DETOXIFICATION AND RECLAMATION OF SUNCORS OIL SAND TAILINGS PONDS

Suncor, Inc., operates an oil sands mining and extraction plant in northern Alberta, and uses tailings ponds for disposal of waste tailings sludge and for conditioning recycle water. In their active state, tailings ponds consist of a layer of toxic top water overlying a viscous layer of sludge containing toxic interstitial water as well as particles of unprocessed bitumen and clay fines. To address the need for reclamation of the mine site, Suncor is exploring a concept of sludge disposal whereby mature sludge would be pumped out of existing tailings ponds into a mined pit area with an overlying layer of top water. This reclamation strategy would retain both top water and sludge on site in contrast to conventional schemes whereby sludge would be dewatered and reclaimed using dry land reclamation techniques (i.e., revegetation). The success of this wet and pond reclamation scheme would rely on natural processes of microbial biodegradation and detoxification over time to achieve improvements in the quality of the top water layer. Although anaerobic interstitial water in the sludge may remain toxic for long periods, the sludge would be permanently isolated beneath a surface layer of top water. Bench-scale and field-scale tests (e.g., test tanks and large pits) were utilized in a series of experiments to assess the feasibility of wet pond reclamation. Toxicological testing of the top water layer characterized the rate of detoxification, and elucidated the nature and extent of subsequent colonization by aquatic plants and animals. The results suggest that after mine abandonment, a reclaimed tailings pond could be designed such that it is transformed over time from a toxic waste pond into a viable and productive ecosystem with biologically complex aquatic communities in its surface water.