New research has concluded that salty, mineral-rich fluids deep beneath Pennsylvania's natural gas fields are likely seeping upward thousands of feet into drinking water supplies.

Though the fluids were natural and not the byproduct of drilling or hydraulic fracturing, the finding further stokes the red-hot controversy over fracking in the Marcellus Shale, suggesting that drilling waste and chemicals could migrate in ways previously thought to be impossible.

The study, conducted by scientists at Duke University and California State Polytechnic University at Pomona and released today in theProceedings of the National Academy of Sciences, tested drinking water wells and aquifers across Northeastern Pennsylvania. Researchers found that, in some cases, the water had mixed with brine that closely matched brine thought to be from the Marcellus Shale or areas close to it.

No drilling chemicals were detected in the water, and there was no correlation between where the natural brine was detected and where drilling takes place.

Still, the brine's presence – and the finding that it moved over thousands of vertical feet -- contradicts the oft-repeated notion that deeply buried rock layers will always seal in material injected underground through drilling, mining, or underground disposal.

"The biggest implication is the apparent presence of connections from deep underground to the surface," said Robert Jackson, a biology professor at the Nicholas School of the Environment at Duke University and one of the study's authors. "It's a suggestion based on good evidence that there are places that may be more at risk."

The study is the second in recent months to find that the geology surrounding the Marcellus Shale could allow contaminants to move more freely than expected. A paper published by the journal Ground Water in April used modeling to predict that contaminants could reach the surface within 100 years – or fewer if the ground is fracked.

Last year, some of the same Duke researchers found that methane gas was far more likely to leak into water supplies in places adjacent to drilling.

Today's research swiftly drew criticism from both the oil and gas industry and a scientist on the National Academy of Science's peer review panel. They called the science flawed, in part because the researchers do not know how long it may have taken for the brine to leak. The National Academy of Sciences should not have published the article without an accompanying rebuttal, they said.