Environmental Engineering Reference
In-Depth Information
10.1 Introduction to Reactive Gas Barriers and Zones
Following a decade of investigation and field-scale testing,
r
eactive
g
as
b
ar-
riers and
z
ones (RGBZ or gas permeable reactive barriers [PRBs]) have been
introduced as a state-of-the-art remediation technology for both organic and
inorganic contaminants in the groundwater zone.
RGBZ technology is sustainable and can achieve long term and stable
attenuation of the negative impacts of these contaminants on groundwa-
ter bodies and flow. It requires a modest initial investment and operational
costs are very competitive with other alternatives. In addition, RGBZ con-
sumes minimal resources (e.g., energy, materials, land, and manpower).
Both the operational risks and risks to human health/and the environmen-
tal are low. The RGBZ technology has demonstrated a high efficiency in
stimulating the intended transformation and exchange processes, while at
the same time showing a low sensitivity to temporal changing geohydraulic
and geobiochemical conditions.
Gas PRBs can be implemented as a stand-alone technology; they are also
suitable for treatment train applications, which are used to treat complex
contaminants (Figure 10.1). There are three basic application methods:
1. In situ gas reactors can operate as full-section gas PRBs (reactive
walls) to prevent the breakthrough of contaminated groundwater
into a sensible object that is being protected. These are typically
used to limit plume propagation or to avoid juridical implications
with respect to downstream land owners.
2. In situ gas reactors can operate as pre- and posttreatment zones for
lumped reactive barriers (e.g., funnel and gate, grain, and gate) or
treatment trains. Pretreatment is defined as the conditioning of a
lumped stream of contaminated water (e.g., to remove iron) to guar-
antee the best technical performance of subsequent treatment steps
(Kassahun et al., 2005). Posttreatment is a polishing step following
the removal of the main contaminant mass. For this treatment to
be optimal, downstream natural attenuation of some remaining or
previously inaccessible compounds needs to be stimulated.
3. In situ gas reactors can also operate as reactive gas zones in cases
where the objective is to lower the state of damage of a sensible
subsurface domain (site decontamination). Reactive gas zones then
act as retention or buffering regions against natural dynamic flow
changes (e.g., coupled aquifers to river systems), impacts from the
top soil (e.g., contaminated overburden or dumps) or from nearby
applications of invasive technologies (e.g., construction or mining
activities).
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