Effective Cleanup of Groundwater Contaminated with Radionuclides Using Permeable Reactive Barriers - Permeable Reactive Barrier: Sustainable Groundwater Remediation - page 156

barriers and sorption barriers. Reductive barriers employ mechanisms that lead
to the reduction of the target compound, or parts thereof, to achieve decom-
position or immobilization of that compound. Barriers utilizing surface reac-
tions that lead to immobilization of the target contaminants by adsorption, ion
exchange, coprecipitation, solid-solution formation, and so on, without altering
the chemical state of the contaminant are usually termed as sorption barriers.
In terms of geometry, two main types of PRB have been used in the field.
These are (i) continuous reactive barriers enabling a flow through its full
cross section, and (ii) “funnel-and-gate” systems (Starr and Cherry 1994) in
which only special “gates” are permeable to the contaminated groundwa-
ter. The continuous PRB configuration is characterized by a single reactive
zone installed across the contaminant plume, while the “funnel-and-gate”
system consists of an impermeable wall that directs the contaminated plume
through one or more permeable gates within the wall (Figure 9.3).
The choice between the two configurations depends on the hydrogeologi-
cal characteristics of the site, the technical applicability of the barrier place-
ment, and on the cost of the reactive material. When a high-cost reactive
material is used, the “funnel-and-gate” configuration is preferable since the
reactive zone requires less material. If a cheap material can be used, it is
more profitable to avoid the construction of the impermeable sidewalls by
employing a continuous barrier.
In PRBs, the residence time of the contaminant in the reactive material
must be long enough to allow a decrease of the contaminant concentrations

Groundwater flow

Contamination

Cleaned
groundwater

Plume

Source

“Funnel”

Gate

FIGURE 9.3
Funnel and gate versus continuous PRB.