WASHINGTON (Reuters) - The U.S. Environmental Protection Agency released on Thursday the locations in five states where it will study the safety of a natural gas drilling technique some blame for polluting water.
The EPA expects the initial results from its study on hydraulic fracturing, or fracking, which was mandated by Congress, will be released by the end of next year.
The agency said it will study fracking in the Haynesville Shale formation in DeSoto Parish, Louisiana, and the Marcellus Shale in Washington County, Pennsylvania.
The EPA said it will monitor "key aspects of the hydraulic fracturing process throughout the lifecycle of a well" at these sites.
It will also do retrospective case studies in North Dakota, Texas, Pennsylvania and Colorado. In those studies, the agency will gather information from reviews, states, industry and communities, and conduct its own field research.
During fracking, drillers blast pressurized water, chemicals and sand deep underground to break rocks and release the gas or oil that is trapped in them.
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.
Environmentalists and some lawmakers want more federal regulation of fracking, but many states say they can handle it themselves.
The case studies were selected by the EPA on criteria including the proximity of people and drinking water supplies to fracking sites. For the retrospective studies, concerns about impaired water quality and health and environmental impacts were also taken into account.
The EPA said its retrospective studies will take place in the following locations:
Bakken Shale - Kildeer, and Dunn Counties, N.D.
Barnett Shale - Wise and Denton Counties, Texas
Marcellus Shale - Bradford and Susquehanna Counties, Pa.
Marcellus Shale - Washington County, Pa.
Raton Basin - Las Animas County, Colo.
(Reporting by Timothy Gardner; editing by Jim Marshall)