The Barnett Shale natural gas field in Denton and Wise counties is one of five finalists to be a case study as part of the Environmental Protection Agency's examination of hydraulic fracturing.

In addition, the Flower Mound/Bartonville area in southern Denton County is one of four candidates for a separate case study that would be part of the EPA project, which will be completed in late 2012 at the earliest.

The choices for potential case studies are cited in a 140-page draft plan released Tuesday Feb8. 2011.

The Barnett Shale in Wise and Denton counties is a finalist for a so-called retrospective study, which will investigate possible contamination of drinking-water supplies from oil and gas industry operations in areas where drilling and hydraulic fracturing have already occurred.

The other four finalists for retrospective studies are the Bakken Shale oil play in North Dakota, two separate areas in Pennsylvania where there has been extensive Marcellus Shale drilling, and the Raton Basin in Colorado.

The EPA said it expects to do three to five retrospective case studies, which means all five finalists could be selected. Study results "may be used to assess the risks posed to drinking-water resources as a result of hydraulic fracturing activities," the EPA said.

The Flower Mound/Bartonville area, if selected, would be the subject of a prospective case study, an investigation of a site where hydraulic fracturing will occur in the near future. Prospective studies would be "made possible by partnering with oil and natural gas companies and other stakeholders," the EPA said.

Sharon Wilson, Texas organizer for the Earthworks Oil and Gas Accountability Project, expressed concern Wednesday about the Flower Mound/Bartonville study.

"I think it's basically using the Flower Mound and Bartonville people as guinea pigs," she said. "I would hope that the leaders in those communities would consider placing a moratorium on hydraulic fracturing until after the study is complete. Let someone else be the guinea pig."

The EPA draft plan listed three other potential sites for prospective case studies: the Bakken Shale in North Dakota, Marcellus Shale in Pennsylvania and Niobrara Shale in Wyoming. Two to three likely will be selected.

The Barnett Shale, a geological formation underlying more than 20 North Texas counties, leads the nation in natural gas production, and Tarrant County is at the epicenter of drilling activity.

Hydraulic fracturing, or "fracking," is typically used to complete wells in the shale. In the fracking process, huge volumes of water and sand, along with a much smaller volume of chemical additives, are pumped down a wellbore under extremely high pressure to fracture dense rocks and allow natural gas and other hydrocarbons to be released.

In December, the EPA filed an endangerment order against Fort Worth-based Range Resources, contending that two of its Barnett Shale wells caused or contributed to contamination of two residential water wells in Parker County.

Range maintains that its wells are not the source of the contamination. It says methane in the water wells likely came from the much shallower Strawn formation, where natural gas wells were drilled in the early 1980s, long before Barnett Shale drilling began.