INVESTIGATION OF SHALE GAS DRILLING AND GROUNDWATER QUALITY, TIOGA COUNTY, PA: A BASELINE STUDY

Nearly 900 unconventional gas wells were drilled in Tioga County, Pennsylvania, between 2008 and 2015, primarily targeting the Marcellus shale. In order to monitor speculated long-term effects of hydrofracturing on groundwater quality, nearly 100 domestic water wells were sampled in 2011 and resampled in 2012-2013 and again in 2015. The resampling of the wells in 2015 incorporated more extensive analyses. Ion concentrations are found to be consistent with the Lock Haven historical data, and no correlation is observed between ion concentrations and distance to the nearest gas well. Methane concentrations are low (only three samples exceed the Pennsylvania Department of Environmental Protection’s recommended 7 mg/L limit), but methane concentrations are correlated to distance to the nearest gas well (N = 45, Spearman’s ρ = -0.446, p = 0.002). Furthermore, methane concentrations are higher for samples taken closer than 400 m from the nearest gas well (Mean = 2.89 ± 2.01 mg/L, N = 23) compared to samples taken further than 400 m from the nearest gas well (Mean = 0.09 mg/L, N = 23, Mann-Whitney U = 360, p = 0.007, r = 0.29). A difference in methane concentrations is also observed for samples closer than 1000 m from the nearest gas well (Mean = 2.08 ± 1.41 mg/L, N = 33) to samples greater than 1000 m from the nearest gas well (Mean = 0, N = 13, Mann-Whitney U = 293, 0.014, r = 0.40). This study serves as a baseline for water quality in an area where unconventional drilling is prevalent, and future sampling will be used to determine whether long-term impacts occur.