Environmental Engineering Reference
In-Depth Information
TCE degradation rate declines by a factor of 2-2.5 at temperatures of 8-10°C
compared with rates measured in the laboratory. Similar results have been
observed at other field sites (Gavaskar et al. 2000).
The bulk density of the reactive medium in the field is generally lower
than that measured in the laboratory. Consequently, the surface area of
reactive medium per unit volume in the field may be lower than the sur-
face area measured during a column testing. Furthermore, the reaction rates
(or half-lives) are proportional to the specific surface area of the reactive
medium (Gillham 1996; Johnson et al. 1996). The field residence time must
therefore be increased to account for the lower expected ratio of reactive sur-
face area:volume of solution. Currently, there is no clear indication of how
large the bulk density correction factor should be (Gavaskar et al. 2000). To a
degree, the surface area of reactive medium per unit volume in the field will
depend on the efficiency of the construction methodology and on how well
the reactive medium consolidates after construction.
3.2.3 Type and Configuration of Barrier
The main requirement of the PRB design is to capture the contaminant
plume throughout its life span and remediate the plume to meet the reme-
diation target. Figure 3.3 shows various PRB types and configurations. The
selection of an appropriate configuration should be made on a site-specific
Continous reactive wall
Funnel-and-gate-varying funnel extention
(a)
(b)
(e)
(h)
(c)
(f )
Multiple reactor system
(d)
(g)
Fully penetrating PRB
(i)
Multiple-gate system
Hanging PRB
FIGURE 3.3
The continuous and various configurations of funnel-and-gate PRBs. (Adapted from Starr, R.,
and J.A. Cherry. In situ remediation of contaminated ground water: The funnel-and-gate sys-
tem.
Ground Water
. 1994. 32(3):465-476. Copyright Wiley-VCH Verlag GmbH & Co. KGaA.)
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