LAURA BARRON-LOPEZ: Earlier this fall, the Defense Department missed a deadline to stop using a firefighting foam that has caused widespread contamination across the country.

While the military continues its transition away from the toxic foam, it's also beginning a massive cleanup that will take decades and billions of dollars.

In the small town of Oscoda, Michigan, a group of citizens has been fighting to hold the Air Force accountable for contaminating their waterways.

In the first of our two-part series, special correspondent Megan Thompson brings us their story.

MEGAN THOMPSON (voice-over): Tony Spaniola and his family have been coming to their vacation home on Van Etten Lake for decades, a relaxing getaway in the wilds of northern Michigan.

But in 2016, Spaniola received a troubling letter from the state.

TONY SPANIOLA, OSCODA MICHIGAN RESIDENT: I got a letter in the mail from the Michigan Department of Health and Human Services saying, don't drink your water.

MEGAN THOMPSON (voice-over): About a year later, Spaniola began noticing something strange on the lake.

TONY SPANIOLA: It was in December and my wife woke up and she said, I think it snowed last night.

There was foam piled up all along the shoreline.

You could see it for miles.

All along -- MEGAN THOMPSON (voice-over): Spaniola had learned his tap water, the lake and this bright white foam were all contaminated with toxic manmade chemicals.

TONY SPANIOLA: It sends you into a different place.

It's a shocking kind of thing.

So the base is right across the lake?

Yeah.

You can see the buildings.

MEGAN THOMPSON (voice-over): It turned out the chemicals were coming from the old Wortsmith Air Force Base.

MARK HENRY, RETIRED ENVIRONMENTAL ENGINEER: This was a fire training area.

MEGAN THOMPSON (voice-over): Mark Henry is a retired environmental engineer for the state of Michigan who worked at the base after it closed in 1993.

MARK HENRY: There used to be a big concrete bowl out here with a simulated aircraft on it.

And then they would bring the fire trucks in and let the people practice.

MEGAN THOMPSON (voice-over): They were practicing putting out jet fuel fires, dousing the burning planes with a special foam that's been used by the military since the 1970s.

It's made from a chemical called PFAS.

COURTNEY CARIGNAN, Michigan State University: PFAS is an acronym that stands for PER and polyfluoroalkyl substances.

MEGAN THOMPSON (voice-over): Courtney Carignan is an environmental epidemiologist at Michigan State University.

She studies human exposure to chemicals.

COURTNEY CARIGNAN: PFAS are characterized by a chain of carbons with fluorine bonds and a functional group.

One end likes water and the other does not and repels it.

MEGAN THOMPSON (voice-over): Those useful properties mean they're contained in all kinds of common products like nonstick pans, stain resistant carpet, and food packaging.

There are around 15,000 types of PFAS, and increasingly research shows they can cause a range of health problems from liver damage to heart disease and cancer.

COURTNEY CARIGNAN: PFAS are often called forever chemicals because they're so persistent in the environment.

They don't break down naturally.

They move very easily into water and groundwater, and so they end up in our fish and our drinking water.

MEGAN THOMPSON (voice-over): Today, about half the nation's drinking water supply has PFAS in it.

And nearly every American has some level of PFAS in their blood.

The military is one of the biggest PFAS polluters in the U.S. but the scale of the problem has only recently become widely known, thanks in large part to Wordsmith, one of the first bases where PFAS contamination was publicly exposed.

In 2010, a colleague of Mark Henry's made the discovery and began sounding the alarm.

Today, the Pentagon has confirmed or suspects PFAS contamination at more than 700 other sites.

MARK HENRY: There is almost no place you can dig a hole here on the base and not find the PFAS in the groundwater even to this day, 50 years after the release.

MEGAN THOMPSON (voice-over): But that polluted groundwater hasn't been staying on the base.

CATHY WUSTERBARTH: So these are the plumes of PFAS that are flowing from the former base.

MEGAN THOMPSON (voice-over): Seeping for years into nearby streams and lakes and the tap water of some homeowners like Tony Spaniola.

TONY SPANIOLA: I'm right there.

Right there.

