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Chemically treated drilling fluid can migrate through thousands of feet of rock and endanger water supplies, said a hydrologist whose research calls into question the safety of hydraulic fracturing for natural gas.

The fluids can migrate faster that previously thought, Tom Myers, a Reno, Nevada, researcher, said Wednesday. His study, published in the online journal "Ground Water" on April 17, says fluids can reach shallow drinking-water aquifers in as little as three years.

"If contaminants reach natural fractures under pressure, the upward flow has the potential to be enhanced greatly," said Myers, an independent consultant who has worked for conservation groups and governments. "It can flow upward if there's a pathway and unless it's completely impermeable, there's always a pathway. It's just a question of how long it takes."

The safety of water supplies is a key concern of critics of fracking, a drilling technique in which water, chemicals and sand are pumped deep underground to free trapped natural gas. Fracking, which has boosted supplies and sent prices to their lowest in a decade, is being investigated by the U.S. Environmental Protection Agency for possible impacts on water.

Drillers say there has been no documented case of fluids reaching drinking water.

Gas industry officials were quick to point out that the study was commissioned by Catskill Mountainkeeper, a Youngsville, New York-based environmental group that opposes fracking, and The Park Foundation in Ithaca, which offers research grants. Computer models used by Myers contain errors that skew his results, according to Terry Engelder, professor of geosciences at The Pennsylvania State University in University Park.

"This is considered settled science," Simon Lomax, research director for Energy in Depth, a Washington-based industry group, said in an interview. "There are thousands of feet of rock between deep-shale formations and shallow aquifers, and it's precisely that barrier that keeps these fluids miles away from shallow drinking-water sources."

Catskill Mountainkeeper commissioned the study after a 2009 finding by New York regulators that fracking fluid couldn't migrate into drinking water, according to Ramsay Adams, executive director of the environmental group. The New York Department of Environmental Conservation is drafting rules for hydraulic fracturing and has so far not allowed the drilling technique.

The Myers study bolsters the group's claim that fracking isn't safe for New York state, home to unfiltered aquifers that provide water to New York City and Syracuse.

"We know less about what's underground than we know what's at the bottom of the deepest oceans," Adams said in an interview. "That blanket statement that there's this impermeable wall that will keep these chemicals down there is false and it changes everything."

While New York regulators are reviewing the Myers study, they have concluded that "no significant adverse impact to water resources is likely to occur due to underground vertical migration of fracturing fluids," Emily DeSantis, a department spokeswoman, said in an e-mail. "The high salinity of native water in the Marcellus and other Devonian shales is also evidence that fluid has been trapped in the pore spaces for hundreds of millions of years, implying that there is no mechanism for the movement of fluids between formations."

Myers used computer models to predict how fracking fluid will react in the Marcellus Shale after it is used to shatter rock and free trapped gas. He found that a process in which water migrates through naturally occurring faults over tens of thousands of years may be accelerated by fracking.

The Marcellus formation, which stretches from New York to Tennessee, may hold enough gas to supply the U.S. for three years. Over 4,000 wells have been drilled by fracking in Pennsylvania since 2009.

Engelder said Myers used an "unrealistically high" number for permeability of rock above the shale layer that contains gas. That produced results that greatly exaggerated the time it could take for fluid to migrate from the fracking zone.

Myers also assumed that pressures created by fracking will drive fluids away from the gas-bearing rock when in fact they will do the opposite, Engelder said.

"In my view the issue is settled, which is that it can't happen on a time scale that is important to mankind," Engelder said in an interview.

A report last year from a task force named by U.S. Energy Secretary Steven Chu found that while fracking poses environmental risks "the likelihood of properly injected fracturing fluid reaching drinking water through fractures is remote."

A study last year by consultants ICF International for New York found that layers of sandstone between shale formations and aquifers assure that fracking in New York poses no "foreseeable risk" to drinking water.

Myers said drillers should map fracking zones for the presence of faults, and use monitoring wells to track hydrology before fracking begins.

"I am suggesting that over a 50 to 100 year time period, that we could be creating lots of places where this stuff could come out," Myers said. "I don't think you've found a dedicated monitoring well anywhere."