BRAT Modelling for Excess Soil Reuse

In 2021, XCG was retained to conduct a desktop study to evaluate the upper limits of concentrations that would be potentially acceptable for soil imported for the rehabilitation of a former gravel pit operation to future farmland use. The Client was previously approved for the generic Minstry of the Environment (Ministry) Table 2 site condition standards, but wanted to determine if the site characteristics would support concentrations that the local municipality wanted to impose [Ontario Regulation (O. Reg.) 406/19 Table 2.1 agricultural standards].

Following a detailed review of existing hydrogeological and annual monitoring reports to determine the actual site conditions (versus using book value ranges), XCG used the Beneficial Reuse Assessment Tool (BRAT Model), as prepared by the Ontario Ministry of the Environment, Conservation and Parks (MECP), to determine the upper limits of concentrations of various chemical parameters in soil that could be considered acceptable for the placement given the site-specific conditions present. The BRAT Model was used to develop site-specific excess soil quality standards by modifying (1) a limited number of physical characteristics of the excess soil and the reuse site; and/or, (2) the soil to groundwater exposure pathways through the use of leachate analysis.

XCG modelled a variety of site use characteristics, such as capping, site building constraints, and land use, to simulate multiple scenarios and generate associated outputs of site-specific soil quality standards.

Based on the results of the BRAT modelling, it was suggested to consider using site-specific soil quality standards generated for industrial/commercial/community property use, with an engineered hard cap and building restrictions. This option may provide the best alternative for future use of the property and maintaining the previously accepted soil quality standards.