MIL-HDBK-1005/7A
(4)
Pressure ridges
(5)
Subsurface barriers
b)
Applications and Limitations of Control Methods.
(1) Modification of Pumping. Seek to reduce the
pumping draft or to rearrange the pumping pattern by moving the
wells inland toward the inflow portion of the groundwater basin.
This is usually the most economical method, although it does not
fully utilize the groundwater storage capacity.
(2) Artificial Recharge. An intruded aquifer may
be artificially recharged from spreading areas or recharge wells
with imported high quality supplemental water, with trapped
surface runoff, or with treated wastewater.
(3) Pumping Trough. This method consists of
forming a trough below the groundwater level, by pumping a
mixture of fresh and salt water to waste from a line of wells
adjacent to and paralleling the source of salt water. It
reduces the usable storage capacity of the basin, wastes fresh
water, and is costly to install and operate; but it is sometimes
used as an expedient until other methods can be installed, or in
conjunction with a pressure ridge.
(4) Pressure Ridge. Control is obtained by
forming and maintaining a fresh water pressure ridge adjacent to
and paralleling the coast. Although it does not reduce the
usable groundwater storage capacity, it requires supplemental
water of high quality and has high initial and operating costs.
(5) Subsurface Barrier. Such a barrier is
feasible when located in a narrow, shallow alluvial canyon
connecting inland to a large aquifer. This method maintains the
storage capacity of the basin, but has a high initial cost.
4.4.2
Springs . Many springs fluctuate in their yield and
are subject to possible pollution. Frequently, spring water is
of less desirable sanitary quality than other underground
sources.
4.4.2.1
Types. Springs may be characterized and classified as
thermal ,gravitational, depression, contact, artesian, and
tubular or fracture. Thermal springs are not used since their
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