Regional aquifer parameters evaluated during mine depressurization in the Athabasca Oil Sands, Alberta

Abstract

Withdrawal of groundwater for depressurization of the "water sands aquifer" under a test pit in the Athabasca Oil Sands of Alberta caused declines in hydraulic heads in two observation wells located 3700 and 6600 m away. Analysis of these declines over a 6 month period by the time–drawdown method indicated transmissivity values of 68 m2/day for both wells. Pumping tests of 24 h duration had previously indicated that transmissivities at the two observation wells were 1.2 and 118 m2/day.Geological assessment of the water sands aquifer revealed that it is discontinuous between the test pit and the observation wells. Variations in lithology and heavy oil saturation as well as relief on the underlying limestone indicate that the water sands aquifer does not meet the "homogeneous and isotropic" criteria necessary for application of the Theis method of analysis. Nevertheless, the excellent fit of the time–drawdown data to the type curve and the identical values obtained for transmissivity indicate that the method can be used for pumping tests of long duration, which reflect conditions over extensive areas of the water sands aquifer.