e 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