MEGAN THOMPSON (voice-over): Spaniola, a politically connected attorney was so alarmed, he teamed up with Oscoda resident Cathy Wusterbarth to launch Need Our Water to call attention to the environmental calamity.

They gave PBS News Weekend a tour of the areas most affected by those PFAS plumes.

TONY SPANIOLA: So this is a youth camp.

It's owned by the YMCA of Detroit.

And there is a PFAS plume that flows right underneath the camp in comes out right here at the shore.

CATHY WUSTERBARTH: This is an area we call three Pipes.

The water is coming off of the base from the storm sewers, flowing uninterrupted into the Au Sable River.

MEGAN THOMPSON (voice-over): Tests found PFAS levels more than 50 times higher than what's allowed by Michigan law.

On the day we visited, dozens of people were swimming and boating nearby, about a mile away is a wildlife area called Clark's Marsh, where birds have been found with some of the highest levels of PFAS contamination ever documented.

The state has issued five separate health advisories for the area warning, do not eat any fish you catch or animals you hunt.

CATHY WUSTERBARTH: So this lake is highly contaminated on the surface.

And when the wind agitates the surface of the water, the foam can build up.

MEGAN THOMPSON (voice-over): Tests conducted by the state have found PFAS levels in the foam as high as 220,000 parts per trillion.

The EPA's new standard for drinking water only allows for 4 parts per trillion.

What's more, Van Eten Lake and the other contaminated streams drain into Lake Huron, one of the Great Lakes and a source of drinking water for around 3 million people in the U.S. and Canada.

PFAS contaminated foam has been found on its shores, too.

TONY SPANIOLA: We can't afford to allow this land, this natural resource, to be poisonous for years and years to come.

And it's got to stop.

MEGAN THOMPSON (voice-over): Spaniola and Wusterbarth have spent the last seven years lobbying Congress and the Pentagon to clean up the mess.

CATHY WUSTERBARTH: They can stop the flow of all of these plumes off of the property right now.

MEGAN THOMPSON (voice-over): Wordsmith is one of the first bases in the country where the Air Force has begun installing PFAS treatment systems, pumping groundwater into huge vats where the contamination is removed.

But 14 years after the PFAS discovery, only a fraction of the pollution is being treated, and the Air Force recently announced delays in cleaning up the rest.

Some systems won't start operating for another four or five years.

TIM CUMMINGS: It's just slow motion.

This is molasses on a cold winter day.

MEGAN THOMPSON (voice-over): A citizens' advisory board meets with the Air Force every three months to provide input meetings that have become increasingly contentious.

MAN: We feel abandoned.

MAN: It's like you're cooking the books.

MEGAN THOMPSON (voice-over): At a meeting in August, board members vented frustrations about the delays and said the cleanup was mismanaged, accusing the military of not conducting enough testing before it started building the latest treatment system this summer.

MARK HENRY: The Air Force did an extremely minimal amount of work to demonstrate that the wells they were planning on putting in were actually in the right place.

So they're only treating a quarter of the known problem, and they have no idea really what exists beyond.

MEGAN THOMPSON (voice-over): Under pressure, the Air Force released the results of an independent review at the latest community meeting this week, confirming concerns about the new system and saying more testing is needed to make sure all the PFAS will be captured.

BRENDA ROESCH, Air Force Civil Engineer Center: We are looking at a reorganization.

MEGAN THOMPSON: Air Force official Brenda Rush also announced a shakeup in the management of the Wortsmith cleanup and promise the new leadership will do better.

BRENDA ROESCH: So I commit to you that we are going to increase the transparency.

We're going to really work hard on accelerating timelines.

MEGAN THOMPSON (voice-over): Tony Spaniola appreciates the new direction, but doesn't plan to let up the pressure because he says Wurtsmith needs to set the example for the rest of the nation.

TONY SPANIOLA: If our government doesn't do it right, what does that say to all the other communities that are impacted?

It's a very critical battle we're fighting here.

MEGAN THOMPSON (voice-over): For PBS News Weekend, I'm Megan Thompson in Oscoda, Michigan.