Hydrogeologic Simulations of a Deep Seated Groundwater System: Bruce Nuclear Site - 14484

A Deep Geologic Repository (DGR) for low and intermediate level radioactive waste has been proposed by Ontario Power Generation for the Bruce nuclear site in Ontario, Canada. The DGR would be constructed in the low permeability argillaceous limestone of the Cobourg Formation at a depth of about 680 m below ground surface. This paper describes the regional-scale numerical groundwater modelling used to investigate the long-term evolution and stability of the groundwater system beneath the DGR site. The groundwater modelling provides a framework to illustrate the factors that influence the long-term performance of the geosphere barrier. The flow and transport groundwater modelling undertaken for this study used the density-dependent FRAC3DVS-OPG code. A representative regional area of approximately 18,000 km 2 was used. The low hydraulic conductivities of Ordovician shales and limestones (less than 10 -12 m/s) at depth resulted in low rates of mass transport in the deep groundwater system, with Mean Life Expectancies of 164 Million years for the area surrounding the proposed repository. The impact of glaciation and deglaciation on the deep groundwater system was investigated through a series of paleohydrogeologic scenarios. The results from these scenarios indicated that surficial recharge during glaciation does not penetrate below the intermediate groundwater zone at the DGR site.