Regional Subsurface Hydrogeology in Northeast Alberta

This report is the second of a two-part study dealing with the hydrogeology of the Phanerozoic succession in northeast Alberta. The first part, completed in August 1991, described the regional-scale geology and hydrostratigraphy of the sedimentary strata in the area defined by latitudes 55°N to 58°N and longitudes 110°W to 114°W (Tp 70-103, R 1-26, W4 Mer). This report presents the hydrogeological regime of formation waters in this study area.

The study was prompted in part by plans of the Alberta Oil Sands Technology and Research Authority (AOSTRA) to expand the Underground Test Facility (UTF) near Fort McMurray in northeast Alberta to a pilot operation. As part of this expansion, disposal of residual waters by on-site deep well injection has been proposed. Environment Canada and the Alberta Research Council initiated in 1990 a collaborative study on the effects of deep injection of residual water at the UTF site, with data support and cooperation from AOSTRA. The evaluation of the effects of deep injection of residual water is based on predictive modeling, which requires knowledge of the initial baseline hydrogeological conditions. Because the data are very scarce and incomplete at the local scale, it was necessary to use regional-scale data for the identification and characterization of the hydrostratigraphic units at the UTF site. The hydrodynamic and hydrochemical characterization (porosity and permeability, formation pressure, and chemistry of formation waters) of the Phanerozoic hydrostratigraphic units in northeast Alberta forms the content of this report.

The hydrogeological regime of formation waters in the Phanerozoic succession in northeast Alberta is very complex because of variability in geometry and lithology of the Phanerozoic strata. Erosion by the Athabasca river system as far down as Paleozoic strata adds to this complexity. As a result, topography and physiographic features exert a strong influence on the flow regime within most aquifers. Local recharge, which introduced fresh meteoric water, takes place in areas of high topography, such as the Birch and Pelican mountains. The valleys of the Athabasca and Clearwater rivers represent discharge areas for aquifers exposed or subcropping near them.

From the point of view of the hydrogeological regime, the Phanerozoic aquifers can be divided into four groups. The aquifers below the thick halite beds of the Prairie Formation exhibit regional flow characteristics, with a northeastward flow direction and depth-related salinity trends. High formation water salinity is associated with the proximity of Elk Point Group evaporites. Buoyancy (density) effects are significant, likely retarding to flow. The flow in the Beaverhill Lake-Cooking Lake aquifer system is intermediate-to-local in nature. Within the subcrop area and along the outcrop, local physiographic influences are superimposed over a regional northeastward trend. The formation water salinity, while depth related, is lower than for the pre-Prairie aquifers. As a result, buoyancy effects are not important when compared with gravity-induced flow. The Grosmont, Winterburn and Wabamun aquifers, present only in the western part of the area, act most probably as a drain for aquifers in hydraulic continuity above and below. The flow is likely toward the northwest, where the Grosmont aquifer is exposed and there the formation waters discharge into Peace River. Because of very low gravity induced hydraulic gradients, buoyancy effects could be important locally, but not on a regional scale. The flow regime in the Cretaceous aquifers is local, with recharge in topographically high areas, and discharge where the aquifers are exposed. The salinity of formation waters is low, with depth (temperature) related trends noticeable only in the southwest. The flow in these aquifers is basically gravity driven.