Bruce D. Lindsey Matthew D. Conlon Andrew G. Hunt Kenneth Belitz Bryant C. Jurgens Brian A. Varela Peter B. McMahon 2019 <p><span>Water samples from 50 domestic wells located &lt;1 km (proximal) and &gt;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. CH</span>₄<span>-isotope, predrill CH</span>₄<span>-concentration, and other data indicate that one proximal sample (5% of proximal samples) contains thermogenic CH</span>₄<span>&nbsp;(2.6 mg/L) from a relatively shallow source (Catskill/Lock Haven Formations) that appears to have been mobilized by shale-gas production activities. Another proximal sample contains five other volatile hydrocarbons (0.03–0.4 μg/L), including benzene, more hydrocarbons than in any other sample. Modeled groundwater-age distributions, calibrated to&nbsp;</span>³<span>H, SF</span>₆<span>, and&nbsp;</span>¹⁴<span>C concentrations, indicate that water in that sample recharged prior to shale-gas development, suggesting that land-surface releases associated with shale-gas production were not the source of those hydrocarbons, although subsurface leakage from a nearby gas well directly into the groundwater cannot be ruled out. Age distributions in the samples span ∼20 to &gt;10000 years and have implications for relating occurrences of hydrocarbons in groundwater to land-surface releases associated with recent shale-gas production and for the time required to flush contaminants from the system.</span></p> application/pdf 10.1021/acs.est.9b01440 en American Chemical Society Hydrocarbons in upland groundwater, Marcellus Shale Region, Northeastern Pennsylvania and Southern New York, USA article