By John Murawski

A group of Duke University scientists often accused of anti-fracking bias have published their most definitive research to date linking shale gas exploration with methane gas contamination of drinking water.

But their paper, published Monday in the Proceedings of the National Academy of Sciences, exonerates fracking from the most serious environmental risks. The study blames the water contamination on leaky well shafts near the earth's surface, not on the process of hydraulic fracturing itself, which takes place thousands of feet underground.

The distinction is critical because fracking foes base much of their opposition to natural gas drilling on the fear that fracturing shale rock poses an environmental danger. They worry that fracturing, or fracking, could cause toxic chemicals and radioactive elements to flow out through fissures and contaminate freshwater aquifers on which residents and farming operations depend.

The findings of the Duke researchers, based on 133 drinking water wells in Texas and Pennsylvania, corroborate claims by the energy industry that the fracturing process alone is not likely to imperil drinking water.

"We're saying to the industry, the good news is we don't think it's actually from the hydraulic fracturing itself," said Avner Vengosh, Duke professor of geochemistry and water quality.

"So far we can say pretty categorically that we have not seen escape of the gas from the shale formation into the overlying aquifers," Vengosh said.

The Duke scientists say their findings apply only to the 113 wells in Pennsylvania and the 20 in Texas they have sampled, but they are likely to also be true for the thousands of other wells that have been horizontally drilled and hydraulically fracked all over the country.

"The worst-case environmental scenario appears to be off the table, based on these studies," said one of the researchers, Thomas Darrah. "In reality, we focused on the areas that had the worst contamination."

Shoddy well construction has been a prevalent problem in shale gas exploration, one that officials here hope to avert before North Carolina's fracking moratorium is lifted next year. One of the cases of methane leakage sampled by the Duke professors was caused by "an underground gas well failure," their study notes.

Vikram Rao, chairman of the state's Mining and Energy Commission, said this latest research is a reminder of why it's crucial that North Carolina have the tools in place to properly regulate shale gas exploration.

"This is exactly why we need good rules, and good adherence to the rules," he said.

The Mining and Energy Commission has proposed well shaft construction standards requiring multiple layers of cement and steel casings to prevent a breach and a potential release of natural gas, brine and chemicals into fissures or directly into water sources. The rules are being finalized and are expected to become effective next year.

Earlier study raises questions

The Duke professors at the Nicholas School of the Environment have been blasted by energy industry critics for their past research. In 2011 they found high methane gas concentrations in drinking water wells near gas drilling sites, putting energy companies on the defensive.

Speaking as an individual and not as chairman of the Mining and Energy Commission, Rao, a former Halliburton chief technology officer, said much of the industry has long known that if water contamination was found it was the result of poor cement jobs.

He said the title of the Duke professors' 2011 paper, "Methane contamination of drinking water accompanying gas-well drilling and hydraulic fracturing," implied a connection that they hadn't proved.

"The title had inferred a causality, which they have now shown not to be the case," said Rao, who is now executive director of the Research Triangle Energy Consortium.

David McGowan, executive director of the N.C. Petroleum Council, said the research echoed his group's emphasis on the importance of establishing and maintaining high well-construction standards.

"We recognize that getting the construction of the well correct the first time is the most efficient and most effective way of ensuring there are no issues with contamination," McGowan said.

Natural gas is itself not poisonous, but in high concentrations it could lead to fires and explosions. In addition, the presence of gas in water sources is a "canary in the coal mine" that indicates a potential pathway for other contaminants, such as chemicals, brines and radioactive elements, Darrah said.

Methane leaking from faulty well shafts is not an irreversible ecological problem because wells can be plugged. If they are not sealed, Vengosh said, the industrial chemicals used in fracking could eventually work their way up toward drinking water sources, though that migration could take decades.

The research was conducted by four Duke scientists and one from the University of Rochester; two of the Duke researchers have since changed jobs -- Darrah now works at Ohio State University and Robert Jackson at Stanford University.

The Duke researchers said their study is the first to distinguish between three potential sources of methane gas in drinking-well water: naturally occurring gas near aquifers, gas dislodged by fracking that migrates to aquifers, and gas that leaks into aquifers from faulty well shafts. Each type of gas has its own chemical fingerprint that can be analyzed with the aid of other elements, such as helium or argon, that are transported with the flowing gas, Vengosh said.

The debate over the safety of fracking has focused largely on the possibility of underground contamination emanating from the point where the shale rock was fractured. Such a release of contaminants below could take years, if not decades, to be detected near the surface where the aquifers are located.

Most fracking mishaps involve surface spills, faulty wells and well blowouts, which can be contained.

But scores of residents in fracking regions have complained of headaches, nausea and other mysterious ailments, often suspecting fracking chemicals in the water.

Advocates of fracking, including several members of the N.C. Mining and Energy Commission, have said it is physically impossible for hydraulic fracturing to contaminate aquifers. They contend fracking fluids and underground brines can't travel upward toward the earth's surface through thousands of feet of solid rock.

Scientists favorable to the energy industry have attempted to assuage public anxiety with research demonstrating the scientific validity of that claim.

One such paper, published in March in the Journal of Unconventional Oil and Gas Resources, said the same forces that have kept natural gas trapped in shale rock for millions of years would also capture fracking fluid, "thus permanently sequestering it."

The authors of that paper include geologist Terry Engelder of Penn State University, sometimes called the chief apologist for fracking in the Marcellus shale, and L. Taras Bryndzia, a geologist with Shell International Exploration and Production in Houston.

Their paper argues that the fact that "gas shale readily imbibes water, and only a fraction of the hydrofracturing treatment water is returned (to the surface), shows that the treatment waters are flowing into, not out of, the shale."

(c)2014 The News & Observer (Raleigh, N.C.)