330  |    ...  |       0
  June  27|    ...  |   1,400  |    ...  |       0
  June  28|    ...  |   1,400  |    120  |       0
  June  29|     220 |     300  |    ...  |       0
  June  30|         |  Sunday. |         |       0
  --------+---------+----------+---------+------------
  July   1|     400 |     600  |     85  |       0
  July   2|     180 |   1,000  |     50  |       0
  July   3|     350 |     310  |     21  |       0
  July   4|         | Holiday. |         |
  July   5|     550 |     400  |     41  |       0
  July   6|     250 |     280  |     22  |       0
  July   7|         |  Sunday. |         |       0
  July   8|     220 |     260  |     27  |       0
  July   9|      50 |      40  |     19  |       0
  July  10|   Lost. |   Lost.  |  Lost.  |       0
  July  11|     150 |      50  |      8  |    1.27
  July  12|     300 |     200  |     13  |    1.27
  July  13|     220 |     160  |     17  |    1.27
  July  14|         |  Sunday. |         |    1.27
  July  15|     375 |     150  |         |    1.27
  July  16|   Lost. |      50  |  Lost.  |    1.36
  July  17|     270 |      60  |      3  |    1.26
  July  18|   1,675 |      70  |         |    1.17
  July  19|     450 |     700  |     11  |       0
  July  20|     300 |     720  |      8  |       0
  July  21|         |  Sunday. |         |       0
  July  22|   1,400 |     560  |     14  |    1.17
  July  23|   3,700 |     490  |     40  |    1.25
  July  24|     770 |     110  |     80  |    1.27
  July  25|     250 |      80  |      5  |    1.22
  July  26|     140 |      40  |      4  |       0
  July  27|     300 |     130  |     21  |       0
  July  28|         |  Sunday. |         |       0
  July  29|     470 |     290  |    100  |       0
  July  30|   Lost. |   Lost.  |   Lost. |       0
  July  31|    July |    July  |    July |       0
  --------+---------+----------+---------+------------
  Aug.   1|   Lost. |   Lost.  |   Lost. |       0
  Aug.   2|     130 |     140  |      4  |       0
  Aug.   3|     120 |     180  |      6  |       0
  Aug.   4|         |  Sunday. |         |
  Aug.   5|     230 |     100  |     44  |       0
  Aug.   6|      85 |     470  |    ...  |       0
  Aug.   7|     200 |     450  |    ...  |       0
  Aug.   8|     100 |     180  |     45  |       0
  Aug.   9|      75 |      80  |     16  |       0
  Aug.  10|      60 |      90  |     11  |       0
  Aug.  11|         |  Sunday. |         |
  Aug.  12|     620 |     260  |     16  |    1.45
  Aug.  13|     820 |     520  |     10  |    1.38
  Aug.  14|     850 |     120  |     26  |    1.22
  Aug.  15|     150 |     260  |      6  |    1.17
  Aug.  16|     270 |     340  |     17  |       0
  Aug.  17|     340 |     200  |     13  |       0
  Aug.  18|         |  Sunday. |         |
  Aug.  19|     180 |     220  |     17  |       0
  Aug.  20|     210 |     180  |     16  |       0
  Aug.  21|   1,300 |     650  |      8  |       0
  Aug.  22|   3,800 |     360  |      6  |       0
  Aug.  23|   2,500 |     700  |     10  |       0
  Aug.  24|   3,900 |     630  |     12  |       0
  Aug.  25|         |  Sunday. |         |
  Aug.  26|     700 |     310  |     16  |       0
  Aug.  27|     470 |     250  |     12  |       0
  Aug.  28|     500 |     160  |     18  |       0
  Aug.  29|     360 |     110  |      9  |       0
  Aug.  30|     320 |     310  |     14  |       0
  Aug.  31|     200 |     100  |    ...  |       0
  --------+---------+----------+---------+------------
  Sept.  5|     360 |     950  |    ...  |    1.04
  Sept.  6|  15,000 |   1,500  |    190  |    1.35
  Sept.  7|   2,000 |     260  |    100  |    1.20
  Sept.  8|         |  Sunday. |    ...  |    1.04
  Sept.  9|     220 |     180  |     38  |    1.04
  Sept. 10|  18,000 |     150  |     29  |    1.06
  Sept. 11|   2,700 |     200  |     37  |    1.04
  Sept. 12|   1,000 |     125  |     19  |    1.04
  Sept. 13|   2,300 |     200  |     72  |    1.20
  Sept. 14|   2,400 |     360  |     36  |    1.12
  Sept. 15|         |  Sunday. |         |    1.04
  Sept. 16|    Lost.|   Lost.  |     38  |    1.04
  Sept. 17|     420 |     200  |     38  |    1.07
  Sept. 18|     900 |     200  |     17  |    1.07
  Sept. 19|   2,000 |     220  |     25  |    1.12
  Sept. 20|   4,200 |     320  |     31  |    1.24
  Sept. 21|   1,100 |     160  |     19  |    1.33
  Sept. 22|         |  Sunday. |         |    1.45
  Sept. 23|   2,100 |     190  |     15  |    1.41
  Sept. 24|   4,000 |     620  |     13  |    1.33
  Sept. 25|  56,000 |     290  |      7  |    1.83
  Sept. 26|   1,300 |     950  |     19  |    2.34
  Sept. 27|   4,000 |   Lost.  |     20  |    1.91
  Sept. 28|  15,000 |   1,000  |      8  |    1.54
  Sept. 29|         |  Sunday. |         |    1.34
  Sept. 30|   Lost. |   Lost.  |     46  |    1.35
  --------+---------+----------+---------+------------
  Oct.   1|     600 |   1,700  |     22  |    1.24
  Oct.   2|   4,400 |     550  |      8  |    1.09
  Oct.   3|     900 |     330  |     15  |    1.04
  Oct.   4|     850 |     250  |     11  |    1.03
  Oct.   5|   2,000 |     450  |     25  |    1.04
  Oct.   6|         |  Sunday. |         |    1.04
  Oct.   7|   1,250 |   2,300  |     42  |    1.04
  Oct.   8|  11,000 |     100  |     15  |    1.04
  Oct.   9|   2,000 |   1,600  |      7  |    1.04
  Oct.  10|     800 |   Lost.  |     24  |    1.04
  Oct.  11|   2,000 |   1,200  |     21  |       0
  Oct.  12|   1,200 |   1,200  |     19  |       0
  Oct.  13|         |  Sunday. |         |       0
  Oct.  14|   1,200 |     830  |     25  |       0
  Oct.  15|     900 |   Lost.  |    105  |       0
  Oct.  16|   Lost. |     550  |     19  |       0
  Oct.  17|     550 |     800  |     21  |       0
  Oct.  18|     260 |     350  |      9  |       0
  Oct.  19|     750 |     310  |     35  |       0
  Oct.  20|         | Sunday.  |         |       0
  Oct.  21|     480 |     540  |     35  |       0
  Oct.  22|     230 |     440  |     17  |       0
  Oct.  23|     250 |     440  |     39  |       0
  Oct.  24|     300 |     500  |     60  |       0
  Oct.  25|     450 |     410  |     65  |       0
  Oct.  26|     450 |     500  |     44  |       0
  Oct.  27|         |  Sunday. |         |       0
  Oct.  28|     190 |     500  |     50  |       0
  Oct.  29|     380 |      60  |     75  |       0
  Oct.  30|     450 |     180  |      3  |       0
  Oct.  31|   2,300 |     390  |     75  |       0
  --------+---------+----------+---------+------------
  Nov.   4|     ... |     ...  |    ...  |       0
  Nov.   5|   6,000 |   1,600  |     90  |    1.70
  Nov.   6|   5,000 |   3,900  |      6  |    1.70
  Nov.   7|  14,000 |     300  |      9  |    1.48
  Nov.   8|   1,900 |     230  |      2  |    1.27
  Nov.   9|   4,000 |   2,700  |    200  |       0
  Nov.  10|         |  Sunday. |         |       0
  Nov.  11|   1,900 |   2,000  |    200  |       0
  Nov.  12|   7,500 |   2,300  |    160  |       0
  Nov.  13|   1,600 |   1,100  |    170  |       0
  Nov.  14|   2,700 |     950  |    130  |       0
  Nov.  15|   1,800 |     800  |     11  |       0
  Nov.  16|   1,100 |     800  |     90  |       0
  Nov.  17|         |  Sunday. |         |       0
  Nov.  18|   1,600 |     700  |    100  |       0
  Nov.  20|   6,500 |     120  |    120  |       0
  Nov.  21|   9,900 |   1,000  |     80  |       0
  Nov.  22|  10,000 |  3, 200  |     90  |       0
  Nov.  23|  18,000 |  2, 400  |    100  |       0
  Nov.  24|         |  Sunday. |         |       0
  Nov.  25|  50,000 |  2, 100  |     65  |    1.68
  Nov.  26|  40,000 |  2, 400  |     95  |    1.76
  Nov.  27|  16,000 |  2, 600  |     60  |    1.74
  Nov.  28|         | Holiday. |         |    1.57
  Nov.  29|  10,000 |  2, 500  |     65  |    1.50
  Nov.  30|   3,800 |  1, 900  |     85  |       0
  --------+---------+----------+---------+------------
  Dec.   6|   Scraped, 1.62 in. of sand removed.
  Dec.   8|         |  Sunday. |         |    1.17
  Dec.   9|   1,200 |     410  |     10  |    1.17
  Dec.  10|     800 |     550  |    150  |    1.17
  Dec.  11|   6,500 |     600  |    130  |    1.52
  Dec.  12|  48,000 |     500  |    130  |    1.99
  Dec.  13|  42,000 |     500  |    120  |    2.06
  Dec.  14|  49,000 |     750  |    150  |    2.12
  Dec.  15|         |  Sunday. |         |    1.69
  Dec.  16|  19,000 |     900  |     20  |    1.28
  Dec.  17|  21,000 |     400  |    170  |    1.17
  Dec.  18|   6,500 |   7,000  |    350  |    1.17
  Dec.  19|   Lost. |   Lost.  |   Lost. |    1.17
  Dec.  20|    Dec. |    Dec.  |    Dec. |    1.17
  Dec.  21|    Dec. |    Dec.  |    Dec. |    1.17
  Dec.  22|         |  Sunday. |         |    1.17
  Dec.  23|   1,400 |   1,300  |    220  |    1.17
  Dec.  24|   9,000 |   1,000  |    140  |    1.49
  Dec.  25|         | Holiday. |         |    2.43
  Dec.  26|  51,000 |   1,000  |     39  |    2.15
  Dec.  27|  55,000 |   1,600  |     70  |    1.91
  Dec.  28|  10,000 |   1,000  |     80  |    1.50
  Dec.  29|         |  Sunday. |         |    1.21
  Dec.  30|   4,400 |     700  |     80  |    1.17
  Dec.  31|  14,000 |   1,200  |     65  |    1.17
  --------+---------+----------+---------+------------
  1908.
  --------+---------+----------+---------+------------
  Jan.   1|         | Holiday. |         |    1.17
  Jan.   2|   4,400 |     700  |     19  |    1.17
  Jan.   3|   3,100 |   1,000  |     13  |    1.17
  Jan.   4|   2,400 |     550  |     19  |    1.17
  Jan.   5|         |  Sunday. |         |    1.17
  Jan.   6|     600 |     230  |     18  |    1.17
  Jan.   7|   1,100 |     370  |     12  |    1.17
  Jan.   8|   1,900 |   1,100  |     20  |    1.17
  Jan.   9|  13,000 |   1,200  |     22  |    1.21
  Jan.  10|  10,000 |     700  |     16  |    1.17
  Jan.  11|  16,000 |   1,200  |     11  |    1.17
  Jan.  12|         |  Sunday. |         |    1.17
  Jan.  13|   8,500 |      90  |      6  |    1.27
  Jan.  14|  16,000 |     150  |     23  |    1.56
  Jan.  15|  24,000 |   1,100  |     19  |    1.92
  Jan.  16|  28,000 |   1,000  |     14  |    2.10
  Jan.  17|  65,000 |     490  |     23  |    1.91
  Jan.  18|   7,000 |   1,600  |     14  |    1.66
  Jan.  19|         |  Sunday. |         |    1.50
  Jan.  21|   Scrape, 1.45 in. of sand removed.
  Jan.  23|     ... |     ...  |    ...  |    1.17
  Jan.  24|   2,300 |     550  |     55  |    1.17
  Jan.  25|   1,100 |     850  |     95  |       0
  Jan.  26|         |  Sunday. |         |       0
  Jan.  27|     300 |     280  |     60  |       0
  Jan.  28|   1,200 |     700  |     70  |       0
  Jan.  29|   1,000 |     900  |     75  |       0
  Jan.  30|   1,400 |     650  |     50  |       0
  Jan.  31|   1,100 |     600  |     36  |       0
  --------+---------+----------+---------+------------
  Feb.   1|     750 |      50  |     25  |       0
  Feb.   2|         |  Sunday. |         |       0
  Feb.   3|   1,300 |     220  |     16  |       0
  Feb.   4|     600 |     370  |     10  |       0
  Feb.   5|     750 |     700  |     21  |       0
  Feb.   6|   2,000 |     650  |      4  |       0
  Feb.   7|     ... |     410  |     26  |       0
  Feb.   8|     900 |     160  |     42  |       0
  Feb.   9|            Sunday.           |       0
  Feb.  10|     850 |     450  |     18  |       0
  Feb.  11|   1,000 |     600  |     26  |       0
  Feb.  12|     750 |     350  |     16  |       0
  Feb.  13|     700 |     120  |     10  |       0
  Feb.  14|   1,200 |     950  |     43  |       0
  Feb.  15|   5,500 |   1,000  |     23  |       0
  Feb.  16|         |  Sunday. |         |       0
  Feb.  17|  33,000 |   6,100  |     36  |       0
  Feb.  18|     ... |   2,000  |     11  |       0
  Feb.  19|  28,000 |   9,000  |    120  |       0
  Feb.  20|  22,000 |   8,500  |    190  |       0
  Feb.  29|     ... |     ...  |    ...  |       0
  --------+---------+----------+---------+------------
  Mar.   1|         |  Sunday. |         |       0
  Mar.   2|   8,000 |   4,400  |     50  |       0
  Mar.   3|  11,000 |   2,100  |     26  |       0
  Mar.   4|   6,000 |   4,700  |      7  |       0
  Mar.   5|   4,400 |  10,000  |     36  |       0
  Mar.   6|   7,000 |   7,400  |     50  |       0
  Mar.   7|   9,500 |   6,500  |     28  |       0
  Mar.   8|         |  Sunday. |         |       0
  Mar.   9|  11,000 |   4,800  |     25  |       0
  Mar.  10|   8,500 |   1,200  |     23  |       0
  Mar.  11|   6,500 |   2,400  |     20  |       0
  Mar.  12|   5,900 |   1,500  |     11  |       0
  Mar.  13|   1,900 |   1,100  |     12  |       0
  Mar.  14|   1,800 |     700  |      6  |       0
  Mar.  15|         |  Sunday. |         |       0
  Mar.  16|   1,400 |     700  |      8  |       0
  Mar.  17|     900 |     800  |     11  |       0
  Mar.  18|   1,000 |     650  |      8  |       0
  Mar.  19|     ... |     600  |     18  |       0
  Mar.  20|   1,300 |     750  |     20  |       0
  Mar.  21|     800 |     480  |     18  |       0
  Mar.  22|         |  Sunday. |         |       0
  Mar.  23|   4,600 |     440  |     19  |       0
  Mar.  24|   2,500 |   1,200  |     10  |       0
  Mar.  25|   1,600 |     650  |     20  |       0
  Mar.  26|     550 |     410  |      7  |       0
  Mar.  27|     900 |     900  |     29  |       0
  Mar.  28|     650 |     250  |     42  |       0
  Mar.  29|         |  Sunday. |         |       0
  Mar.  30|     500 |     650  |     28  |       0
  Mar.  31|     750 |     290  |     30  |       0
  --------+---------+----------+---------+------------
  Apr.   1|     750 |     390  |     32  |       0
  Apr.   2|   1,100 |     280  |     47  |       0
  Apr.   3|   1,500 |     550  |     70  |       0
  Apr.   4|     700 |     380  |      4  |       0
  Apr.   5|         |  Sunday. |         |       0
  Apr.   6|     440 |     150  |      4  |       0
  Apr.   7|     650 |     270  |     42  |       0
  Apr.   8|     550 |     210  |     65  |       0
  Apr.   9|     390 |     160  |     95  |       0
  Apr.  10|     500 |     130  |    130  |       0
  Apr.  11|     430 |     145  |    100  |       0
  Apr.  12|         |  Sunday. |         |       0
  Apr.  13|     490 |     160  |     80  |       0
  Apr.  14|     550 |     170  |     90  |       0
  Apr.  15|     420 |     160  |     12  |       0
  Apr.  16|     360 |     130  |     90  |       0
  Apr.  21|   Scraped, 0.12 in. of sand removed.
  Apr.  23|     140 |     140  |    ...  |       0
  Apr.  24|     200 |   Lost.  |    150  |       0
  Apr.  25|      85 |     550  |     45  |       0
  Apr.  26|         |  Sunday. |         |       0
  Apr.  27|      95 |     850  |     50  |       0
  Apr.  28|      70 |     220  |     48  |       0
  Apr.  29|     110 |     210  |     95  |       0
  Apr.  30|      70 |     140  |     29  |       0
  --------+---------+----------+---------+------------
  May    1|     130 |     210  |     65  |       0
  May    2|     140 |     140  |     55  |       0
  May    3|         |  Sunday. |         |       0
  May    4|      85 |     210  |     75  |       0
  May    5|     130 |     150  |     48  |       0
  May    6|     230 |     430  |     50  |       0
  May    7|     160 |      90  |     40  |       0
  May    8|     375 |     425  |      7  |       0
  May    9|   1,209 |     180  |      6  |       0
  May   10|         |  Sunday. |         |       0
  May   11|   2,800 |     150  |     12  |       0
  May   12|   2,900 |     225  |     26  |       0
  May   13|   1,800 |     450  |     53  |       0
  May   14|   2,700 |     550  |     10  |       0
  May   15|     950 |     300  |     65  |       0
  May   16|     800 |     250  |     49  |       0
  May   17|         |  Sunday. |         |       0
  May   18|     700 |   1,700  |     80  |       0
  May   19|     375 |     950  |     53  |       0
  May   20|     425 |     700  |     46  |       0
  May   21|     300 |     600  |      6  |       0
  May   22|     950 |     230  |     17  |       0
  May   23|   2,400 |      32  |     28  |       0
  May   24|         | Sunday.  |         |       0
  May   25|   1,100 |     850  |      9  |       0
  May   26|   3,200 |     150  |     17  |       0
  May   27|   1,450 |     175  |      8  |       0
  May   28|   1,000 |     132  |      7  |       0
  May   29|   1,100 |     230  |      8  |       0
  May   30|         | Holiday. |         |       0
  May   31|         |  Sunday. |         |       0
  --------+---------+----------+---------+------------
  June   1|     ... |     ...  |    ...  |       0
  June   2|     ... |     ...  |    ...  |       0
  June   3|     ... |     ...  |    ...  |       0
  June   4|     ... |     ...  |    ...  |       0
  June   5|     ... |     ...  |    ...  |       0
  June   6|     ... |     ...  |    ...  |       0
  June   7|     ... |     ...  |    ...  |       0
  June   8|     ... |     ...  |    ...  |       0
  June   9|     ... |     ...  |    ...  |       0
  June  10|     ... |     ...  |    ...  |       0
  June  11|     ... |     ...  |    ...  |       0
  June  12|     ... |     ...  |    ...  |       0
  June  13|     ... |     ...  |    ...  |       0
  June  14|     ... |     ...  |    ...  |       0
  June  15|     ... |     ...  |    ...  |       0
  June  16|     ... |     ...  |    ...  |       0
  June  17|     ... |     ...  |    ...  |       0
  June  18|     ... |     ...  |    ...  |       0
  June  19|     ... |     ...  |    ...  |       0
  June  20|     ... |     ...  |    ...  |       0
  June  21|     ... |     ...  |    ...  |       0
  June  22|     ... |     ...  |    ...  |       0
  June  23|     ... |     ...  |    ...  |       0
  June  26|     ... |     ...  |    ...  |       0
  June  27|     ... |     ...  |    ...  |       0
  June  28|     ... |     ...  |    ...  |       0
  June  29|     ... |     ...  |    ...  |       0
  June  30|     ... |     ...  |    ...  |       0
  --------+---------+----------+---------+------------
  July   1|      80 |      75  |      3  |       0
  July   2|     290 |      20  |      3  |       0
  July   3|     350 |     140  |      4  |       0
  July   4|         | Holiday. |         |       0
  July   5|         |  Sunday. |         |       0
  July   6|     300 |      52  |      4  |       0
  July   7|     110 |      35  |      2  |       0
  July   8|      85 |     105  |      2  |       0
  July   9|      85 |      80  |      3  |       0
  July  10|     300 |      65  |      1  |       0
  July  11|     145 |      95  |     11  |       0
  July  12|         |  Sunday. |         |       0
  July  13|     115 |     105  |      7  |       0
  July  14|     800 |      34  |      1  |       0
  July  15|     180 |     165  |      3  |       0
  July  16|     100 |      95  |      2  |       0
  July  17|      65 |      65  |      1  |       0
  July  18|      38 |     200  |     24  |       0
  July  19|         |  Sunday. |         |       0
  July  20|      95 |      31  |      1  |       0
  July  21|      70 |     100  |      2  |       0
  July  22|     450 |      13  |      4  |       0
  July  23|     650 |     325  |      4  |       0
  July  24|   1,650 |     325  |    ...  |       0
  July  25|   2,600 |      55  |      2  |       0
  July  26|         |  Sunday. |         |       0
  July  27|  35,000 |   1,200  |      6  |       0
  July  28|   1,200 |     675  |      6  |       0
  July  29|   2,000 |     270  |     11  |       0
  July  30|     800 |     190  |      2  |       0
  July  31|   1,000 |     310  |      6  |       0
  ========+=========+==========+=========+============


