Investigate, Delineate First - Dig Later

Residential home owners (the Client) noticed drips of fuel oil coming from the bottom of a 910-litre steel fuel oil AST in the basement of their house. They contacted the company that maintains the AST to come and assess/repair the leak. During the tank inspection a section of the tank shell come off, releasing fuel oil to the basement floor. The Client indicated that the fuel tank was approximately ¾ full at the time of the release, but also noted that they were able to recover approximately half of a tank of fuel (i.e. 450 litres) by pumping it out. The exact volume of fuel oil released onto the concrete floor is unknown. Absorbent material was placed on the floor below the tank and in areas impacted by the release (i.e. along concrete walls).  

The Client contacted XCG and a number of other environmental consultants to determine the appropriate course of action and the estimated costs. The other consultants indicated that a large section of the floor needed to be removed in order to complete the clean-up and that underpinning of the house would likely be required. They also specified that since the extent of impacts below the basement floor were unknown, they could not provide cost estimates for the work they were proposing. The Client was not satisfied with these proposals, in particular with the lack of the estimated costs. XCG suggested that before any remedial activities take place, an investigation should be completed to first determine whether or not any fuel oil had migrated below the concrete floor slab, and if it did, to delineate the extent of the impacts, before commencing any remedial activities. XCG explained to the Client and the Client’s insurer that the proposed approach would allow to estimate the costs associated with the excavation of the impacted soil, if any, and will allow to come up with the best approach for site remediation. XCG also explained to the Client that the proposed approach would prevent the highly disruptive, costly, and if there is no evidence of impact below the floor, ultimately unnecessary removal of the basement floor and underpinning of the house. This approach was deemed by the Client and the Client’s insurer to be the most logical and cost effective, and as a result XCG was retained by the Client to provide the necessary environmental consulting services on this project.

The scope of work included the advancement of eight interior and eight exterior boreholes in the vicinity of the fuel oil release and along the foundation walls. Three of the exterior boreholes were instrumented as monitoring wells. Based on the field observations made during the investigation and the review of the analytical results, no evidence of fuel oil-related impacts to soil and/or groundwater quality beneath the basement floor or adjacent to the house were found.

By choosing the approach proposed by XCG over the more intrusive spill response work plans proposed by other consultants, the Client was able to confirm relatively quickly that no fuel oil had migrated below the floor slab, and there was no need to remove the floor slab, and underpin the building walls. This outcome was also good news for the insurance company. 

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