Data Release for Hydrocarbons in Upland Groundwater, Marcellus Shale Region, Northeastern Pennsylvania and Southern New York, USA

Water samples from 50 domestic wells located <1 kilometer (km) (proximal) and >1 km (distal) from shale-gas wells in upland areas of the Marcellus Shale region were analyzed for chemical, isotopic and groundwater-age tracers. Uplands were targeted because natural mixing with brine and hydrocarbons from deep formations is less common in those areas compared to valleys. Methane (CH4) -isotope and pre-drill CH4 data indicate one proximal sample (5 percent of proximal samples) contains thermogenic CH4 (2.6 milligrams per liter (mg/L)) associated with shale-gas production. Chloride (Cl), bromide (Br), lithium (Li), and neon-20 (20Ne)/argon-36 (36Ar) data suggest that CH4 leaked from a nearby gas well in a gas phase. Another proximal sample contains volatile hydrocarbons (0.03-0.4 micrograms per liter (µg/L)), including benzene, found in some hydraulic fracturing fluid. Modeled groundwater-age distributions, calibrated to tritium (3H), sulfur hexafluoride (SF6), and carbon-14 (14C) concentrations, indicate that water recharged prior to shale-gas development, suggesting surface releases associated with shale-gas production were not the source of those hydrocarbons, although leakage from a nearby gas well directly into the old groundwater cannot be ruled out. Estimated age distributions in the samples span ~20 to >10,000 years and have implications for relating occurrences of hydrocarbons in groundwater to surface releases associated with recent shale-gas production, and to the time required to flush contaminants from the system. This data release contains isotopic tracer, noble gas, and groundwater-age tracer concentration data collected by the U.S. Geological Survey and data for pH, specific conductance, major ions, and methane collected by Chesapeake Energy Corporation.