Water quality assessment of a novel pilot-scale pit lake in the alberta oil sands region.

The Alberta oil sands (AOS), Canada, represent a vital energy resource; however, the extraction of oil from these deposits poses significant environmental challenges. In particular, the eventual reclamation of significant volumes of waste materials is required. As a potential solution to incorporate and remediate AOS mine wastes in-situ, a pilot-scale pit lake, Lake Miwasin (LM), was constructed in 2017-18. It used a combination of coagulated and flocculated fluid fine tailings (bottom substrate) capped with a blend of oil-sands process affected water and runoff water from the surrounding catchment. The objective of the study described here is to assess the resultant surface water quality of this artificial lake and its regional comparability with natural systems. Furthermore, we explored the physicochemical characteristics, the mechanisms regulating lake water chemistry, and calculated various water quality indices for both LM and surrounding natural water bodies. Based on water quality indices, our study results showed that the overall water quality of LM's surface water was not yet similar to surrounding water bodies in the AOS region. Surface water from LM is slightly alkaline with elevated total dissolved solids (TDS) and differs chemically from surrounding water bodies. Predominant ions in LM are Na, K (pore water from tailings), whereas surrounding water bodies exhibit Ca, CO, and HCO (gypsum, dolomite, and calcite dissolution). Therefore, water chemistry of LM is more typical of a Na-Cl water type, while surrounding bodies show a Ca-HCO water type. Evaluations based on different water quality indices highlighted the importance of monitoring specific variables in LM such as conductivity, TDS, alkalinity, and NH. The analysis and assessment of LM surface water is imperative for gaining insight into the potential character and trajectories of water quality in future pit lakes and informing design considerations and application of this novel reclamation approach in the AOS region.