Homes in a Texas community face worsening water contamination caused by nearby gas production, according to a study released Sept. 15.

The findings from an analysis by independent academics rebut statements by driller Range Resources Corp. and state regulators, who have said their evidence shows gas drilling wasn’t responsible for the presence of explosive methane in the homeowners’ water wells. Separate testing that found evidence of contamination from drilling at seven areas in Pennsylvania also was included in the study.

“People’s water has been harmed by drilling,” Rob Jackson, professor of environmental and earth sciences at Stanford University and Duke University, said in a statement. “In Texas, we even saw two homes go from clean to contaminated after our sampling began.”

The study, published in the peer-reviewed Proceedings of the National Academy of Sciences, linked contamination to failures of cement or production casing. It counters supporters of oil and gas, who say there is no evidence that drilling or production has contaminated drinking water.

The spread of horizontal drilling and fracking, in which water, chemicals and sand are shot underground to free trapped gases, has led to a boom in U.S. production, much of it in the Marcellus Shale in Pennsylvania and the Barnett Shale in Texas. The boom in production has spurred complaints from homeowners who say their well water has become unhealthy.

Safe Levels

The study didn’t find that the injection of chemicals into the ground to free gas caused contamination.

The case in Weatherford, Texas, has drawn international media scrutiny, intervention by the U.S. Environmental Protection Agency that was later shelved and lawmakers’ scrutiny of the EPA’s actions. Residents have appealed to the EPA to reopen its investigation.

The results from the Duke-led study showed the water from five of the 20 wells tested exceeds minimum safety level, including the two wells that were clean and then acquired dangerous levels of methane in later tests. Researchers said the gas wasn’t from the production zone of the Barnett shale, but from the shallower Strawn formation. That gas was likely conducted through the drilling rings to the groundwater, the paper said.

Range Resources has said it wasn’t responsible for the methane in the drinking wells.

No Link

“Range’s operations did not cause or contribute to the long-standing and well-documented matter of naturally occurring methane,” spokesman Matt Pitzarella said earlier this year. The Texas Railroad Commission, which regulates oil and gas drilling in the state, reached the same finding in 2011. Pitzarella didn’t immediately respond to an e-mail.

The Weatherford case is one of only three in which the EPA has preliminarily linked water woes to hydraulic fracturing, and then subsequently dropped its investigation in the face of congressional and industry criticism.

In 2010 the EPA did its own testing in Weatherford and found dangerous levels of methane it termed “an imminent and substantial endangerment” to homeowners. It issued a notice of violation and sued Range soon after. Two years later, the agency settled with an agreement that called for Range to conduct four sets of tests of 20 wells in the area. The results showed minimal levels of methane, except in one well that has been disconnected by the homeowner.

Jackson and the four other researchers analyzed the quantity and isotopes of noble gases such as helium and neon in the groundwater near shale-gas wells in order to try to determine if the fugitive gases are naturally occurring or caused by gas production. They said it’s the first time this analysis of noble gases has been done.

The research linked contamination to failures of cement or production casing. In one case an underground gas well failed, they said.