Environmental Engineering Reference
In-Depth Information
reactivity, permeability, and contaminant under or over the PRB, or leakage
through funnel walls if present as illustrated in Figure 3.5.
The location of monitoring wells is a critical element in determining
whether the PRB is meeting compliance and performance criteria deter-
mined from hydrogeological modeling (see Section 3.2.2.1). Although site-
specific conditions should always dictate the placement of monitoring wells,
performance monitoring wells should be located up-gradient and down-
gradient and, if possible, within the PRB. In addition, wells at each end of the
PRB are necessary to verify hydraulic capture and evaluate potential plume
bypass, particularly if impermeable funnels are used to intercept and control
GW flow. Figure 3.5 illustrates idealized monitoring networks for continuous
and funnel-and-gate PRB design, respectively (Carey et al. 2002). Regulatory
requirements for location monitoring wells and sampling frequency vary.
Therefore, regulatory-specific monitoring well requirements should be con-
sidered during well design and construction.
3.3 PRB Construction Techniques
The installation method for a PRB system is very critical for their success-
ful performance and includes geotechnical/civil design considerations, the
method of construction, service and infrastructure, waste management, and
health and safety requirements. Important factors for suitable construction
for a specific site include
• Soil quality at site and soil waste generation
• Designer and contractor's expertise
• Aquifer and aquitard characteristics
• Construction constraints at the site (space availability for construc-
tion of barriers)
• Construction budget
Excavation and injection methods are the two major types of construction
techniques for PRB installations. The depth to the GW table plays a part in
the selection of the construction techniques, that is, for a shallow depth, exca-
vation techniques are suitable and for a deeper barrier, injection methods
are suitable. Depending on the contaminants present and disposal methods,
the soil generated also influences the choice of the construction technique.
Contaminated site soil quality influences the type of excavation in terms of
the side wall support. In general, the excavation technique generates more
spoil than injection-based techniques, however, excavation techniques are
relatively easy and straightforward. In most cases it is assumed the aquifer
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