Hydrogeological Characterization and Numerical Flow Modelling of an Active Mine Tailings Site in Abitibi-Témiscamingue, Québec, Canada

Tailings from Agnico Eagle’s Goldex mine are stored in a tailings pond built in 2007. Used only as a secondary pond since its construction, it will eventually be used as the main facility, which could entail hydrogeological changes in the tailings and surrounding aquifers. To ensure the protection of groundwater during future mine operations, further site characterization and numerical modelling was undertaken to better understand the current hydrogeological system. Detailed new field work was recently completed and a 2D vertical-plane numerical model along the main flow direction of the tailings site was built with the SEEP/W code to simulate the local-scale steady-state flow system. Although piezometric levels were accurately simulated throughout most of the deposition area, the simulated piezometric levels near the dikes were consistently lower than those observed. A sensitivity analysis on hydraulic conductivities and recharge highlighted the importance of relatively lower hydraulic conductivities in maintaining the watertable as high as possible near the dikes, without overflow in the center of the deposition area. This study improved understanding of the hydrogeological behavior of mine tailings at an active site using modelling to better predict the potential impacts on the local groundwater flow system.