EFFECT OF SHALE GAS DRILLING ON GROUNDWATER QUALITY, TIOGA COUNTY, PENNSYLVANIA

The study examines water quality related to Marcellus-Shale-gas extraction in Tioga County, PA by horizontal drilling and slick-water hydrofracturing. In Phase I (January 2011 through May 2011), 46 private drinking water wells less than 400 m from the nearest gas drill site (mean distance = 282 m) and 52 private drinking water wells greater than 400 m from the nearest gas drill site (mean distance = 1736 m) were selected by a randomization procedure, sampled, and tested for pH and conductivity; barium and strontium concentrations also were measured by atomic emission spectroscopy and used as a proxy for presence of flowback fluid. Statistical tests reveal no significant difference between water samples taken less than 400 m from the nearest gas drill site and water samples taken more than 400 m from the nearest gas drill site, but there was a weak negative correlation between conductivity and distance to the nearest well. In Phase II, most of the water wells (n = 89) were resampled and analyzed (October 2012 through May 2013). Preliminary results indicate a repeat of the Phase I finding of a weak negative correlation between conductivity and distance to the nearest well; a modest county-wide increase in median pH over two years; and evidence of changes in analyte concentrations when new gas wells were drilled within 400 m of a drinking water source.