Association of groundwater constituents with topography and distance to unconventional gas wells in NE Pennsylvania.

Recently we reported an association of certain diseases with unconventional gas development (UGD). The purpose of this study is to examine UGD's possible impacts on groundwater quality in northeastern Pennsylvania. In this study, we compared our groundwater data (Columbia 58 samples) with those published data from Cabot (1701 samples) and Duke University (150 samples). For each dataset, proportions of samples with elevated levels of dissolved constituents were compared among four groups, identified as upland far (i.e. ≥1km to the nearest UGD gas well), upland near (<1km), valley far (≥1km), and valley near (<1km) groups. The Columbia data do not show statistically significant differences among the 4 groups, probably due to the limited number of samples. In Duke samples, Ca and CI levels are significantly higher in the valley near group than in the valley far group. In the Cabot dataset, methane, Na, and Mn levels are significantly higher in valley far samples than in upland far samples. In valley samples, Ca, Cl, SO4, and Fe are significantly higher in the near group (i.e. <1km) than in the far group. The association of these constituents in valley groundwater with distance is observed for the first time using a large industry dataset. The increase may be caused by enhanced mixing of shallow and deep groundwater in valley, possibly triggered by UGD process. If persistent, these changes indicate potential for further impact on groundwater quality. Therefore, there is an urgent need to conduct more studies to investigate effects of UGD on water quality and possible health outcomes.