The natural-gas-drilling surge is polluting groundwater, but that doesn't mean the controversial practice of hydraulic fracturing is to blame. At least not directly.
That's the conclusion of a new paper from researchers at several universities, published in the Proceedings of the National Academy of Sciences, who studied movement of gases in Texas and Pennsylvania regions with lots of gas drilling.
They found that problems with gas-well construction, not fracking itself, is letting gases escape and reach drinking-water wells in some cases.
"In general, our data suggest that where fugitive gas contamination occurs, well-integrity problems are most likely associated with casing or cementing issues. 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," states the paper from researchers with Ohio State, Duke, Stanford, Dartmouth, and the University of Rochester.
The researchers found drilling-related contamination in eight clusters of drinking water-wells in Pennsylvania's Marcellus Shale region and the Barnett Shale in Texas. Those are two of the places where gas production has boomed thanks to the marriage of horizontal drilling and fracking, which involves high-pressure injections of water, sand, and chemicals that create fissures in rock formations to enable trapped energy to flow.
"People's water has been harmed by drilling," Robert B. Jackson, professor of environmental and earth sciences at Stanford and Duke, said in a statement. "In Texas, we even saw two homes go from clean to contaminated after our sampling began."
The research linking gas development to migration of methane into drinking water included water wells in Parker County, Texas, where several years ago EPA launched but later backed off a probe of contamination.
Ohio State earth-sciences professor Thomas Darrah said that while elevated gas levels in wells are often naturally occurring, there's "clear evidence" that energy development is to blame in some instances.
He said that the findings are "relatively good news" because "most of the issues we have identified can potentially be avoided by future improvements in well integrity."
But the researchers don't rule out an indirect link between the contamination and fracking, even if the more direct culprits are problems with well casing and cementing. The study notes that the fracking process may affect the integrity of gas wells.
"Future work should evaluate whether the large volumes of water and high pressures required for horizontal drilling and hydraulic fracturing influence well integrity," the paper concludes.
And indeed, it's advancements in horizontal drilling and fracking that have fueled the development surge that has made the U.S. the world's largest gas producer. So the issues of water quality and fracking can't be considered in isolation regardless of what's allowing contaminants to escape.
Still, the paper notes that improving the structural integrity of gas wells is hardly pie in the sky. "In our opinion, 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 study states.
The "geochemical forensics" the authors employed, which traced other gases that move along with methane, enabled them to distinguish between naturally occurring methane in the water and "stray gas" from the drilling sites. They studied more than 130 water wells.
"This is the first study to provide a comprehensive analysis of noble gases and their isotopes in groundwater near shale-gas wells," Darrah said in a statement. "Using these tracers, combined with the isotopic and chemical fingerprints of hydrocarbons in the water and its salt content, we can pinpoint the sources and pathways of methane contamination, and determine if it is natural or not."
The National Science Foundation and Duke's Nicholas School of the Environment funded the study.