Water wells within 1 kilometer (0.6 miles) of gas drilling had 17 times more methane than more distant wells, according to the findings. The results are the first peer-reviewed study to show a link between well water and drilling in the Marcellus Shale, a band of rock in the eastern U.S., said Robert Jackson, a Duke professor who is one of the authors of the study.
The Duke researchers didn’t test water from municipal supplies, rivers or lakes. They found no evidence of the chemicals used as part of the rock-fracturing process common in natural-gas drilling.
Gas found in the water probably escaped through faulty well casings on Marcellus gas wells, Jackson said. Some gas may also seep naturally from shallower formations closer to the aquifers feeding the wells, Jackson said. The levels of gas were high enough to cause a risk of explosion, according to the study, published today in the Proceedings of the National Academy of Sciences.
The Duke research bolsters the argument that most drilling- related pollution comes from poor well construction, not from fracturing, Scott Anderson, a senior policy adviser for the New York-based Environmental Defense Fund, said in an interview.
“It raises interesting questions about what might have gone wrong,” Anderson said.
The results come amid a growing debate about the environmental effects of gas drilling in the Marcellus Shale and similar rock formations where rocks must be fractured to make the gas flow in commercial quantities.
The Environmental Protection Agency is studying the effects of gas fracturing on water supplies. In December, the agency ordered Range Resources Inc. to clean up around two wells after gas turned up in residential wells near Fort Worth, Texas.
Pennsylvania has a history of naturally occurring water- well contamination, Aubrey McClendon, chief executive officer of Chesapeake Energy Corp. (CHK), said in an April 8 speech in Dallas. Chesapeake is the most active driller in the U.S. and is searching for gas on 1.6 million acres in the Marcellus Shale region.
“You can go back 100 years and people talk about gas in their water wells,” he said. “It’s not from fracking.”
McClendon said Marcellus drilling may have contributed “inconveniences,” and said “every one of those problems has an engineering solution to it.”
The researchers tested 68 sites across five counties in Northeastern Pennsylvania and New York. Gases such as methane, ethane and propane were found in the water at 85 percent of the sites tested. The concentrations were higher the closer the samples were taken to gas drilling sites.
Researchers found that some of the gas sampled from the water wells originated from the same deep rock tapped by gas drillers, as opposed to the gas that naturally seeps from shallower formations. Those samples showed “specifically matching natural gas geochemistry from local gas wells,” the researchers said in their paper.
“This study lacks key data that would be needed to validate its conclusions,” Daniel Whitten, a spokesman for America’s Natural Gas Alliance, a Washington-based trade group, said in an e-mail. “The existence of methane in the environment is often due to naturally occurring geological phenomena that has no relation to natural gas development.”
On April 19, Pennsylvania regulators asked gas companies to stop disposing of drilling wastewater at sewage treatment plants after drilling-related byproducts turned up in local rivers. Pennsylvania enacted tougher regulations for gas wells in 2010 and began requiring drillers to test water within 1,000 feet of new drilling sites.
An April 12 study by Cornell University calculated that gas extraction from shale formations contributed more to global warming, over its life cycle, than oil or coal.
Much of the water studied by the Duke researchers originated in the Lock Haven aquifer, an underground system that supplies wells in northeastern Pennsylvania. The researchers didn’t cite any corresponding samples from the Lock Haven aquifer that weren’t affected by drilling, said John Conrad, a consulting geologist who has done tests for the gas industry.
“I’m not sure you can take 68 wells over a very broad geographic area and make any statistical conclusion,” he said. “Methane types and methane concentrations can vary radically over very short distances.”
Jackson said the Duke researchers plan to collect more samples in the Lock Haven aquifer.
“If the companies would be willing to help us sample some non-active wells and have homeowner contacts in that area, we’d love to get them,” he said in an e-mail.
A database should be created that would include all the research on the affects of natural-gas drilling on water supplies, Jackson said. He’d also like to see research showing the effect of methane on human health.
“It needs a lot of follow-up, by not just us but by many other groups, too,” he said.
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