e
leakage, leaving 0.0032 cu. ft. per sec. or 0.00000081 cu. ft. per sec.
per lin. ft. of tunnel to be accounted for as general seepage
distributed over the whole length.

It was not feasible to stop every leak in the tunnel, most of which were
indicated simply by damp spots on the concrete; a rather simple method
was devised, however, for stopping the leaks at the eight or ten places
in each tunnel where water dripped from the arch or flowed down the face
of the concrete. The worst leak in any tunnel flowed about 0.0023 cu.
ft. per sec. To stop these leaks, rows of 1-in. holes, at about 4-in.
centers, were drilled with jap drills through the concrete to the flange
of the iron. These rows were from 3 to 18 ft. long, extending 1 ft. or
more beyond the limits of the leak. The bottoms of the holes were
directly on the caulking groove and the pounding of the drill usually
drove the caulking back, so that the leak became dry or nearly so after
the holes were drilled. If left alone the leaks would gradually break
out again in a few hours or a few days and flow more water than before.
They were allowed to do this, however, in only a few cases as
experiments. After the holes were drilled, the bottom 4 in. next the
flange was filled with soft neat cement mortar. Immediately on top of
this was placed two plugs of neat cement about 2-1/2 in. long, which
were 5 or 6 hours old and rather hard. Each was tamped in with a round
caulking tool of the size of the hole driven with a sledge hammer. On
top of this were driven in the same way two more plugs of neat cement of
the same size, which were hard set. These broke up under the blows of
the hammer, and caulked the hole tight. When finished, the tamping tool
would ring as though it was in solid rock. Great pressure was exerted on
the plastic mortar in the bottom of the hole, which resulted in the
re-caulking of the joint of the iron. No further measurable leakage
developed in the repaired cracks, during a period of four months, and
the total leakage has been reduced to about 0.002 cu. ft. per sec. in
each tunnel, an average of 0.00000051 cu. ft. per sec. per lin. ft.

SUMP AND PUMP CHAMBERS.

To take care of the drainage of the tunnels, a sump with a pump chamber
above it was provided for each pair of tunnels. The sumps were really
short tunnels underneath the main ones and extending approximately
between the center lines of the latter. They were 10 ft. 9-1/2 in. in
outside diamete