High-volume hydraulic fracturing (HVHF) gas-drilling operations in the Marcellus Play have raised environmental concerns, including the risk of groundwater contamination. Fingerprinting water impacted by gas-drilling operations is not trivial given other potential sources of contamination. We present a multivariate statistical modeling framework for developing a quantitative, geochemical fingerprinting tool to distinguish sources of high salinity in shallow groundwater. The model was developed using new geochemical data for 204 wells in New York State (NYS), which has a HVHF moratorium and published data for additional wells in NYS and several salinity sources (Appalachian Basin brines, road salt, septic effluent, and animal waste). The model incorporates a stochastic simulation to predict the geochemistry of high salinity (>20 mg/L Cl) groundwater impacted by different salinity sources and then employs linear discriminant analysis to classify samples from different populations. Model results indicate Appalachian Basin brines are the primary source of salinity in 35% of sampled NYS groundwater wells with >20 mg/L Cl. The model provides an effective means for differentiating groundwater impacted by basin brines versus other contaminants. Using this framework, similar discriminatory tools can be derived for other regions from background water quality data.

Prior work suggests spatial parameters (e.g., landscape position, distance to nearest gas well)can be used to estimate the amount of dissolved methane in domestic drinking water wells overlying the deep Marcellus Shale. New York (NY) provides an opportunity to investigate methane occurrence prior to expansion of high-volume hydraulic fracturing because unconventional gas production is currently banned in the state. We sampled domestic groundwater wells for methane in 2013 (n 5 137) across five counties of NY bordering Pennsylvania, and then resampled a subset of those wells in 2014 for methane concentrations and d 13 C-CH 4 and dD-CH 4 . The majority of waters from wells sampled (77%) had low concentrations of methane (<0.1 mg/L), and only 5% (n 5 7) had actionable levels of methane (>10 mg/L). Dissolved methane concentrations did not change as a function of proximity to existing vertical gas wells, nor other parameters indicating subsurface planes of weakness (i.e., faults or lineaments). Methane levels were significantly higher in wells closer to hydrography flow lines, and most strongly correlated to Na-HCO 3 water type. The distribution of methane between Ca-HCO 3 (n 5 76) and Na-HCO 3 (n 5 23) water types significantly differed (p < 0.01), with median methane concentrations of 0.002 and 0.78 mg/L, respectively. Combined classification of sampled waters based on the dominant water cation, well topographic position, and geologic unit of well completion effectively identified wells with a greater than 50% probability of having methane concentrations exceeding 1 mg/L. Such classification schemes may be useful as a screening tool to assess natural versus gas production-related sources of methane in domestic wells.

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