METHANE EBULLITION CAN INFLUENCE INTERNAL MASS LOADING IN OIL SANDS END PIT LAKES

Internal mass loading from fluid fine tailings (FFT) to the overlying water cover may impact water quality in oil sands end pit lakes. Previous conservative transport models for Base Mine Lake (BML), the first oil sands end pit lake in northeastern Alberta, Canada, indicated that advective-dispersive transport could not fully explain field observations. These models invoked a periodic lake mixing event to simulate depth profiles of conservative tracers across the tailings-water interface. Residual naphtha solvent from bitumen extraction supports methanogenesis and methane (CH₄) ebullition within FFT stored in BML. We propose that variably continuous mixing by CH₄ ebullition influences chemical mass transfer across the tailings-water interface. Here, we develop a modelling framework explore (i) the relationship between CH₄ dynamics, (ii) the spatial and temporal distribution of FFT mixing processes, and (iii) the impact of mixing on internal mass loading. First, we characterize the temporal and spatial variation in CH₄ saturation in BML tailings. Next, we simulate the effect of CH₄ ebullition as enhanced diffusion in advective-dispersive models of conservative transport. We then compare these results to physical and chemical data from ongoing field investigations. Our findings indicate that inclusion of variably continuous mixing due to CH₄ ebullition strongly affects depth profiles of conservative tracers and, therefore, internal mass loading in BML. Overall, these results offer new insight into internal mass loading and, therefore, inform predictions of long-term water quality within oil sands end pit lakes.