Hydrochemistry of the Peace River Arch Area, Alberta and British Columbia

The Peace River Arch area is defined as 54° to 58°N and 114°W to the eastern limit of the disturbed belt. More than 30,000 formation water analyses from the area were entered into the Alberta Geological Survey Well Data Base, verified, and subjected to electronic and manual-electronic culling to leave a data base of about 9600 fairly reliable analyses. Following study by means of composition distribution maps, cumulative frequency plots of log Cl, and data compilations, the final data base comprised about 6800 analyses, or just over 22% of the original data base.

Salinity ranges from freshwater to 380,000 mg/l. Salinity distribution maps are of two major types. Pre-Cretaceous aquifers have salinity trends parallel to the structure contours, and show higher salinity with increased depth, hence increased temperature. This pattern may be modified by the presence of halite or high permeability trends within individual aquifers. Both modifications result in relatively higher salinity for comparable depths. Cretaceous aquifers below the Harmon-Joli Fou aquitard show salinity trends unrelated to structure contours and possibly more related to surface topography. However, this association may be spurious when considering relatively shallow aquifers in regions with strongly contrasting surface topography. There are too few aquifers above the Harmon-Joli Fou aquitard to permit general statements.

Distribution patterns for Cl, Ca and Mg closely resemble that for salinity, and as a broad generalization for any specific aquifer, the higher salinity has a relatively lower HCO₃ content compared to the lower salinity area. Except for the association of SO₄ > 2500 mg/l with anhydrite in the Charlie Lake aquifer, SO₄ generally shows no obvious regional trends. Generally, the salinity distribution map provides a broad indication of the distribution of other components in the aquifer.

The report is illustrated with 36 salinity distribution maps and 4 maps for individual components. Although the data distribution only averages 60 analyses per cubic kilometre the patterns which emerge suggest strong relations among formation water composition, depth, temperature and water-rock reactions. As such the hydrochemical information presented should form a sound basis for future hydrogeological studies in the Peace River Arch area.