           ~Table 20--Summary of Results of Experimental Filters.~
  ==================+========+========+========+=========+=========+========
  Filter number.....|   1    |   2    |   3    |   4     |   5     |   6
                    |        |        |        |         |         |
  Number of runs....|   3    |   6    |  11    |  12     |  25     |  28
  ------------------+--------+--------+--------+---------+---------+--------
  Rate, million gallons per acre per day:
      Maximum.......|   1.35 |   3.95 |   7.96 |   12.60 |   37.5  |  118.9
      Minimum.......|   0.62 |   2.30 |   3.73 |    5.77 |    6.68 |    7.1
      Average.......|   1.06 |   3.26 |   6.69 |   10.17 |   26.1  |   38.54
  ------------------+--------+--------+--------+---------+---------+--------
  Length of run, in days:
      Maximum.......| 233.5  | 150.5  |  75.2  |   90.9  |   48.71 |   39.83
      Minimum.......| 181.7  |  42.0  |  14.5  |   10.1  |    0.67 |    0.62
      Average.......| 206.4  | 109.6  |  48.89 |   40.5  |   14.41 |   12.61
  ------------------+--------+--------+--------+---------+---------+--------
  Million gallons filtered per acre per run:
      Maximum.......| 242.61 | 484.46 | 534.67 |  960.72 |1,463.35 |1,022.27
      Minimum.......| 202.60 | 135.66 |  93.79 |   92.57 |   19.53 |   53.32
      Average.......| 218.58 | 302.82 | 326.76 |  417.23 |  374.14 |  361.92
  ------------------+--------+--------+--------+---------+---------+--------
  Cubic yards of sand removed per acre at end of each run:
      Maximum.......| 269    | 269    | 672    |1,612    |2,420    |3,360
      Minimum.......| 269    | 134    | 101    |  134    |  134    |  101
      Average.......| 269    | 213    | 272    |  392    |  583    |  635
  ------------------+--------+--------+--------+---------+---------+--------
  Cubic yards of    |        |        |        |         |         |
    sand removed    |        |        |        |         |         |
    per acre per    |        |        |        |         |         |
    million gallons |        |        |        |         |         |
    filtered........|   1.23 |   0.70 |   0.83 |    0.94 |    1.55 |    1.72
  ------------------+--------+--------+--------+---------+---------+--------
  Average initial   |        |        |        |         |         |
    loss of head....|   0.07 |   0.19 |   0.51 |    0.78 |    3.88 |    5.38
  ------------------+--------+--------+--------+---------+---------+--------
  Turbidity, influent:
      Maximum.......| 120    | 120    | 120    |  120    |   90    |  100
      Minimum.......|   2    |   2    |   2    |    2    |    2    |    2
      Average.......|  20    |  20    |  21    |   22    |   18    |   19
  ------------------+--------+--------+--------+---------+---------+--------
  Turbidity, effluent:
      Maximum.......|  11    |  13    |  17    |   18    |   30    |   30
      Minimum.......|   0    |   0    |   0    |    0    |    0    |    0
      Average.......|   1    |   1    |   2    |    2    |    4    |    3
  ------------------+--------+--------+--------+---------+---------+--------
  Percentage        |        |        |        |         |         |
    reduction       |  95.0  |  95.0  |  90.5  |   90.9  |   77.8  |   84.3
  ------------------+--------+--------+--------+---------+---------+--------
  Bacteria, influent:
      Maximum.......|180,000 |180,000 |180,000 | 110,000 | 180,000 | 37,500
      Minimum.......|     22 |     20 |     22 |      20 |      25 |     24
      Average.......|  4,800 |  5,100 |  4,500 |   4,200 |   6,900 |  5,900
  ------------------+--------+--------+--------+---------+---------+--------
  Bacteria, effluent:
      Maximum.......|  4,000 |  1,300 |  3,200 |   5,400 |  12,800 |  2,400
      Minimum.......|      2 |      3 |      1 |       1 |       2 |      2
      Average.......|    160 |     85 |    110 |     120 |     190 |    180
  ------------------+--------+--------+--------+---------+---------+--------
  Percentage,       |        |        |        |         |         |
    Reduction.......|   96.7 |   98.3 |   97.6 |    97.3 |    97.3 |   97.0
  ------------------+--------+--------+--------+---------+---------+--------
  Number of samples examined for _bacillus coli_ in influent:
      10 c.c........|  549   |  478   |  476   |   436   |   325   |  336
       1 c.c........|  560   |  492   |  486   |   445   |   335   |  342
       0.1 c.c......|  525   |  459   |  452   |   413   |   318   |  317
       0.01 c.c.....|  511   |  443   |  439   |   405   |   308   |  304
       0.001 c.c....|  500   |  434   |  429   |   394   |   299   |  294
  ------------------+--------+--------+--------+---------+---------+--------
  Number of samples examined for _bacillus coli_ in effluent:
      10 c.c........|  512   |  452   |  454   |   404   |   296   |  309
       1 c.c........|  513   |  454   |  457   |   406   |   299   |  311
       0.1 c.c......|  480   |  419   |  426   |   383   |   271   |  286
       0.01 c.c.....|  478   |  406   |  410   |   367   |   261   |  276
       0.001 c.c....|  478   |  406   |  410   |   367   |   261   |  276
  ------------------+--------+--------+--------+---------+---------+--------
  Number samples positive, influent:
      10 c.c........|  226   |  211   |  201   |   258   |   136   |  152
       1 c.c........|  127   |  123   |  116   |   108   |    81   |   93
       0.1 c.c......|   55   |   59   |   54   |    51   |    43   |   42
       0.01 c.c.....|   26   |   34   |   33   |    33   |    27   |   25
       0.001 c.c....|    6   |    6   |    5   |     6   |     3   |    3
  ------------------+--------+--------+--------+---------+---------+--------
  Number samples positive, effluent:
      10 c.c........|  100   |  109   |  134   |    98   |    94   |  106
       1 c.c........|   51   |   61   |   55   |    56   |    46   |   50
       0.1 c.c......|    9   |   13   |   16   |    16   |     4   |   13
       0.01 c.c.....|    0   |    0   |    0   |     0   |     0   |    0
       0.001 c.c....|    0   |    0   |    0   |     0   |     0   |    0
  ------------------+--------+--------+--------+---------+---------+--------
  Percentage of samples showing _bacillus coli_ in influent:
      10 c.c........|   41.2 |   44.2 |   42.2 |    59.2 |    41.9 |   45.2
       1 c.c........|   22.7 |   25.0 |   23.9 |    24.3 |    24.2 |   27.2
       0.1 c.c......|   10.5 |   12.8 |   11.9 |    12.3 |    13.5 |   13.2
       0.01 c.c.....|    5.1 |    7.7 |    7.5 |     8.2 |     8.8 |    8.2
       0.001 c.c....|    1.2 |    1.4 |    1.2 |     1.5 |     1.0 |    1.0
  ------------------+--------+--------+--------+---------+---------+--------
  Percentage of samples showing _bacillus coli_ in effluent:
      10 c.c........|   19.5 |   24.1 |   29.5 |    24.2 |    31.7 |   34.3
       1 c.c........|   10.0 |   13.4 |   12.0 |    13.8 |    15.4 |   16.1
       0.1 c.c......|    1.9 |    3.1 |    3.8 |     4.2 |     1.5 |    4.5
       0.01 c.c.....|    0   |    0   |    0   |     0   |     0   |    0
       0.001 c.c....|    0   |    0   |    0   |     0   |     0   |    0
  ------------------+--------+--------+--------+---------+---------+--------
  Cost per million  |        |        |        |         |         |
  gallons for       |        |        |        |         |         |
  sand handling.....|  $0.43 |  $0.25 |  $0.29 |   $0.33 |   $0.54 |  $0.60
  ------------------+--------+--------+--------+---------+---------+--------
  Interest charges  |        |        |        |         |         |
    at 3%...........|   6.85 |   2.25 |   1.12 |    0.73 |    0.32 |   0.22
  ------------------+--------+--------+--------+---------+---------+--------
      Total.........|   7.28 |   2.50 |   1.41 |    1.06 |    0.86 |    .82
  ==================+========+========+========+=========+=========+=========
                             _Coli_ tests presumptive.




DISCUSSION


~Allen Hazen, M. Am. Soc. C. E.~ (by letter).--This paper contains a
most interesting and instructive record of the actual operation of a
large filter plant, and also a record of a number of experiments.
The author has described some useful arrangements for improving the
efficiency or reducing the cost.

The utility of raking, as an intermediate treatment between
scrapings, seems to have been clearly demonstrated. Its practical
effect is to allow a greater quantity of water to be passed between
scrapings, thereby saturating--if the term may be used--the surface
layer with clay and other fine matter before removing it, instead of
taking it off when only a thin surface layer of it has been thus
saturated.

