MONDAY, June 24 (HealthDay News) -- Homes that are close to
fracking sites are at higher risk of having their drinking water
contaminated by combustible gases, according to a new study.
Researchers from Duke University in Durham, N.C., analyzed
drinking water samples from 141 private water wells in the
Marcellus shale basin in northeastern Pennsylvania, where companies
are using hydraulic fracturing to tap hard-to-access pockets of
They detected methane in 82 percent of the drinking water
samples, with the average concentrations six times higher for homes
less than one kilometer -- about six-tenths of a mile -- from a
natural gas well, according to findings published online June 24 in
Proceedings of the National Academy of Sciences.
In the study, which was strongly disputed by the oil and gas
industry, the scientists also found higher concentrations of ethane
and propane in drinking water wells less than six-tenths of a mile
from shale gas drilling. Ethane concentrations were 23 times higher
in water wells located near gas drilling, while propane was found
in 10 wells all within a kilometer of a drill site.
"We were surprised to find such high concentrations, but we were also surprised to see such a strong effect of proximity to gas wells," said Robert Jackson, a professor of environmental sciences at Duke's Nicholas School of the Environment.
Jackson added that there is no biological source of ethane and
propane in the region, which makes the Marcellus wells the chief
suspect for the contamination.
The risk of fire and explosion is the main public health risk
from the presence of these gases in drinking water, said Dr.
Georges Benjamin, executive director of the American Public Health
Association in Washington, D.C.
"These are volatile gases and in particular concentrations, they burn," Benjamin said. "If they leak into your home and build up, particularly in enclosed spaces, there's an explosive risk."
Based on what is now known, there seems to be no risk involved
in ingesting the gases by drinking the water. "I just can't imagine
how anyone would drink enough to make them sick," Benjamin
Hydraulic fracturing, also called fracking, is a controversial
process that involves pumping water, sand and chemicals deep
underground at high pressure to crack open hydrocarbon-rich shale
and extract natural gas. Prior studies have raised concerns that
such drilling techniques could lead to contamination of drinking
Jackson believes the contamination is the result of faulty well
construction, with gases escaping from flaws in either the steel
tubing or the concrete seal that surrounds the tubing.
"We don't think the gases are migrating up through thousands of feet of rock to contaminate ground water," he said. "If the well isn't sealed properly with cement, you can have gas from thousands of feet down move up the outside of the well and into people's drinking water without ever seeing natural gas leak out from the Marcellus."
Industry spokesman Jim Smith criticized what he called key flaws
in the Duke study. For example, he noted that the water samples
were not taken randomly, but from wells chosen by the researchers
in cooperation with homeowners' associations and other local
Smith, a spokesman for the Independent Oil and Gas Association
of New York, added that the researchers found no fracking fluid in
the contaminated wells.
"If the methane that was found in the water was a result of fracking, then certainly frack water would be found in those wells as well, and they found no evidence of that," he said.
Smith also doubted that poor well construction would be involved
in the contamination, citing the stringent regulations adopted by
the state of Pennsylvania to regulate gas drilling.
Jackson argues that flaws in the concrete seal would allow gas
to migrate while still preventing leakage of fracking fluid.
He also noted that his team has researched potential well
contamination from fracking in five states, most recently from the
Fayetteville shale formation in Arkansas. His team believes faulty
well construction is involved in Pennsylvania because other
locations have revealed no contamination at all.
"We don't see any evidence of contamination in the homes there," he said of the Arkansas study. "We don't see the same problems everywhere we look."
The U.S. Geological Survey offers a primer on
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