On the other hand, however, at each depression or point where water
could collect from any cause, such as by leakage through a cable
manhole cover or by the breaking of an adjacent water pipe, or the
like, a sump pit or drain has been provided for carrying the water
away from the interior of the tunnel.
For all locations, where such drains, or sump pits, are located above
the line of the adjacent sewer, the carrying of the water away has
been easy to accomplish by employing a drain pipe in connection with
suitable traps and valves.
In other cases, however, where it is necessary to elevate the water,
the problem has been of a different character. In such cases, where
possible, at each depression where water is liable to collect, a well,
or sump pit, has been constructed just outside the shell of the
tunnel. The bottom of the well has been placed lower than the floor of
the tunnel, so that the water can flow into the well through a drain
connecting to the tunnel.
Each well is then provided with a pumping outfit; but in the case of
these wells and in other locations where it is necessary to maintain
pumping devices, it has not been possible to employ a uniform design
of pumping equipment, as the various locations offer different
conditions, each employing apparatus best suited to the requirements.
In no case, except two, is an electric pump employed, as the
employment of compressed air was considered more reliable.
The several depressions at which it is necessary to maintain a pumping
plant are enumerated as follows:
No.
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