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of gallons of water flowing past Louisville, Kentucky's pumping station every day, where the city's utility sucks it up to turn it into tap water.

To ensure it tastes good and is safe to drink, a small team of scientists and technicians is constantly testing the water for pH, odors, heavy metals and microbes. 

But unlike many smaller municipal utilities across the U.S., the 

That's a class of chemicals, used by manufacturers for decades to make things like nonstick pans, cosmetics, raincoats, food wrappers and firefighting foam.

 like cancer, reduced immune system functioning, high cholesterol, and developmental delays in children. 

They're also known as "forever chemicals" because they're practically indestructible. Their strong chemical structures make them degrade incredibly slowly in the environment. 

 sources across the world and can be found in the 

One type of PFAS that the Louisville water technicians are tracking is HFPO-DA, though it's perhaps better known by a trade name, 

Almost a year ago, workers noticed an unexpected spike in the level of GenX detected in a sample of the raw, untreated water drawn from the Ohio River for filtering and processing.

In water, PFAS concentration is measured in parts per trillion. The GenX levels they found last December were 15 times higher than the previous month: 52 parts per trillion versus 3.4 parts per trillion.

"A part per trillion is like one second in 32,800 years. Put your head around that, right?" said 

, the city utility's director of water quality and research. 

Another way to think of it: One part per trillion would be a single drop within 20 Olympic swimming pools.

So the increased levels were still pretty low, he said.

But Goodman's team was curious about what was going on. They traced the chemical up the Ohio River, past Cincinnati and through Appalachian forests, all the way to a West Virginia factory about 400 miles upstream.

, a special plastic critical to the semiconductors that power our phones. 

Its Washington Works facility near Parkersburg, West Virginia, also has a 

 the company knew that a type of PFAS it was using, called PFOA, was toxic but didn't disclose that information.

 claiming it contaminated local environments with forever chemicals, although the company repeatedly has denied wrongdoing.

At the Louisville Water Co., the team's calculations eventually showed that the December 2024 spike in GenX levels corresponded to publicly-available data from Chemours, about its chemical discharges into the Ohio River.

Still, Goodman told NPR he wasn't worried about local customers' safety — even with last year's spike.

That's because risks posed by low PFAS concentrations are measured over a lifetime of exposure, he said. And recent data from Louisville show the 

 fell within planned federal safety limits.

Plus, water is just one way people can be exposed to PFAS, Goodman added. "Because you get a lot more of these pollutants from packaging, from prefixed food, cake mixes, weird things, you know, popcorn boxes," he said.

Chemours did not return a request for comment NPR.

 filed by a West Virginia environmental group, the company denied their discharges are connected to Louisville's GenX spike. (Louisville is not a party in the lawsuit.)

The company also contended that sampling data showed levels of GenX in the river and in downstream utilities' treated drinking water are "indisputably safe."

Louisville Water's data showed the water sample it drew in December 2024 had elevated GenX levels, compared to previous months. 

But after the water underwent typical treatment and filtering, the level fell under the new federal safety limit, which isn't scheduled to kick in until 2029.

The federal government has long regulated the levels of 

 in drinking water, like arsenic, E. coli and lead. 

But the EPA didn't issue regulations regarding PFAS until 2024, during the final year of the Biden administration.

 in drinking water. Starting in 2029, utilities which exceed the limits would be required to treat the water to reduce the contamination.

After Trump's re-election, his new EPA administrator 

 the agency will keep the rules for only two types of PFAS, called PFOA and PFOS, but drop the restrictions on the other four types, including GenX.

In addition, the EPA announced it will give water utilities two additional years, until 2031, to comply with the remaining rules, in part because of the financial burden on rural water plants.

Many utilities, large and small, probably will need to 

 estimated about 45% of U.S. tap water contains at least one type of PFAS.

When it announced the final PFAS limits, the Biden administration 

 that up to 10% of the estimated 66,000 U.S. public drinking water systems affected by these regulations might have PFAS levels high enough to require them to take action to reduce the contamination.

PFAS removal will challenge water utilities

Under current federal environmental regulations, Chemours 

release some chemicals into the Ohio River. But it has exceeded the legal limits repeatedly over several years, according to court filings and 

 in 2023, when it said it found Chemours' West Virginia factory had repeatedly exceeded permit limits for two types of forever chemicals, GenX and PFOA. 

But West Virginia Rivers Coalition said in a court filing that the EPA's consent order for Chemours "is not being diligently prosecuted."

Chemours declined to answer questions from NPR, citing ongoing litigation, except to point out that Louisville's "finished drinking water is safe for consumption" because the PFAS levels are below the EPA's regulatory limits, as stated on Louisville Water's 

of Cincinnati, which also draws from the Ohio River

As research into the health effects of PFAS exposure continues, environmental advocates say it's imperative for companies to meet the limitations set by government permits.

"Environmental regulatory permitting is a license to pollute," said 

"You're permitting someone to put something into the atmosphere, into water, into soil that would not be there otherwise. And so when we talk about the safe levels … stop using the word 'safe,' right? This is the maximum allowable limit."

It is possible to remove PFAS from drinking water. For example, Louisville's utility is spending about $23 million to redesign its powdered activated carbon system, which is one method used to take out PFAS.

But PFAS removal can get expensive, especially for small, rural towns, Hart said. Preventing contaminants like PFAS from getting into a community's drinking water supply is easier and less costly, compared to removing it on the back end, he added.

In Chemours' responses to the lawsuit, the company acknowledged that it's

violating its current permit but noted it's working with government regulators on an eventual fix.

over-polluting. The company quickly filed an appeal.

The West Virginia Rivers Coalition, which filed the lawsuit, declined to speak with NPR but did point to its 

"This is a victory for public health and the Ohio River," Autumn Crowe, the organization's deputy director, said in a statement. "The Court recognized what communities have known for years: Chemours has been polluting our water and ignoring its legal obligations."

 said that elevated levels of GenX could make it more challenging for water utilities like Louisville's to comply with federal rules for safe drinking water.

In regards to Chemours specifically, Goodmann told NPR that when government regulators issue the company's next

permit, he wants them to take into account the water treatment plants downstream.

"So what we do is manage risk, and we start that at the river," he said. "It sounds weird, but source water protection – keeping the stuff out of the river – is a big deal."

This story comes from NPR's health reporting partnership with 

Environmental News

Water

Morgan Watkins

Author

Workers at the drinking water plant in Louisville, Ky. saw a sudden spike in the level of a 'forever chemical.' They traced it up the Ohio River to a factory embroiled in a pollution lawsuit. 

More cities are seeing PFAS pollution in drinking water. Here's what Louisville found

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