The large proportion of the total purification that takes place in
passing through three reservoirs successively, holding in the
aggregate a quantity of water equal to about 7 days' use, is very
striking. Taking all the records, the percentage remaining after
passing through these reservoirs, is as follows:

    Sediment for the year, 1909-1910, Table 2....................17%
    Turbidities, 5-year average, Table 3.........................25%
    Bacteria, 5-year average, Table 4............................24%
    Bacteria, selected winter months with high
      numbers in the raw water...................................20%
    Bacteria, selected summer months with high
      numbers in the raw water................................... 2.5%

There is considerable seasonal fluctuation in the results of
settling and filtering, as is shown in Table 21.


       ~Table 21--Average Removal of Turbidity and Bacteria by
       Washington Filters for Whole Period, Arranged by Seasons~.
  ===========================+========+========+========+========+========
                             | Winter.| Spring.| Summer.|  Fall. |  Year.
  ----------------+----------+--------+--------+--------+--------+--------
  Turbidity, in   | raw      |    135 |     96 |    144 |    42  |    105
  parts per       | settled  |     33 |     28 |     27 |    15  |     26
  million:        | filtered |      4 |      3 |      1 |   0.5  |      2
  ----------------+----------+--------+--------+--------+--------+--------
  Percentage      | settling |     24 |     29 |     19 |    36  |     25
  left from:      | filtering|     12 |     10 |      4 |     3  |      8
                  | both     |      3 |      1 |    0.3 |     1  |      2
  ----------------+----------+--------+--------+--------+--------+--------
  Bacteria per    | raw      | 16,600 |  4,150 |  4,100 | 1,960  |  6,700
  cubic           | settled  |  6,300 |    980 |    160 |   270  |  1,940
  centimeter:     | filtered |    149 |     29 |     18 |    22  |     54
  ----------------+----------+--------+--------+--------+--------+--------
  Percentage      | settling |  38    |  24    |   4    | 14     |  29
  left from:      | filtering|   2.4  |   3.0  |  11.2  |  8.2   |   2.8
                  | both     |   0.90 |   0.79 |   0.44 |  1.12  |   0.81
  ================+==========+========+========+========+========+========


The fluctuation in the efficiency of the plant as a whole by seasons
is greater with the turbidity than with the bacteria. During the
winter the effluent contains 3% of the turbidity of the raw water,
and in summer only 0.3 per cent. Most of this difference is
represented by the increased efficiency of the filters in summer,
and only a little of it by the increased efficiency of settling.
With bacteria, on the other hand, the seasonal fluctuation of the
plant as a whole is comparatively small, but the settling and
storage processes are much more efficient in summer than in winter,
the filters being apparently less efficient. The writer believes
that they are only apparently less efficient, and not really so, the
explanation being that some bacteria always grow in the under-drains
and lower parts of the filter, and are washed away by the effluent.
The average number of bacteria in summer in the settled water is 160
per cu. cm. and in the filtered water 18. These are very low
numbers. It is the writer's view that nearly all of these 18
represent under-drain bacteria, and practically bear no relation to
those in the applied water, and, if this view is correct, the number
of bacteria actually passing through the various processes is at all
times less than the figures indicate. In the warmer part of the year
the difference is a wide one, and the hygienic efficiency of the
process is much greater than is indicated by the gross numbers of
bacteria.

The reduction of the typhoid death rate has not been as great with
the change in water supply as was the case at Lawrence, Albany, and
other cities, apparently because the Potomac water before it was
filtered was not the cause of a large part of the typhoid fever.

The sewage pollution of the Potomac is much less than that of the
Merrimac and the Hudson, and it is perhaps not surprising that this
relatively small amount of pollution was less potent in causing
typhoid fever than the greater pollution of rivers draining more
densely populated areas.

The method of replacing the washed sand hydraulically seems to have
worked better than could have been reasonably anticipated, and the
writer believes that this was due, in part, to the excellent method
of manipulation described in the paper. It is his feeling, however,
that part of the success is attributable to the very low uniformity
coefficient of the sand. In other words, the sand grains are nearly
all of the same size, due to the character of the stock from which
the filter sand was prepared; and, therefore, there is much less
opportunity for separation of the sand according to grain sizes than
there would be with the filter sand which has been available in most
other cases. Filter sand with a uniformity coefficient as low as
that obtained at Washington has been rarely available for the
construction of sand filters, and while the method of hydraulic
return should certainly be considered, it will not be safe to assume
that equally favorable results may be obtained with it with sands of
high uniformity coefficients until actual favorable experience is
obtained.

The writer believes that in calculating the cost of the water used
in the plant itself the price chosen by the author, covering only
the actual operating expenses of pumping and filtering, is too low.
The capacity of the whole Washington Aqueduct system is reduced by
whatever quantity is used in this way, and, in calculating the cost
of sand handling, the value of the water used should be calculated
on a basis which will cover the whole cost of the water, including
all capital charges, depreciation, operating expenses, and all costs
of every description. On this basis the water used in the
sand-handling operations would probably be worth five or more times
the sum mentioned by the author.

The cost of operation of the plant has come within the estimates
made in advance, and has certainly been most reasonable. The cost of
filter operations has averaged only about 50 cents per million
gallons, and is so low that it is obvious that the savings which may
be made by introducing further labor-saving appliances would be
relatively small. It will be remembered that ten or fifteen years
ago the cost of operating such filters under American conditions was
commonly from $2 to $5 per million gallons.

The experiments represented by Tables 17 to 19, inclusive, serve to
show that preliminary filtration, or multiple filtration, or any
system of mechanical separation is incapable of entirely removing
the finer clay particles which cause the residual turbidity in the
effluent. They also show that this turbidity may be easily and
certainly removed by the application of coagulant to the raw water
during the occasional periods when its character is such as to
require it.

These general propositions were understood by those responsible for
the original design of the plant, as is shown by the author's
quotations. These experiments, however, were necessary in order to
demonstrate and bring home the conditions to those who thought
differently, and who believed that full purification could be
obtained by filtration alone, or by double filtration, without
recourse to the occasional use of coagulant.

The experiments briefly summarized in Table 20 are of the greatest
interest and importance. Six small filters, otherwise alike and like
the large filters, all received the same raw water and were operated
at different rates to determine the effect of rate on efficiency.

That the experimental results from the filter operating at the same
rate as the large filters were on the whole somewhat inferior to
those from the large filters for approximately the same period, may
be attributed to the fact that the experimental filter was new while
the large filters had been in service for some time and had thereby
gained in efficiency. The greatest difference was in the _coli_
results in Table 20, where it is shown that 24% of the 10-cu. cm.
effluent samples from the experimental filter contained _coli_, in
comparison with only from 1 to 3% of such samples from the main
filters.

The results from the experimental filter operating at a rate of
1,000,000 gal. per acre daily may fairly be excluded, as the
effluent probably contained more under-drain bacteria in proportion
than filters operated at higher rates. The number of bacteria in the
filter operating at a 3,000,000-gal. rate were 1.7% of those in the
applied water; for the filter operating twice as fast, the
percentage was 2.4; and, for the one operating more than ten times
as fast, was only 3.0; thus indicating a surprisingly small increase
in the number of bacteria with increase in rate.

Further and more detailed study by the writer of the unpublished
individual results, briefly summarized in Table 20, confirms the
substantial accuracy of the comparison based on the average figures
as stated in that table.

It must be kept in mind, in considering these results, that the
number of bacteria in each case is made up of two parts, namely,
those coming through the filter--which number is presumably greater
as the rate is greater--and, second, those coming from harmless
growths in the under-drains and lower parts of the filter--the
numbers of which per cubic centimeter are presumably less as the
rate is greater--and these two parts, varying in opposite
directions, may balance each other, as they seem to do in this case,
through a considerable range. It may thus be that the number of
bacteria really passing the filter varies much more with the rate
than is indicated by the gross results.

It is also of interest to note that the sand filter (called a
preliminary filter) in Table 18, filled with the same kind of sand,
when operated at an average rate of 50,000,000 gal. per acre daily
for a year, allowed 18% of the applied bacteria to pass, in
comparison with 3% found in Filter No. 6 of Table 20, operated at an
average rate of 38,000,000 gal. per acre daily.

There was one point of difference in the manipulation: the
preliminary filter was washed by a reversed current of water, as
mechanical filters are washed, while Filter No. 6 was cleaned by
scraping off the surface layer, as is usual with sand filters.
Whether the great difference in bacterial results with a relatively
small difference in rate is to be attributed to this difference in
manipulation the writer will not undertake to state.

If the experimental results of Table 20 indicate correctly the
conditions which obtain in filtering Potomac water, then increasing
the rate of filtration so as to double it, or more than double it,
would make but little difference in the quality of the effluent as
measured by the usual bacterial methods. If the increase in rate
were accompanied by the preliminary filtration of the water, then,
presumably, there would be little change in the quality of the
effluent, and the maintenance of excellent results might be
incorrectly attributed to the influence of the preliminary filter.

It would also seem that the apparatus which is sometimes used for
determining and controlling the rate with more than the ordinary
degree of precision is hardly justified by such experimental results
as those presented by the author.

In contrast to these results may be mentioned those obtained by Mr.
H. W. Clark,[1] for experimental filters operated with Merrimac
River water, at rates ranging from 3,000,000 to 16,000,000 gal. per
acre daily. The results are the average of nearly two years of
experimental work, the period having been nearly coincident with
that covered by the author's experiments, and of many hundreds of
bacterial analyses of each effluent, and form, with the author's
experiments, the most thorough-going studies of the effect of rate
on efficiency that have come to the writer's attention.

Mr. Clark's results are given in Table 22.


                                   ~Table 22.~
  ===========+============+===========+=============+===========+============
             |            |           |             |           | _B. Coli_
             |            |           |             |           |in 1 cu.cm.
   Effective |            |    Rate   | Bacteria per|           |(percentage
    size of  |            | in gallons|    cubic    | Bacterial |of positive
      sand.  | Filter No. |acre daily.|centimeter in|efficiency.|   tests).
  -----------+------------+-----------+-------------+-----------+------------
      0.28   |     A      | 3,000,000 |      48     |    99.1   |     5.0
      0.25   |     B      | 5,000,000 |      85     |    98.4   |     24.0
      0.22   |     C      | 7,500,000 |     105     |    98.1   |     25.0
      0.22   |     D      |10,000,000 |     110     |    98.0   |     25.0
      0.22   |     E      |16,000,000 |     280     |    95.0   |     38.0
  ===========+============+===========+=============+===========+============


It will be seen that the number of bacteria passing increases
rapidly with the rate, and whether the total number of bacteria is
considered or the _B. coli_ results, the number passing is
approximately in proportion to the rate. In other words, doubling
the rate substantially doubles the number of bacteria in the
effluent.

This is entirely in harmony with all the Lawrence experimental
results extending over a period of 20 years. There have been
occasional apparent exceptions, but, on the whole, experience with
Merrimac River water has uniformly been that more bacteria pass as
the rates are higher.

The theory sometimes advanced, that the efficiency of filtration is
controlled to a certain extent by gelatinous films, and that, as far
as thus controlled, is less dependent on rate, would not seem to be
borne out by these results. The Merrimac River water, carrying large
amounts of organic matter, would certainly seem better adapted to
the formation of such films than the clay-bearing Potomac water,
comparatively free from organic matter; but it is the Potomac water
which seems to show the least influence of rate on efficiency.

  [Footnote 1: _Journal_, New England Water-Works Association, Vol.
   24, p. 589.]

The experiments show that turbidity passes more freely at the higher
rates with the Potomac water, as has also been found to be the case
with other clay-bearing waters.

In the last lines of Table 20 are given cost per million gallons for
filtering at various rates. There is no discussion of these figures,
and as they differ considerably from those which the writer has been
accustomed to use, the calculation in Table 23, made three years ago
for a particular case, may be of interest.


         ~Table 23--Relative Cost of Filtering at Different Rates.~
  ======================+===================================================
                        |Nominal rate, in millions of gallons per acre daily:
                        +------------+------------+------------+------------
                        |      3     |     5      |     10     |    20
  ----------------------+------------+------------+------------+------------
  Percentage which      |            |            |            |
  average yield is of   |            |            |            |
  nominal rate..........|     85     |     80     |     75     |      65
  ----------------------+------------+------------+------------+------------
  Average output per    |            |            |            |
  acre, in millions of  |            |            |            |
  gallons per day.......|       2.55 |       4.00 |       7.5  |      13.0
  ----------------------+------------+------------+------------+------------
  Cost of that part of  |            |            |            |
  filters per acre      |            |            |            |
  dependent on rate.....| $12,000    | $20,000    | $40,000    | $80,000
  ----------------------+------------+------------+------------+------------
  Cost of that part of  |            |            |            |
  filters per acre not  |            |            |            |
  dependent on rate.....|  50,000    |  50,000    |  50,000    |  50,000
  ----------------------+------------+------------+------------+------------
  Total cost of filters |            |            |            |
  per acre..............|  60,000    |  70,000    |  90,000    | 130,000
  ----------------------+------------+------------+------------+------------
  Cost per million      |            |            |            |
  gallons of capacity...|  20,600    |  14,000    |   9,000    |   6,500
  ----------------------+------------+------------+------------+------------
  Cost per million      |            |            |            |
  gallons of average    |            |            |            |
  daily output..........|  24,400    |  17,500    |  12,000    |  10,000
  ----------------------+------------+------------+------------+------------
  Capital charges and   |            |            |            |
  depreciation at 6% on |            |            |            |
  cost per million      |            |            |            |
  gallons...............|       4.00 |       2.87 |       1.97 |       1.64
  ----------------------+------------+------------+------------+------------
  Operating expenses,   |            |            |            |
  the same at all       |            |            |            |
  rates.................|       1.00 |       1.00 |       1.00 |       1.00
  ----------------------+------------+------------+------------+------------
  Total cost of         |            |            |            |
  filtering, excluding  |            |            |            |
  pumping, storage, and |            |            |            |
  all auxiliaries.......|       5.00 |       3.87 |       2.97 |       2.64
  ----------------------+------------+------------+------------+------------
  Relative cost.........|       1.29 |       1.00 |       0.77 |       0.68
  ======================+============+============+============+============


When the costs of pumping, pure-water reservoirs usually necessary,
etc., are taken into account (which add equally to the cost at all
rates), the cost of filtering will vary less with the rate than is
indicated.

The effect of rate on cost, as calculated in Table 23, and also the
percentages of the bacteria of the raw water found in the effluents
by the author and by Mr. Clark, are shown on Figure 10.

Considering all these results together, and also all the other
evidence known to the writer bearing on this point, it seems clear
that filters are not as sensitive to changes in rate, within
reasonable limits, as has been frequently assumed; but, on the other
hand, there is usually a substantial increase in the percentage of
bacteria passing through a filter with increased rate.

Filters furnish relative, not absolute, protection against
infectious matter in the raw water. The higher the bacterial
efficiency, the more complete is this relative protection.

The cost of filtering does not decrease in inverse ratio to the
rate, but at a much slower rate. This is especially true with rates
of more than 5,000,000 or 6,000,000 gal. per acre daily.

In general, a rate of filtration may rationally be selected at which
the value of the possible danger resulting from an increase in rate
is equal to the saving that may be made in cost by its use. This
point must be a matter of individual judgment. The tendency of the
last few years has been to use higher rates, or, in other words, to
cheapen the process and to tolerate a larger proportion of bacteria
in the effluent. The use of auxiliary processes has been favorable
to this, especially the use of chloride of lime, in connection with
either the raw water or the effluent.

