Concentrations of methane, ethane and propane were found in higher levels in drinking water for homes within a kilometer of shale gas wells in parts of the Marcellus Shale in northeast Pennsylvania, according to a study released Monday. It was the third such study by Duke University's Robert Jackson, a professor of environmental sciences.
Like the other Duke-led studies, and a third study released Friday by the U.S. Geological Survey (USGS), the latest study found no evidence of current contamination by hydraulic fracturing (fracking) fluids, Jackson and his co-authors acknowledged. Their peer-reviewed paper was published in an online early edition of the Proceedings of the National Academy of Sciences.
A previous Duke study on the topic was labeled by industry and heads of the Pennsylvania Department of Environmental Protection as biased, irresponsible, unfathomable and just plain wrong (see Shale Daily, June 8, 2011; May 11, 2011).
The Marcellus Shale Coalition had no immediate response to Jackson's latest report, but the CEO of the coalition, Kathryn Klaber, reminded an Associated Press reporter that migrating, naturally occurring methane has been a public health issue in Pennsylvania for decades.
Jackson and his co-authors analyzed 141 drinking water samples from private water wells across northeastern Pennsylvania where residents had specifically complained about the presence of methane in their water supplies.
Duke's research found methane concentrations on average were six times higher and ethane concentrations 23 times higher in homes within a kilometer of a shale gas well. Propane was detected in 10 samples, again all from homes within a kilometer of a gas well.
"The methane, ethane and propane data, and new evidence from hydrocarbon and helium content, all suggest that drilling has affected some homeowners' water," Jackson said. "In a minority of cases the gas even looks 'Marcellus-like', probably caused by poor well construction."
Critics of the Duke report question how accurate a picture it portrays, given that the samples all came from water wells in which the local residents had complained about contamination.
USGS said in its report last week that it found naturally occurring dissolved methane at several household wells used for drinking water in Sullivan County, PA, during pre-drill baseline testing at sites not near existing oil and gas drilling in the Marcellus Shale (see Shale Daily, June 21). The agency said it had randomly selected 20 water wells in the county and took water samples from them last August and September. USGS said seven of the 20 wells contained dissolved methane, and two of the seven tested above one milligram per liter (mg/L), considered an elevated concentration warranting an isotopic analysis.