Groundwater flow and solute transport modelling of an oil sands mine to aid in the assessment of the performance of the planned closure landscape

Abstract

Syncrude is updating the Mildred Lake Mine (Lease 17/22) closure plan for regulatory submission in 2011. The role of groundwater in closure landscape design and performance was assessed to support the regulatory submission and closure planning generally. A three-dimensional MODFLOW-SURFACT groundwater flow model was developed to help understand past, current, and expected future groundwater flow and solute transport conditions. Hydraulic properties, climate data, and groundwater recharge and discharge estimates were compiled from regional and site specific references. The data were used to develop a conceptual hydrogeologic model and numerical models to simulate pre-development, current (2008), and closure (0 to 200 years after closure) conditions. The groundwater modelling study was developed at the lease-scale (i.e. a roughly 250 km2 lease within a 900 km2 model domain) to meet the current industry and regulatory closure needs. The simulation results provided insight on dominant groundwater flow and solute transport patterns on the scale of hundreds of metres to kilometres and helped inform groundwater management decisions and at a lease-wide scale. Smaller scale models would be needed to evaluate processes occurring at smaller scales of interest contained within the lease, such as within planned closure watersheds and landforms. Results of the hydrogeologic analysis were integrated with overall closure planning. Groundwater modelling results were used to aid in the assessment of groundwater interactions with the designed surface water drainage network, groundwater flow directions and velocities for tracking potential solute flow pathways, groundwater and surface water quality, wetland design, and salt management for the reclaimed landscape.