HOW BIG IS YOUR MAN-MADE AQUIFER? GROUNDWATER FLOW AND SALT TRANSPORT IN A SAND TAILINGS STORAGE FACILITY, FORT MCMURRAY, ALBERTA

The extraction of bitumen from the Athabasca oil sands in Alberta, Canada produces large volumes of sand tailings. Sand tailings, along with associated process water, are impounded in large storage facilities. Syncrude’s Southwest Sand Storage (SWSS) Facility contains 300 million m3 of tailings and is currently one of the three largest dams in the world. The movement of water and salts within this structure needs to be understood for successful construction, maintenance and reclamation of the structure. Some keys issues at the SWSS are the water table location and movement of salty tailings water that may impact the reclamation soils and vegetation. Steady-state groundwater flow and transient movement of salts at the local (bench and slope) and intermediate (pile) scales at the SWSS are investigated.

Water levels, seepage and groundwater quality (including TDS) were measured for over two years along detailed transects at two locations. The field data have been used to complete traditional hydrogeological interpretations of the site, and to develop a conceptual model of flow and transport. The local and intermediate flow systems and salt transport in the dam are being evaluated with numerical models. The models will allow testing of future hydrogeological behavior of the structure. Field results show differences in flow systems and salinity distribution that depend on the slope construction of the SWSS. Groundwater flow model results indicate the flow system is highly sensitive to changes in the amount of recharge and material placement. Flushing time for salts will vary between current and post-closure groundwater flow systems. This research will facilitate better long-term environmental management of this and similar sites.