Laboratory studies investigating chemical flux across tailings-cap water zones, simulating an End Pit Lake in the Athabasca oil sands region

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The economic opportunities associated with expanded oil sands operations in the Athabasca region are substantial, but so too are the by-products of the bitumen extraction process. Of particular environmental importance in the context of landscape remediation is tailings management, more specifically the possibility of using closed mine pits as tailings repository basins. In order for these so-called end-pit lakes (EPLs) to represent an acceptable disposal alternative, tailings must be capped with a fresh water layer that, over time, develops into a self-sustaining ecosystem. Indeed ecosystem maturation is expected to occur simultaneously with tailings dewatering so that EPLs become a natural component of the boreal forest. It is useful to understand biogeochemical processes governing partitioning of contaminants in tailings and identify contaminant transport pathways to cap water. Modulating contaminant release and transport is the overall objective of the present multidisciplinary proposal. Research objectives will be met by considering two different types of laboratory experiments: (i) large volume kinetic tests conducted at elevated temperatures to accelerate processes that evolve slowly in-situ, and, (ii) small volume tests that will more specifically probe the fundamental aspects of chemical partitioning. In the former case, our analysis will include a sequencing of key microbes and a chemical characterization of clay minerals, expressed porewater and cap water. In the latter case, attention will be focused on nutrient limitation, detritus and cap water dilution effects. We also propose to separately investigate those factors (wind stress, etc.) that lead to mixing between the fluid fine tailings and cap water layers. Throughout, results will be communicated with our industrial partner and with affiliated research groups for purposes of maximizing the impact of our findings and recommendations.