* USGS sampled 127 wells in Fayetteville shale area
* Study shows fracking can be done safely, author says
* Draft EPA study linked fracking, water pollution in Wyoming
By Ayesha Rascoe
WASHINGTON, Jan 9 (Reuters) - The U.S. government said it found no evidence that shale gas drilling had contaminated water in two Arkansas counties where concerns were raised about the drilling technique called hydraulic fracturing, or fracking.
The U.S. Geological Survey (USGS) sampled 127 shallow domestic wells in Van Buren and Faulkner counties in the Fayetteville Shale area, where 4,000 wells have been drilled since 2004.
"It does show this can be done and done right with no impacts," Tim Kresse, one of the USGS study's authors and a water quality specialist with USGS, told Reuters.
Still, Kresse stressed that the results should not be used to draw conclusions about the safety of fracking around the country because geology varies widely from state to state.
Among other things, the USGS study assessed concentrations of chloride, a naturally occurring compound that would be one of the best indicators of water contamination by fracking fluids, Kresse said.
The researchers found that chloride concentrations in the 2011 samples were not higher than samples collected in nearby areas between 1951 and 1983.
Advances in fracking, which involves injecting a cocktail of water, sand and chemicals underground to extract fuel, have unlocked the nation's vast shale gas reserves.
But the boom in shale gas development has led to protests that the production may be polluting groundwater and air in places like Arkansas and Pennsylvania.
Responding to concerns about the possible hazards associated with fracking, the Obama administration has attempted to balance support for more gas drilling with calls to ensure that drilling is safe.
The USGS study should provide ammunition for oil and gas producers who have strongly disputed suggestions that fracking is responsible for fouling drinking water.
USGS also studied methane concentrations in 51 of the sampled wells and found that any methane detected was naturally occurring or could not be linked to the drilling.
A draft study released by the Environmental Protection Agency in 2011 linked fracking to water contamination in Pavillion, Wyoming, sparking a firestorm of debate, with state officials and drilling groups slamming the report.
The EPA retested the water in Pavillion in 2012 and has extended the public comment period on the report until Jan. 15.
The EPA is currently also conducting a long-term study on fracking and drinking water that is due to issue conclusions in 2014.