Temporal and Spatial Analysis of Groundwater Quality and Unconventional Gas Well Density in Washington County, Pennsylvania

A total of 265 household water supply samples were collected from 154 houses in Washington County, Pennsylvania between 2012 and 2014. The inorganic and anion constituent concentrations were compared to active unconventional gas well density relative to each household. Cross-sectional, temporal, and spatial analytical techniques were employed to explore potential relationships between analyte concentrations or change in analyse concentrations and gas well density or change in gas well density. Overall, the groundwater in Washington County is of good quality and there was no evidence for systematic deterioration of water quality due to gas well density. Manganese and pH exceeded the United States Environmental Protection Agency (USEPA) and Pennsylvania Department of Environmental Protection (PADEP) secondary maximum contaminant levels (SMCLs) in ∼12% of samples each, but these exceedances were expected due to the long history of acid mine drainage throughout the County. Eight analytes (Cr, Co, Li, Hg, Ni, K, Sn, and temperature) exhibited statistical significance when their initial and subsequent sample event medians were compared. There were seven analytes (Al, Cr, Fe, Pb, Li, Na, U) found to have significant relationships between the concentration or change in concentration and gas well density or change in gas well density. Lithium exhibited correlations in almost all statistical tests and had a median value (7.7 ppb) almost three times higher than the national median (2.8 ppb). Correlations for all analytes may be explained by various anthropogenic sources, both from unconventional gas extraction activities and from other unrelated activities. Further characterization of causal pathways is needed to clarify these relationships.