This March 27, 2008, file photo, shows the Pentagon in Washington. Credit: Charles Dharapak | AP

WASHINGTON — The Pentagon’s inspector general is examining the military’s use of a dangerous but ubiquitous class of man-made chemicals that has leached into the drinking water of millions of Americans, including many living near military bases across the country.

The compounds — known as polyfluoroalkyl and perfluoroalkyl substances, or PFAS — have for years been used in specialized firefighting foams on military bases.

Now the military’s watchdog agency will assess the legacy of using those chemicals. Among the questions the inspector general’s office may address are what the Pentagon knew about the dangers posed by the chemicals, how well the military has communicated those risks to service members and how quickly it plans to phase out their use.

“There may have been an awareness of the dangers of PFAS as threatening to human health long before the Department of Defense decided to do anything about it, and I think that’s fundamentally problematic,” Rep. Dan Kildee, D-Michigan, said in an interview. “The mission of the Defense Department is to protect Americans.”

The Pentagon assessment will bring the issue of PFAS contamination even more to the fore than it already is, with dozens of members of Congress on both sides of the aisle clamoring for regulators to do more and with a major Hollywood film about the toxic chemicals slated for release next month.

The watchdog agency’s “evaluation” — the office is not calling its action an investigation — comes after the request made in July by a bipartisan group of 31 House members led by Kildee and Rep. Brian Fitzpatrick, R-Pennsylvania. The Pentagon itself kicked off its own task force to address the contamination in August.

“We reviewed your July request and decided to initiate an evaluation related to PFAS concerns,” Michael Zola, the Pentagon’s assistant inspector general for legislative affairs and communications, wrote in an Oct. 7 letter back to lawmakers.

The exact scope of the assessment is still fuzzy, but should come into focus by early next year, according to the letter. And it’s unclear when the inspector general’s office will be done with its work.

“There’s not a real timeline associated with it,” said Dwrena Allen, spokeswoman for the Pentagon’s Office of Inspector General.

Its widespread use at U.S. bases around the world — most notably during firefighting training exercises — had led to the buildup of the chemical in groundwater near military installations. The Defense Department is tracking at least 401 sites for potential PFAS contamination.

That contamination is dangerous because exposure has been associated with an array of health problems, including thyroid disease, weakened immunity, infertility and certain cancers. And once in the water, the chemical can last for a long time without being naturally broken down — leading many to call them “forever chemicals.”

For decades the military has used a foam containing the chemical to extinguish the persistent flames of jet fuel and other aircraft-related fires. The Defense Department says it stopped land-based use of the foam during training exercises in 2016.

But the public doesn’t have a handle on how often the military has deployed the compounds in other ways, said Erik Olson, who directs the Natural Resources Defense Council’s advocacy on health, food, and agriculture.

“There may be literally dozens of other uses,” Olson said. “We just don’t know.”

But communities such as Oscoda in northeast Michigan, where contamination from a now-decommissioned air base has led to advisories to avoid drinking from private wells and against eating venison and certain fish, have heard promises of military investigations “for years and years” with little action afterward, according to Anthony Spaniola, an attorney and a founding member of the local advocacy group Need Our Water.

“It’s a good step that they’re conducting an investigation, but I’m skeptical,” said Spaniola, whose family owns a lakeside home in Oscoda. “I hope they get to the bottom of it. But they’re going to have to dig pretty hard.”

One big question the assessment may tackle: When did the military first understand how dangerous to human health the compounds are? The chemical giants DuPont and 3M have in the past been accused of concealing and playing down the risks of PFAS.

Those accusations have even caught the eyes of Hollywood producers. Robert Bilott, an environmental lawyer who successfully sued DuPont on behalf of plaintiffs in Ohio and West Virginia, will be the subject of a new film starring Mark Ruffalo called “Dark Waters.”

Earlier this year, the Environmental Protection Agency vowed to rein in the chemicals, but stopped short of marshaling its full regulatory might to issue drinking water rules. According to reporting from Politico earlier this year, Pentagon officials raised alarms with the White House over a draft study showing the chemicals were more harmful than previously indicated.

“I have very little faith that the EPA is taking PFAS seriously enough,” Kildee said.

That has led exasperated Republicans and Democrats in Congress, who for years have fielded calls from contaminated communities, to do something relatively rare in Washington nowadays: actually try to pass some legislation.

Attached to a defense reauthorization bill passed by both the House and Senate is a provision phasing out the military’s use of firefighting foam, among other PFAS-related measures. Negotiators from both chambers are now hammering out differences between their two versions of the broad defense package.