Methane contamination of drinking water accompanying gas-well drilling and hydraulic fracturing

in

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From SAFE’s historical archive
January 15, 2013

Report from Duke University

Stephen G. Osborna, Avner Vengoshb, Nathaniel R. Warnerb, and Robert B. Jacksona,b,c,1

aCenter on Global Change, Nicholas School of the Environment, bDivision of Earth and Ocean Sciences, Nicholas School of the Environment, and

cBiology Department, Duke University, Durham, NC 27708

Edited* by William H. Schlesinger, Cary Institute of Ecosystem Studies, Millbrook, NY, and approved April 14, 2011 (received for review January 13, 2011)

Directional drilling and hydraulic-fracturing technologies are dramatically

increasing natural-gas extraction. In aquifers overlying

the Marcellus and Utica shale formations of northeastern Pennsylvania

and upstate New York, we document systematic evidence for

methane contamination of drinking water associated with shalegas

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 ¼ 26), a potential

explosion hazard; in contrast, dissolved methane samples in neighboring

nonextraction sites (no gas wells within 1 km) within similar

geologic formations and hydrogeologic regimes averaged only

1.1 mgL−1 (P < 0.05; n ¼ 34). Average δ13C-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 ratios

of methane-to-higher-chain hydrocarbons, and δ2H-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-concentration

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 contamination

of drinking-water samples with deep saline brines or fracturing

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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