National Republican., 1876-05-12
THE ruRBIp POTOMAC.
Information from Mr.. T. B. samo-Replies to
Or, Verdi

Dr.. Verdi.
In answer to a resolution of Congress, request
ing the Board of Health of Washington to in
quire into the causes of the present turbid condi
tion of the Potomac water supplied by the Wash
ington aqueduct:
OFFICE OF WASHINGTON AoUKDUcT,l
Hon. T. C. verdi, Member r. Of the Board Of Geatth,
SIR have the honor to acknowledge the re-
ceipt of your communication of the 18th instant,
requesting me to furnish you with answers 10 the
following questions relating to the Washington
formation as this office contains.
Question l. When were the Washington aque-
engineers by whom designed and built.
Answer. The construction of the Washington
aqueduct was begun November s 1853, BY Frank
works were designed on their present general
plan and location by Montgomery G. Meigs, cap
engineers have been Captain NJ. Q. Meigs, viii
liam r. Hutton, Q. f; Silas Seymour, Q. T.;
Theodore B: Samo; Q. e; Major Nathaniel Mich
Ter, MAJOR George H. Elliott and Colonel o. E.
Babcock.
Question 2. Under what organization were the
Answer. The works were built by order of the
Congress of the United States for the purpose Of
bringing water into the cities of Washington and
Georgetown, and since they were begun until the
present time have been under the charge of the
General Government.
Question g. Under what organization are they
Answer. Since July, 1867, the works have, by
act of Congress, been under the charge of the
chief Of engineers, United States army.
Question Z. What is the source of supply?
Answer. The source of supply is the Potomac
Question s. Quality Of the water and analysis
Answer. The Potomac water was analyzed las.
year. under the direction of the Surgeon General
United States army. The following table is one of
the results: The quantities are in ten millionths
or so many milligrammes in ten htres Of water,
equivalent TO maQy grains in hundred and
seventy.o one gallons:
C!orine 0O1
Ammonia VI
Albumenoid ammonia. nia....................... O.82
Permauganate potash. ACKNOWLEDGEMENTS. S2i
The first constituent, the clorine is an indication
Of the probable amount OF animal matter after which men
ammonia the next line of this includes the
ammonia of the ammonical salts. and of the urea.
BY the albumenoid ammonia is understood the
ammonia produced when water is acted on by q
permanganate in the presence Of a considerable
amount of alkali, under which circumstances the
nitrogen of any albuminOus matter present is dis
engaged in the form of ammonia.
The last line Of the table gives the amounts of
permanganate ofpot ash decompOsed by warming
for half an hour with acidulated water.
The Potomac water is, as regards hardness,
rather better than the average Of river waters,
being 10 4-l0 degrees of Clarke's scale.
Question 9. Cost Of works, original and addi-
tions?
Answer. In 1858 the estimated cost of the works
was $3.50 They are not yet finished, but
the actual expenditure for all purposes from 1858
to the present time, including construction and
maintenance is S3,7:S,267.
Question No. I. Cost of maintenance of works
annual?
Answer. The annual cost of maintenance of
works, including engineering, superintendent
dollars.
Question No. s. Population of Washington and
Georgetown, number of consumers and quantity
of water used?
Answer. The population of the two cities is
supposed to be l4S,OOo. The quantity of water
used by the citizens and Government Depart
ments averages twenty-three million United
States gallons in twenty -four hours.
Question No. 9. Character of supply, gravity
steam pumping or water power? If by gravity,
size, form and grade of conduits?
Answer. For the city of Washington and a
part of Georgetown the supply of water is brought
by gravity. For Georgetown Heights steam
pumping is the power used. The conduit of the
Washington Aqueduct is circular in section, nine
feet interior in diameter, twelve inches long, with
a uniform grade of nine and one half inches to
each mile.