[Illustration: ~Figure 10--Rate Million Gallons Per Acre Daily.~]

By the judicious use of this substance, efficiency may be maintained
while using higher rates than would otherwise have been desirable.

The writer believes that there will be many cases where the added
risk of using too high a rate is not worth the relatively small
saving in cost that accompanies it.

~George A. Johnson, Assoc. M. Am. Soc. C. E~.--This paper contains
information of an exceedingly interesting nature. There is
comparatively little difficulty in obtaining accurate figures on the
cost of construction of water purification works, but, with costs of
operation of such works, it is different. The data available in
published reports and papers are usually more or less fragmentary,
and unexplained local conditions with reference to the character of
the raw water, the cost of labor and supplies, and methods of
apportioning these costs, introduce variables so wide as frequently
to render the published figures almost useless for purposes of
comparison.

Mr. Hardy's paper is noteworthy in that it presents certain
relatively new features of slow sand filter operation which have
been only lightly touched on in water purification literature up to
the present time. These refer particularly to means whereby a filter
may be continued in service without removing a portion of the
surface layer of the filter surface itself when the available head
has become exhausted, and to methods whereby washed sand may be
expeditiously and more economically restored to the filter than has
been the case hitherto.

Sand handling is the most important item of expense in the operation
of a slow sand filter. Quite recently a charge of $1.50 per cu. yd.
for sand scraping, transportation to sand washers, washing, and
restoring to the filter, was not considered exorbitant, but the
improved methods developed during recent years at Washington,
Philadelphia, Albany, and more recently at Pittsburg (at all of
which places hydraulic ejection plays an important part), have
shown the feasibility of reducing this figure by nearly, if not
quite, two-thirds.

The practice observed at Washington of raking over the surface of
the sand layer when the available head becomes exhausted, in order
to avoid the cost and loss of time necessitated by shutting down the
filter and scraping off the surface layer, is unquestionably one of
the most striking advances in slow sand filter operation in recent
years. In rapid sand filter operation, to prolong the period of
service between washings, agitation of the filter surface has been
used to advantage for many years. The full value of surface raking
may not be generally appreciated, but the results which have
followed a trial of this procedure at Washington, Philadelphia, and
Pittsburg have shown that the output of filtered water between
scrapings may be doubled or trebled thereby, with no injury to the
filter itself or to the quality of the filtered water. The cost of
raking over the surface of a 1-acre slow sand filter unit is less
than $10 at all the above-mentioned places, which fact in itself
shows the great saving in money and time effected by periodically
substituting surface raking for scraping. Under ordinary conditions
it has been found that a filter can be raked to advantage at least
twice between scrapings.

In the case of filters thus raked, a deeper penetration of suspended
matter into the sand layer is inevitable, but at Pittsburg, as at
Washington, such penetration does not extend more than about 2 in.
below the filter surface. When the filter is finally scraped, a
deeper layer is removed, of course, but it is clearly more
economical to remove a deep layer at one operation than to remove
separately several thinner layers of an equal total thickness.

The lost-time element is an important one, and at Washington this
was the main reason for trying surface raking. It became necessary
to increase the output of the filters, and the ordinary scraping
consumed so much time that the sand-handling force was increased,
working day and night. The raking expedient introduced at this time
overcame this, and Mr. Hardy states that it is still followed when
the work is at all pressing. The speaker has found at Pittsburg, as
Mr. Hardy has found at Washington, that raking is nearly if not
quite as effective as scraping in restoring the filter capacity.

Eleven years ago the speaker was connected with the preliminary
investigations into the best methods of purifying the Potomac River
water for Washington. It then appeared that while for the greater
part of the time during an average year the Potomac River could be
classed among the clear waters of the East, there were periods when
excessive turbidity made it necessary to consider carefully methods
of preparatory treatment before this water could be filtered
effectively and economically. As Mr. Hardy has said, considerable
prejudice existed against the use of a coagulating chemical, and the
expedient was therefore adopted of giving the water a long period of
sedimentation in order to remove enough of the suspended matter to
allow the clarified water to be treated on slow sand filters. The
expert commission, consisting of Messrs. Hering, Fuller, and Hazen,
recommended the occasional use of a coagulating chemical, but this
recommendation was not carried out.

The Potomac River is somewhat peculiar, in that the turbidity of its
waters, as shown by the results presented in Mr. Hardy's paper,
ranges from 3,000 to practically nothing. The bacterial content also
varies widely, and Mr. Hardy's tables show this variation to be from
76,000 to 325 per cu. cm. Such a water as this requires particularly
careful preparatory treatment. The Dalecarlia Reservoir has a
capacity of something like 2 days' storage, the Georgetown Reservoir
the same, and the McMillan Park Reservoir nearly 3 days, making a
total sedimentation of more than 7 days. Without the use of a
coagulant, it is significant that during a period of five years,
even with 7 days' sedimentation, the average maximum turbidity of
the water delivered to the filters was 106 parts per million, and
the maximum average turbidity in one month was 250 parts per
million. The water filtration engineer can readily understand that
waters as turbid as this cannot be treated economically and
efficiently in slow sand filters. It would appear that coagulating
works might advantageously have been installed at the entrance to
the Dalecarlia Reservoir. If this had been done, and coagulant had
been added to the water at times when it was excessively turbid, a
considerably shorter period of subsequent sedimentation than now
exists would in all probability have rendered the water at all times
amenable to efficient and economical slow sand filter treatment.

The prejudice in Washington against the use of coagulants has also
manifested itself in other localities, but the results which have
been obtained during the past twenty years from rapid sand filters
and from slow sand filters, treating waters previously coagulated
with salts of iron or alumina, have shown how thoroughly
unreasonable were these objections. In this connection it is
interesting to note that there are in the United States more than
350 rapid sand filter plants, and that nearly 12% of the urban
population of Continental United States is being supplied with water
filtered through rapid sand filters, in connection with all of which
a coagulating chemical is used in the preparatory treatment.


    ~Table 24--Typhoid Fever Death Rates in Cities of the United
         States with Populations in 1910 of 100,000, or More.~

     Statistics gathered by correspondence and from Reports of
     the Bureau of the Census, Department of Commerce and Labor,
                        Mortality Statistics.

~Note~.--Statistics from Birmingham, Ala., Dayton, Ohio, Fall River,
         Mass., Louisville, Ky., Memphis, Tenn., Oakland, Cal., and
         Providence, R. I., are not included, as they are
         incomplete.

    Columns:
      A - Average for six years, 1900-05, inclusive.
      B - Average for five years, 1906-10, inclusive.
      C - Average for 11 years, 1900-11, inclusive.

  ====================+===============================================
                      |           ~ Typhoid Fever Death Rate
         City.        |             per 100,000 Population~.
                      +-----+-----+-----+-----+-----+-----+-----+-----
                      | 1906| 1907| 1908| 1909| 1910|  A  |  B  |  C
  --------------------+-----+-----+-----+-----+-----+-----+-----+-----
  Albany, N. Y.       |  20 |  20 |  11 |  19 |  15 |  25 |  17 |  21
  Atlanta, Ga.        |  50 |  64 |  47 |  44 |  43 |  65 |  50 |  58
  Baltimore, Md.      |  34 |  41 |  31 |  23 |  41 |  36 |  34 |  35
  Boston, Mass.       |  22 |  10 |  26 |  14 |  11 |  23 |  16 |  20
  Bridgeport, Conn.   |  10 |  13 |  13 |  13 |   9 |  15 |  12 |  14
  Buffalo, N. Y.      |  24 |  29 |  21 |  23 |  20 |  29 |  23 |  26
  Cambridge, Mass.    |  18 |  10 |  10 |   9 |  12 |  18 |  12 |  15
  Chicago, Ill.       |  18 |  18 |  15 |  12 |  14 |  27 |  16 |  22
  Cincinnati, Ohio    |  71 |  46 |  19 |  13 |   6 |  54 |  31 |  44
  Cleveland, Ohio     |  20 |  19 |  13 |  12 |  19 |  51 |  17 |  36
  Columbus, Ohio      |  45 |  38 | 110 |  17 |  13 |  61 |  45 |  54
  Denver, Colo.       |  68 |  67 |  58 |  24 |  30 |  37 |  49 |  42
  Detroit, Mich.      |  22 |  28 |  22 |  19 |  16 |  17 |  22 |  19
  Grand Rapids, Mich. |  39 |  30 |  30 |  17 |  27 |  34 |  28 |  31
  Indianapolis, Ind.  |  39 |  29 |  26 |  22 |  31 |  76 |  30 |  55
  Jersey City, N. J.  |  20 |  14 |  10 |   8 |  10 |  19 |  12 |  16
  Kansas City, Mo.    |  38 |  40 |  35 |  23 |  38 |  48 |  35 |  42
  Los Angeles, Cal.   |  18 |  23 |  19 |  18 |  12 |  35 |  18 |  27
  Lowell, Mass.       |   7 |   9 |  24 |  11 |  21 |  19 |  14 |  17
  Milwaukee, Wis.     |  31 |  26 |  17 |  21 |  45 |  19 |  28 |  23
  Minneapolis, Minn.  |  33 |  26 |  18 |  20 |  58 |  38 |  29 |  34
  Nashville, Tenn.    |  66 |  85 |  62 |  53 |  48 |  54 |  58 |  56
  Newark, N. J.       |  18 |  24 |  12 |  11 |  13 |  17 |  16 |  17
  New Haven, Conn.    |  54 |  30 |  34 |  20 |  17 |  44 |  31 |  38
  New York, N. Y.     |  15 |  17 |  12 |  12 |  12 |  19 |  14 |  17
  New Orleans, La.    |  30 |  56 |  31 |  25 |  28 |  40 |  34 |  37
  Omaha, Nebr.        |  28 |  24 |  22 |  31 |  75 |  20 |  36 |  27
  Paterson, N. J.     |   4 |  11 |  10 |   5 |   7 |  25 |   7 |  17
  Philadelphia, Pa.   |  74 |  60 |  36 |  22 |  17 |  47 |  42 |  45
  Pittsburg, Pa.      | 141 | 135 |53[1]|13[1]|12[1]| 132 |  71 | 104
  Richmond, Va.       |  44 |  41 |  50 |  24 |  22 |  66 |  36 |  53
  Rochester, N. Y.    |  17 |  16 |  12 |   9 |  13 |  15 |  13 |  14
  St Louis, Mo.       |  18 |  16 |  15 |  15 |  14 |  33 |  16 |  25
  St Paul, Minn.      |  21 |  17 |  12 |  20 |  20 |  14 |  18 |  16
  San Francisco, Cal. | ... |  57 |  27 |  17 |  15 |  20 |  29 |  24
  Scranton, Pa.       |  11 |  76 |  11 |  11 |  14 |  18 |  35 |  26
  Syracuse, N. Y.     |  10 |  16 |  15 |  12 |  30 |  14 |  17 |  15
  Toledo, Ohio        |  45 |  36 |  40 |  31 |  32 |  36 |  37 |  36
  Worcester, Mass.    |  12 |  14 |  10 |   8 |  16 |  17 |  12 |  15
  Washington, D. C.   |  52 |  36 |  39 |  33 |  23 |  59 |  37 |  49
  ====================+=====+=====+=====+=====+=====+=====+=====+=====

  [Footnote 1: Filtered water section. Allegheny District not
   included.]


Attention has repeatedly been called to the fact that the relatively
high typhoid death rate in Washington, since the filter plant was
installed, was a possible indication that the filters were
inefficient. It is true that there has not been the marked reduction
in the typhoid death rate in Washington, following the installation
of the water filtration works, that has been observed in other
cities in America. For the six years prior to the date on which
filtered water was supplied to the citizens of Washington, the
average typhoid fever death rate was 59 per 100,000 population, as
against 37 per 100,000 for the five years following, a reduction of
37 per cent. At Albany, N. Y., where the first modern slow sand
filter was built in 1899, the typhoid death rate has been reduced by
75 per cent. At Cincinnati, Ohio, the average death rate from
typhoid ranged around 50 per 100,000 for years, but since the
installation of the filtration plant it has been reduced to a point
which places that city, with respect to freedom from typhoid fever,
at the head of all the large cities in America; in 1910 the death
rate from typhoid in Cincinnati was 6 per 100,000. Similarly, at
Columbus, Ohio, where the typhoid death rate before the installation
of the filtration plant in 1906 was even higher than at Cincinnati,
it was reduced to less than 13 per 100,000 in 1910, whereas, for the
previous five years, it was 61 per 100,000. Philadelphia, before the
installation of the filtration works, had a typhoid death rate of 60
or more per 100,000, and in 1910 the death rate from this disease
was 17. Pittsburg, at least that part of it now supplied with
filtered water, for years had a typhoid death rate of more than 130
per 100,000, but the present rate is about 12 per 100,000.


     ~Table 25--Average Monthly Results for the
                Period, 1905-1910.~

  Columns:
    A - Period of sedimentation in days.
    B - Turbidity in parts per million.
    C - Bacteria per cubic centimeter.
  ============+=====+=====+=======+=====================
              |     |     |       |~Percentage Removed~
   Reservoirs.|  A  |  B  |   C   |----------+----------
              |     |     |       | Turbidity| Bacteria
  ------------+-----+-----+-------+----------+----------
  River       | ... | 106 | 6,400 |   ...    |   ...
  Dalecarlia  | 2.2 |  50 | 5,000 |    53    |    22
  Georgetown  | 2.2 |  38 | 3,400 |    24    |    32
  McMillan    | 2.8 |  26 | 2,000 |    31    |    41
  ------------+-----+-----+-------+----------+----------
  Totals and  |     |     |       |          |
  averages    | 7.2 | ... |  ...  |    75    |    69
  ============+=====+=====+=======+==========+==========


While it may perhaps seem unreasonable to single out Washington as a
particular sufferer in this respect, it is highly probable that a
large share of the typhoid is still caused by secondary infection,
flies, impure milk, and private and public wells. The speaker
remembers distinctly that ten years ago, when he made an
investigation into the purity of the water of about 100 public wells
in that city, a large number of them showed unmistakable evidence of
being polluted with sewagic matter. Conclusive evidence would be
secured to dispel any doubt as to the sanitary quality of the
filtered product if hypochlorite of lime were added to the filtered
water throughout one year or throughout the typhoid months. It seems
strange to the speaker, that for this, if for no other reason, this
safe and non-injurious germicide has not as yet been used at
Washington, in view of the fact that at the present time it is being
used continuously or intermittently in the treatment of the water
supplies of scores of the most important cities of this country,
among which may be mentioned New York, Philadelphia, Cincinnati,
Pittsburg, St. Louis, and Minneapolis.

~Morris Knowles, M. Am. Soc. C. E~. (by letter).--This description
of the operation of the Washington Filtration Works is timely and of
great interest. It is ten years since the writer, in collaboration
with Charles Gilman Hyde, M. ~Am. Soc~. C. E., presented a similar
record for the Lawrence, Mass., filter. That paper was the first
complete, detailed, and continuous history of the actions and
results obtained for a long period of time with such a purification
works.[1] Since then, the art of filtration has advanced in many
ways, particularly in regard to the methods of cleaning slow sand
filters and in the accompanying processes. It is well, therefore,
again to take account of stock and see really what progress has been
made. Therefore, Mr. Hardy's paper, giving a description of the
operations of a system thoughtfully designed, after long
consideration of the problem, and of operations carried on under
efficient and economical administration, with thorough record of all
details, should furnish a groundwork for the careful consideration
of the question stated above.

