Mapping the Vulnerability of Groundwater to Wastewater Spills for Source Water Protection in a Shale Gas Region

Source water protection in areas of shale gas development encompasses identifying areas that are the most vulnerable to groundwater quality deterioration due to spills of natural gas production wastewater. This study uses the density-dependent flow and transport code TOUGH2 to quantify the time and distance of travel of saline wastewater plumes for different hydrogeological settings in Northeast British Columbia. The models were designed to address three main factors identified from the DRASTIC method for vulnerability assessment: (1) depth to water, (2) impact of vadose zone, and (3) conductivity of the aquifer materials. The vadose zone permeability and depth to water table are dominant controls on the wastewater migration rate and footprint. Overall, the vulnerability in the region is relatively low, with exceptions near river valleys and areas with shallow water tables. The vulnerability maps can be used as a preliminary risk assessment tool, as they are based on the main factors influencing the potential of a wastewater spill to contaminate an aquifer.