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

Abstract

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 CH 4 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 mg L −1 (P < 0.05; n ¼ 34). Average δ 13 C-CH 4 values of dissolved methane in shallow groundwater were significantly less negative for active than for nonactive sites (−37 AE 7‰ and −54 AE 11‰, respectively; P < 0.0001). These δ 13 C-CH 4 data, coupled with the ratios of methane-to-higher-chain hydrocarbons, and δ 2 H-CH 4 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, andpossibly-regulation are needed to ensure the sustainable future of shale-gas extraction and to improve public confidence in its use.groundwater | organic-rich shale | isotopes | formation waters | water chemistry

Analysis of BTEX groundwater concentrations from surface spills associated with hydraulic fracturing operations

“…Public concerns have been expressed about drinking-water contamination from migration of chemicals used during the hydraulic fracturing process, as well as from the escape of methane from fractured rock and well casings (Dammel et al, 2011;Groat and Grimshaw, 2012;Osborn et al, 2011;Rozell and Reaven, 2012;U.S. EPA, 2011).…”

“…However, strong scientific evidence to support these concerns is lacking. To our knowledge, only one study has been published in the scientific literature evaluating the potential for groundwater contamination with methane (Osborn et al, 2011). These authors reported methane contamination of aquifers overlying the Marcellus Shale formation and noted that the contamination accompanied gas-well drilling and hydraulic fracturing activities in the area.…”

“…These authors reported methane contamination of aquifers overlying the Marcellus Shale formation and noted that the contamination accompanied gas-well drilling and hydraulic fracturing activities in the area. However, the authors concluded that more research was still needed to clearly understand the mechanism of contamination (Osborn et al, 2011).…”

“…Wells producing crude oil in addition to methane gas are a potential source of petroleum hydrocarbon release into groundwater via surface spills. Of particular interest is the release of benzene, toluene, ethylbenzene, and xylene (i.e., BTEX), which are present in low percentages in crude oil and, at sufficient doses, have been associated with adverse human health effects (ATSDR, 2000(ATSDR, , 2007a(ATSDR, , 2007b(ATSDR, , 2010Osborn et al, 2011). Opportunities for surface spills and leaks of BTEX-containing liquids include lined holding ponds, which are often constructed at well sites for temporary storage of "flowback" or "produced water," which is the water that comes to the surface with the oil and gas following the hydraulic fracturing procedure.…”

Modelling the hypothetical methane-leakage in a shale-gas project and the impact on groundwater quality

“…This contrasts with the little information on hydrochemical aspects associated with the potential methane leakage during such an operation. Some papers deal with the stable isotopes of carbon, hydrogen and helium, which are meant to distinguish between man-made sources and natural occurrences (Taylor et al 2000;Breen et al 2007;Osborn and McIntosh 2010;Osborn et al 2011;Stuart 2012;Jackson et al 2013;Molofsky et al 2013;McMahon et al 2013). There are reports on elevated concentrations of arsenic, selenium and strontium in groundwater near fracking sites in the Barnett Shale formation of north Texas but it is not known whether the contaminants have a near-surface origin or are derived from a deep source (Fontenot et al 2013).…”