Environmental Engineering Reference
In-Depth Information
very challenging cleanup targets and deadlines, the Notice required Orica
to develop a Groundwater Cleanup Plan and to implement contaminant con-
tainment using hydraulic containment in two particular areas—Southlands
and an area hydraulically downgradient of Southlands—and ex situ treat-
ment to clean up the extracted groundwater.
The resultant “pump and treat” system started up in stages, commenc-
ing in October 2004 and culminating in January 2006 with the introduction
of contaminated groundwater feed from three lines of extraction wells (114
wells in total) into a newly constructed Groundwater Treatment Plant on the
BIP designed to treat up to 14.5 ML/day of groundwater to effectively drink-
ing water quality. (The pump-and-treat system is described in some detail in
the Orica website www.orica.com.) Operation of the Groundwater Treatment
Plant and the associated hydraulic containment well network effectively
made the reactive iron barrier a redundant remediation measure, as the
reduction in groundwater levels caused by the extraction systems reduced/
eliminated groundwater discharge to Springvale Drain. The EPA eventu-
ally permitted Orica to remove plans for a full-scale reactive iron barrier
from the Groundwater Cleanup Plan, which was replaced by a Groundwater
Remediation and Management Plan in October 2009.
12.10 Additional Sampling and Analysis
Follow-up investigations have been conducted on an ad hoc basis, and have
shown significant changes in the influent and effluent groundwater quality.
The aforementioned regulatory requirement to install and operate a large
pump-and-treat system (which was commissioned in January 2006 and today
typically extracts and treats approximately 6-6.5 ML/day of groundwater
*
)
resulted in significant changes in the direction and speed of the CHC plumes.
These changes are illustrated in Table 12.2. First, the data for month 91—
late November 2006, 10 months after the commissioning of the Groundwater
Treatment Plant—show that concentrations of most of the CHCs into the
reactive iron barrier have decreased to a total of <60 mg/L, but EDC concen-
trations have risen up to 127 mg/L. Second, the reactivity and permeability
of the reactive iron barrier do not appear to have diminished significantly
with time. Most notably, though, EDC is now being removed in the reactive
iron barrier—by up to one or two orders of magnitude. Results in May 2002
*
As mentioned above, the design capacity of the Groundwater Treatment Plant was 14.5 ML/
day, which turned out to be much more than required. The excess design capacity resulted
from incorrect groundwater level data provided by a third party and subsequently used in
the hydraulic modeling during the design period. By the time the anomalous data were dis-
covered, it was too late to alter the plant design. However, the additional capacity has proved
useful during plant commissioning and maintenance.
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