SPATIAL PARAMETERS CONTROLLING SALINITY AND DISSOLVED METHANE CONCENTRATIONS IN PRIVATE WELLS PRIOR TO HYDRAULIC FRACTURING

In this study, we explored whether spatial parameters (e.g. landscape position, distance to nearest gas well, hydrologic unit of extraction) correlate with the spatial distribution of water salinity and methane concentrations in domestic drinking water wells prior to hydraulic fracturing in Southern New York State, where there is currently a moratorium on production of shale gas. We used geochemical fingerprinting tools, such as strontium isotopes and carbon and hydrogen isotopes of methane, to examine the potential for natural migration of Appalachian Basin brine and thermogenic methane to shallow aquifers. Domestic groundwater wells (n=204) were sampled across five counties (Broome, Chemung, Chenango, Steuben, and Tioga) in New York from 2012-2014, in an area where the Marcellus shale is sufficiently deep (>610 m) for shale gas production via high volume hydraulic fracturing, and there is political support for unconventional shale gas production in the future. Based on analysis of homeowner wells in 2013 (n=145), 13% had measurable concentrations of methane (> 1 mg/L) and 7 wells had actionable levels of methane (> 10 mg/L), in the absence of shale gas production. Dissolved methane concentrations were not strongly correlated with landscape position, as observed in prior studies, but were strongly correlated with geochemical parameters (such as salinity and Br:Cl ratios) and proximity to inferred regional faults. Stable isotopes of CH₄ (¹³C and ²H) were used to explore whether sources of dissolved methane were more likely biogenic or thermogenic. Prior work suggests Appalachian Basin brines and road salt runoff are common sources of elevated salinity in the sampled wells; additional analysis of regional road salt chemistry and strontium isotopes in samples of well water suggest both road salt runoff and formation brine may be impacting shallow groundwater chemistry in the region.