Hydrogeologic characterization of a newly constructed saline-sodic clay overburden hill

Abstract

Syncrude Canada Ltd (Syncrude) Mildred Lake operation is the largest producer of crude oil from oil sands mining in Canada. A saline-sodic clay-shale overburden known as the Clearwater Formation (Kc) must be removed in order to access the oil-bearing McMurray Formation (Km). The potential concerns associated with the reclamation of overburden structures include shale weathering and salt release and migration, resulting in salinization of groundwater, surface water, and reclamation soil covers. South Bison Hill (SBH) is one example of a Kc overburden structure located at the Syncrude Mildred Lake Operation. The general objective of this study is to develop a preliminary conceptual/interpretative model of the hydrogeology of the newly reclaimed SBH at the Syncrude mine site. A number of tasks were undertaken to meet this general objective. The first, and most important aspect of this study was to develop a geological model of SBH including pile geometry and depositional history of the hill. Secondly, to gain an understanding of the field conditions, a program was carried out over 2002 and 2003 to obtain pile physical characteristics. The geological model revealed that there are four main geological sections of SBH of different materials using different construction methods. The field data were used to verify the geological model, which illustrated the differences in hydraulic conductivities and geochemical signatures between the different sections. All information was used to develop a simple steady-state numerical seepage model of SBH to be used as a tool to investigate the response of the water levels of SBH to variations in the model parameters. The model illustrated that groundwater flow is largely controlled by a more permeable section on the south side of SBH and an unstructured Kc fill at the base of the pile. A sensitivity analysis was conducted on the model changing the flux into the pile, the permeability of the materials, and most importantly the head value of the tailings facility located on the north side both showing to be influential on the elevation of the water table through SBH.