National Academy of Sciences of the
United States of America
Increased stray gas abundance in a subset of drinking
water wells near Marcellus shale gas extraction
Horizontal drilling and hydraulic fracturing are transforming energy
production, but their potential environmental effects remain
We analyzed 141 drinking water wells across the Appalachian
Plateaus physiographic province of northeastern
natural gas concentrations and isotopic signatures with proximity to
shale gas wells.
Methane was detected in 82% of drinking water samples, with
average concentrations six times higher for homes <1 km from natural
gas wells (P = 0.0006).
Ethane was 23 times higher in homes <1 km from gas wells (P
= 0.0013); propane was detected in 10 water wells, all within
approximately 1 km distance (P = 0.01).
Of three factors previously proposed to influence gas
concentrations in shallow groundwater (distances to gas wells,
valley bottoms, and the Appalachian Structural Front, a proxy for
tectonic deformation), distance to gas wells was highly significant
for methane concentrations (P = 0.007; multiple regression), whereas
distances to valley bottoms and the Appalachian Structural Front
were not significant (P = 0.27 and P = 0.11, respectively).
Distance to gas wells was also the most significant factor
for Pearson and Spearman correlation analyses (P < 0.01).
For ethane concentrations, distance to gas wells was the
only statistically significant factor (P < 0.005). Isotopic
signatures (δ13C-CH4, δ13C-C2H6, and δ2H-CH4), hydrocarbon ratios
(methane to ethane and propane), and the ratio of the noble gas 4He
to CH4 in groundwater were characteristic of a thermally postmature
Marcellus-like source in some cases.
Overall, our data suggest that some homeowners living <1 km
from gas wells have drinking water contaminated with stray gases.
Robert B. Jacksona,b,1,
Thomas H. Darraha,
Nathaniel R. Warnera,
Robert J. Poredac,
Stephen G. Osbornd,
Kaiguang Zhaoa,b, and
Jonathan D. Karra,b
Edited by Susan E. Trumbore, Max Planck Institute for
Biogeochemistry, Jena, Germany, and approved June 3, 2013 (received
for review December 17, 2012)
Proceedings of the National Academy of Sciences