The U.S. Environmental Protection Agency says it is prepared to “move forward” with a plan to address the PFAS contamination that has tainted drinking water and groundwater in communities nationwide, including taking steps to begin the process of creating a drinking-water limit for the chemicals.

Amid public outcry and mounting pressure from elected officials, acting Administrator Andrew Wheeler will detail the plan during a news conference Thursday in Philadelphia, the EPA said Wednesday. About 70,000 residents in Bucks and Montgomery Counties were among the first in the nation to discover their drinking water had been contaminated for decades.

A congressional aide briefed on the matter said the EPA’s five-part plan includes looking at setting an enforceable limit for PFAS under the Safe Drinking Water Act, and adding the chemicals to a list of hazardous substances, which could allow communities to hold polluters accountable. The plan also involves more monitoring and research about the chemicals by the federal government, according to the aide, who was not authorized to speak publicly about the announcement.

The suggestion that the EPA would take steps toward creating a maximum contaminant level — a standard for how much of the chemicals is safe to drink — for PFOA and PFOS, two types of PFAS, could run contrary to a Politico report last month that the EPA would not pursue a drinking water limit for the chemicals. That report sparked outrage from environmentalists and elected officials, and drew suggestions that PFAS could be an issue in Wheeler’s confirmation to the administrator post.

It remains unclear whether the EPA will create such a limit. Even if it did, the process would be lengthy and the limit less restrictive than hoped for by advocates.

In recent weeks, members of Congress, including representatives from the Philadelphia region, announced the formation of a PFAS task force, saying they would put pressure on the EPA to regulate the chemicals.

“I am pleased the administration is finally putting together an action plan to address the PFAS issues in drinking water across our nation," Sen. Bob Casey (D., Pa.) said on Wednesday. “I have long pushed and petitioned them to address these issues impacting Bucks and Montgomery Counties. I look forward to seeing the results and plan on keeping a close watch on their progress."

On Wednesday evening, Wheeler told ABC News that the chemicals were a “very important threat” and that the “new management plan” would “protect Americans’ drinking water.”

The plan to be unveiled will also “continue our enforcement actions and clarify our cleanup strategies, expand monitoring of PFAS in the environment, and enhance our research and scientific foundation for addressing PFAS by developing new analytical methods and tools,” according to the EPA.

“This action is long overdue, and acting EPA Administrator Wheeler must ensure that PFAS remediation is an immediate priority of the agency,” said Rep. Brian Fitzpatrick (R., Pa.). "I am hopeful Thursday’s announcement will unveil an aggressive and impactful strategy to counter this public health crisis affecting communities in Bucks and Montgomery Counties and across the United States.”

Activists, residents, and state agencies have pushed for action from the EPA on the chemicals, which in 2014 were widely discovered to have leaked into water supplies near military bases nationwide, including sites in Willow Grove and Warminster.

Used in firefighting foams by the military — as well as contained in many common household products — PFAS, or per- and polyfluoroalkyl substances, have been linked to health issues including cancer and reproductive problems. During the summer, EPA officials conducted a “listening tour” to visit affected areas, including Horsham.

“After years of calling for federal action to address the water contamination and any resulting health issues they’ve caused in my community, I’m looking forward to learning more about the action plan to be released Thursday," said State Rep. Todd Stephens (R., Montgomery), who lives in Horsham. "I remain hopeful that the EPA may finally be stepping up to fulfill their obligations to our residents.”

Creating an enforceable drinking water limit can take years. The EPA has created drinking water regulations for only 90 contaminants, and last made changes to those regulations in 2013.

Currently, the EPA has only issued a nonbinding health advisory that many scientists and activists say is too lax. Some states have started the process of creating their own drinking water standards that are much stricter.

A recent analysis by the Inquirer found that the chemicals are present in drinking water in at least 22 towns in the suburbs of Philadelphia in addition to Horsham, Warrington, and Warminster Townships, where the military has taken responsibility for contamination that spread from former naval bases. There, recent blood testing revealed high levels of the chemicals in residents’ bloodstreams.