Wendy Koch, USA TODAY As natural gas production increases in the United States, so, too, have reports of well water contaminated with methane. Now a study, the first to make comprehensive use of "stray gas forensics," not only found pollution in multiple wells but also identifies the culprit.
"Our data clearly show that the contamination in these clusters stems from well-integrity problems such as poor casing and cementing," says co-author Thomas Darrah, assistant professor of earth science at Ohio State. While a scientist at Duke University, he led the research team, which includes experts from Duke, Stanford, Dartmouth and the University of Rochester.
Over a two-year period, the researchers took samples from 130 drinking water wells where contamination had been suspected in the two states. They found contamination in eight clusters of wells — seven in Pennsylvania and one in Texas — from deep underground in the Marcellus shale and from shallower, intermediate levels in both states.
Then they did detective work. They used a novel combination of noble gas and hydrocarbon tracers to look at the methane's chemical signature and determine its source. These tracers indicated the methane was neither naturally occurring nor the result of hydraulic fracturing, or fracking, in which a water mixture is blasted underground to break apart shale rock and extract natural gas from its pores.
"These results appear to rule out the possibility that methane has migrated up into drinking water aquifers because of horizontal drilling or hydraulic fracturing, as some people feared," says Avner Vengosh, Duke professor of geochemistry and water quality.
In four of the contaminated clusters, methane occurred because of insufficient rings of cement around a gas well's shaft, the study says. In three clusters, it leaked through faulty well casings, and in one, it was linked to an underground well failure.
"We caught contamination happening" in Parker County, Texas, says co-author Rob Jackson, Stanford professor of environmental and earth sciences. He says two homes there switched from having clean to contaminated water during the 2012-13 sampling period.
"Well integrity is the most important issue for maintaining drinking water quality," Jackson says. While companies can retrofit many gas wells to ensure proper sealing, he says such measures can be expensive and not all existing wells can be fixed.
An industry group raised questions about the study, published in the Proceedings of the National of Sciences and funded by the National Science Foundation as well as Duke's Nicholas School for the Environment.
Well integrity failures are "exceedingly rare," occurring in a fraction of 1% of wells, says Katie Brown, spokeswoman of Energy In Depth, a program of the Independent Petroleum Association of America. The IPAA represents natural gas and oil producers.
"They (researchers) have no evidence the wells violated state rules," Brown says, noting the Texas Railroad Commission has done studies that found the methane in Parker County's well water was naturally occurring and that the wells met its requirements.
She says other studies, including a peer-reviewed one by Echelon Consulting, found that the methane in well water overlying the Marcellus shale in Pennsylvania was also naturally occurring.
Fracking, combined with horizontal drilling, has spurred not only a U.S. energy boom but also a slew of controversy. The oil and gas industry says it's a safe way to bolster the U.S. economy and lessen the nation's dependence on foreign sources of energy.
Yet peer-reviewed studies have linked it to possible birth defects, higher lung disease risks, and elevated endocrine-disrupting chemical activity in groundwater. A Yale University-led study last week found that people living near natural-gas wells were more than twice as likely to report upper-respiratory and skin problems than those farther away.
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