US shale gas research uncovers risk of drinking water contamination

Homeowners living near shale gas wells in Pennsylvania's Marcellus Shale basin could be at a higher risk of drinking water contamination from stray gases, according to a new study from North Carolina's Duke University.

Scientists at the US university analysed 141 drinking water samples from private water wells across the shale basin in the region where extraction has been taking place and found that, on average, methane concentrations were six times higher and ethane concentrations were 23 times higher at homes within a kilometre of a shale gas well.

Propane was also detected in 10 samples, all of them from homes within a kilometre of drilling.

“The methane, ethane and propane data, and new evidence from hydrocarbon and helium content, all suggest that drilling has affected some homeowners’ water,” said Robert B. Jackson, professor of environmental sciences at Duke’s Nicholas School of the Environment. “In a minority of cases the gas even looks Marcellus-like, probably caused by poor well construction.”

The ethane and propane data were “particularly interesting,” he noted, “since there is no biological source of ethane and propane in the region and Marcellus gas is high in both, and higher in concentration than Upper Devonian gases” found in formations overlying the Marcellus shale.

The scientists examined which factors might explain their results, including topography, distance to gas wells and distance to geologic features. “Distance to gas wells was, by far, the most significant factor influencing gases in the drinking water we sampled,” said Jackson.

The team published its peer-reviewed findings this week in the online Early Edition of the Proceedings of the National Academy of Sciences.

Shale gas extraction is a process that includes horizontal drilling and hydraulic fracturing (fracking) and has fuelled concerns in recent years about contamination of nearby drinking water supplies.