Samuel Shaheen , Tao Wen , Zhong Zheng, Lingzhou Xue, Jennifer Baka, Susan L. Brantley

While unconventional oil and gas development (UOGD) is changing the world economy, processes that are used during UOGD such as high-volume hydraulic fracturing (“fracking”) have been linked with water contamination. Water quality risks include leaks of gas and salty fluids (brines) that are co-produced at wellpads. Identifying the cause of contamination is difficult, however, because UOG wells are often co-located with other contaminant sources. We investigated the world’s largest shale gas play with publicly accessible groundwater data (~29,000 analyses from the Marcellus Shale in Pennsylvania, U.S.A.) and discovered that concentrations of brine-associated species barium ([Ba]) and strontium ([Sr]) show small regional increases within 1km of UOGD. Higher concentrations in groundwaters are associated with greater proximity to and density of UOG wells. Concentration increases are even larger when considering the locations of i) spill-related violations and ii) some wastewater impoundments. These statistically significant relationships persist even after correcting for other natural and anthropogenic sources of salts. The most likely explanation is that UOGD slightly increases salt concentrations in regional groundwaters not because of fracking but because of the ubiquity of wastewater management issues. The high frequency of spills and leaks across shale gas basins suggests other plays could show similar effects.