Brief

As part of a commercial redevelopment project in Stouffville, Ontario, a property located down-gradient of an active retail gas bar required the installation of a remediation system to mitigate potential environmental and legal risks associated with the dissolved phase plume migrating onto the property. The groundwater plume consisted of BTEX (Benzene, Toluene, Ethylbenzene, and Xylenes) and PHC (Petroleum Hydrocarbons) F1 and F2 compounds.

The impacted groundwater was located in a heterogeneous aquifer with the unconfined aquifer’s hydraulic conductivity contrasting greater than 4 orders of magnitude. The contamination, resulting from historical releases of gasoline from leaking underground storage tanks and associated piping up-gradient of the site, was flowing within the shallow groundwater towards, and possibly onto, the client’s site. The nature of the aquifer, municipal infrastructure, and presence of a long-term source, limited the available remedial options.

Process

The landowner, a large national retailer, contracted an Ontario-based environmental consulting rm to characterize the site and complete initial sampling. The consultant managed the tendering of the project for bid to three contractors, who each submitted recommendations for remediation. IRSL earned the contract with the retailer based on their innovative approach, which cost signi cantly less than the other methods proposed.

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 enabled the client to address the migrating plume.

IRSL used Aerobic Bioremediation to mitigate the BTEX (Benzene, Toluene, Ethylbenzene, and Xylenes), along with the PHC (Petroleum Hydrocarbons) F1 and F2 fraction plume flowing onto their client’s site.

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 3 metres of the permeable barrier.

Operating and maintenance costs have decreased relative to inflation with time.

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