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New study: Recent natural gas fracking operations have tainted the ground water, but it's actually good news, because it's the well casings that are to blame and they can be fixed.

The shale-gas boom of recent years has contaminated drinking-water wells in North Texas’ Barnett Shale and the Marcellus Shale in Pennsylvania, a study published Monday concludes.

The study, by researchers from five universities, concludes that neither drilling itself nor the hydraulic fracturing that follows it is directly to blame.

Instead, gas found in water wells appeared to have leaked from defective casing and cementing in gas wells, meant to protect groundwater; or from gas formations not linked to zones where fracking took place.

“Our data do not suggest that horizontal drilling or hydraulic fracturing has provided a conduit to connect deep Marcellus or Barnett formations directly to surface aquifers,” the authors wrote.

The study, published in Proceedings of the National Academy of Sciences, adds to a growing body of science that examines the environmental impacts of natural gas production, which has seen a rush of drilling and processing in numerous states over the past decade.

In an email, lead author Thomas Darrah of Ohio State University said tracing the blame to well construction problems instead of fracking offers hope of protecting groundwater supplies.

“This is relatively good news because it means that most of the issues we have identified can potentially be avoided by future improvements in well integrity,” said Darrah, who teaches in the School of Earth Sciences at Ohio State.