WASHINGTON - Drinking water that is contaminated by natural gas near hydraulic fracturing operations in the United States likely got that way due to faulty wells, not the drilling operations themselves, researchers said Monday.
The study in the Proceedings of the National Academy of Sciences examined eight clusters of contaminated wells near fracking operations in Texas and Pennsylvania.
Researchers from Ohio State University, Duke, Stanford, Dartmouth, and the University of Rochester came up with a new method of "geochemical forensics" to trace the path that gas was taking as it migrated beneath the Earth's surface.
They found no evidence that horizontal drilling or hydraulic fracturing of shale deposits caused the natural gas contamination at the 130 wells they examined.
Instead, the culprit appeared to be failures in the cement process used to make wells.
"Many of the leaks probably occur when natural gas travels up the outside of the borehole, potentially even thousands of feet, and is released directly into drinking-water aquifers" said Robert Poreda, professor of geochemistry at the University of Rochester.
When fracking, operators pump water deep below ground -- and beneath the water table -- to break up shale, then push gas upward through long vertical pipes that are coated in cement to keep the gas from leaking.
Such problems could be avoided in the future by improving construction standards for cement well linings and casings at hydraulic fracturing sites, the researchers said.
"These results appear to rule out the migration of methane up into drinking water aquifers from depth because of horizontal drilling or hydraulic fracturing, as some people feared," said Avner Vengosh, professor of geochemistry and water quality at Duke.
The research was funded by the National Science Foundation, Duke University, and a gift from Duke alumni Fred and Alice Stanback to the Nicholas School of the Environment.
Copyright Agence France-Presse, 2014