Effective Cleanup of Groundwater Contaminated with Radionuclides Using Permeable Reactive Barriers - Permeable Reactive Barrier: Sustainable Groundwater Remediation - page 154

contaminated sites are not remediated at all. Passive in situ methods offer
the advantage that after installation of the system only low operating costs
occur and the environment is only disturbed to a small degree (Simon et al.
2005).
Passive in situ groundwater remediation using permeable reactive barriers
(PRBs) is a relatively new and innovative technology with a high potential to
significantly reduce the cost of treating contaminated shallow aquifers and
therefore, contribute to the preservation of groundwater resources. A PRB
is a subsurface structure situated across the groundwater flow path down-
stream of a contaminant source (Figure 9.2).
The barrier is a trench filled entirely or in part with a granular reac-
tive material that is hydraulically permeable and reacts with the passing
groundwater to remove or degrade the contaminants from the groundwater.
Processes taking place in the reactive material of the barrier include physical,
chemical, or biological contaminant retention or degradation and reactions of
other groundwater constituents with the material. Suitable materials for use
as reactive components in PRBs are elemental iron, activated carbon, zeolites,
iron oxides/oxyhydrates, phosphates, clay minerals, and others. The most
commonly used mechanisms are redox and sorption reactions. The choice of
reactive materials and retention mechanisms depend upon the type of con-
taminant to be treated by the barrier system.
PRBs are defined by the US Environmental Protection Agency as passive
in situ treatment zones of reactive material that degrades or immobilizes
contaminants as groundwater flows through it. PRBs are installed as perma-
nent, semipermanent, or replaceable units across the flow path of a contami-
nant plume. Natural gradients transport contaminants through strategically

Heavy
metals
retained

Permeable
zone

Remediated
groundwater

Organics
degraded

Contaminated plume

Permeable
reactive barrier

Bedrock

FIGURE 9.2
Scheme of PRBs.