The writer, using as a text some of the ideas given in the paper,
but more particularly some of those becoming prevalent elsewhere,
desires to discuss methods and costs of operation, especially in
relation to sand handling; and to offer suggestions looking toward
greater efficiency, as well as economy, in carrying out the standard
and well-tried methods.

_Theory of Slow Sand Filtration._--First, what is the process of slow
sand filtration? The answer to this question involves many factors, some
of which are even yet but imperfectly understood. In the early history
of filtration, at the time of the construction of the London filters,
only the straining capacity of the sand bed, to remove gross particles,
was known. Later, when the organic contents of water had become better
understood, the chemical or oxidizing powers of the process were
recognized as performing an important part. Finally, co-existent with
the discovery of the so-called "germ theory of disease," a study of the
bacterial action of filters resulted in the recognition of its
importance. It is now universally thought that each of these factors
performs its useful function; that the size of the sand, the amount of
organic matter remaining on the surface of the bed, the turbidity of the
applied water, and the bacterial content of the influent, are some of
the things on which depends the determination of the relative importance
of each.

  [Footnote 1: _Transactions_, Am. Soc. C. E., Vol. XLVI, p. 258.]

Engineers have been taught to believe, by the German school of
thought, that the film of organic matter on the surface of the sand
plays a very important role in filtration. This _Schmutzdecke_, as
it is called, has been considered so precious that stress has been
placed on treating it with great care. It was not to be wholly
removed at the time of cleaning, and it was not to be walked on, or
indented, or in any other way consolidated or destroyed. In fact, in
some cases, the wasting of the first water after cleaning has been
advocated, for the reason that not a sufficient amount of this
organic film would be left on top of the sand to begin the
filtration process properly immediately after the cleaning.

In late years, however, there has been a tendency to depart from
this fundamental doctrine of slow sand filtration. Various new
processes for cleaning the sand surface have been advocated; some of
these partly destroy and others completely exterminate any semblance
of a bacterial film on the sand bed. These ideas, advanced without
any real and serious discussion of their intrinsic merits, or their
effects on the public health, are not founded on long continuous
records of such results as are necessary to establish confidence in
the final value of any of these methods.

Rapid advances along this line have been made more recently,
notwithstanding the occurrence of notable instances of trouble and
the resultant need of complete repair of filtration beds. Because of
the rough treatment of the sand surface, a penetration of organic
matter and filth into the bed had taken place. This caused deep
clogging, prevented the usual yield of water, and brought about a
lessened bacterial efficiency, due to the attempt to force water
through the filters, and because some organic matter and growths in
the lower part of the bed had furnished a breeding place for more
bacteria.

All these endeavors to reduce the work of cleaning have been
commendable, because scraping and sand handling are the items of
greatest expense in slow sand filter maintenance. Every one has been
desirous of minimizing this cost. However, as the writer will
endeavor to show, it seems that attempts along this line should be
with the idea of doing more economically, as well as efficiently,
the things which one knows will accomplish the proper results,
rather than unwisely to adopt new methods which have not been tried
for a long enough period to determine their effect on the public
health.

_Pittsburg Methods._--When first taking up the problem of design in
Pittsburg, in 1902, the writer had presented to him for
consideration and adoption, a suggestion that a certain method of
cleaning sand filters, which would involve the washing of the sand
in place (similar to that recently tried at the Jerome Park
Experiment Station, New York City), would be advisable and
economical. The decision then made has never been regretted. As this
plan involved such a complete departure from those principles which
had been well tried and had proven successful, it was believed that
it was not safe to adopt such a method on the municipal filtration
works, from which the people were to derive their drinking water.
There is more to be considered in such a problem than mere economy
of operation; the economy of human life, the effect on which
requires far longer than a few months of trial to determine, is a
much more important factor. Believing that no one should depart,
until after a long period of conclusive experimentation, from that
principle which is known to be safe (viz., to take off a small
portion of the clogging surface), the writer studied to determine
more efficient and economical methods of accomplishing this end.

A device for scraping the material, in just the same way as with
shovels, but more efficiently and more exactly, was developed by
George P. Baldwin, M. Am. Soc. C. E., under the general supervision
of the Bureau of Filtration, of which the writer was in charge.
However, on account of the unfortunate and earlier arrangement of
other constructive matters, which the City's Legal Department
advised could not be changed without upsetting the contract, the
entrance doors to the original forty-six filters were not built
large enough to permit the rapid and economical transfer of these
machines, and, as this act takes so large a proportion of the total
time of operation, it has not been found economical to use them. The
additional ten filters, recently constructed, with doors especially
designed and large enough to pass the machines, have not yet been
placed in operation. This is said to be on account of lack of funds
and of employees. Therefore, there has been no opportunity to
demonstrate what the scraping machines can do, under the conditions
for which they were designed to operate. The restoring machine, a
complementary device in mechanical operation, which simply replaces
the sand in the same condition that it would be if wheeled back,
but, with a small percentage of moisture, has accomplished its
purpose well and economically. The sand is placed in the filters so
that there is no further settling; with a smooth surface, needing no
additional adjustment; with absolutely no possibility of sub-surface
clogging; and with the filters starting off exceedingly well in
operative results.

_Washington Methods._--In Washington, it is stated that the filters
are still cleaned by the old-fashioned method of scraping with
shovels, throwing the sand into piles, and afterward removing it
with a movable ejector. Between scrapings there is also an
occasional mid-period action of raking the unwatered sand surface,
for the purpose of stirring up the dirty film. This process does not
remove any of the clogging material from the bed, but it is said
that no injurious effects are produced, and that it is economical.
It is stated that the so-called "Brooklyn method," of stirring the
surface of the sand while the water is on the bed, has been tried at
Washington, but with unsatisfactory results. It seems to have been
advocated with greater fervor in some other places.

The method of dry raking does not remove the dirty material, but
loosens up the pores of the surface, and through this porosity
permits clogging to penetrate deeper into the filter. The method of
raking with water on the bed, although it removes some of the
organic dirt, also permits deeper penetration of the remainder. The
latest devised system of washing the sand in place, by upward
spraying with water, called the "Blaisdell method," thoroughly
destroys the _Schmutzdecke_ above, and, at the same time, must
permit the formation of a subsidiary one below. In the Nichols
method, the material removed by shovel scraping is conveyed by an
ejector to a portable separator, where it receives a single washing;
the dirty water overflows to the sewer, while the washed sand is
discharged through a hose and deposited on the recently scraped
surface. As the latter is partly impregnated with impurities, there
is, by this process, a tendency toward sub-surface clogging.

All these processes are marked and serious departures from the
well-tried method of cleaning slow sand filters, which, it is well
known, will operate successfully to purify polluted river waters and
make them safe to drink. In all there is the danger that they have
not been sufficiently and carefully tried, under scientific
observation, as to results and possible effects on the public
health, to be sure that the bacterial efficiency can long continue
to be satisfactory, with the application of specifically infected
waters. It is dangerous, and may even jeopardize the safety of human
lives, to experiment on water which is furnished for drinking
purposes. There is also the added danger, well known from past
experience, that in a few years (it may be more or less, depending
on the extent and intensity of the new workings) the filters will
need renovation, partly, if not wholly, throughout the entire bed.
Thus, considering the total cost during a long term of years, the
apparently cheaper method may become the most expensive.

There is also an interesting query in regard to the Washington
method of replacing sand in the filters, and it is worthy of most
careful thought and attention. If the process described can be
carried on with success and safety, it will prove to be a long and
progressive step in the methods of operation. The difficulty,
however, is in determining from any short-term runs whether such a
process can be continued permanently without impairing the
efficiency of the sand bed. Apparently good conditions may change,
after a few years' trial, and be followed by unsafe results and
predicaments. This replacing of sand with whatever dirt and detritus
may travel with it in the carrying water is certainly not equivalent
to the care with which it has been understood that sand should be
deposited in filters. It is not comparable with the care with which
it is placed, when wheeled from a washer, where dirty water
overflows the lip, or where it is placed by a machine restorer in
the filter, where the transporting water also overflows the weir and
is carried to the sewer.

These cheap and rapid methods of doing the work, advanced in the
interests of economy, and the idea that sand filters, receiving
polluting waters, can operate at higher rates than those which we
have demonstrated, and, therefore, have been led to believe are
safe, is a speeding up of the whole organization and of operating
conditions. It is like speeding up a machine for the purpose of
getting a greater output, with the usual result that fast running
means quicker wearing out of both man and machine. Quicker
operations generally mean carelessness in doing the work, especially
in municipal service. Carelessness is engendered by the thought that
such work can be handled in a rough and rapid way, and, further, by
the ridicule of all these things, which we have learned to be
careful about, as old-fogyish, out-of-fashion, and archaic.
Carelessness in operation breeds contempt for the art. Some of the
less efficient filter plants, from the standpoint of effect on the
public health, may reflect such ill-considered methods

_Economy with Efficiency in Operation._--It is particularly important to
find out whether one can secure the desired economy, and, at the same
time, the required efficiency. The development of efficiency in every
line of human endeavor is receiving much attention at present, and not
the least cause for this is the growing recognition of the demand for a
high standard of service for the expense caused. One of the first
requirements is to have well-defined ideals and standards. When one
knows how to secure a good and safe result, it is unwise to depart
therefrom for a mere whim, or to secure a supposedly lessened expense,
unless other facts be also determined favorably. The desire for economy
must be tempered by good sense, which means that one should be willing
to change a method only when the wisdom of such has been clearly
demonstrated. Efficient service can only be secured by strict
discipline, accompanied by fair dealing. This means employing no more
men than are actually necessary, paying them on the basis of the
standard of service and output produced, taking an interest in the
working conditions, and providing for their health and welfare.

About twelve years ago, the writer made some investigations of the
efficiency of laboring gangs in scraping and handling sand at filter
beds,[1] and found that ten men was the most economical number to
use in scraping the surface of the Lawrence filter, as then built
and operated. This result was determined by numerous studies of the
output per man per minute, with different numbers of men working
under different conditions. This same sort of study has been carried
further by adepts in the art, in reference to shop and similar
management, but one fails to find corresponding development along
this line in municipal organization except by a few of the scattered
Bureaus of Municipal Research. These results, also, have related to
a few of the more common and general factors, such as determining
the cost per mile, or per square yard, of street cleaned, or per
million gallons of water pumped.

  [Footnote 1: _Transactions,_ Am. Soc. C. E., Vol. XLVI, p. 291.]

The cost of the management of water-works, one of the largest
factors of public enterprise, has never been investigated
extensively and thoroughly. There is much possibility in planning
for greater efficiency and in determining what can be accomplished
under economical administration. Every one is aware of the
multiplicity of men in municipal service. Some of these are entirely
incompetent, others partly so; the recent appointees may be more
efficient, but the majority of them gradually deteriorate under the
subtle influence of the prevailing atmosphere, and each new incoming
administration places more and more men on the work, without reason
or necessity. All these tendencies have made the cost and
maintenance of public work greater and greater, and, at the same
time, have resulted in frequently and steadily decreasing the output
and efficiency per employee.

The Washington situation, however, presents an admirable contrast to
this, because of the methods of administration of the public works
of the District of Columbia and their freedom from petty political
influence. The limited number of employees has tended toward
economy, and rendered this plant the envy of all who have desired to
obtain good management. Its cost items have been looked on as a
result long hoped for, but seldom obtained. It is to be regretted,
therefore, that such an abrupt change in methods of removing
clogging material and replacing sand has taken place without years
of experimental trial on filters not furnishing drinking water to
the public, and without an attempt, under such excellent conditions,
to maintain the efficiency by a better labor output and by improved
working and machine methods in the performance of the older and
established order of doing things.

In preparing water for the use of the people, the realms of the
unknown are so much larger than those which have been investigated
and developed that there may be many undiscovered factors affecting
the public health, and many ways in which it is dangerous to depart
from well-known and surely safe methods. Who can say that in some
subtle and, at present, unknown manner, the failure in some places,
where filtration is practiced, to reduce the death rate from typhoid
fever may not be due to the introduction of radical departures from
the older, slower, safer, and more efficient methods which have
produced such excellent results, both in America and in Europe?
Further, in cases where there has been a falling off in the typhoid
death rate, the failure to secure an accompanying improvement in
general health conditions, which follows so closely in communities
supplied by water filtered in accordance with the more conservative
principles, may be due to the introduction of some of these not
thoroughly tried processes. Some day full information may be
available as to the influence of these methods of plant operation on
the health of the community. Until that time, is it not a much
better policy to follow the principles which have been proven by
many years of experience to produce safe results, and to make the
foremost object the improvement of the methods of operation in
accordance with these established truths?

There is opportunity for the upbuilding of greater efficiency in the
conduct of employees and in securing the maximum output, by
establishing more comfortable and healthful conditions than usually
exist. The elimination of political influence from municipal service
is also a task which challenges the people of to-day, and the
operating and managing engineer is in a position to perform an
important part in accomplishing this end. The number of employees
can be reduced to those actually needed, and the way opened for the
employment of men who thoroughly understand the necessities of
honesty and efficiency in the conduct of public affairs. It should
be remembered that to design and construct well is only half the
job; to operate economically and efficiently is even more of a
problem than to build, and requires just as good talent, just as
keen appreciation of the various problems, and is even more
essential to public welfare. It seems to the writer that the logical
development of the art of obtaining economy as well as efficiency
should be along these lines, rather than to revolutionize methods,
without having a long-period test of their value, and at the same
time allow political influences to control, to a large extent, the
labor item.

_Preliminary Treatment._--The decision as to the preliminary
treatment of the Potomac River water before filtration is of
interest, particularly because various other conclusions have been
reached in different sections of the country. However, in the main,
these decisions have been due to differences in the character of the
waters, but it must be evident that they have sometimes been the
result of ill-considered action, or the desire to promote some
special interest. The use of preliminary filters, which involves a
large investment, is not always to be commended, particularly
because at times of reasonably good water the removal of some of the
organic matter is really injurious and lessens the effect of the
final filters.

For a long time, the writer has believed that, where other things
are equal, and where there is no important reason for double or
preliminary filtration, long periods of storage, accompanied by the
use of coagulant at times of severe and extreme muddiness, as
planned at Washington, solves the problem in the most practical and
economical way. It is true that the investment for a large storage
basin may equal, or even exceed, that required for preliminary
filters; but the influence of storage on the quality of raw water is
never injurious, and, by ripening the condition of the water, may be
greatly beneficial in the process of filtration.

The storage available in such a basin makes it possible to shut off
the supply from the river during the worst conditions of the water.
The duration of the most troublesome spells ordinarily does not
exceed a few days, and it is usually possible to secure sufficient
capacity in the basin to tide over these periods. Then again, long
periods of storage, in addition to assisting in breaking up organic
matter, permit the dying out of bacteria, particularly many of the
pathogenic kind, and, therefore, the water is rendered much safer
from this standpoint. In other words, there is additional insurance
in long storage against the faulty and careless operation of
incompetent filter employees. The addition of coagulant, especially
the fact that only a very small investment of capital is required
for the necessary apparatus for dosing the water, and that the cost
of the coagulating materials has to be met only when used, seems to
give the process, in a most satisfactory manner, the requirement for
economical management and thoroughness in preparing the water for
final filtration.

