Evening star., 1925-08-23

| concrete gun at the base OF the shaft.
A 4-inch porta BILE pipe shoots the con-
crete under mighty air pressure to the
most distant part OF the tunnel.
The concrete is delivered from the
gun at the crown of the duct. Work
men with tamping bars and shoYels
assist in packing the binding material
into place above the metal forms.
Logically, the floor of the duct is laid
first. Then the temporary track line
| is placed directly on the floor of the
concrete duct when it hardens suffi-
ciently. The concrete forms are
! moved from station to station along
| this tramway as desired. Manhole
entrances into the tunnel are left at
each end. Thus workmen can enter
| in future years, as the need for such
action develops. in order to repair the
| curious waterway.
The ventilating air for the tunnel Is
| forced underground by a special S.
| inch ventilating fan, which is kept
| going continuously. The electrical
| power at the plant consists of current
which aggregates $4,000 volts, and
| which Mr.. Pope transforms to serve
his many mechanical purposes. One
of these is to operate the fan.
THE huge granite deposit which is
in that wedge of land bordered by
| Massachusetts. Wisconsin and Ne
| bras avenues is being blasted to
depths OF 35 TO 125 feet below the sur.
| face in order to provide a smooth
course for our future water supply tc
flow from the second high-pressure
reservoir. The total fall of the rock.
cut tunnel will be only Il inches in
$3.50 feet. Granite, as you may know
,. is one of the hardest rock materials
to cut through that the rock miners
usually meet. It breaks in great
seams, so that large rocks are show
cred over the bottom Of, the heading
after each dynamite shotfs fired.
| The new District water system will
be fully completed and ready for ac
tive service by January, 1927. 1t will
constitute one of the best municipal
/ water supplies in use under the sun
The total cost will be S., 900 ,0O0
The supply will be handled by the
old and new conduits which convey
| the water from Great Falls to the new
filtration plant at Dalecarlia, near the
District line. This Is a distance OF
| miles, SO that the combined length
Of the major water ducts amounts to
18 miles. After the water Is filtered
at this new, rapid, sand filter plant
| WItiSH W COSI .Sz,OVU,VUu, II Will Dt
carried to three special reservoirs.
The first high-storage reservoir
with capacity of 100000 gallons
Is being built of reinforced concrete
near the intersection of Ridge roac
and Reservoir street. This plant will
cost $500, 900. The second high reser
voir, of similar capacity and cost, is
being constructed above Nebra ska
tavenue and Van Ness street. The ole
Reno reservoir, of 4,5oo. 900 gallons
| capacity, will be used as the thirc
high reservoir.
A battery of nine centrifugal pumps
which will be installed at the new fl
tration plant will be used to pump
the purified water from Dalecarlia tc
1 the three storage reservoirs, whence
1t will flow by gravity, as needed, tc
the high-elevation sections of Wash
ington.
4 The filtration plant is on the old
Dalecarlia plantation of 800 acres
which the District purchased about
1853. The nominal capacity OF the
new filtrat ton plant will be about
sc. 900, 900 gallons daily. In time OF
emergency it could handle as much as
100 ,00o, 900 gallons daily. The slow
sand filter plant in Mcmillan Park
near Soldiers Home, with a capacity
of so 900 200 gallons daily, will con
tinue to be ssed to purify. the water