Fracking Fallout: Methane Higher in Water Wells

Wednesday, May 11, 2011 @ 11:05 AM gHale


High levels of leaked methane in well water collected near shale-gas drilling and hydrofracking sites, a new study found.

Water samples collected from 68 private groundwater wells across five counties in northeastern Pennsylvania and New York showed the high methane levels, researchers said.

“At least some of the homeowners who claim that their wells were contaminated by shale-gas extraction appear to be right,” said Robert B. Jackson, the Duke University Nicholas Professor of Global Environmental Change and director of Duke’s Center on Global Change.

Hydraulic fracturing, also called hydrofracking or fracking, involves pumping water, sand and chemicals deep underground into horizontal gas wells at high pressure to crack open hydrocarbon-rich shale and extract natural gas.

The study found no evidence of contamination from chemical-laden fracking fluids, which drillers inject into gas wells to help break up shale deposits, or from “produced water,” wastewater they extract back out of the wells after they fractured the shale.

“We found measurable amounts of methane in 85 percent of the samples, but levels were 17 times higher on average in wells located within a kilometer of active hydrofracking sites,” said Stephen Osborn, postdoctoral research associate at Duke’s Nicholas School of the Environment. The contamination mainly occurred in Bradford and Susquehanna counties in Pennsylvania.

Water wells farther from the gas wells contained lower levels of methane and had a different isotopic fingerprint.

“Methane is CH4. By using carbon and hydrogen isotope tracers we could distinguish between thermogenic methane, which is formed at high temperatures deep underground and is captured in gas wells during hydrofracking, and biogenic methane, which is produced at shallower depths and lower temperatures,” said Avner Vengosh, professor of geochemistry and water quality. Biogenic methane is not associated with hydrofracking.

“Methane in water wells within a kilometer had an isotopic composition similar to thermogenic methane,” Vengosh said. “Outside this active zone, it was mostly a mixture of the two.”

The scientists compared the dissolved gas chemistry of water samples to the gas chemistry profiles of shale-gas wells in the region, using data from the Pennsylvania Department of Environmental Protection. “Deep gas has a distinctive chemical signature in its isotopes,” Jackson said. “When we compared the dissolved gas chemistry in well water to methane from local gas wells, the signatures matched.”

Methane is flammable and poses a risk of explosion. In very high concentrations, it can cause asphyxiation. There has been little research on the health effects of drinking methane-contaminated water. In addition, officials do not consider methane a contaminant in public water systems under the EPA’s National Primary Drinking Water Regulations.

The Duke team collected samples from counties overlying the Marcellus shale formation. Accelerated gas drilling and hydrofracking in the region in recent years has fueled concerns about well-water contamination by methane, produced water and fracking fluids, which contain a proprietary mix of chemicals that companies often don’t disclose.



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