EVALUATING THE IMPACT OF UNCONVENTIONAL OIL AND GAS DRILLING ON GROUNDWATER QUALITY IN THE APPALACHIAN BASIN WITH MIXED LAND USES

The fast rise of unconventional oil and gas development (UOGD) over the past decade has raised major public concerns over its groundwater quality and possible human health impacts, especially for the rural population who rely mostly on domestic wells for their drinking water. The most common UOGD-related impairments have been elevated salt content and methane (CH4) levels in groundwater, with methane being the most extensively investigated of the two. However, attributing these contaminants to UOGD is often difficult, particularly in areas with mixed land uses. This study uses a large hydrogeochemistry dataset obtained from four sources that include 16 geochemical analytes for 17,794 groundwater samples in the rural northern Appalachia, i.e., 19 counties on the border of Pennsylvania (PA; UOGD is permitted) and New York (NY; UOGD is prohibited). We aim to examine the potential sources of inorganic solutes and methane in groundwater using statistical (non-parametric test Wilcoxon Mann Whitney or WMW; Principal Component Analysis or PCA; Non-negative Matrix Factorization or NMF) and geospatial (Sliding Window Geospatial Tool or SWGT) analyses. WMW shows that UOGD counties have higher Cl and CH4 concentrations than non-UOGD counties. In addition, from non-UOGD to UOGD counties, Fe and Mn concentrations increase while sulfate concentration declines. The major salinity source in NY and PA is Appalachian Basin Brine (ABB), while septic effluent is an additional salinity source for NY waters. Geospatial analyses reveal road salting and spill as potential sources of excessive chloride levels across the region. The elevated levels of salt content and methane from these analyses suggest that UOGD has a regional impact on groundwater quality.