&EPA
www.epa.gov/research
EPA/600/F-13/324
science in ACTION
INNOVATIVE RESEARCH FOR A SUSTAINABLE FUTURE
PERFORMANCE ASSESSMENT OF A PERMEABLE REACTIVE BARRIER FOR GROUND WATER
REMEDIATION FIFTEEN YEARS AFTER INSTALLATION
ORD research in the Sustainable Healthy
Communities program has a focus on
sustainable solutions for contaminated sites.
Remediating contaminated sites contributes to
community sustainability by eliminating risks to
receptors and bringing the properties back into
commerce. Remediation technology itself can
contribute to sustainability by having low cost
and operating characteristics which are
acceptable to the surrounding community.
Research on permeable reactive barriers (PRB)
fits these requirements and scientific research
on their performance provides the basis for
correct application of this technology.
Interest in site-specific evaluations of PRB
performance is high, particularly with regard to
issues relating to media longevity and hydraulic
performance. Compared to the large number of
full-scale PRB applications around the world that
have been constructed to remediate ground-
water contamination, comparatively few long-
term data sets are available in the literature that
provide detail on performance. Higgins and
Olson (2009) recently conducted a life-cycle
comparison of PRBs versus pump-and-treat
operations for ground-water remediation.
Based on their analysis, environmental impacts
from PRBs are driven largely by material
production requirements and by energy usage
during construction, while for pump-and-treat
systems environmental impacts are driven by
energy demand. Higgins and Olson (2009)
conclude that the minimum longevity of
granular iron PRBs required to out-compete
pump-and-treat systems is 10 years.
Consequently, a key aspect of life-cycle analysis
U.S. Environmental Protection Agency
Office of Research and Development
Permeable Reactive Barrier
^H
and cost/performance assessment is to have
predictive tools that reasonably estimate long-
term PRB performance using site-specific
parameters such as groundwater chemistry and
hydrologic conditions. Development of such
predictive tools requires long-term data sets.
The granular iron PRB installed at the U.S.
Coast Support Center located near Elizabeth
City, NC (USA) is a well-documented full-scale
PRB designed and constructed for removing
hexavalent chromium from ground water.
Current research provides an update on the
contaminant removal efficiency of this PRB after
15 years of operation.
-------
Study Findings:
Results of the long-term performance
evaluation (Wilkin et al., 2014) at the Elizabeth
City site indicate that the reactive barrier there
continues to remove contaminants from ground
water after fifteen years of operation. Key
results are:
• Removal of contaminants, Cr and TCE,
continues after fifteen years of PRB operation.
In all cases, chromium concentrations have been
reduced to below regulatory thresholds and in
the majority of sampling events Cr was
undetected in monitoring wells located
downgradient from the PRB. Concentrations of
volatile organic compounds have been
significantly reduced, but TCE concentrations
above the MCL have been observed in some
downgradient wells.
• After fifteen years, ground water in the PRB is
moderately alkaline (pH>9) and moderately
reducing (negative EH values). Time trends in
pH suggest quasi-steady-state conditions. Time
trends in EH, however, suggest that the PRB is
gradually losing the capacity to produce
reducing conditions due to progressive exposure
to ground water.
• The Elizabeth City PRB has consistently
removed inorganic carbon, sulfate, and calcium
from influent ground water. These components
have either been precipitated out in the PRB, or
have been chemically transformed by biotic or
abiotic processes.
Wilkin, RT, Acree, SA, Ross, RR, Puls, RW, Lee,
TR, and Woods, LL (2014). Fifteen-year
assessment of a Permeable Reactive Barrier
for treatment of chromate and
trichloroethylene in groundwater. Science of
the Total Environment, v. 468/469, p. 186-
194.
CONTACTS:
Richard Wilkin, Ph.D., Office of Research and
Development, 580-436-8874,
wilkin.rick@epa.gov;
Jim Weaver, Ph.D., Office of Research and
Development, 580-436-8550,
weaver.iim@epa.gov;
David Jewett, Ph.D., Office of Research and
Development, 580-436-8560,
iewett.david@epa.gov
REFERENCES:
Higgins, MR and Olson, TM (2009). Life-cycle
case study comparison of permeable reactive
barrier versus pump-and-treat remediation.
Environmental Science and Technology, v. 43,
p. 9432-9438.
U.S. Environmental Protection Agency
Office of Research and Development
------- |