Hydrogeological Characterization of the Grimshaw Area, Northwestern Alberta

Gravel deposits in the Grimshaw area form an important aquifer system and aggregate resource in northwestern Alberta. The stratigraphy and geometry of the gravel deposits were updated by the Alberta Geological Survey, and informally named the Grimshaw gravels, Old Fort gravel and Shaftesbury gravel from highest to lowest. Identification of three stratigraphically and geometrically distinct components of the gravel deposit provided an opportunity to re-examine the hydrogeological characteristics of the aquifer system that is hosted within the gravel deposits. The study focuses on variations in groundwater chemistry and spatial and temporal trends in groundwater levels across the three gravel units. A key finding of this assessment is that observations of varying groundwater quality and availability across the area are better explained by considering the aquifer as a terraced system corresponding with the three gravel units rather than a single aquifer.

This study found that groundwater levels are relatively flat across the Grimshaw gravels with Cardinal Lake receiving some groundwater discharge along the west and north shorelines, and recharging groundwater along the south and east shorelines. The groundwater in the Grimshaw gravels is generally of good quality and sourced primarily from snowmelt. Groundwater recharge was estimated to be in the range of 10 to 50 mm per year. The groundwater level across the Old Fort gravel slopes toward the Peace River valley and appears to have a consistent pattern of flow direction through time. Groundwater in the Old Fort gravel is sourced primarily from bedrock formations, leading to poorer water quality and zones of sodium- and/or sulphate-rich groundwater.