The Environmental Protection Agency on Thursday released the outlines of its long-awaited probe into whether hydraulic fracturing _ the unconventional drilling technique that's led to a boom in domestic natural gas production _ is contaminating drinking-water supplies.
Investigators will try to determine the impact of large-scale water withdrawals, aboveground spills of drilling fluids, and the fracturing process itself on water quality and quantity in states where tens of thousands of wells have been drilled in recent years.
Hydraulic fracturing, or fracking, involves the high-pressure injection of millions of gallons of water, along with sand and chemical additives, deep underground to extract natural gas trapped in shale rock. Energy companies have greatly expanded their use of fracking as they tap previously unreachable shale deposits, including the lucrative Marcellus Shale formation in Pennsylvania and neighboring states.
The industry has long contended that fracking is safe, but environmentalists and some residents who live near drilling sites say it has poisoned groundwater. The EPA study, mandated by Congress last year, is the agency's first look at the impact of fracking in shale deposits.
EPA will examine drilling sites in Pennsylvania, Colorado, Louisiana, North Dakota and Texas. The earliest results will be available in 2012.
Industry groups said Thursday they are confident the study will vindicate their position that fracking does not harm the environment or human health.
"The industry has taken the lead in working with state regulators to constantly improve operations, industry practices and guidelines as well as improve communications with local communities," said Stephanie Meadows, a senior policy adviser at the American Petroleum Institute.
The institute and five other industry groups recently complained to EPA Administrator Lisa Jackson that agency staff began collecting field data and water samples months before the study plan was finished. The industry groups, in an Oct. 20 letter to Jackson, also questioned the study design itself and said it could undermine the credibility of the findings.
The EPA said it began work over the summer so that it could finish the study by 2014.
The federal agency has studied fracking before, in 2004, looking at its use in coalbed methane deposits. It concluded then that the technology is safe, but its methodology was widely criticized as flawed.
The new EPA study will look at the entire water lifecycle of hydraulic fracturing in shale deposits, beginning with the industry's withdrawal of huge volumes of water from rivers and streams and ending with the treatment and disposal of the tainted wastewater that comes back out of the wells after fracking. Researchers will also study well design and the impact of surface spills of fracking fluids on groundwater.
The EPA has taken steps recently to boost federal regulation of fracking, announcing it will develop national standards for the disposal of the briny, chemical-laced wastewater and proposing for the first time to control air pollution at oil and gas wells, particularly where fracking is used.
Drillers have resisted enhanced federal regulation, saying it should be left up to individual states.
Associated Press writer Dina Cappiello in Washington contributed to this story.