Evening star. [volume] (Washington, D.C.) 1854-1972, 1907-07-12
REPORT ON POTOMAC WATER
MAI. COSBY STATES CONDITIONS
OF CITY SYSTEM.
Record of Daily Observations of
Turbidity of Filtered Product.
Well Water Discussed,

OF the Washington aqueduct has made a
special report to Gen. Mackenzie, chief
of engineers, regarding the condition of the
Potomac water at various parts of the sys-
tenn at different times during the past fiscal
year. From appended tables it appears that
the turbidity OF the water applied to the
filters exceeded 80 on sixty-four days during
the year, and it exceeded 100 on only ten
days. Series of observations the ap-
pearance of filtered water having different
degrees of turbidity,' says the report, in
Dictated that when viewed in a clear tumbler
or carafe against dark background tur-
bidity of l destroys the brilliancy of the
water. In an ordinary drinking glass a
turbidity of is noticeable, and one of is
decidedly objectionable.
THE record of daily observations shows
that the turbidity of the filtered water was
l or more for 40 per cent. or more for 10
per cent, and or more for Il per cent of
the year. While il is true that the small
amount of turbidity in the city water does
not affect its quality from a sanitary stand
point, it is also true that just as long as 1t
exists brilliant-looking spring or well waters
will he used by some people In preference
to the city supply.
These waters may be safe or otherwise.
Their purity cannot however, be judged
from their appearance. A protest from the
inhabitants of the vicinity is made prac-
tically every time a public well is closed,
even though us lnStinltdEy anu
condition may have been established beyond
a reasonable doubt. AS long as the filtered
water continues to show periods of turbidlty
it will be difficult to establish public con-
fidenCe in it.
Experimental Plant.
An experiment; filtration plant has been
built and opera ted since February I, 1907,
for the purpose of ascertaining the best
practicable method of clarifying the water.
The operations show that as yet we have
failed to find any system Of simple itra-
ton which promises to give satisfactory
results Neither double nor triple filtration
removes the exceedingly fine particles of
clay which remain after the first filtration.
The most practical method so far found
appears to be the use of a coagulant for
part of the time, and the experimental
work indicates that by that means the
water supplied to the consumer may be
made as clear and sparkling as spring
water. The cost of coagulation cannot be
definitely estimated from the data now at
hand. and 1t is believed advisable to wait
for the result of full years tests before
making any recommendation this SUBJ
ject.
THE experimental filtration plant at the
Dalecarlia or receiving reservoir comprises
three systems of filtration, as follows: Sys-
TEN A. consisting of rapid and a slow
sand filter: system B. consisting of Ma ig-
men scrubber and slow sand filter; system
C, consisting of settling coagulating
basin and slow sand filter.
No Satisfactory Combination.
up to the present time says Maj Cos
by mo combination of filters has been
found which has satisfactorily clarified the
Potomac water. While the preliminary FL
tiers remove the greater part of the sus-
pended matter and leave comparative
very little work for the slow sand filters to
do the grains of mud remaining in the
water after the first filtration are SO ex-
ceedingy small that they are not entirely
ton. In order to arrest these fine grains
layer of very finely powdered animal
charcoal was applied to the surface of the
slow sand filter of system b, but without
any apparent success. The results from
system c (the modified slow sand system)
show. however. that 1t has SO far been
successful in keeping the water free at all
times of turbidity by the occasional use Of
a coagulant and subsequent filtration.
The experience thus far gained with this
system indicates that II will be found to
be the most practical method of clarifying
the Potomac water at a reasonable cost,
and at the same time utilizing the plant
already installed. The bulk of the mud is
not only removed by coagulation, but the
small amount which remains is SO changed
in character that 1t can readily be removed
by filtration 1t also tends to form a
filter sand which assists In arresting parti-
Giles of mud in the applied water for sew
eral days after the use of the coagulant has
ceased