Evening star. [volume] (Washington, D.C.) 1854-1972, 1906-11-08

made by them was that the water reaches
the filter in a settled condition. and sus-
gested the installation of apparatus for
adding a coagulant to the water and for
Transforming one of the local reservoirs
into a more efficient sedimenting basin in
order to overcome the difficulty. They
also claimed that the turpid condition of
the local water has certain effect on the
mortality rate of the District. They said
that the sand used at the Washington i'll
tratiOn plant was required by specifications
to have a greater freedom from fine par
ticles than the sand used with such salts
factory results elsewhere.
At the requisite of the officials of the So
ciety DR.. William c. Woodward, the health
officer Of the District, who is thoroughly
familiar with the nature of the filtration
plant from public health point OF view,
prepared a paper, in which he discussed the
paper of Messrs. HaZen and Hardy, and
which was also read before the society last
night Regarding the sand which Is re-
ferred to in the paper of Messrs. Hazen
and Hardy, it was to have greater
freedom from fine particles than the sand
used elsewhere, DR.. Woodward said:
This, as | understand it, means in eff
| feet that it was desired that the interspaces
between the grains should be larger ana
| that the filter was designed with that end
| in view. Why, then, when the excessively
| fine particles that are suspended in the ap-
piled water find their way further into the
| sand layer than is usually the case, Should
we say that it is due to the peculiar COM
position d the applied water instead of
| saying that it is due to the unusual char
| acter of the sand layer?'
Proposed Coagulant.
Continuing his discussion DR.. Woodward
said, relative to the proposed coagulant and
| the alleged settled condition OF the water,
| as follows:
1--WE are told that the water that reaches
| the filters has been settled to an unusual
extent, and that no filters of the type of
| those Washington have been used IN
America with water settled anything like
so much This, 1t is said, Is the cause OF
| that peculiar condition of the applied water
that is responsible for the penetration OF
suspended matter so deeply into the hlters,
| and project is submitted for.the installa-
| tion of apparatus for adding a coagulant to
the water and for Transforming one OF our
reservoirs into more efficient sedimenting
basin in order to overcome the difhcuity
! The question naturally arises, Why is It
necessary to permit such excessive sedl-
mentation to continue!
Queries Propounded.
HAS 1t been demonstrated that as mat
ter Of fact the penetration Of the fine clay
into the sand layer for distance Of two
or three inches does harm? Apparently 1t
renders it necessary to remove more sand
| at each scraping. but does 1t not proper
tionately diminish the frequency OF the
scrapngs? Have not the freshly scraped
filters been found to be as efficient as any
other freshly SCTdpSO IilSIS <tuo Hdo
not the bacterial efficiency Of the Washing
ton filters been equal to that of any filter
where the sediment penetrates less deeply
into the sand?
Existing Conditions.
He stated that under the conditions ex-
listing at he local plant it is doubtful If
chemistry and mechanics of coagulation
and sedimentation can be controlled so as
to unerringly throw out of suspension an
amount of sand and clay in excess of the
amount of the precipitate that will reach
the sand layer.
And finally" declared DIR. Woodward in
further discussion of the use of coagulants.
lis It so. certain that the cost Of oper-
ating the system with the use of coagulants
would not be materially greater than now?
At the very beginning we have an outlay
of $105,OO0 for the necessary apparatus for
adding the coagulant and for renodeiing
one OF the reservoirs to meet the changed
conditions And II to the interest and
sinking fund based on this investment we
add the cost of labor and material, the
total annual cost of the coagulating works
would be very considerable. What evil
dence is there to show that this would be
Offset by a reduction in the cost of cleaning
the filters?
Question Of Turbidity.
DIR. Woodward admits that the only rea-
| son for adding coagulant seems to be as
a guard against the appearance Of any tnr-,
| bidity in the water. He said, as a medical