Scientists identify fracking gas-leak culprit

A 3D model of a natural gas rig shows how hydraulic fracturing works. The water pumped underground to break up shale is far below the water table.

Faulty wells are the likely culprits for contamination of groundwater associated with hydraulic fracturing – better known as fracking – a study has found. But the problem may be fixable.

And the good news is that neither horizontal drilling nor hydraulic fracturing of shale deposits seems to have caused any of the natural gas contamination.

A team led by a researcher at Ohio State University, with researchers from Duke, Stanford, Dartmouth, and the University of Rochester, identified eight clusters of contaminated drinking-water wells in Pennsylvania and Texas.

Water pumped underground to break up shale during the fracking process is at a depth far below the water table.

The long vertical pipes that carry the resulting gas upward are encircled in cement to keep the natural gas from leaking out along the well.

The study suggests that natural gas that has leaked into aquifers is the result of failures in the cement used in the well.

"There is no question that in many instances elevated levels of natural gas are naturally occurring, but in a subset of cases, there is also clear evidence that there were human causes for the contamination," said Thomas Darrah, assistant professor of earth sciences at Ohio State. "However our data suggests that where contamination occurs, it was caused by poor casing and cementing in the wells," Darrah said.

The solution could be as simple as improved construction standards for cement well linings and casings at hydraulic fracturing sites.

The research was published this week in the Proceedings of the National Academy of Sciences.

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