Evening star. [volume] (Washington, D.C.) 1854-1972, 1906-09-15
DAMAGE BY RAINFALL
LIEUT.. DENTS REPORT UPON
LOCAL AQUEDUCT SYSTEM
Condition of Water Served to the
People-Cost Of Operating
Filter Beds.

Lieut.. Elliot J. Dent, corps of engineers.
who is temporarily in charge Of the water
supply system of the District, has made a
report to Gen. Mackenzie, chief of engineers,
In which he tells of damage done to the
aqueduct system during an exceptionally
heavy fall of rain In the valley of Mill
creek on the afternoon of August "a. The
seven-foot drainage tunnel under Brooke's
hill at Dalecarlia reservoir was unable to
carry off the water, although there were
no distractions in it. The water backed
up until it stood at a level about four feet
above the crown of the arch. At that
point it began to overflow the sides of the
drainage canal and soon cut out the en-
bankment for distance of a bout fifty feet
and to a depth of about two and a half
feet. The amount of damage is estimated
at SIS.
This is the second time since the COM
pletion of the drainage canal eleven years
ago, says Lieut.. Dent, that the banks have
been washed out on account of the re-
stricted capacity of the tunnel. On the
previous occasion 1t was caused by an ex-
cess1ve rainfall over a considerable area
On this occasion 1t was the result of an
excessive railfall on the water shed of Mill
creek, but not materially affecting Falls
branch, an adjacent stream. The high
water lasted only about two hours
Regarding the physical condition of the
water served to the people of the District
during the month of August Lieut.. Dent
says:
Turbidities for the Month.
The turbidities for the month have been
unusually high. At Great Falls they aver
aged higher than for any previous month
since the plant was put in service.
Notwithstanding the fact that the gates
were closed for four short periods when the
water was especially muddy, enough of the
turbid water passed into the reservoirs be-
low to make their turbidities high The
average turbdity in the Washington CITY
reservoir was 45 and that of the filtered
water only 2.
The bacterial contents of the water at the
inlet of the Daiecarlia reservoir were a lit
tie lower than for last month, while those
at the other reservoirs were higher. The
filters were unusually efficient in this re-
spect, however SO that the average num-
Der Of bacteria in the filtered water was
lower than for any previous month. Only
once did 1t exceed % per cubic centimeter,
and then it reached only so.
The tests for the coon bacillus were car
ried on as usual. The percentage Of positive
tests were higher than usual.
The alkalinity and hardness were some
what less than for last month, owing to
the effect of the dilution of the water. due
to heavy and almost incessant rains. AS
usual, the raw and filtered water had about
the same degree of hardness.
AS only two filters were cieaned this
month the amount of sand removed from
them was small. The wr.. of washing the
sand previously scraped and stored was
continued, but owing to the rainy weather
the progress was not as great as would
otherwise have been the case.
Cost of System.
The total cost Of operation, including all
labor and materials. was $461 per million
gallons filtered. This was much greater
than for any previous month, and was due
to the purchase Of additional supplies for
the sand-washing apparatus, which, 1t is
hoped, will suffice for at least six months
The rainy weather also retarded the prog
ress of the work and made it impossible to
do 1t as economically as usual.
The average daily amount of water pump
ed to the filters was 6S. 100000 gallons, or
100000 gallons less than for last month,
while the daily amount of water used for
sand-washing averaged $4,000 gallons. or
less than one-half of that used last month.
The duty, or efficiency, of the. pumping
plant as whole was quite satisfactory, be-
ing higher than for any month since No
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