The EPA took another step toward tightening oversight of hydraulic fracturing today, announcing it would initiate a process to set national rules for treating wastewater discharged from gas drilling operations.

Until now, the agency has largely left it to states to police wastewater discharges. Some have allowed drillers to pump waste through sewage treatment plants that aren't equipped to remove many of the contaminants, leading to pollution in some rivers and to problems at drinking water facilities.

Cynthia Dougherty, EPA's director of ground water and drinking water, told a Senate panel today that the agency has an important role to play in bolstering state standards.

"I wouldn't say they're inadequate," she said of states' regulations, "but they could use the help."

When drillers frack a gas well, they inject thousands of gallons of chemicals, some of which are highly toxic even at low concentrations. When the fluid comes back up, it carries extremely salty water that can contain heavy metals and radioactive elements.

In Western states, most drilling wastewater is injected deep underground for permanent storage. There are fewer injection wells in the East, however, so much of the waste from drilling in the Marcellus Shale was initially discharged into surface waters.

The EPA has the authority to issue permits for such discharges, but current rules allow shale gas drillers to pass their waste through public sewage plants even if those plants are not equipped to remove pollutants. (There are currently no rules covering wastewater from coalbed methane drilling, a type of gas production that drills into coal seams, so those wastes can be discharged without treatment.)

For years, Pennsylvania allowed growing volumes of wastewater to flow into the state's rivers. As ProPublica reported two years ago, the water's high salt and mineral content was believed to have elevated pollutant levels in some streams. It also may have clogged industrial equipment, killed fish and caused contamination in drinking water.

In March, the EPA sent a letter to environmental officials in Pennsylvania expressing alarm at high pollutant levels in the wastewater that was being discharged into the state's waterways. The agency urged the state to increase monitoring. The next month, the state asked drillers to stop discharging waste unless it was properly treated. By June, state officials said that no waste was being discharged without full treatment.

In an email to ProPublica, the EPA said that concerns about releases in Pennsylvania and "other information" led the agency to initiate the process to set new national rules. The agency said about 22 billion gallons of wastewater from coalbed methane drilling go into surface waters across the country each year. The EPA does not have data on how much shale gas wastewater is being discharged nationwide.

"This is just a really good opportunity to be able to track the amount and the content of the waste at these wells," said Jason Pitt, a spokesman for the Sierra Club. "You really can't treat these chemicals as they come up without really knowing what's in them."

The Independent Petroleum Association of America issued a statement today saying it would work with the EPA to develop new standards and noted that drillers are increasingly cleaning and reusing their wastewater. Officials in Pennsylvania and at the EPA have said that increased recycling has been an important factor in reducing wastewater discharges.

The EPA said it would propose wastewater rules for coalbed methane drilling in 2013. Similar rules covering shale gas will come a year later, after the agency gathers more data on discharges.

The plan is one of several recent moves to increase federal oversight of fracking. Earlier this year, the EPA proposed rules that would limit air emissions from fracking operations. The Interior Department, which regulates drilling on federal lands, has said it will issue rules covering fracking within the month.