Characterizing the baseline hydrogeochemistry of a shallow groundwater system in the Peace Region, Northeast British Columbia

In most areas that support resource development, the natural/baseline groundwater quality is poorly understood, limiting our ability to assess groundwater quality impacts. This research utilized an integrated multivariate/descriptive statistical – numerical geochemical modeling approach to characterize the baseline hydrogeochemistry of a shallow groundwater system in the Peace Region, northeast BC, where O&G development has raised concerns for groundwater quality. K-means clustering was used to define groundwater types and construct hydrochemical maps, geochemical modeling was used to simulate the hydrogeochemical evolution of the groundwater, and radiocarbon/tritium dating provided groundwater residence times. In unconsolidated aquifers, carbonate dissolution driven by CO2/CH4 flux produces Ca-HCO3 and Ca-Mg-HCO3 groundwater, often exhibiting elevated sulphate/sodium; outside of paleovalleys, the groundwater is typically <60 years old. In the bedrock, cation exchange and carbonate, gypsum, and silicate dissolution driven by CO2/CH4 flux produce Na-Ca-Mg-HCO3-SO¬4, Na-SO4-HCO3, and Na-HCO3 groundwater. Groundwater residence times in the bedrock range from hundreds to 10,000+ years.