Hydrogeology of the Edson area, Alberta

The hydrogeology of the Edson map area can be discussed with respect to three physiographic regions: the Interior Plains, the Rocky Mountain Foothills, and the front ranges of the Rocky Mountains.

In the interior Plains, fractured sandstones of the Paskapoo Formation are the most important bedrock aquifers. Transmissivity for this formation ranges from less than 1.5 m2/d to over 100 m2/d, depending on the degree of fracturing. Safe yield values range from 0.1 l/sec to 38 l/sec. The buried Edson valley aquifer is the most important surficial aquifer in the area with transmissivity values between 150 m2/d and 1200 m2/d and safe yields from 8 l/sec to 38 l/sec.

In the foothills, the Paskapoo Formation is also the main bedrock aquifer but is slightly less productive with transmissivity values of 1.5 m2/d to 15 m2/d and safe yields of 0.4 l/sec to 2 l/sec. The most important surficial aquifers in the foothills are outwash gravels between Brule and Gregg Lakes. These aquifers have been assigned safe yields of 2 l/sec to 38 l/sec.

In the Rocky Mountains bedrock aquifers exist because of fractures. Depending on the rock types, safe yields can range from 0.1 l/sec to 2.0 l/sec. Surficial deposits in the Rocky Mountains are mainly recent alluvium or glaciofluvial deposits. Southwest of Brule Lake these deposits are assigned a safe yield of 8 l/sec to 38 l/sec.

Hydrochemistry is discussed according to categories. Groundwaters of the area are generally of good quality.

Bedrock groundwaters are of three basic types: Ca, Mg-HCO3, CO2 from shallow bedrock aquifers; Na, K-HCO3, CO2 from moderately deep to deep bedrock aquifers; and mixed types dominated by sulfates from various bedrock aquifers.

Total dissolved solids content (TDS) of bedrock waters ranges from 200 to 1000 mg/l. Drift waters are usually of the Ca, Mg-HCO3 type with varying amounts of sulfates (up to 40% epm). The maximum TDS of drift waters is 700 mg/l. Seventy-five percent of spring discharges are Ca, Mg-HC03 groundwaters with TDS ranging from 100 to 1000 mg/l. Of these, ninety percent have TDS of less than 50 mg/l.