Abstract
Canada’s oil sands surface mining industry, located in northern Alberta, produces ~1.6 million bbl/d of bitumen (AER, 2023). Bitumen is recovered using a water-based extraction process that separates bitumen from the mineral surfaces of the ore. While oil sands ore contains trace concentrations of iron sulfide minerals, the bitumen extraction process has been shown to preferentially segregate and relatively concentrate these geochemically reactive minerals in the froth treatment tailings (FTT) stream. At Syncrude’s Mildred Lake mine site, FTT has been deposited in an external tailings facility since operations began in the late 1970’s resulting in the development of a sub-aerial and sub-aqueous deposit. Recent geochemical characterization has identified FTT as classifying as potentially acid generating that if allowed to oxidatively weather can generate acidic and metal rich porewater. This paper provides an overview of the integrated research approach taken to assess the potential geochemical closure risk of FTT within the site-specific context of the landform, supported by University research partners. An environmental risk assessment source-pathway-receptor approach of assessing the source (physical properties, mineralogical and geochemical variability) and pathway (environmental kinetic rates, natural attenuation mechanisms, and landform hydrogeology) is being leveraged towards developing a closure landform geochemical model. This model will be used to evaluate the potential geochemical closure risk to the closure landform’s surface water quality (receptor). Relying on early assessments of only the mineralogical hazard may have led to an over-determination of the potential geochemical closure risk. The outcomes of this work will inform any further evaluation of potential mitigation options and closure planning.