GEOPHYSICAL CHARACTERIZATION OF AN UNDRAINED OIL-SAND TAILINGS POND DAM, ALBERTA, CANADA

Constructed dams and large tailings ponds are created as part of oil-sand mine operations. Sodium hydroxide (NaOH) is added to recycled water during the bitumen extraction process, which results in sodium rich tailings composed primarily of coarse-grained sediments and water, with some fine-grained sediments and residual bitumen. The process-affected coarse tailings are subsequently used as the dam construction material. An understanding of the movement and distribution of water and solute within the dams is needed in order to manage the tailings ponds and their future reclamation. Geophysical studies were conducted as part of a hydrogeological study of the dam of an active tailings pond at an oil-sand mine site situated in northeast Alberta, Canada. The tailings pond occupies 25 square kilometres and the tailings dam is up to 40 m high and over 1 km wide. A series of direct push electrical conductivity, electrical resistivity tomography (ERT) and EM38 surveys were conducted between 2001 and 2008. In addition, hydraulic head, aqueous electrical conductivity, temperature, water chemistry and soil-moisture content were monitored. The geophysical methods indicate a strong relationship between bulk electrical conductivity and soil-moisture. ERT inversions clearly delineated the water table. Quantitative salinity estimates could not be made from the resistivity data due to image resolution limitations and the dominant control of moisture content on resistivity values. The data will be used to help calibrate an future groundwater flow and transport models