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Groundwater
contamination is a major concern worldwide.
It has been estimated that there are
300,000 to 400,000 contaminated sites in the
United States alone (National Research
Council, 1994).
With this many sites, cleanup efforts
could cost as much as $1 trillion over the
thirty year period beginning in 1995.
The most common technology for
cleaning up groundwater has been the
traditional pump and treat system in which
pumping wells are used to extract
contaminated groundwater to the surface for
treatment and disposal.
In a recent assessment, 89% (588 out
of 663) of Superfund sites were found to be
using some form of pump and treat strategy
(U.S. EPA, 1999).
However, studies have shown that not
only is this method costly, but clean up to
the desired levels may not be possible or
may take too long to be feasible (Mackay and
Cherry, 1989; Travis and Doty, 1990; U.S.
EPA, 1992; National Research Council, 1994).
This realization started a movement
toward in situ remediation methods, with the
goal of providing more economical and better
performing systems than the traditional pump
and treat approach can provide (National
Research Council, 1994; Nyer et al., 1996).
One alternative to pump and treat is the funnel and
gate system, which was proposed by Starr and
Cherry (1994).
This system employs the use of
impermeable barriers, such as slurry walls,
to ‘funnel’ groundwater through one or
more subsurface contaminant treatment cells,
i.e., the gate.
As this technology is increasing in
popularity, the need to understand the
performance of these systems in “real
world” aquifers and develop preliminary
design screening tools is becoming
increasingly necessary.
Effective design and implementation
of such a system may, however, prove
difficult for settings that experience large
or unpredictable variations in contaminant
plume or ambient groundwater flow
characteristics. Furthermore, understanding
the effects of heterogeneity on
funnel-and-gate system performance can be
the difference between a successful
remediation project and a project that fails
to meet its cleanup goals.
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