Question No. 10. Number of reservoirs, size,
method of construction
Answer There are two reservoirs-the receiv
ing ana nbnt taS miIes rom tbs head of the
Aqueduct, its area at the flow line (li5 feet above
tide-water) is 81 acres. 1t is natural basin
formed by building an earthen dam across the
valley, of Powder-Mill branch, small creek
that formerly emptied into the Potomac. 1t is
now seldom used. The distributing reservoir is
miles from Great Falls, is in form nearly rectan-
gle, and has an area at the flow line of forty-four
",
faces are protected by slope wall of dry rubble
masonry from II to Is inches in thickness, laid on
a bed of small broken stones inches in thick
ness.
Question. No. II. Have you estimated the flow
Of the Potomac river above Great Falls? II SO,
what was the result?
Answer The Potomac was gauged above Great
Falls. near the head of Conn's Island A mean
measurement OF thirteen experiments with floats
The area of water section was S,0i2 $40 square
feet, and the estimated discharge, per D'Aubis-
sons formula, was 900 900 imperial gallons in
Question No. T. How much of the Potomac
water can be discharged by the conduit into the
distributing reservoir in twenty-four hours?
Answer 1fthe dam at the head of the aqueduct
was continued entirely across the river to the
Virginia shore the conduit, running I mil full could
twenty-fO hours. The present dam extends
across the Maryland channel only; and the guam
pends upon the depth Of water above this dam.
During the season Of drought the minimum flow
of the Maryland channel is about 20 oO1 600 gallons
in twenty-four hours all of which is brought by
the conduit to the distributing reservoir.
Question 1S. By what process can the Potomac
water be clarified SO as to render mt for use the
quantity required for the daily supply of Wash
ingtOn and Georgetown? If filtration is necessary
what should be the number and size Of the filter
beds?
Answer. For the present the Potomac water
can be brought to respectable condition Of purity
yoir TO such an extent as will afford it ample time
to settle and to deposit its sediment "At fu-
ture day the water of the Potomac, like that of
many other rivers, will need hltrati0n to render
II potable" The successful use of the filter bed
presuppOses the preparation of the water in
has been made to use filter beds without that
preliminary aid they have either failed altogether
or rendered the water but partially clarified"
THE materials used for filtration on large
scale are very simple. They are sand, gravel and
broken stone; the depth Of the whole varying from
five to six and one half feet"
Each filter bed at short intervals varying with
the condition of the water, must have the deposit
that accumulates on the surface Of the sand
cleaned of or removed, and while any one is un-
dergOing this cleansing process the other remain
ing filters must be competent to deliver the re-
quired supply" ''If then, there are seven filters
six Of them must be competent to the full duties
of the service"
Mr. James p Kirkwood, an eminent authority
on hydraulics, when chief engineer of the st.
Louis Water Works assumed half a'cubic foot of
water per hour per square foot of the sand floor
as fair exponent of the best English practice,
and as rate which, with the usual attention, will
be certain to insure satisfactory results. This
rate is equivalent to SgA United States gallons
per square foot per diem.
Assuming the size of a filter-bed for such a city
as Washington TO be one acre, this area gives
filtration Of Se09, $40 gallons in twenty-four
this size would be necessary, on the supposition
that the flow of water through six of them would
be continuous G through the y twenty-IOur hours S
fornly distributed throughout the city of Wash
ington, and can the present pressure in the mains
Answer Comparatively uniform distribution of
water can be insured in any city, if it is divided
into districts, each district mapped in reference
to altitude and provided with main proportioned
to its area The pressure can be increased by lay
ing more mains from the distributing reservoir.
In the law concerning the fow Of water in pipes
under uniform head velocity and pressure become
interchangeable terms; as velocity increases pres
sure diminishes until 1t disappears in velocity,
and rice versa. This velocity being checked,
pressure is regained.
Very respectfully yours,
THEODORE B. SAMo,
Assistant Engineer of the washington Aoueduct
STANDING ROOM" LEFT FOR BEECH