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Methane Contamination of Drinking Water Accompanying Gas-well Drilling and Hydraulic Fracturing

Methane Contamination of Drinking Water Accompanying Gas-well Drilling and Hydraulic Fracturing

Full Title:   Methane Contamination of Drinking Water Accompanying Gas-well Drilling and Hydraulic Fracturing
Author(s):
Publisher(s):  Proceedings of the National Academy of Science
Publication Date: April 1, 2011
Full Text: Download Resource
Description (excerpt):

Directional drilling and hydraulic-fracturing technologies are dra- matically increasing natural-gas extraction. In aquifers overlying the Marcellus and Utica shale formations of northeastern Pennsyl- vania and upstate New York, we document systematic evidence for methane contamination of drinking water associated with shale- gas extraction. In active gas-extraction areas (one or more gas wells within 1 km), average and maximum methane concentrations in drinking-water wells increased with proximity to the nearest gas well and were 19.2 and 64 mg CH4 L−1 (n 1⁄4 26), a potential explosion hazard; in contrast, dissolved methane samples in neigh- boring nonextraction sites (no gas wells within 1 km) within similar geologic formations and hydrogeologic regimes averaged only 1.1 mg L−1 (P < 0.05; n 1⁄4 34). Average δ13 C-CH4 values of dissolved methane in shallow groundwater were significantly less negative for active than for nonactive sites (−37`7‰ and −54`11‰, respectively; P < 0.0001). These δ13C-CH4 data, coupled with the ra- tios of methane-to-higher-chain hydrocarbons, and δ2 H-CH4 values, are consistent with deeper thermogenic methane sources such as the Marcellus and Utica shales at the active sites and matched gas geochemistry from gas wells nearby. In contrast, lower-concentra- tion samples from shallow groundwater at nonactive sites had isotopic signatures reflecting a more biogenic or mixed biogenic/ thermogenic methane source. We found no evidence for contam- ination of drinking-water samples with deep saline brines or frac- turing fluids. We conclude that greater stewardship, data, and— possibly—regulation are needed to ensure the sustainable future of shale-gas extraction and to improve public confidence in its use.

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