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A study of water quality in the Barnett Shale region of North Texas has found elevated levels of arsenic in wells that are closer to natural gas extraction sites. But the reasons behind the contamination are far from clear, and the study, published last week in the peer-reviewed journal
Environmental Science & Technology, is sure to fuel an already fierce debate over the impacts of hydraulic fracturing.

University of Texas at Arlington researchers tested 100 private water wells in 2011 in Tarrant and surrounding counties in the Barnett Shale region, where oil and gas companies have been injecting a combination of fluid, chemicals and sand to release shale gas from rock formations in a process known as hydraulic fracturing, or fracking. Those with dangerously high levels of arsenic – about one-third of the wells – tended to be much closer to natural gas wells than those that were not contaminated. Long-term exposure to arsenic is linked to several major diseases, including prostate, lung, skin and liver cancers.

Fracking could have contributed to the elevated arsenic levels, said lead author Brian Fontenot. Faulty gas well casings or excess water pumping could add metals to the water, or the vibrations that come from drilling “can shake the rust on older private water wells,” he said. That rust could contain arsenic.

“We’re not saying that they’ve injected arsenic into these wells,” Fontenot said. But he said the study, which is self-funded, could show “indirect ways” of contamination by drilling activities, especially because the wells his team tested that were far from drilling activities did not contain high levels of arsenic.    

Rob Jackson, a Duke University scientist who has studied the impacts of fracking in different shale regions, said the study is a valuable contribution to a growing body of research on the issue.

“It’s the first study that I know of looking at the Barnett Shale and water quality,” Jackson said. “The Barnett’s an important place, because this kind of drilling has been happening longest in the Barnett.”

The possibility that arsenic contamination could be linked to fracking also caught Jackson’s attention. His study on Pennsylvania’s Marcellus Shale found that drinking water near gas wells contained stray gases like methane, the main component of natural gas. And though drilling companies say the recipe of chemicals that they inject into the ground is secret, they do generally use substances that are collectively referred to as BTEX – benzene, toluene, ethylbenzene and xylene – but the researchers in the UTA study didn’t find those.