The natural gas industry on Tuesday was alternately disputing the findings of a new Duke University study on methane contamination of drinking water near gas well sites, or dismissing the study's results as highlighting an old problem that the industry and regulators are already fixing.
The study, published Monday in the Proceedings of the National Academy of Sciences, examined dozens of drinking water wells in northern Pennsylvania and southern New York. It found that concentrations of methane were, on average, 17 times higher in wells closer to active gas drilling sites than in wells where no gas development activity was underway nearby.
"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," the authors of the study wrote.
But Chris Tucker, a spokesman for Energy in Depth, a group representing independent oil and gas developers, argued on Tuesday that the data set used by the Duke researchers was far too small to draw any broad conclusions about methane contamination.
"The biggest weakness is the lack of baseline data," Tucker argued. "It’s well known that methane migrates upward from source rock over the course of geologic time -- but these guys are trying to argue that it’s migrating upward almost instantaneously as a result of development. That’s just not a case you can credibly make with this sort of data set, these sort of assumptions, and this sort of methodology."
The lack of baseline data -- essentially measurements taken from the same water source both before drilling operations arrived, and then again after -- was recognized by the researchers as a weakness in the analysis.
But Dr. Stephen Osborn, one of the authors of the Duke study, suggested that the correlation implied by the analysis was nonetheless strong, and that water samples gathered from wells furthest from gas development will provide the sort of baseline data needed for future studies.
"Our sampling in non-active extraction areas are effectively baseline and will be important as natural gas extraction operations migrate into these areas," Osborn said. "We hope to continue sampling in these non-active areas as drilling and fracking occur there."
To be sure, methane can be found naturally in groundwater -- often in high concentrations in some parts of Pennsylvania. But according to the Duke study, the molecular characteristics of the methane found in the various wells the researchers examined suggested that industry, rather than naturally occurring events, was behind the increased methane concentrations.
The researchers conceded, however, that more study would be needed before such an assertion could be considered conclusive.
Even so, Matt Pitzarella, a spokesman for Range Resources, a natural gas developer with operations in Pennsylvania, said that methane migration tied to poorly designed wells is a well-known problem -- and one that state regulators in Pennsylvania have been endeavoring to fix for some time.
"Naturally occurring methane has been a long standing and documented issue in this part of the state, where Range is not as active," Pitzarella said in an email message. "Either way we employ the same high standards for well casing in the southwest even though the risk is significantly lower. It’s our job and that of regulators to ensure that natural gas drilling is responsible and does not exacerbate this issue. While the study has grabbed headlines, it’s actually old news and an issue that was addressed by state regulators and supported by industry several years ago."
Hanger noted, for example, that the state's Department of Environmental Protection had proposed new gas drilling rules in 2009, and those rules became final last February.
"The new rules raise standards for the design, construction and operation of gas wells to reduce gas migration pollution," Hanger said. "Gas migration has been a problem in Pennsylvania for decades, well before the first Marcellus well was drilled in 2005. The new, strong rules and the attention to this problem make this the time to reduce it sharply."
For all this, the Duke study appeared to lend a measure of support to long-standing complaints among some residents in areas of dense gas development that their drinking water supplies became infused with methane only after gas prospectors moved into the neighborhood.
That phenomenon prompted an entire genre of online videos depicting homeowners setting faucet water ablaze. Such imagery was among the most memorable arising from last year's Oscar-nominated documentary, "Gasland".
The study did not, however, reveal contamination from chemicals used in hydraulic fracturing, or fracking, the contentious process used in virtually all new drilling done in the area. It involves the high-pressure injection of water, sand and chemicals deep underground to break up and prop-open rock formations in order to release and extract the gas.
Environmental groups and residents had long feared that the chemicals were -- or could be-- finding their way from the well bore and into drinking water well, but the Duke study found no evidence of this.
This story has been updated with comments from Duke researchers.