Environmental Engineering Reference
In-Depth Information
Vadose zone
Permeable reactive
material
Backfill-selected
material
GWT
Aquifer
Contaminated plume
Treated GW
GW flow direction
Confining layer (Aquitard)
FIGURE 1.3
PRB intercepting a contaminant plume.
designed to be more permeable than the surrounding aquifer materials so
that contaminants are treated as groundwater readily flows through with-
out significantly altering its hydrogeology. As groundwater passes through
the wall under a natural gradient, contaminants are either trapped by the
reactive barrier or removed via chemical degradation and transformed into
harmless substances that flow out of the wall (Figure 1.3).
Although the applications of PRBs are limited to certain site conditions,
where applicable, they are most favored particularly in the urban environ-
ment and in built-up areas due to no obstruction of aboveground activi-
ties. A major benefit of PRB techniques is that as an in situ technology, an
extensive range of contaminants can be treated, often reducing their con-
centration to below their detection limits. Research on PRBs increased sig-
nificantly during the 1990s leading to a number of new approaches in terms
of PRB design, suitable reactive materials, and target contaminants (ITRC,
2011). There are two main types of configuration for the installation of a
PRB in the field and these include (a) continuous reactive barriers enabling a
flow through its full cross section, and (b) “funnel-and-gate” systems where
only part of PRB wall gates are permeable to contaminated groundwater
(Roehl et al., 2005a). Cut-off walls (the funnel) modify flow patterns so that
groundwater primarily flows through high permeability wall (the gate). The
material used for constructing the funnel includes slurry walls, sheet piles,
a geotextile membrane, or a soil admixture applied by soil mixing or jet
grouting (Figure 1.4).
Understanding the groundwater flow regime on a more localized scale (i.e.,
tidal and/or seasonal variation, aquifer heterogeneity, the evapotranspiration
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