The Environmental Protection Agency on Thursday announced a national plan to regulate a class of chemicals that have contaminated water supplies across the U.S.

The EPA will launch a process for setting a drinking water limit for two toxic chemicals known as perfluoroalkyl and polyfluoroalkyl substances, or PFAS.

Acting EPA Administrator Andrew Wheeler has been under intense pressure to set a drinking water limit for the chemicals, including from Senate Republicans who live in states with PFAS contamination. Wheeler needs support from GOP senators if he's going to be confirmed as the EPA's administrator.

“The PFAS Action Plan is the most comprehensive cross-agency plan to address an emerging chemical of concern ever undertaken by EPA,” Wheeler said. “For the first time in agency history, we utilized all of our program offices to construct an all-encompassing plan to help states and local communities address PFAS and protect our nation’s drinking water.”

EPA’s plan is not a formal regulatory proposal. But Wheeler said the agency intends to begin a rulemaking process this year to set a “maximum contaminant level” under the Safe Drinking Water Act for the amount of PFAS allowed in drinking water. He said EPA would propose a rule by the end of the year.

Sen. Shelley Moore Capito of West Virginia, whose state has a major PFAS contamination problem, was among the Republicans who had considered opposing Wheeler because she was “troubled” by media reports that he wouldn’t seek to set a drinking water limit for the chemicals.

She ultimately voted for him in the Environment and Public Works Committee, which advanced his nomination to the Senate floor, where it is still pending.

Sen. John Barrasso, R-Wyo., the chairman of that committee, stopped short of celebrating EPA's action Thursday, calling on the agency to fulfill its promise to regulate PFAS.

“Local communities and state regulators from across the country as well as members of Congress are concerned about PFAS pollution,” Barrasso said. “The Environmental Protection Agency’s PFAS plan is only a first step. As I have said before, EPA must speak clearly about the risk that this class of chemicals poses to public health and the environment. The agency must be willing to take decisive action where it is warranted.”

House lawmakers last month, meanwhile, created a bipartisan task force to pressure the federal government to prioritize clean-up of sites tainted by PFAS. That group called for the EPA to set a national standard for the amount of PFAS allowed in drinking water.

The Democratic leaders of the House Energy and Commerce Committee said Thursday they would provide oversight to ensure EPA sets a drinking water limit for PFAS.

“If EPA intends to drag its feet, Congress will have to step in and lead the fight to protect Americans from these dangerous chemicals," said Reps. Frank Pallone of New Jersey, the committee's chairman, and Paul Tonko, D-N.Y.

An analysis published last year by the Environmental Working Group found that up to 110 million U.S. residents may be exposed to drinking water contaminated with PFAS, which has been linked with thyroid defects, problems in pregnancy, and certain cancers.

The stain-resistant chemicals have been used since the 1940s in Teflon, nonstick pans, electronics, water-repellent clothes, food packaging and firefighting foam. The contamination problem is particularly bad around military bases, likely because of firefighting exercises that occur there.

Wheeler did not say how strict the new EPA rule would be, and how it would compare to a voluntary health advisory the agency issued for PFAS in 2016 that recommended a drinking water limit of 70 parts per trillion. Some states have already set drinking water limits tougher than that guidance.

Wheeler said EPA would propose setting the level based on what “the science dictates” and what is “legally defensible.” EPA has not regulated a new chemical under the Safe Drinking Water Act since Congress created the law in 1996. That's because the law has strict requirements, forcing EPA to show that a chemical it wants to regulate is dangerous, and that setting a drinking water limit offers "a meaningful opportunity for health risk reduction" in a financially-sound manner.

EPA’s plan also begins a process of declaring PFAS "hazardous" under the Superfund law, forcing polluters to clean up contamination. It includes more research into whether other chemicals in the PFAS family should be regulated, and commits EPA to better monitor and detect PFAS contamination in states and communities, and to communicate the risk of exposure.

EPA’s action continues a process started by Wheeler’s predecessor Scott Pruitt.

Pruitt held a “National Leadership Summit” in May 2018 with state and local officials to discuss how to combat PFAS contamination, during which he declared combating the chemicals a “national priority.”

Pruitt promised that EPA would work to declare PFAS a “hazardous substance,” and planned to introduce a management plan for the chemicals that fall, but the process was delayed.

The agency also undertook a nationwide listening tour, visiting PFAS-contaminated communities to learn about their problems and expectations.