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 natural gas.
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 the 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 said.
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 water supplies.
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 contacts.
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 water quality.