Brief

As part of a commercial redevelopment project in Barrie, Ontario, a property located in an active commercial setting, in a major urban area, required remediation to mitigate potential environmental and legal risks associated with a dissolved phase plume consisting of high concentrations of BTEX (Benzene, Toluene, Ethylbenzene, and Xylenes) and PHC (Petroleum Hydrocarbons) F1 and F2 compounds.

The groundwater at the site was impacted at depths greater than 20m below ground surface due to historical releases of gasoline from leaking underground storage tanks and associated piping. The releases were thought to have occurred over a number of years, thus impacting the thick (i.e. 20m) vadoze zone, which is acting as a long-term source of PHC contamination. The depth, size, concentration, extent, and presence, of this long-term source limited the available remedial options to the client.

Process

As part of their bid, IRSL conducted a Remedial Option Review of over 25 technologies, including: pump & treat, air sparging, biosparging, soil vapour extraction, multi- phase extraction, chemical oxidation, and aerobic bioremediation. Based on the option review, IRSL worked with the general contractor and environmental consultant to develop a remedial approach that allowed the client to address the source at the same time as the associated plume.

To mitigate the BTEX, PHC F1 and F2 with minimal disruption to the active gas bar and local businesses, IRSL developed and executed a progressive in-situ aerobic bioremediation plan. The surface footprint required was less than 4m2, thus ensuring a very small ecological footprint.

A total of 29 4”-wells were installed perpendicular to the plume, on a one-metre spacing, to create a semi-passive reactive barrier designed to intercept the plume and treat the compounds of concern using Waterloo Emitters. Waterloo Emitters consistently release oxygen into the groundwater without destabilizing the hydrocarbons. Designed to run continuously for extended periods of time, the emitters are low maintenance, require no energy, and leave a very small ecological footprint.

Results

Dissolved oxygen concentrations within the Emitter wells are greater than 12 mg/L.

Independent sampling of down-gradient wells indicate that all contaminants have been reduced to below the Ministry of Environment’s Table 3 Standards for commercial sites for BTEX, PHC F1 and F2 parameters within 10 metres of the permeable barrier.

Operating and maintenance costs have decreased relative to in ation with time.

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