_Parking Public Works._--It is disappointing that the author has not
mentioned some of the steps contemplated in reference to the
landscape treatment of the Washington filtration area. Probably
every one has been impressed by the barren aspect of the works as
they are approached, and as one looks over them. Recently, however,
it is stated that some steps have been taken to lay out the grounds,
treat the surface in an attractive manner, and make a park of the
area. The writer has a firm opinion that when an investment is made
for public works, it costs but little in addition to construct
buildings along appropriate architectural lines, to treat the
grounds in a pleasing manner, and to make the entire works a credit
to the municipality from an artistic standpoint. When treated on
broad lines, such areas become public parks, and afford open
breathing places for the residents, and, if near centers of
population, may well be equipped with playground facilities for the
children. When thus developed they should have care, that the
planting and equipment should not deteriorate and the last state
become worse than the first.

The influence which these ever-present examples of attractiveness
have on the community is becoming better recognized by students of
social progress, and there seems to be no doubt that spending money
on such features is not only desirable from the artistic standpoint,
but is justified on practical grounds as well. It is cheaper than to
create parks, when necessity and demand can no longer be resisted,
by buying property and occasionally tearing down buildings and
constructing _de novo._ That this work is now being done in
Washington, even after construction, is certainly a recognition of
the advisability of original efforts in this direction.

~George C. Whipple, M. Am. Soc. C. E.~ (by letter).--Mr. Hardy's
paper is an excellent presentation of the results of the operation
of the Washington water filtration plant from the time of its
construction in 1905 until June, 1910. Papers of this character are
altogether too infrequent, and the actual results from the filters
now in use are not readily accessible in detailed form. Yet it is
only by studying the results obtained by filters in actual use that
improvements can be made and the art advanced.

Among the many important facts brought out by Mr. Hardy, only a few
can be selected for discussion. One of these is the operation of
filters under winter conditions. It is well known that the
efficiency of sedimentation basins and filters is lower during
winter than at other times, yet it is just at this season of the
year that there is the greatest danger of typhoid fever and similar
water-borne diseases being transmitted by water. Most of the great
typhoid epidemics have occurred during cold weather, and the very
use of the term "winter cholera" is of significance. Apparently,
typhoid bacilli and similar bacteria are capable of living and
retaining their vitality longest during that season of the year.
Just why this is so, bacteriologists have not satisfactorily
explained. Doubtless many factors are involved. Because of the
increased viscosity of the water, sedimentation takes place less
readily at lower temperatures, and inasmuch as sand filtration is
partly dependent on sedimentation, the efficiency tends to fall off
in cold weather. During winter some of the external destroying
agencies are less potent, such as the sterilizing effect of
sunlight, and the presence and activity of some of the larger forms
of microscopic organisms which prey on the bacteria. Another factor
may be the greater amount of dissolved oxygen normally present in
water during cold weather, as experiments have shown that dissolved
oxygen favors longevity.

Still another reason for the larger numbers of bacteria that pass
through a water filter during cold weather may be the effect that
the low temperature has on the size of the bacteria themselves. A
few experiments made recently by the writer appear to indicate that
at low temperatures the gelatinous membrane which surrounds the
bacterial cells tends to become somewhat contracted, thus decreasing
the apparent size of the bacteria as seen under the microscope.
Either this contraction occurs, or the cells themselves are smaller
when they develop in the cold. It is possible also that low
temperature affects the flagella of the organisms in the same way.
It is not unreasonable to suppose that the effect of low temperature
is to form what may be, in effect, a protective coating around the
cells, which tends to make them smaller, less sticky, and less
subject to outside influences. This would tend to make them pass
through a filter more readily. In line with this idea also is the
well-known fact that disinfection is less efficient in cold water
than in warm water.

Another way of viewing the matter is that cold retards the growth of
bacteria on the filter, thus reducing the effect of the
_Schmutzdecke_. Still another view of the greater danger from
bacterial contamination in winter is the theory that cold prolongs
the life of the bacteria by merely preventing them from living
through their life cycle and reaching natural old age and death as
rapidly as in warm weather.

Another topic in Mr. Hardy's paper which has interested the writer
is that of preliminary filters. The experiments described at length
indicate clearly that such devices would prove of little or no
benefit under the conditions existing in Washington, and that when
the river contains considerable amounts of suspended clay nothing
less than chemical coagulation will suffice to treat the water so
that the effluent will be perfectly clear. Preliminary filters have
been used for a number of years at various places and with varying
success. In few instances have they been operated for a sufficient
length of time or been studied with sufficient care to determine
fully their economy and efficiency as compared with other possible
methods of preliminary treatment.

Among other experiments on this matter are those made at Albany, N. Y.,
and published by Wallace Greenalch, Assoc. M. Am. Soc. C. E., in
the Fifty-ninth Annual Report of the Bureau of Water for the year
ending September 30th, 1909. The Hudson River water used at Albany
is quite different in character from the Potomac River water used at
Washington, as it is less turbid and contains rather more organic
matter. The results obtained in these experiments showed that during
the summer the number of bacteria in the effluent from the
experimental sand filter used in connection with a preliminary
filter did not differ widely from the number found in the effluent
of the city filter where there was no other preliminary treatment
than sedimentation. In the winter, however, the numbers of bacteria
did not increase in the effluent from the experimental filter as
they did in the effluent from the city filter. This is shown by
Table 26, taken from the report mentioned.

Apparently, therefore, at Albany the benefits of the preliminary
filter, as far as bacterial efficiency is concerned, would be
confined to a short period of three or four months in each year.
Under such circumstances it may well be questioned whether the
advantages of preliminary filtration justify its cost.


          ~Table 26--Results of Experiments with
            Preliminary Filter at Albany, N. Y.~
  ==========+==========+==========+============+=============
    Month,  | Bacteria | Bacteria | Bacteria in|Bacteria in
    1906.   |  in raw  |  in pre- |  effluent  |  effluent
            |  water.  | liminary |    from    |    from
            |          |  filter  |experimental|city filter.
            |          | effluent.|sand filter.|
  ----------+----------+----------+------------+-------------
  March     |  133,480 |   36,000 |     151    |     706
  April     |   77,420 |    4,810 |      72    |     155
  May       |   15,800 |    2,250 |      48    |      37
  June      |    4,520 |      358 |      38    |      34
  July      |    2,090 |      163 |      25    |      22
  August    |    2,740 |      121 |      36    |      22
  September |    8,280 |      445 |      20    |      24
  October   |   38,350 |    4,235 |      67    |     227
  November  |   67,910 |   15,570 |     337    |     341
  December  |  645,500 |   25,440 |     144    |   2,783
  ----------+----------+----------+------------+-------------
  1907.     |          |          |            |
  January   |  127,560 |    4,660 |      48    |     443
  February  |   28,000 |    1,800 |      13    |     116
  ==========+==========+==========+============+=============


On the diagram, Figure 11, will be found various data taken from the
published records of the Albany filter, from 1899 to 1909. These
data include: The numbers of bacteria before and after filtration;
the percentage of bacteria remaining in the effluent; the average
quantity of water filtered, in millions of gallons per day; the
quantities of water filtered between scrapings; the turbidity of the
raw water; the cost of filtration, including capital charges and
cost of operation; and the typhoid death rates of the city per
month. Several points are brought out conspicuously by this diagram.
One is the uniformly low death rate from typhoid throughout the
entire period. The filter was operated from 1899 until the fall of
1907 with raw water taken from what is known as the "Back Channel."
Since then it has been taken from a new intake which extends into
the Hudson River itself. Until the fall of 1908 the preliminary
treatment consisted merely of sedimentation, but since then the
water has received an additional preliminary treatment in mechanical
filters operated without coagulant, along the lines of the
experiments just mentioned. During this time the average rate of
filtration of the sand filter has not changed materially, although
it is said that the maximum rate has been increased since the
preliminary filters were put in service. The study of the
bacteriological analyses shows that the best results were obtained
during 1902, 1903, and 1904. Since then the numbers of bacteria in
both the raw and filtered water have increased. This was especially
noticeable during the winters of 1907 and 1908 when the water was
taken from the new intake. It will be interesting to compare the
results after the preliminary filters have been operated for a long
period to ascertain their normal effect on efficiency and on the
increased yield.

[Illustration: ~Figure 11--Filters at Albany, N. Y. Results of
Operation. 1899-1909. Compiled from data in Annual Reports.~]

Another fact to be drawn from the plotted Albany data is the
increase in the cost of filtration, both in capital charges and in
operation. From 1899 until 1906 the cost of operation, including the
cost of low-lift pumping, was approximately $5 per million gallons
of water filtered; and the total cost of filtration, including
capital charges, was about $10 per million gallons. During the year
ending September 30th, 1909, the cost of operation had increased to
$7.63 per million gallons, and the total cost of filtration to
$15.92 per million gallons, or approximately 50% in three years.


      ~Table 27--Results of Bacteriological Analyses of Samples of
         Water at Peekskill, N. Y., Before and After Filtration.~

                     ~Bacteria per cubic centimeter.~
  ==============+=======+=======+========+========+========+========+========
                | Raw   | Clear |Effluent|Effluent|Effluent|Effluent| Tap in
       Date.    | water.| reser-| No. 1. | No. 2. | No. 3. | No. 4. | city.
                |       |  voir.|        |        |        |        |
  --------------+-------+-------+--------+--------+--------+--------+--------
  1909.
  --------------+-------+-------+--------+--------+--------+--------+--------
  December 29th |  190  |  100  |   ...  |   ...  |   ...  |   ...  |  ...
  --------------+-------+-------+--------+--------+--------+--------+--------
  1910.
  --------------+-------+-------+--------+--------+--------+--------+--------
  February 15th |  135  |   10  |    10  |    30  |    20  |   ...  |  265
  March 31st    |  225  |   50  |    25  |    45  |    60  |   ...  |   35
  May 18th      |  300  |   29  |    22  |    26  |    35  |    43  |   36
  July 6th      |  300  |   44  |     9  |     3  |    41  |    10  |   31
  August 16th   |   60  |    5  |     0  |     4  |     1  |    13  |   15
  October 3d    |  550  |   14  |    12  |    14  |    38  |   ...  |  ...
  November 21st |  315  |   22  |    26  |    17  |     6  |   ...  |  ...
  --------------+-------+-------+--------+--------+--------+--------+--------
  1911.
  --------------+-------+-------+--------+--------+--------+--------+--------
  January 25th  |  415  |    7  |     8  |     4  |     6  |   ...  |    7
  --------------+-------+-------+--------+--------+--------+--------+--------
  Average       |  277  |   30  |    14  |    16  |    26  |    22  |   65
  ==============+=======+=======+========+========+========+========+========


           ~Table 17~--(_Continued._)
             ~Tests for~ _B. Coli._
  ==================+======================
                    |~Percentage of Samples
  Quantity of water |Containing~ _B. Coli_.
       tested.      +--------+-------------
                    |  Raw.  | Filtered.
  ------------------+--------+-------------
  0.1  cu. cm.      |    0   |    0
  1.0  cu. cm.      |   20   |    0
  10.0 cu. cm.      |   40   |    0
  ==================+========+=============


As a matter of record, the results of a series of analyses made at
Peekskill, N. Y., during 1910 are presented in Table 27. A sand
filter was constructed for the water supply of this city in 1909,
and put in operation in December. The filter has a capacity of
4,000,000 gal. per day. The supply is taken from Peekskill Creek,
and the water receives about one week's nominal storage before
flowing to the filters. An aerator is used before filtration during
the summer, when algae are likely to develop in the reservoir. The
filter was installed after an epidemic of typhoid which was
apparently caused by an infection of the water supply. Normally, the
water has been little contaminated, but the supply is subject to
accidental contamination at any time, among other possible sources
of infection being the camps of workmen now engaged in constructing
the Catskill Aqueduct for New York City.


      ~Table 28--Average Results of Chemical Analysis at Peekskill,
           N. Y., Made at Intervals of Six Weeks During 1910.~
  =====================+=================+================+=================
                       |   ~Parts per    |                |    ~Parts per
                       |    Million.~    |                |     Million.~
                       |--------+--------|                |--------+--------
                       | Raw    |Filtered|                | Raw    |Filtered
                       | water. | water. |                | water. | water.
  ---------------------+--------+--------+----------------+--------+--------
  Turbidity            |  2.    |  0     |Total residue   | 70.    | 76.00
  Color                | 25.    | 20.    |Loss on ignition| 19.00  | 17.00
  Nitrogen as albumi-  |        |        |Fixed residue   | 50.00  | 59.00
    noid ammonia       |  0.112 |  0.076 |Iron            |  0.17  |  0.13
  Nitrogen as free     |        |        |Total hardness  | 38.70  | 45.10
    ammonia            |  0.024 |  0.006 |Alkalinity      | 33.90  | 42.60
  Nitrogen as nitrites |  0.001 |  0.001 |Incrustants     |  4.60  |  4.50
  Nitrogen as nitrates |  0.06  |  0.06  |Chlorine        |  2.60  |  2.70
  =====================+========+========+================+========+========


~F. F. Longley, Assoc. M. Am. Soc. C. E.~ (by letter).--In this
paper the author has presented a mass of data which will be welcomed
by engineers engaged in water purification work, because complete
operating records form a substantial basis for improvement in the
art, and are often the inspiration for interesting discussions and
the exchange of experiences of different observers whose views are
mutually appreciated.

Recent tendencies in filtration engineering have been largely in the
direction of reducing the cost of operation. A comparison of the
operating costs of the earlier American plants of about a decade
ago, with those here presented of the Washington plant, is very
gratifying to those who have been intimately connected with the
latter work. Through perfection in design and reasonable care in
operation, the cost of filter cleaning, which is a very considerable
part of the total cost, has been reduced to an unusually low figure,
without any sacrifice in efficiency, and in the interests of the
public health.

Table 14 shows that, from the first year, there has been a
progressive increase in the total cost of operation per million
gallons filtered, but this has not meant an increase in the annual
total expenditure. The largest percentage of increase in any item
has been in "Care of Grounds and Parking," and covers much-desired
landscape improvements. Aside from this, the principal factor
affecting the table of costs has been the reduction in water
consumption in the District of Columbia. Nothing pertaining to this
reduction has produced any corresponding reduction in the force
required for the maintenance and operation of the filtration plant,
office and laboratory, and pumping station, though probably there
has been some reduction in filter cleaning. Obviously, then, the
total cost per million gallons would increase.

This decrease in consumption has been brought about by the
elimination of waste in the distribution system, which is not in the
same department as the filtration plant, but with regard to which a
word may not be amiss in connection with this discussion.

The Washington Aqueduct was built half a century ago on lines which
at that time were considered extraordinarily generous. Until
recently, therefore, there has been no occasion for concern over the
high rate of consumption. During recent years, however, the use and
waste of water have increased, reaching a climax under unusual
conditions in the winter of 1904-05. The maximum capacity of the
aqueduct system is about 90,000,000 gal. The maximum daily
consumption at the time mentioned arose almost to 100,000,000 gal.,
with the result that, before normal conditions were restored, the
reservoirs of the system were almost depleted.

This had a beneficial effect, as provision was made for an active
campaign for reducing the waste of water, which was known to be very
large. These investigations, using the pitometer, were begun in
July, 1906, and have been pursued continuously since that time, with
most excellent results. Up to January, 1909, leaks aggregating about
12,000,000 gal. per day were detected and eliminated, and about half
the house services had still to be covered by the pitometer bureau.

Although this reduction in waste has brought about an apparent
increase in the cost of filtration, its economical results have been
far-reaching. The causes which brought about this investigation also
resulted in securing an appropriation for the study of the question
of increased supply. The writer was in charge of these studies, and
the most significant conclusion was that, owing to the excellent
results of the efforts for waste restriction, the total consumption
and waste of water in the district during the next few years would
be far enough below the safe working capacity of the existing
aqueduct system to make it entirely safe to postpone the
construction of new works, involving the expenditure of several
million dollars, in spite of the threatening conditions of a few
years ago.

