Earth Sciences Report 1976-05

Earth Sciences Report 1976-05

ESR 1976-05

Hydrogeology of the Mount Robson-Wapiti area, Alberta

Author(s) Barnes, R.G. Date 1977-01-01

Within the Rocky Mountains and Foothills, bedrock aquifers are characterized by fracture permeability and have structural rather than lithological boundaries. Flow systems are thought to be generally shallow and are bounded by major thrust fault zones which form highly permeable conduits for groundwater movement in both horizontal and vertical planes. Discharge from shallow bedrock aquifers is most abundant along these fault zones and flow rates increase with decreasing elevation from about 10 igpm to more than 1500 igpm (0.75 to 110 l/s). The direction of groundwater movement and residence time is determined mainly by relief, regional geological strike and dip, faulting and fracture permeability. The presence of thermal springs discharging groundwater with total dissolved solids content in the 1000 to 2000 ppm range and high sulfate content and releasing hydrogen sulfide gas suggests locally high thermal gradients. The more promising and also more readily accessible aquifers are surficial deposits.

Northeast of the Rocky Mountains, the dissected Western Alberta High Plains are underlain by fractured sandstone and shale of the Paskapoo Formation. Fracture permeability leads to rapid transmission of groundwater and water quality is excellent. The water table is often deep below the surface and calcium-magnesium ion ratios range between 3 and 4. The Paskapoo Formation outcrop is thought to be the major recharge area in the map area.

Northeast of the High Plain natural discharge features are rare. Total dissolved solids contents of groundwater from shallow bedrock aquifers increase from less than 500 ppm on the northeast edge of the High Plains to highs of 2000 to 2500 ppm on the Wapiti Plain, and sodium and potassium gradually become the dominant cations. Infiltration of precipitation and surface runoff is minimal due to the presence of surficial deposits containing high proportions of impermeable silt and clay. The groundwater of the Wapiti Plain is thought to be derived from a deep flow system originating in the High Plains to the southwest or farther west in British Columbia. Local recharge occurs in areas devoid of surficial deposits.

Yields range from 100 to 500 igpm (7.6 to 38 l/sec) in alluvial outwash gravels of the Rocky Mountain Foothills and High Plains, and 1 to 25 igpm (0.076 to 1.9 l/sec) in sandstone, shale and coal aquifers of the Upper Cretaceous Wapiti Formation. Yields from bedrock aquifers of the Rocky Mountains are generally unpredictable, but carbonate rock types are probably the most highly yielding. Fractured sandstones and shales of the Paskapoo Formation are the most productive bedrock aquifers in the plains area, with yields ranging from 25 to 100 igpm (1.9 to 7.6 l/s), although the probability of intersecting fractured rock is difficult to assess.

Barnes, R.G. (1977): Hydrogeology of the Mount Robson-Wapiti area, Alberta; Alberta Research Council, ARC/AGS Earth Sciences Report 1976-05, 37 p.