ASSESSMENT OF THE IDENTITY AND BIODEGRADATION POTENTIAL OF HYDROCARBONS IN AN OIL SANDS PIT LAKE

Efforts are underway to develop effective methods to manage tailings and reclaim the land impacted by the mining and extraction of bitumen from the Alberta oil sands. Syncrude Canada Ltd. has undertaken the first full scale demonstration of water-capped Fluid Fine Tailings (FFT) via the development of Base Mine Lake (BML), an oil sands pit lake commissioned in 2012. A key component of this reclamation technology is the maintenance of an oxic water column which is required to support ecosystem functioning within the lake and provides the most effective conditions for the biodegradation of any toxic organics. However, the oxidation of dissolved methane released from the underlying tailings can reduce dissolved oxygen levels in the water column and impede EPL function. Methane is produced primarily via fermentation of organic residues within the tailings. Understanding the character, abundance, and variability of these organics will enable assessment of methane generation potential from the tailings and inform future management decisions. In this study, fluid fine tailings (FFT) samples were collected from 2 depths at 3 locations, and two time points from BML. Gravimetric analysis of total lipid extracts (TLEs) indicated that the total solvent extractable material was present at 25-42 mg/g. After fractionation on silica gel it was found that the TLE was dominated by the polar fraction (30- 52 %) while the saturates and aromatics ranged between 21-43 % each. Subsequently, these fractions were analyzed using multidimensional gas chromatography (GC-GC) in order to resolve the individual compound families that could have the greatest role in methane generation. GCGC based analysis of the TLEs showed that the primary group of compounds present are well resolved groups of C₁-C₅alkylated aromatics, branched and cyclic branched alkanes in addition to steranes and hopanes. These compounds were present in all of the samples, however the abundance of the alkylated aromatics and alkanes compared to the internal standard showed a variability spatially and temporally while the steranes and hopanes were invariant. Ongoing research will further assess the distribution patterns and variability of these compounds in order to determine their biodegradation potential and role in methane generation.