There has been so much controversy over typhoid fever in the
District of Columbia that the writer hesitates to discuss this
subject. Viewing the situation through the perspective of several
years, however, it does not seem to be as hopeless as the criticisms
of four or five years ago would lead one to believe.

In Table 9, showing the typhoid death rates, out of nine years given
prior to 1905-06, when the filters were started in operation, only
one shows an annual death rate as low as the highest one since that
year. Further than this, the annual average typhoid death rate for
the period since that year has been one-third lower than for a
corresponding period before the filters were started.

The exhaustive researches of the Public Health and Marine Hospital
Service into this whole question, covering a period of about four
years, have raised the present filtered water supply of the District
of Columbia above any well-founded criticism. There has long been a
strong and growing feeling that the water supply, before filtration
was introduced, had been blamed for more than its share of the
typhoid, and this is borne out by much evidence that has been
presented from time to time.

It is not an unreasonable conjecture, therefore, that perhaps the
reduction of one-third in the total typhoid death rate may represent
a much larger reduction in that part of the total which was due to
polluted water alone; and that, as the authorities in the District
of Columbia and in certain other cities, particularly in the South,
are now recognizing, the fight against much of the remaining typhoid
must be in the direction of the improvement of milk supplies,
precautions against secondary infection, and attention to a large
number of details surrounding the individual, which may effectively
protect him against the insidious attack of the disease favored by
unknown agencies.


~Experiments in Filter Cleaning~.

The author refers to the difficulty encountered during the first two
summers in keeping the filters cleaned fast enough to maintain the
capacity of the plant. The real seriousness of this may be judged
from the following facts. The average increase in loss of head on
all the filters for the entire year, July 1st, 1906, to July 1st,
1907, was about 0.053 ft. per day. During the 1906 period of low
capacity under discussion, the loss of head on twelve of the filters
increased for a period of eight days at the average rate of 0.45 ft.
per day, or about nine times the normal rate of increase. This
difficulty was caused by the presence of large numbers of
micro-organisms in the applied water. During the first summer (1906)
this fact was not recognized, but the sudden decrease in capacity
was supposed to have been caused by the unusually high and
long-continued turbidity which prevailed during that summer in the
Potomac River, and persisted in the water supplied to the filters
even after about four days of sedimentation in the reservoirs.
During the second summer (1907) the same phenomenon of suddenly and
rapidly increasing losses of head appeared again, but without any
unusual turbidity in the applied water. Investigation, however,
showed the presence of large quantities of organisms, particularly
_melosira_ and _synedra_, in the applied water, and examinations in
subsequent years have shown a periodic recurrence of these forms in
quantities sufficient to cause the trouble mentioned. In June, 1907,
examination showed repeatedly more than 1,000 and 1,500 standard
units of _melosira_ per cu. cm., and one count showed nearly 3,000
standard units.

Several expedients were tried in an effort to restore the rapidly
decreasing capacity of the filters. One of the earlier conjectures
as to the cause of the trouble was that it might be due to the
accumulation of large quantities of air under the surface of the
sand, as air had been observed bubbling up through the sand,
especially in filters which had been in service for some time. The
expedient was tried, therefore, of draining the water out of the
sand and then re-filling the filter in the usual manner from below,
in the hope of driving out the entrained air. Presumably this
treatment got rid of the air, but it did not restore the capacity of
the filter, as the point of maximum resistance was in the surface of
the sand and not below it.

As the author states, raking the filters was tried and found to give
results which were satisfactory enough to meet the emergencies
already referred to. When the filters were first put in operation,
in the fall of 1905, the method of bringing back the capacity of a
filter after the end of a run was to remove all the dirty sand to a
depth determined by the marked discoloration caused by the
penetration of the clay turbidity. This sometimes necessitated the
removal of large quantities of sand at a cleaning, as the turbidity
was exceedingly fine, and penetrated at times to a depth of 3 or 4
in.

With the idea of effecting an economy in the cost of cleaning the
filters, a schedule of experiments was arranged shortly before July
1st, 1907. The general object of the experiments was to determine,
first, the relative costs of all different methods tried; second,
whether the removal of only a thin layer of sand, or the mere
breaking up of the surface of the sand by thorough raking, would
give the filter its proper capacity for the succeeding run; third,
whether the filters under these treatments would maintain a high
standard of quality in the effluents; fourth, whether the continued
application of any less thorough method than the one then in use
might materially affect the future capacity of the filters.

To this end the filters were divided into four groups which, during
a period of about six months, were subjected to treatments as
follows:

    Group _A._--Filters scraped deep at the end of each run;
    Group _B._--Filters scraped light at the end of each run;
    Group _C._--Filters raked at the end of each run, until raking
                failed to bring back the proper capacity; then they
                were scraped light, and at the end of the next run
                the raking was resumed;
    Group _D._--Light scrapings and rakings alternate at ends of
                runs.

The term "deep scraping" means the removal of practically all the
discolored sand, in accordance with the usual practice prior to the
beginning of these experiments; "light scraping" means the removal
of only a thin surface layer of sand. This depth has usually
averaged about 3/8 in. "Raking" means the thorough breaking up of
the clogged surface of the filter by iron-toothed rakes, to a depth
of about 1 or 2 in.

_Results._--A general summary of the results of these experiments is
given in Table 29, which also shows the relative costs of the
different methods per million gallons of water filtered. A normal
period of 9 months just prior to the beginning of these experiments
shows a labor cost (corresponding to that in Table 29) of $0.29-1/4
per million gallons filtered.


                         ~Table 29--Average Results.~

  Columns:
    A - Group.
    B - Number of filters.
    C - Number of days of service.
    D - Million gallons filtered.
    E - Cost of labor per treatment.
    F - Sand removed in cubic yards.
    G - Sand removed in cubic yards.
    H - Cost of labor.
    I - Bacteria per cu. cm. in effluent.
    J - Turbidity in effluent.

  =========================================+===============+==============
                                           |  Per Million  |       |
                  Per Run:                 |    Gallons    |       |
                                           |   Filtered    |   I   |   J
  -----+-----+-----+-------+-------+-------+-------+-------+       |
    A  |  B  |  C  |   D   |   E   |   F   |   G   |   H   |       |
  -----+-----+-----+-------+-------+-------+-------+-------+-------+------
   _A_ |   5 |  82 | 221.2 |$68.44 |  215  |  1.11 |$0.309 |   13  |   1
   _B_ |   9 |  36 | 101.4 | 29.25 |   84  |  0.83 | 0.288 |   16  |   1
   _C_ |   5 |  21 |  60.0 | 10.92 |   24  |  0.40 | 0.182 |   18  |   1
   _D_ |  10 |  32 |  86.0 | 20.10 |   46  |  0.54 | 0.234 |   22  |   1
  =====+=====+=====+=======+=======+=======+=======+=======+=======+======


_Capacity of Filters._--The capacity of the filters under the
different methods of treatment are shown in a general way in Table
29 for days of service and millions of gallons filtered per run.
This element by itself is decidedly in favor of the deep scrapings,
and least in favor of the repeated rakings.

A clearer conception of the capacities of the filters under these
different conditions may be obtained from the four diagrams, Figure
12, showing, for the four different groups, the average number of
days of service of the successive runs. The diagram for Group _A_
shows that the variations in the period of service of the filters
scraped each time to clean sand follow a more or less definite curve
from year to year. For the period covered by this curve, the
tendency seems to be toward a slight decrease in capacity from year
to year, as shown by the lower average maximum and minimum in the
second year than in the first. Group _B_ shows a sudden decrease in
capacity following the first light scrapings and, since that time, a
low but quite constant capacity. Group _C_ shows a constantly
decreasing capacity with successive rakings. The only significance
attaching to the curve after the first raking is the prohibitively
low capacity indicated, and the ineffectiveness of the measures
taken to restore the capacity after the sixth raking. Group _D_,
after the first raking, shows a prohibitively low and constantly
decreasing capacity. The diagrams for _C_ and _D_ indicate a
dangerous reduction in capacity if long persisted in. The method
followed with Group _C_ may be dismissed with the statement that it
is entirely insufficient, and would be of use only in the rarest
emergencies.

As far as the question of capacity is concerned, these diagrams indicate
that a filter in normal condition may safely be raked once. It is
believed that the constantly decreasing capacity shown in Group _D_ is
not due so much to the rakings as to the small quantities of sand
removed at the alternate scrapings, and therefore it would not be proper
to condemn this method of treatment without a further trial in which
this defect was remedied. This view seems to be supported by the results
of Group _B_. The low but approximately constant capacity there shown
would undoubtedly have been higher if a greater depth of sand had been
removed each time.

[Illustration: ~Figure 12--Average Number of Days of Service of
Successive Runs for Groups _A_, _B_, _C_, and _D_.~]

_Quality of the Effluent._--The averages given in Table 29 show but
little difference in the bacterial contents of the effluents from
the four groups of filters. All are entirely satisfactory, and the
differences in favor of one method or another are small. In looking
for possible differences in the quality of the effluents from the
four groups, it was thought that such differences might be most
apparent at a time when the entire plant was working under the most
adverse conditions. The bacterial counts, therefore, were summarized
for the period from December 23d, 1907, to January 6th, 1908,
inclusive, following a period of high turbidity and high bacteria in
the raw water, with results as follows:

    Group....... _A_   _B_   _C_   _D_
    Maximum..... 204   178   189   206
    Minimum.....  61    45    62    57
    Average..... 120   107   104   155

The following is a summary of the turbidity results for a similar
period:

    Group.......  _A_    _B_   _C_   _D_
    Maximum..... 10.8   11.7   8.7   9.3
    Minimum.....  6.7    4.7   6.2   5.7
    Average.....  8.7    8.3   7.2   7.9

These numbers, though high, do not show any significant differences.
All the averages for each group are less than the lowest maximum,
and all are greater than the highest minimum, and therefore vary
less than do the individual filters, from other causes, within the
different groups.

_Future Capacity of the Filters._--An indication of the dangers
which might affect the future capacity of the filters was shown in
the above discussion of the present capacity. A more effective way
of showing this was obtained by a study of the initial resistances
or losses of head in the four groups. A filter kept in ideal
condition would show no increase in this initial loss of head from
one run to the next. If there is such an increase, it means that at
some future time measures more heroic than ordinarily used would be
necessary to restore the proper capacity.

The average initial losses of head for the different groups are
plotted on the diagram, Figure 13. Group _A_ shows an initial loss of
head, increasing gradually but slightly during more than two years
of service. In Group _B_ the initial loss of head increased in a
manner similar to that in Group _A,_ up to the time of the beginning
of these experiments; after which the increase becomes more rapid.
Groups _C_ and _D_ show conditions generally similar to Group _B_,
with some variations which are self-explanatory.

_Conclusions._--The quality of the effluents from all four groups
was satisfactory, and no consistent difference was apparent in favor
of one or another method of treatment. The method pursued with Group
_C_ was entirely insufficient to maintain the capacity indefinitely.
The methods pursued in Groups _B_ and _D_ were both insufficient,
but would have been more effective if a greater depth of sand had
been removed. The costs of treatment of Groups _B_ and _D_ were less
than for Group _A_. It appears, then, that a treatment which would
be more economical than the old method of Group _A_, and would still
maintain the proper capacity, would be one similar to that of Groups
_B_ or _D_, with the removal of a quantity of sand greater than was
done in the case of these two groups, but less than in the old
method.

[Illustration: ~Figure 13--Average Initial Losses of Head for Groups
_A_, _B_, _C_, and _D_ for Successive Runs.~]

At the time the above results were summarized, it was proposed to
proceed with the filter treatment along the lines just mentioned.
The writer did not have an opportunity to study the subsequent
results, as he was transferred to other work. A statement by the
author of any new facts that may have come to light in this
connection would be of interest.

Mention should be made, too, of another expedient that was used to
hasten the restoration of the capacity of a filter, which proved to
be a most useful one. The removal of the scraped sand from a filter
was a matter of a good many hours' work, under the most favorable
conditions. To get the filters quickly into service again, the dirty
sand in a number of them was simply scraped from the surface, heaped
into piles, and left there; then the water was turned in, and the
filter was started again. This was done with some hesitation at
first for fear the presence of the piles of dirty sand might cause
high bacterial counts in the effluents of those filters. No such
effect was observed, however, the counts being entirely normal
throughout. The writer subsequently found the same treatment being
applied as an emergency measure at the Torresdale plant, in
Philadelphia, and, through the courtesy of the Chief Engineer of the
Bureau of Filtration, was furnished with the bacterial counts
through a number of runs made under these conditions, and there,
too, the results were entirely normal.

There was practically no economy in this method, as the sand had
ultimately to be ejected and washed. The piling up of the sand had
the effect of reducing the effective filtering area by a small
percentage, with a corresponding increase in the actual rate of
filtration, but this was of trifling importance. The great benefit
derived from the method was the saving of time in getting a filter
back into service after scraping, and in this respect it was very
valuable.


~Physical Theory of Purification of Water by Slow Sand Filters~.

The first and most natural conception of the action of a sand filter
is that the removal of impurities is effected by a straining action.
This, of course, is perfectly true as far as it relates to a large
part of the visible impurities. Much of this is gross enough to be
intercepted and held at the surface of the sand. This very straining
action is an accumulative one. After a quantity of suspended matter
thus strained out mats itself on the surface of the sand, it in turn
becomes a strainer, even better adapted than the clean sand surface
which supports it for the removal of suspended matter from the
water.

This, however, cannot explain certain features of the purification
of water by a layer of sand. The removal of color, the reduction of
nitrates, and certain other changes in the organic content of the
water have for a long time been recognized as due to a bio-chemical
action carried on by certain bacteria in the sand. Both the
straining action and this bio-chemical action are not all-sufficient
for the explanation of certain phenomena, and it has been
recognized, too, that sedimentation in the pores of the sand played
a large part in the purification process in those cases in which it
was apparent that the biological agencies were not the chief ones.

In the purification of water containing only insignificant
quantities of suspended matter, but a relatively large amount of
unstable organic matter, it will be conceded at once that the chief
factor in the purification is the nitrification produced by the
bacteria in the upper layers of the sand. On the other hand, the
purification by sand filters of a hypothetical water containing no
organic matter, but only finely-divided mineral matter in
suspension, could take place only by the physical deposition of the
particles upon the sand grains. Between these two extremes lie all
classes of water. In all problems of water purification by
filtration through sand, both these factors--biological action and
sedimentation--play their parts, assisting and supplementing each
other, the relative importance of one factor or the other depending
on the place of the particular water in question on the scale
between the two extreme conditions just mentioned.

In Mr. Hazen's paper on "Sedimentation"[1] there is an interesting
development of the theory of the removal of suspended matter by
sedimentation in the pores of a layer of sand. The factors influencing
this removal are the rate of filtration, the effective size of the sand,
and the temperature of the water. For the conditions at the Washington
plant, it may be assumed that the first two of these factors are
constant. The third factor, however, varies through wide limits, and the
observations on the turbidity removal, and on the different phases of
the filter operation of which the turbidity of the water is a factor
under varying temperature conditions, together with the known relations
between hydraulic values and temperatures of water, furnished good
substantiative evidence that this highly-induced sedimentation may be a
considerable factor in the purification of the water as effected at this
plant. This temperature relation, briefly stated, is as follows: For
particles of a size so small that the viscosity of the water is the
controlling factor in determining the velocity of their subsidence in
still water, that velocity will vary directly as (T + 10) / 60, in which
T is the temperature, in degrees, Fahrenheit. That is, when the
temperature of the water is between 70 deg. and 80 deg. Fahr., a
particle will settle with twice the velocity it would have if the water
were near the freezing point.

