This research project evaluates the environmental performance of two tailings management areas at a decommissioned mine site in Ontario. The tailings areas are decommissioned with a water cover and continue to be managed and monitored with ongoing water treatment. The project revisits groundwater modelling that was conducted prior to the decommissioning of the site and updates it using nearly three decades of environmental monitoring data and advancements in software. The groundwater model will determine the rates and directions of groundwater flow from the tailings areas.