Disposal of oil sands tailings in ponds is a common method used by oil sands operators to manage the large volume of tailings generated from oil sands mining. This study considered a large tailings pond with an 11 km long ring dyke that was constructed of permeable tailings sand and equipped with drains and seepage collection ditches designed to collect process-affected water (PAW) from the dyke. The effectiveness of this seepage collection system was examined at the downgradient end of the tailings pond and dyke system using a focussed field investigation supported by groundwater flow modelling. A network of piezometers and drive points were installed in a 1 km2 area to facilitate hydraulic measurements and water sampling to characterize the surface water and groundwater flow system. Chemical tracers suggest migration of PAW in a shallow, permeable sand deposit beyond an inner seepage collection ditch, but elevated hydraulic heads beyond the outer ditch have prevented further migration. A groundwater flow model was used to simulate the observed hydraulic dyke conditions and estimate the amount of PAW discharging into the shallow aquifer in the study area. Under the present hydraulic conditions, the seepage collection system is currently working to effectively contain PAW.