Association between unconventional oil and gas (UOG) development and water quality in small streams overlying the Marcellus Shale

Unconventional oil and gas (UOG) development has increased dramatically in the Marcellus Shale region over the past decade, and there is widespread public concern about the potential effects that UOG development may have on water quality. The goal of this study was to assess whether a suite of stream water quality constituents was related to the intensity of UOG development in corresponding catchments. Nineteen streams in southwestern Pennsylvania, where UOG development is prevalent, and 10 streams in western Maryland, where no UOG development has occurred, were sampled in summer 2013. Dissolved metals, radium isotopes, radon, specific conductance, stream discharge, and pH were measured. Principal component analysis revealed that samples tended to cluster by state, but some overlap in water quality existed between Maryland and Pennsylvania. Linear models were used to assess how response variables were related to UOG, other extractive activities, and landscape characteristics. These models showed that an index of oil and gas development had significant explanatory power for specific conductance, As, Ca, K, Mg, Na, and Sr. Other land use and land cover variables, such as forest, urban development, and coal mining, as well as stream discharge and pH, also were significantly associated with response variables. These results suggest that, in the Marcellus Shale region, UOG may elevate specific conductance and dissolved element concentrations in streams, but it should be considered in the context of broader patterns of land use and human activity.