Groundwater recharge in a confined paleovalley setting, Northeast British Columbia, Canada

Ancient river channels or subglacial drainage networks infilled with younger sediments can include significant deposits of highly permeable sands and gravels. Despite being hidden at surface, such systems are ubiquitous globally, can form highly productive groundwater reservoirs and have significant influence on regional hydrogeology, contaminant transport and local water resources. Consequently, the hydraulic characteristics of such buried-valley or “paleovalley” aquifers have been the subject of increasing study. In this study, the hydrogeology of the Sunset Paleovalley in Northeast British Columbia (NEBC, Canada) was conceptualized using data from newly installed, scientifically designed monitoring wells and available hydrogeological data for buried-valley aquifer systems in NEBC and the Western Canadian Sedimentary Basin. Using this conceptual model, a regional-scale, steady-state, groundwater-flow model was constructed to assess recharge magnitude and mechanisms, fluxes and residence times to inform aquifer management. The calibrated average aerial recharge rate was 16 mm/year, within the range of recharge estimates previously reported for NEBC (0.5–78 mm/year). The average residence times for buried valley sand/gravel and weathered bedrock aquifers were estimated at 3,200 and 2,900 years, respectively, and are indicative of a slowly flushed system, consistent with the 1,300 mg/L average total dissolved solids groundwater chemistry. The current groundwater extraction rates are a small fraction of the simulated groundwater discharge to the Kiskatinaw River. The findings can support management of groundwater resources in similar hydrogeological settings common to NEBC.