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Case Study of PRB Application for the Remediation of Groundwater
installed in 2001 and sampled in a number of monitoring events along possible alignments in Southlands to assess the types and concentrations of CHCs
in those locations.
Concurrent with the assessment of potential impacts from the operation of
a large-scale reactive iron barrier, in late 2001, Orica also sought expressions
of interest from 18 local and overseas contractors for the construction of such
a barrier. No single contractor had all the capabilities required; so, it was
necessary for the contractors and consultants to form consortia before formal
tendering could begin. Options for construction methods included trenching (with biodegradable guar polymer to hold the trench open prior to iron
emplacement) and hydrofracking (azimuth-controlled hydraulic fracturing)
with the injection of a mixture of biodegradable polymer and micron-sized
iron particles. Unfortunately, no suitable technology could be found to reliably and predictably emplace such a large reactive iron barrier in the flowing
sands characteristic of the Botany Sands Aquifer (i.e., the sands have poor
structural stability; so, there was a high risk of sand slumping into the trench
prior to iron emplacement).
Discussions continued through 2002 with a short list of contractors to find
ways to overcome the technical challenges presented by the Botany site. In
December 2002, Orica also attended the RTDF meeting on PRBs, which confirmed that no reactive iron barrier had been installed in an aquifer with the
low pH, high sulfate, and high dissolved organic compounds that characterized the proposed location of the full-scale barrier.
Ongoing concerns about the potential for elevated dissolved iron concentrations to persist downgradient of the proposed full-scale barrier resulted
in additional groundwater monitoring in the vicinity of the pilot-scale barrier being undertaken in mid-2003. The results confirmed that increased
dissolved iron did persist in groundwater downgradient of the pilot-scale
barrier. Surface water monitoring in March 2003 in Springvale Drain
hydraulically downgradient of the pilot-scale barrier also identified elevated
dissolved iron concentrations downstream of the inferred seeps from the
barrier.
As a consequence of these factors, implementation of the proposed fullscale barrier was put on hold pending the outcome of a groundwater remediation strategy review. A number of investigation tasks were identified in
the review to address concerns around dissolved iron impact, depth (e.g.,
shallow vs. deep installation to bedrock) and alignment of the proposed fullscale reactive iron barrier, alternative installation techniques, and alternative
reactive barrier technology including in situ enhanced bioremediation.
In October 2003, as a result of a number of factors, the EPA issued a Notice
of Clean Up Action to Orica. Although, the EPA considered the full-scale
reactive iron barrier and bioremediation to be still important in the mid- to
long term, they believed that Orica’s stated cleanup goals were unlikely to
be achieved within the stated time frames and that more certainty around
the application of remediation technology was required. Among a range of
Case Study of PRB Application for the Remediation of Groundwater
installed in 2001 and sampled in a number of monitoring events along possible alignments in Southlands to assess the types and concentrations of CHCs
in those locations.
Concurrent with the assessment of potential impacts from the operation of
a large-scale reactive iron barrier, in late 2001, Orica also sought expressions
of interest from 18 local and overseas contractors for the construction of such
a barrier. No single contractor had all the capabilities required; so, it was
necessary for the contractors and consultants to form consortia before formal
tendering could begin. Options for construction methods included trenching (with biodegradable guar polymer to hold the trench open prior to iron
emplacement) and hydrofracking (azimuth-controlled hydraulic fracturing)
with the injection of a mixture of biodegradable polymer and micron-sized
iron particles. Unfortunately, no suitable technology could be found to reliably and predictably emplace such a large reactive iron barrier in the flowing
sands characteristic of the Botany Sands Aquifer (i.e., the sands have poor
structural stability; so, there was a high risk of sand slumping into the trench
prior to iron emplacement).
Discussions continued through 2002 with a short list of contractors to find
ways to overcome the technical challenges presented by the Botany site. In
December 2002, Orica also attended the RTDF meeting on PRBs, which confirmed that no reactive iron barrier had been installed in an aquifer with the
low pH, high sulfate, and high dissolved organic compounds that characterized the proposed location of the full-scale barrier.
Ongoing concerns about the potential for elevated dissolved iron concentrations to persist downgradient of the proposed full-scale barrier resulted
in additional groundwater monitoring in the vicinity of the pilot-scale barrier being undertaken in mid-2003. The results confirmed that increased
dissolved iron did persist in groundwater downgradient of the pilot-scale
barrier. Surface water monitoring in March 2003 in Springvale Drain
hydraulically downgradient of the pilot-scale barrier also identified elevated
dissolved iron concentrations downstream of the inferred seeps from the
barrier.
As a consequence of these factors, implementation of the proposed fullscale barrier was put on hold pending the outcome of a groundwater remediation strategy review. A number of investigation tasks were identified in
the review to address concerns around dissolved iron impact, depth (e.g.,
shallow vs. deep installation to bedrock) and alignment of the proposed fullscale reactive iron barrier, alternative installation techniques, and alternative
reactive barrier technology including in situ enhanced bioremediation.
In October 2003, as a result of a number of factors, the EPA issued a Notice
of Clean Up Action to Orica. Although, the EPA considered the full-scale
reactive iron barrier and bioremediation to be still important in the mid- to
long term, they believed that Orica’s stated cleanup goals were unlikely to
be achieved within the stated time frames and that more certainty around
the application of remediation technology was required. Among a range of