Remedial Activities Following Fuel Oil Release - Uxbridge, Ontario

XCG was retained by the Ontario School Boards’ Insurance Exchange (OSBIE) and the Durham District School Board (DDSB) to conduct a peer review of historical investigations and remedial activities for a study area located near the Uxbridge Secondary School (USS) in Uxbridge, Ontario. 

The study area included historical fuel oil [petroleum hydrocarbon (PHC)] releases from the USS property that migrated off-property and affected two municipal roadways and eight residential properties. Following the peer review, XCG was retained as the prime consultant to manage the on-going remedial activities and prepare a Contaminant Management Plan (CMP) for the Study Area. To mitigate liability and control exposure to the impacts, the insurance provider purchased five of the residential properties.

Remedial activities in the Study Area included the excavation of more than 35,000 tonnes of PHC-impacted soil. During the excavation activities, accumulated water (groundwater and rainwater), as well as light non-aqueous phased liquid (LNAPL) within the excavation, was pumped out and directed to an on-site water treatment system. During the excavation activities, demolition of the dwellings on three of the residential properties was completed to facilitate the excavation and removal of PHC-impacted soil.

Due to restrictions based on overhead and underground utilities and building locations, residual impacts remained on the USS property, the Brock Street East road allowance, and two residential properties. Physical barriers were installed during excavation activities to prevent migration of impacts into remediated sections of the Study Area. A groundwater recovery and treatment system was also installed on the USS property at the downgradient end of the PHC-plume to maintain hydraulic control behind the physical barrier.

XCG completed a delineation program to identify the lateral extent of the residual LNAPL and dissolved phase PHC impacts beneath the road allowances. The delineation program included the installation of 13 groundwater monitoring wells and subsequent  groundwater sampling. To mitigate the migration of dissolved phase PHCs impacts in groundwater from the road allowances, XCG observed the installation of a permeable reactive barrier wall along the downgradient residential property boundaries. XCG is currently monitoring the effectiveness of this barrier.

The on-going CMP to address the residual LNAPL and dissolved phase PHCs in the Study Area involves quarterly groundwater and subsurface methane monitoring, continuous monitoring of VOC sensors (calibrated to methane) located inside the USS, manual removal of LNAPL from monitoring wells as observed, operation of the LNAPL and groundwater recovery system, and in-situ remedial chemical injections to reduce PHC concentrations in soil and groundwater.

In an effort to divest of remediated properties, XCG completed Phase I Environmental Site Assessments (ESAs) on four of the residential properties and Record of Site Conditions (RSCs) were successfully filed. Once RSCs were received, OSBIE sold three of the properties to a local developer. XCG completed a Phase One ESA and Phase Two ESA in accordance with Ontario Regulation (O. Reg.) 153/04 as amended for the Fourth Avenue South road  allowance and a RSC was successfully filed.