Brief

During the decommissioning of a retail gas bar in a highly populated Toronto area, petroleum hydrocarbon impacts, in the form of gasoline, were discovered in the soil and groundwater. Another contractor attempted to remediate the source area using dig and dump methodology coupled with dewatering. However, due to the high hydraulic conductivity of the aquifer, this approach failed and further spread the impacts vertically. The backfilling also mixed highly permeable materials into the native soil, causing highly heterogenetic conditions. Combined with the presence of NAPL, this complicated geologic and hydrogeologic setting created significant remedial challenges.

Process

As part of their bid, IRSL conducted a Remedial Option Review of various technologies, including: physical removal, pump & treat, air sparging, biosparging, soil vapour extraction, multi-phase extraction, chemical oxidation and aerobic bioremediation. They earned the contract based on their cost-effective, innovative approach:

1. Surfactant Flushing

2. Chemical Oxidation

3. Aerobic Bioremediation

To mitigate the BTEX (Benzene, Toluene, Ethylbenzene, and Xylenes), along with the PHC (Petroleum Hydrocarbons) F1, F2 and F3 fraction compounds in the soil and groundwater of this highly heterogenetic aquifer, IRSL developed and executed a progressive in-situ remediation approach using three technologies sequentially.

Results

Dissolved oxygen concentrations within the Emitter wells are greater than 12 mg/L with dissolved oxygen levels in down-gradient wells increasing by up to 500% over the original concentrations.

PHC mass within the soil decreased with observed NAPL being extracted during the surfactant flushing activities.

Soil and groundwater concentrations continue to decrease in alignment with the objective of meeting the Ministry of Environment’s Table 3 Standards for BTEX, PHC F1, F2 and F3 parameters within 1.25 years.

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