Monitoring Spatial Distribution of Solvent Extractable Organics in Pit Lake Fluid Fine Tailings

Abstract

The extraction of bitumen from the cretaceous oil sands ore within the Athabasca Oil Sands Region (AOSR) in Northern Alberta has generated over 1.18 trillion liters of by product in the form of Fluid Fine Tailings (FFT) and Oil Sands Process Water (OSPW)3. A reclamation strategy being investigated is water capped tailings technology (WCTT), that involves the development of Pit Lakes (PLs) by sequestering FFT below a water cap composed of both OSPW and fresh water to steadily densify these tailings over time4. A challenge that may impede this reclamation strategy is that as FFT densifies porewater containing oxygen consuming constituents (OCC) derived from anaerobic microbial degradation of labile petroleum hydrocarbons, such as gases (e.g. H2S, CH4), dissolved organic carbon (DOC) and dissolved ions (e.g. NH4+, HS-, and Fe2+), have the potential to be mobilized into to the overlying water cap. This dissertation is focused on developing an optimized comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC/TOFMS) methodology for analyzing the spatial distribution for a subset of identifiable solvent extractable PHCs species from FFT within Base Mine Lake (BML) the first full-scale demonstration of PL technology. The chemical “fingerprint” constructed from the concentration of each identified PHC isomer at a given depth and cosine theta (cos-Ɵ) similarity metric suggested the contribution of a singular source of PHCs within BML. Although a similar source fingerprint persisted throughout the study site, the spatial distribution for the isomers identified suggested differences in PHC input contributions across the FFT sampling platforms with the largest variation in concentration being attributed to the labile low molecular weight n-alkanes (C11 – C13) and postulated biomarker, drimane. These low molecular weight compounds, with the exception of drimane, are suspected components of residual naphtha, and the large variabilities in concentration are suggestive that these species may be linked with fluctuating inputs and/or sorption of naphtha to the organic phase of the FFT. Equally possible, the pronounced variability in the low molecular weight n-alkanes concentrations