A study by Duke University researchers has found high levels of leaked methane in well water collected near shale-gas drilling and hydrofracking sites. The scientists collected and analyzed water samples from 68 private ground water wells across five counties in northeastern Pennsylvania and New York.
least some of the homeowners who claim that their wells were contaminated by
shale-gas extraction appear to be right," says Robert Jackson, Nicholas
Professor of Global Environmental Change and director of Duke's Center on
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.
found no evidence of contamination from chemical-laden fracking fluids, which
are injected into gas wells to help break up shale deposits, or from
"produced water," wastewater that is extracted back out of the wells
after the shale has been fractured.
peer-reviewed study of well-water contamination from shale-gas drilling and
hydrofracturing appears in the onlineEarly Edition of the Proceedings of the
National Academy of Sciences.
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," says Stephen Osborn, postdoctoral research associate
at Duke's Nicholas
School of the
Environment. The contamination was observed primarily in Bradford and
Susquehanna counties in Pennsylvania.
farther from the gas wells contained lower levels of methane, and had a
different isotopic fingerprint.
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,"
says Avner Vengosh, professor of geochemistry and water quality. Biogenic
methane is not associated with hydrofracking.
in water wells within a kilometer had an isotopic composition similar to
thermogenic methane," Vengosh says. "Outside this active zone, it was
mostly a mixture of the two."
scientists confirmed their finding by comparing 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 says. "When
we compared the dissolved gas chemistry in well water to methane from local gas
wells, the signatures matched."
flammable and poses a risk of explosion. In very high concentrations, it can
cause asphyxiation. Little research has been conducted on the health effects of
drinking methane-contaminated water, and methane isn't regulated as a
contaminant in public water systems under the EPA's National Primary Drinking
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.