MIL-HDBK-1005/7A
e) Valves should be placed at the end of the
collecting pipes discharging into the sump, and thus providing a
means for back flushing to improve the capacity and for
isolation for repairs.
4.4.3.3
Tunnel or Gallery . For
diameters from 2 to 5 ft, use
concrete or masonry conduits with
perforated openings
constructed by open excavation or
tunneling. Design strength
requirements for buried pipes are
applicable.
4.4.3.4
Underground Dam. Subsurface sheet piling, masonry, or
chemically solidified barrier dams may be used in conjunction
with other collection systems where groundwater is confined in a
narrow valley. Locate the dam downstream from the collecting
system. It must reach to an impervious formation, in order to
seal off the underflow and store it for withdrawal by the
upstream collector system.
4.4.3.5
Radial Type Collector. Buried perforated pipes,
driven radially from a collecting sump, may be installed near a
place of recharge from surface waters, and occasionally
elsewhere. This type is best adapted to permeable alluvial
aquifers. Yields may range from 300 to 14,000 gpm.
4.4.4
Skimming Wells . Horizontal wells, termed Maui wells,
are the same type as the infiltration galleries in horizontal
tunnels.
4.4.4.1
Locations . These wells are used when the seawater is
in contact with the fresh groundwater on one or more sides at
the following locations:
a) Islands, atolls, peninsulas, spits, or bars
surrounded by the sea.
b)
Artesian aquifers which outcrop under the sea.
4.4.4.2
Construction . Skimming wells should, if possible, be
constructed above sea level, and near the thickest section of
the fresh water lens so as to utilize the greatest available
hydrostatic pressure and storage. In Pacific atolls,
construction below sea level may be permissible to allow
withdrawal at low tide.
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