Case Study of PRB Application for the Remediation of Groundwater - Permeable Reactive Barrier: Sustainable Groundwater Remediation - page 273

the indigenous microflora than commonly observed. The most abundant
sequence detected in the libraries belonged to a member of the Dechlorosoma
genus, reported to respire chlorate (which would not be expected to be pres-
ent in the site groundwater) and to oxidize ferrous iron (Lack et al., 2002).
The DNA extracted from Samples A and B was subjected to nested PCR
using universal bacterial primers followed by primers specific for the
Dehalococcoides and Dehalobacter genera. While Dehalobacter sequences were
detected in DNA from both Samples A and B, only Sample B returned a
positive PCR for Dehalococcoides . This supports the findings from the clone
library analysis that Dehalococcoides is more abundant inside the reactive bar-
rier compared with 1 m upgradient from the barrier.
Although this phenomenon has been observed at the laboratory scale for
other compounds (Scherer et al., 2000), this appeared to be the first docu-
mented instance for EDC. Exploiting this phenomenon (say, by augmenting
the reactive iron barrier with a dehalorespiring enrichment culture) might
broaden the capability of reactive iron barriers to reductively dechlorinate
hitherto recalcitrant dissolved phase compounds.
12.11 Conclusions
At the time of the installation of the first reactive iron barrier in Australia
in February 1999, it was certain whether it would be able to successfully
degrade elevated concentrations of volatile CHCs in a low-pH, high-DOC
aquifer. Nor was it envisaged that the hydrogeochemical conditions would
be dramatically altered due to the subsequent installation and operation
of a large hydraulic containment system. Yet, through these periods, the
pilot-scale reactive iron barrier installed by Orica at its Botany site was
able to achieve significant contaminant MR, and the mode of degrada-
tion evolved from abiotic to biological reductive dechlorination. The trial
demonstrated the long-term efficacy and adaptability of reactive iron bar-
riers, and—at least in the context of the Botany site—illustrated the engi-
neering challenges faced when scaling up the technology for full-scale
implementation.
References
Duran, J.M., J. Vogan, and J.R. Stening. 2000. Reactive barrier performance in a com-
plex contaminant and geochemical environment. In: G.B. Wickramanayake,
A.R. Gavaskar, and A.S.C. Chen (eds.), The Second International Conference on