&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.

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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

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