WASTEWATER SPILLS DURING SHALE GAS DEVELOPMENT AS A DRIVER OF INCREASED GROUNDWATER SALINITY

Over the past two decades, advances in horizontal drilling and hydraulic fracturing have greatly increased U.S. natural gas production from low-permeability formations such as shale. However, the large volumes of saline wastewater co-produced with natural gas during shale gas development necessitates proper handling and disposal to avoid negative environmental impacts. In this study, we analyzed a dataset of ~29,000 groundwater samples from the Marcellus Shale region of Pennsylvania (U.S.A.). We observed small but significant increases in the concentrations of species present in shale gas wastewater (Ba, Sr, Cl) associated with greater proximity to and higher density of shale gas wells. These increases are greatest when we consider correlations with documented wellpad spills, and especially with high-volume (>2000 L) spills of shale gas wastewater. In the southwestern portion of the study area, we also observed significant correlations with wellpad impoundment violations. Using a geospatial statistics tool, we mapped out subregions where correlations between salt concentrations and shale gas development were especially strong. In a handful of these “hotspots”, the calculated increase in salt concentrations attributed to shale gas development implies trace species also present in shale gas wastewaters could exceed water quality standards and pose a potential human health risk. Our results are consistent with localized wastewater spills during shale gas development translating into small but significant regional impacts on groundwater salinity.