  [Footnote 1: _Transactions_, Am. Soc. C. E., Vol. LIII, p. 59.]

The layer of sand in a slow sand filter may be considered as a very
great number of small sedimentation basins communicating one with
another, not in the manner of basins connected in series, but
rather, as Mr. Hazen has expressed it, as a long series of
compartments connected at one side only with a passageway in which a
current is maintained. In any section of the sand layer there are
areas through which the water passes with a velocity much greater
than its mean velocity through the total area of voids, while there
are other areas in which the velocity is very much less, perhaps in
an almost quiescent state from time to time, greatly favoring the
deposition of particles, but with a gentle intermittent circulation,
displacing the settled or partly-settled water and supplying from
the main currents water containing more suspended matter particles
to be removed. There is thus a considerable percentage of the total
volume of voids in which the water is subjected to very favorable
conditions for sedimentation, almost perfect stillness and an
exceedingly small distance for a particle to settle before it
strikes bottom on the surface of a grain of sand.

If sedimentation were the predominating factor in the purification
of the water, we would then expect to find the following phenomena
in the operation of the filters: A more rapid deposition of a given
amount of sediment under summer temperature conditions than under
winter, as the water passes through the sand, and therefore, for the
former condition of higher temperature:

  (a) A greater concentration of this turbidity-producing material
      in the top layer of sand, or, in other words, a thinner sand
      layer to be removed in scraping if all the dirty sand is
      removed;

  (b) Because of the greater concentration, a greater rate of
      Increase of the loss of head, and consequently shorter periods
      of service between scrapings;

  (c) A higher limit for turbidity in the water applied to the
      filter to produce a given turbidity in the effluent.


  ~Table 30--Service Periods and Scraping Depths for Runs
     Ending In Various Months; Covering Entire Period,
         October 1st, 1905, To March 1st, 1907.~
  ==========+=========+===========+===============+=============
            |         |  Average  |    Average    |     Mean
            |  Number | period of | depth of sand | temperature,
    Month.  |    of   |  service  |  removed, in  |  in degrees,
            | filters.|  in days. |    inches.    |  Fahrenheit.
  ----------+---------+-----------+---------------+-------------
  January   |    13   |     75    |      2.09     |     39
  February  |     6   |     98    |      2.46     |     37
  March     |     5   |    130    |      2.66     |     41
  April     |     8   |    149    |      2.96     |     53
  May       |     7   |    130    |      2.80     |     67
  June      |    11   |    124    |      2.35     |     77
  July      |    17   |     70    |      2.12     |     81
  August    |     2   |     49    |      1.98     |     80
  September |     5   |     73    |      2.48     |     76
  October   |    37   |     70    |      1.56     |     64
  November  |    20   |     42    |      0.81     |     49
  December  |    14   |     57    |      0.94     |     40
  ==========+=========+===========+===============+=============


The operation of this plant during the first year and a half offered an
excellent opportunity for the study of sedimentation in the sand, and
the data in Table 30 are presented to show that certain of the phenomena
of filter operation observed during this period seem to be fairly
explicable by the physical theory of purification. These data are given
only for the period of operation before the summer of 1907. At that time
the experiments in filter cleaning already described were begun. Before
that time, whenever a filter had been cleaned, all the discolored sand
had been removed, leaving for the following run a new sand surface
substantially in the perfect condition of a newly-constructed filter.
After that time the experimental methods of cleaning, and the new
routine adopted as a result thereof, interfered with the tracing of the
evidence as clearly as during the earlier periods.

[Illustration: ~Figure 14--Periods of Service and Depths of Scraping
for Runs Ending in Various Months Covering Entire Period Oct. 1, 1905,
to Mar. 1 1907.~]

Table 30 and the corresponding diagram, Figure 14, show the general
variations in the length of runs and depth of penetration, with the
seasonal temperature changes. The increase in length of runs and
quantity of sand removed under low temperature conditions is very
marked. There is, however, a secondary maximum which appears, as the
diagram shows, where a minimum for the year would be expected. This
may have been an irregularity occurring this one year, which will
not appear in the average of several years, and caused by some
factor which has escaped observation. A careful analysis of the data
at hand fails to show any explanation for it. It may exist in some
of the little-understood biological actions which have their maximum
effect under warm-water conditions, or it may be due--in some
obscure way--to the liberation of air under the surface of the sand,
accumulating with pressure enough to break the surface at
innumerable points, thereby reducing the loss of head and extending
the period of service. Some evidence was observed pointing to this
explanation, but it was never conclusively proven.

The general effect of temperature changes on the rapidity of removal
of the sediment and its consequent concentration in the sand layer,
however, seems plainly evident.

In corroboration of the third point mentioned in the theoretical
consideration of turbidity removal in the filters, the daily
turbidities of the filtered water have been classified and
summarized for different turbidities in the applied water, and also
for different temperatures. The average turbidities thus obtained
are given in Table 31.

          ~Table 31--Turbidity in Filtered Water at
             Different Temperatures Produced by
              Given Turbidity in Applied Water.~
  ==========+=================================================
  Turbidity |
      of    |     ~Temperature, in Degrees, Fahrenheit.~
   applied  |---------+---------+---------+---------+---------
    water.  |   40    | 40 - 50 | 50 - 60 | 60 - 70 |   70
  ----------+---------+---------+---------+---------+---------
  20        |   1.8   |   1.3   |   1.2   |   1.5   |   1.7
  20-40     |   4.8   |   5.0   |   3.5   |   3.0   |   2.6
  40-60     |   7.9   |   6.9   |   5.4   |   ...   |   3.7
  60-80     |  10.7   |   7.7   |   ...   |   ...   |   5.4
  80-100    |  11.3   |   ...   |   ...   |   ...   |   ...
  100       |   ...   |   ...   |   ...   |   ...   |  12.0[1]
  ==========+=========+=========+=========+=========+=========

  [Footnote 1: For an average turbidity = 150. approximately.]


The influence of the temperature of the water on the turbidity of
the effluent is very pronounced. For a temperature of less than 40 deg.
Fahr. (actual average temperature about 35 deg.), the turbidity of the
filtered water for a given turbidity of the applied water is
practically twice as great as for a temperature greater than 70 deg.
(actual average temperature about 75 deg.). This fact fits in very
nicely with the influence of temperature on sedimentation. Referring
again to this temperature relation, as set forth on a previous page,
the hydraulic subsiding value of a particle in water, of a size so
small that viscosity is the controlling factor in its downward
velocity, is approximately twice as great at 75 deg. as at 35 degrees.
We would then expect to find that, in order to obtain a given
turbidity in the filtered water, a raw water may be applied at 75 deg.,
having twice the turbidity of the water applied at 35 deg., to produce
the same turbidity; and further, as the turbidity of the filtered
water, for a given temperature condition, varies quite directly in
proportion to the turbidity in the applied water, it follows that an
applied water of given turbidity will produce an effluent at 35 deg.
with a turbidity twice as great as at 75 degrees. This is quite in
accordance with the facts obtained in actual operation, as indicated
on the diagram, Figure 15.

_Preliminary Treatment of the Water._--The most striking features of
the bacterial results given in Table 4 are, first, the uniformly low
numbers of bacteria in the filtered water during perhaps 8 or 9
months of the year, and the increase in numbers each winter. This is
shown clearly in the analysis of bacterial counts in Table 32.


    ~Table 32--Classification of Daily Bacterial Counts in
        the Filtered-Water Reservoir During the Period,
          November 1st, 1905, to February 1st, 1908.~
  ==========================+==============+======================
   Bacterial count between: | No. of days. | Percentage of whole.
  --------------------------+--------------+----------------------
   0 and  20 per cu. cm.    |     291      |    41.0
  20 and  40 per "   "      |     245      |    34.6
  40 and  60 per "   "      |      63      |     8.9
  60 and  80 per "   "      |      30      |     4.2
  80 and 100 per "   "      |      28      |     4.0      92.7
  --------------------------+--------------+----------------------
  100 and 200 per "   "     |      29      |     4.1
  200 and 300 per "   "     |      13      |     1.8
  300 and 500 per "   "     |       5      |     0.7
  500 and 1000 per "   "    |       5      |     0.7       7.3
  --------------------------+--------------+----------------------
                            |              |             100.0
  ==========================+==============+======================


The tests for _Bacillus Coli_ in Table 5 show results which
correspond closely to these, with this organism detected only
infrequently, except during the periods of high bacteria, and both
of these are parallel to the turbidity variations in the filtered
water. These variations follow closely the variations in the
turbidity and in the bacterial content of the water applied to the
filters.

By all standards of excellence, the sanitary quality of the water
during the greater part of the time is beyond criticism. In view of
the close parallelism of turbidity and bacterial results in the
applied and in the filtered water, it is entirely logical to
conclude that, if the quality of the applied water could be
maintained continually through the winter as good as, or better
than, it is during the summer, then the filtered water would be of
the perfect sanitary quality desired throughout the entire year.

This was all foreseen ten years ago, when Messrs. Hering, Fuller,
and Hazen recommended auxiliary works for preliminary treatment of
the supply, although, as the author states, these works were not
provided for in the original construction. As prejudice against the
use of a coagulant seemed to be at the bottom of the opposition to
the preliminary treatment, a campaign of education bearing on this
point was instituted, in addition to the systematic studies of
different preliminary methods to which the author refers. As a
result of the combined efforts of all those interested in promoting
this improvement, an appropriation was finally made for the work in
1910. The coagulating plant has since been built, and the writer is
informed that coagulation was tried on a working scale a short time
ago during a period of high turbidity. A statement of the results of
this treatment on the purification of the water in the reservoir
system and in the filter plant would be of great interest.

[Illustration: ~Figure 15-- Turbidity in Applied Water.~]

_Hydraulic Replacing of Filter Sand._--The author has adopted a
method of replacing clean sand in the filters which will commend
itself to engineers as containing possibilities of economy in
operation. The first experiments in the development of this method
at the Washington plant were carried out some three years ago, while
the writer was still there. Substantially the same methods were used
then as are described in this paper, but examination of the sand
layer by cutting vertically downward through it after re-sanding in
this manner showed such a persistent tendency toward the segregation
of the coarse material as to hold out rather discouraging promises
of success. The greatest degree of separation seemed to be caused by
the wash of the stream discharging sand on the surface. It was
observed that, near the point where the velocity of the stream was
practically destroyed, there seemed to be a tendency to scour away
the fine sand and leave the coarse material by itself, and pockets
of this kind were found at many points throughout the sand layer.
The author states that, in the recent treatment of the filters by
this method, there has been no apparent tendency for the materials
to separate into different sizes, and it is fortunate if this work
can be done in such a manner as to avoid this separation entirely.

It may be questioned whether a certain amount of segregation of the
materials will make any practical difference in the efficiency of a
filter. In all probability this depends on the degree of the
segregation, the quantity of pollution in the water to be filtered,
the rate of filtration, and the uniformity of methods followed in
the operation, etc. For an applied water as excellent in quality as
that of the Washington City Reservoir during favorable summer
conditions, a considerable degree of segregation might exist without
producing any diminution in efficiency. For a badly polluted water,
however, such as the applied water at this plant during certain
winter periods, or the water of a great many other polluted
supplies, it might be found that even a slight lack of homogeneity
in the sand might make an appreciable difference in the results of
filtration.

As a result of the experiments herein described, however, this
method may be applied at other plants where conditions seem to
warrant it, with a largely increased measure of confidence;
although, as in the case of the adoption of any new or radical
departure, that confidence must not be permitted to foster contempt
of the old and tried methods, but its operation must be watched with
the utmost caution, until long experience shall have demonstrated
its perfect suitability and defined its limitations.

~E. D. Hardy, M. Am. Soc. C. E.~ (by letter).--It was not the
writer's original intention to enter into a discussion of either the
theory of water purification or of the experimental work on sand
handling, but simply to present the main results of operation
largely in tabular form. He is gratified, however, to have these
sides of the question so ably brought out in Mr. Longley's
discussion.

Mr. Hazen referred to the inferior efficiencies of the experimental
filters for rate studies (as shown in Table 20) in the removal of the
_B. Coli_ from the water tested. This inferiority is really less than
the figures in the table would indicate, as the tests for the
experimental filters were presumptive only (as shown by the note at the
foot of Table 20), while those for the main filters were carried through
all the confirmatory steps.

From experiments[1] made by Messrs. Longley and Baton in the
writer's office, it would seem reasonable to assume that about
one-half of the positive results, would have been eliminated had the
confirmatory steps been taken. In other words, the figures showing
the number of positive tests for _B. Coli_ in Table 20 should be
divided by two when comparing them with corresponding ones for the
main filters.

  [Footnote 1: Published in the _Journal of Infectious Diseases_,
   Vol. 4, No. 3, June, 1907.]

Mr. Knowles seems somewhat apprehensive regarding the methods described
in the paper of restoring the capacity of the filters by raking, and
replacing sand by the hydraulic method, and yet, from Mr. Johnson's
discussion, it would seem that the practice of raking filters between
scrapings had recently been adopted at the Pittsburg plant.

Before the practice of raking was finally adopted as a part of the
routine filter operation, the subject was given a great deal of
thought and study, as may be seen by referring to Mr. Longley's
discussion.

The re-sanding has been done by the hydraulic method, for nearly two
years, and, as far as the writer is able to judge, this method has
been more economical and also more satisfactory in every way than
the old one. As Mr. Hazen states, this does not prove that the
hydraulic method would be as satisfactory for other filter plants
and other grades of sand. The elevated sand bins at the Washington
plant fit in well with this scheme, and save the expense of one
shoveling of the sand; and the low uniformity coefficient of the
sand is favorable in decreasing its tendency to separate into
pockets or strata of coarse and fine sand. The method of washing is
also well adapted to this method of re-sanding, as the sand is made
very clean in its passage through the washers and storage bins. The
hydraulic method of replacing sand tends to make it cleaner still,
because any clay which may be left in the sand is constantly being
carried away over the weir and out of the bed, to the sewer. Sand
replaced by the hydraulic method is much more compact than when
replaced by other methods, and consequently the depth of penetration
of mud in a filter thus re-sanded is less. Careful tests of the
effluents from filters which have been re-sanded by the two methods
have invariably shown the superiority of the hydraulic method.

The experiment of replacing sand by water, referred to by Mr.
Longley, was not considered a success at the time, and the method
was abandoned for about a year. At that time an attempt was made to
complete the re-sanding of a filter which had been nearly completed
by the old method. The precaution of filling the filter with water
was not taken, nor was any special device used for distributing the
sand. When this method was again taken up, various experiments were
tried before the present method was adopted.

Mr. Whipple's remarks on the results from the operation of filters
under winter conditions are very interesting, and, considering his
standing as an authority in such matters, they are worth careful
consideration.

In the operation of the Washington plant, it has always been
noticeable that the results were much poorer in winter than in
summer. In fact, nearly all the unsatisfactory water which has been
delivered to the city mains has been supplied during the winter
months. On the other hand, the typhoid death rate has always been
comparatively low in cold weather. These facts would seem to
indicate that the water supply was not responsible for the typhoid
conditions.