Evaluating the biogeochemistry of oil sands tailings in end pit lakes

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The oil sands are a vital component to the Canadian economy; however, the environmental impacts of oil sands operations are also growing. Tailings impoundments are used almost exclusively for waste management with a combined footprint more than 220 km2. Processed oil sands ore yields tailings slurries that are discharged into a settling basin and must eventually be reclaimed and integrated into mine closure landscapes. However, due to the low solids/high clay content of tailings, they are slow to dewater, making reclamation of oil sands tailings particularly challenging. One proposed reclamation method is end pit lakes (EPLs), which involve depositing thick layers of tailings capped with water in decommissioned open pits. Theoretically, EPLs are a suitable reclamation strategy because the tailings can slowly dewater while the water cap serves as habitat for an aquatic ecosystem. However, the first full-scale demonstration EPL showed that there are several challenges with this strategy, including turbidity generation and water cap quality. As such, depositing coagulant- (alum) and flocculant-treated (polyacrylamide, PAM) tailings in EPLs was proposed to improve tailings dewatering and reduce turbidity generation. This technology is called permanent aquatic storage structure (PASS). To date, the biogeochemical implications of depositing PASS-treated tailings in EPLs remain unknown, and the biodegradation and environmental fate of PAM, PAM degradation products, and aluminum are not well understood. This program will elucidate the biogeochemical behavior of untreated and treated tailings in EPLs and will evaluate whether EPLs are a suitable, environmentally responsible tailings reclamation strategy. The objectives of these studies are to investigate PAM biodegradation in treated oil sands tailings, and evaluate the biogeochemical evolution of untreated and treated oil sands tailings in EPLs. Microcosm studies with microorganisms indigenous to oil sands tailings will investigate biodegradation in PAM-treated tailings under aerobic and anaerobic conditions. My previous research has now developed into decades worth of knowledge in studying complex anaerobic bioremediation systems and uniquely positions us to tackle this equally complex PAM bioremediation system. With upcoming oil sands mine closures over the next 50 years, it is vital to understand the long-term effects of current tailings reclamation practices. The proposed research will provide critical information on the biogeochemical implications of using EPLs for reclamation. The knowledge gained from this research will assist in identifying and reducing the long-term environmental impacts of mine closure practices and will guide future research and development. Canadians have a vested interest in ensuring the proposed research project provides the oil sands industry with information needed to make sound tailings management and mine closure planning decisions.