WASHINGTON U.S. environmental regulators issued a draft plan on Tuesday outlining how they will determine whether a technique for drilling natural gas harms supplies of drinking water.
Congress commissioned the Environmental Protection Agency to study hydraulic fracturing, or "fracking", after complaints that the process pollutes water. The EPA is slated to make public initial results of the study by the end of next year.
The study will investigate reported instances of drinking water contamination in three to five sites across the country where fracking has occurred, the agency said in the draft.
In addition, the EPA will conduct two to three prospective case studies, to take samples before, during and after water extraction, drilling and production of gas.
During fracking, drillers blast pressurized water and chemicals deep underground to break rocks and release gas or oil from coal beds, shales and tight sands.
The technique has been around for decades, but companies have expanded its use in recent years to extract abundant but hard-to-reach reserves of shale gas.
Congressman Ralph Hall, chairman of the House Committee on Science, Space and Technology, said in a statement that he would closely review the study because he felt fracking had been the subject of "misleading attacks".
"Natural gas is a vital resource, and hydraulic fracturing is a well-established process that is enabling greatly increased production of clean, affordable energy," he said.
The EPA's science advisory board plans to review the draft on March 7 and 8, and the public will be able to comment on the plan during that time.
Several U.S. cities have begun to take action on fracking. Pittsburgh, Pennsylvania and Buffalo, New York have preemptively banned the process.
(Reporting by Timothy Gardner; Editing by Dale Hudson)