PITTSBURGH -- An ongoing U.S. Environmental Protection Agency study on natural gas drilling and its potential for groundwater contamination has gotten tentative praise so far from both industry and environmental groups.

Glenn Paulson, the EPA's science adviser, describes the project as "one of the most aggressive public outreach programs in EPA history."

The final report won't come out until late 2014. But a 275-page progress report was released in December and, for all its details, shows that the EPA doesn't plan to address one contentious issue -- how often drinking water contamination might occur.

Congress ordered the EPA to study the potential effects of hydraulic fracturing, or fracking, which entails blasting a mixture of water, sand and hazardous chemicals at underground shale to release the gas or oil captured in the rock.

As a gas rush surged in parts of the Marcellus Shale region that underlies Pennsylvania, New York, Ohio and West Virginia concerns arose for the watershed that provides drinking water for 17 million people from Philadelphia to New York City.

For the study, the EPA is talking to experts from the industry, the environmental community, and universities. It's conducting its own research and using federal supercomputers to analyze the possibility of contamination.

In the report, the EPA describes what it is and isn't studying. The agency also indicates its final report won't provide a measurement of the likelihood of contamination -- for example, once every 100,000 wells or once every 1,000.

The industry and many federal and state officials say fracking is safe when done properly, but environmental groups and some scientists contend the risk of contamination is too great.

Earthworks, an environmental group based in Washington, said it welcomes the EPA study but has concerns with plans not to include some probability of groundwater contamination in the final report.

The EPA had planned to do both computer simulations of water contamination and actual field tests at drilling sites. But the agency hasn't found a drilling company to partner with to test groundwater around a drilling site. That leaves the computer simulations. But the EPA said those won't be able to address the likelihood of contamination "occurring during actual field operations."

"In its inability to find a single company willing to test water quality before and after drilling and fracking, the EPA is being thwarted in perhaps the most important part of its study of fracking's impacts," Earthworks said in a statement.

"Computer simulations are not enough," Alan Septoff, a spokesman for Earthworks, said.

He said the EPA study and any future studies should consider the likelihood of water contamination.

The EPA did not immediately respond to requests for comment.

The progress report says the EPA is studying the possible impact on drinking water at several stages of the fracking process: when water is drawn from reservoirs or underground sources and used for fracking; when a chemical mix is injected into the ground to break up rock; when wastewater from fracking is disposed of; how the drilling wells and wastewater-storage wells are constructed; and the potential for toxic fluids to migrate from deep underground to near-surface drinking water supplies.

The American Petroleum Institute, an industry lobby based in Washington, said in a statement that the progress report "is just the first step in a multi-year research study."

"More collaboration, continued transparency and stakeholder involvement are essential elements for any scientifically sound study, and we hope that the rest of this process remains open and any data released has the necessary context," API policy adviser Stephanie Meadows said.

Despite its concerns, Earthworks described the EPA study as a positive step.

"It represents a step towards EPA's first real scientific inquiry into the safety of fracking," the group said.

Online:

http://www.epa.gov/hfstudy/