National Academy of Sciences of the
United States of America
Methane contamination of drinking water
accompanying gas-well drilling and hydraulic fracturing
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 shale-gas
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 = 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 mg L-1 (P < 0.05; n = 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.
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
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.
Stephen G. Osborna,
Nathaniel R. Warnerb, and
Robert B. Jacksona,b,c,1
Edited* by William H. Schlesinger, Cary Institute of Ecosystem
Studies, Millbrook, NY, and approved April 14, 2011 (received for
review January 13, 2011)
Proceedings of the National Academy of Sciences