Fourteen-Year Assessment of a Permeable Reactive Barrier for Treatment of Hexavalent Chromium and Trichloroethylene - Permeable Reactive Barrier: Sustainable Groundwater Remediation - page 106

maximal concentrations in the effluent actually increase relative to maxi-
mum concentrations in the influent groundwater. The TCE concentrations
have been significantly reduced, yet the breakdown of daughter products is
incomplete.
Results from the Elizabeth City PRB with respect to TCE remediation are
comparable to other reports on PRB long-term performance (e.g., Phillips
et al., 2010; Warner et al., 2005). Collectively, these studies indicate that gran-
ular iron can be effective in treating TCE contamination over for more than
10 years.
6.5 Conclusion
There is a continuing need for long-term performance assessments of
groundwater remedial systems. The literature on PRB technology has sev-
eral examples of remedial longevity that extend to 10 years and beyond. The
Elizabeth City PRB is one example that has shown positive results for the
treatment of hexavalent chromium and TCE. This system is perhaps the first
demonstrated example of a PRB that shows reactive performance that sur-
passes the lifetime of the contaminant plume (in the case of chromium). The
sustained performance of the PRB can be linked to several key factors: (i)
pH and redox conditions within the barrier have been maintained at ideal
levels for chromium reduction to the trivalent state; (ii) influent groundwater
chemistry is low in dissolved solids, so mineral accumulation due to car-
bonate precipitation has not significantly impacted reactivity and hydraulic
conductivity, and (iii) the influent dissolved oxygen loading has been low,
so iron corrosion reactions have not significantly impacted reactivity or
hydraulic conductivity.
References
Flury, B., Frommer, J., Eggenberger, U., Mäder, U., Nachtegaal, M., and Kretzschmar,
R. 2009. Assessment of long-term performance and chromate reduction mech-
anisms in a field scale permeable reactive barrier. Environmental Science and
Technology 43, 6786-6792.
Higgins, M.R., and Olson, T.M. 2009. Life-cycle case study comparison of permeable
reactive barrier versus pump-and-treat remediation. Environmental Science and
Technology 43, 9432-9438.
Kahn, F.A., and Puls, R.W. 2003. In situ abiotic detoxification and immobilization of
hexavalent chromium. Ground Water Monitoring and Remediation 23, 77-84.