Oil and gas activities – but not hydraulic fracturing – tainted drinking water wells atop North Texas' Barnett Shale and Pennsylvania's Marcellus formation, according to a new study.
High levels of methane escaped poorly constructed natural gas wells and migrated into shallow aquifers, the paper said. Poor cementing likely caused the issues in Texas.
"Where fugitive gas contamination occurs, well integrity problems are most likely associated with casing or cementing issues," researchers from Duke, Ohio State, Stanford, Dartmouth and the University of Rochester concluded. "In contrast, our data do not suggest that horizontal drilling or hydraulic fracturing has provided a conduit to connect deep Marcellus or Barnett formations directly to surface aquifers."
The peer-reviewed study, published Monday in the Proceedings of the National Academy of Science, adds a new chapter to a saga that has pitted Texas regulators against the U.S. Environmental Protection Agency.
Researchers collected samples from 133 water wells, mostly in Pennsylvania, where they linked three clusters of wells to integrity problems. The study also included a 20-well cluster in Parker County, home to a contamination case that thrust a neighborhood into the national discussion about the impacts of oil and gas drilling. So much methane has migrated into Steve Lipsky's well, for instance, that he can ignite the stream that flows from it. He is not alone. Scientists have found large amounts of methane in some of his neighbors' wells, stirring health and safety concerns.
In 2010, the Environmental Protection Agency charged Range Resources, a local driller, with tainting the Trinity Aquifer well and ordered the company to provide drinking water to Lipsky and a neighbor. But the agency withdrew that order after the Railroad Commission of Texas said Range was not linked to the contamination.
Following more complaints from Lipsky and his neighbors, the commission took a second look at the contamination. Its report last May said evidence was "insufficient" to implicate the driller. The methane "may be attributed" to unrelated processes, including migration from the shallower Strawn formation, which lies just beneath the aquifer.
Range has maintained it is not to blame, and it is suing Lipsky for defamation in a case that has reached the Texas Supreme Court.
"Exhaustive studies have clearly indicated that no aspects of Range's activities caused or contributed to the long-standing and well documented fact that gas is naturally occurring in the Trinity Aquifer," Matt Pitzarella, a Range spokesman, said on Monday.
Much of the debate over Range's responsibility has centered on whether the methane migrated from the productive Barnett or the Strawn. If the gas originated in the Strawn – above where the company drilled and blasted – Range could not be responsible, some researchers have suggested. The opposite would be true if research traced the gas to the Barnett.
But latest study, relying on a novel set of geochemical tracers, picked apart that line of thinking.
"We think this is somewhere in between – literally and figuratively," said Rob Jackson, a geoscientist at Stanford University who co-authored the paper. "We think it's most likely Strawn, but we think that a subset of homes in that subdivision, their water has been affected by drilling."
The scientists measured changes in noble gases that often mix with methane: helium, neon and argon. That data helped the scientists determine whether the methane migrated as a free gas or was dissolved in water.
"What's much more useful in understanding of what's responsible is not where it came from, but how it got there," said Thomas Darrah, of Ohio State University, the paper's lead author.
In Parker County, the gases arrived in the aquifer without undergoing typical geologic changes, data showed. "The only way that could happen would be that if they came up through a pipe and didn't interact with any water or any rocks in the crust," Darrah said.
Researchers suggested that the results could help the industry and regulators zero in on methods to prevent future troubles.
"Optimizing well integrity is a critical, feasible and cost-effective way to reduce problems with drinking water contamination and to alleviate public concerns accompanying shale gas extraction," the paper said.
Ramona Nye, a spokeswoman for the Railroad Commission, which regulates the state's oil and gas industry, said the agency had no comment on a study it had not seen.
The Railroad Commission last updated its well integrity rules in 2013, drawing support from industry advocates and environmentalists. The major overhaul strengthened requirements for drilling wells, putting pipe down them and cementing things in place. It also contained some new requirements for fracking.
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