A Duke University study has documented the first systematic link between methane gas from deep Marcellus and Utica shales and contamination of drinking water wells near active gas wells in northeastern Pennsylvania and New York.
The study found that methane levels in private drinking water wells was 17 times higher on average in wells within 1,000 feet of a deep natural gas well, based on water sampling done at 68 wells. Methane was found in 85 percent of the wells.
Duke researchers were able to match the chemical composition of the methane in three of the drinking water wells to the methane present in three of the nearby gas wells, according to the study abstract.
Robert B. Jackson, a professor of biology in Duke's Nicholas School of the Environment and one of the study's authors, said that in those three instances the chemical analysis supported the claims of landowners that their wells were contaminated by Marcellus Shale well drilling.
"Based on the chemical isotope, the signature of the methane is much more like the gas deep underground," said Mr. Jackson, who conceded that the Marcellus gas was "quite variable, that the researchers only had actual chemical gas values for three of the deep gas wells, and that additional study is needed. Still, the water wells match quite well what that data shows."
Gas from the Marcellus Shale is typically about 90 percent methane.
The study found no evidence of contamination of drinking water wells with either salty brines from the mile-deep Marcellus Shale formation or chemicals used in hydraulic fracturing, a procedure that pumps water, toxic chemicals and sand into the shale to crack it and release the gas it contains.
The study was published in the online Early Edition of the Proceedings of the National Academy of Sciences.
John Hanger, former secretary of the Department of Environmental Protection, said the study confirmed two points that the agency already knew: that gas migration has impacted some water wells, and that no fracking fluid has polluted those wells.
That was the case with incidents of well-water contamination in the northeastern Pennsylvania town of Dimock, Mr. Hanger said. Faulty drilling procedures and improper well casing resulted in methane gas migrating to the water wells of 19 families.
In the Dimock case, most of the wells showed an immediate reduction in methane after the nearby gas wells were plugged and repaired. "If the fracking had been the cause," instead of problems with cement around the well, "that wouldn't have been the case," Mr. Hanger said.
The Dimock migration case also resulted in stronger rules for how wells are constructed, governing the materials and design as well as disclosure of the chemicals used in the fracturing process, he said. It also gave the department the power to impose stronger precautions in areas like the state's northeast, where the geological conditions make gas migration more likely than in southwestern Pennsylvania.
"I think the new rules will greatly reduce the incidents and rate of gas migration," Mr. Hanger said, adding that those rules would need to be vigorously enforced.
Katy Gresh, spokeswoman for the state Department of Environmental Protection, said the agency was reviewing the report. "They would like to see all of the authors' backup data to review their methodology," she said in a statement
Industry sources questioned the objectivity of the study authors as well as their findings.
"Pennsylvania has an extensive and well-documented history of naturally occurring methane impacting private water wells, long before Marcellus development began just a few years ago," said Kathryn Klaber, president of the Marcellus Shale Coalition, a gas industry lobbying organization. She labeled the report "at best inconclusive," and noted that it was edited by an "outspoken natural gas production critic."
Matt Pitzarella, a spokesman for Range Resources, one of the biggest Marcellus Shale gas drillers in southwestern Pennsylvania, said several parts of the study were "questionable or incomplete" but added that the company supports best practices on construction of well casings.