Every day, the Ohio River sends billions of gallons of water flowing past Louisville's pumping station, where the Kentucky 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 in the U.S., Louisville Water regularly checks for PFAS — per- and polyfluoroalkyl substances.
That's a class of chemicals used by manufacturers for decades to make things like nonstick pans, cosmetics, raincoats, food wrappers, and firefighting foam.
Research studies have linked PFAS to health risks like cancer, reduced immune system functioning, high cholesterol, and developmental delays in children.
They're also known as "forever chemicals" because their strong chemical structures make them degrade incredibly slowly in the environment.
Today, they litter soil and water sources around the world and can be found in the blood of almost everyone in the U.S.
One type of PFAS that the Louisville water technicians are tracking is HFPO-DA, also known by a trade name, GenX.
Just over a year ago, workers noticed an unexpected increase in the level of GenX detected in a sample of the raw, untreated water drawn from the Ohio River for filtering and processing.
The GenX levels Louisville found in December 2024 were 15 times the reading from the previous month: 52 parts per trillion versus 3.4 ppt.
"A part per trillion is like one second in 32,800 years. Put your head around that, right?" said Peter Goodmann, the city utility's director of water quality and research.
He offered another way to think of it: One part per trillion would be a single drop of water in 20 Olympic swimming pools.
Goodmann told KFF Health News and NPR he wasn't worried about local customers' safety, because the increased levels were still pretty low.
Risks posed by low PFAS concentrations are measured over a lifetime of exposure, he said. And recent data from Louisville shows the PFAS levels in city drinking water fell back within planned federal safety limits.
Plus, water is just one way people can be exposed to PFAS, Goodmann 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.
Louisville Water's data showed that the elevated levels of GenX in the water sample drawn in December 2024 fell once the water underwent typical treatment and filtering.
Federal regulation fight
The federal government has long regulated the levels of certain contaminants in drinking water, such as arsenic, E. coli, and lead.
But the Environmental Protection Agency didn't issue regulations regarding PFAS until 2024, during the final year of the Biden administration. The new limits applied to six types of PFAS in drinking water. Starting in 2029, utilities that exceeded the limits would have been required to treat the water to reduce the contamination.
But after Donald Trump's reelection, new EPA administrator Lee Zeldin announced 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, attributing the change in part to the financial burden on rural water plants.
Many utilities, large and small, may need to invest in infrastructure to remove PFAS.
A federal study 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 anticipated 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.
Finding the source
Goodmann's team traced the increased levels of PFAS up the Ohio River, past Cincinnati, and through Appalachian forests, all the way to a West Virginia factory about 400 miles upstream.
There, the Chemours Co. uses GenX to make fluoropolymers, a plastic critical to the semiconductors that power phones.
Its Washington Works facility near Parkersburg, West Virginia, has a history of PFAS pollution.
A lawyer, Robert Bilott, fought the plant's previous owner, DuPont, in court, ultimately revealing the company knew that a type of PFAS it was using, PFOA, was toxic but didn't disclose that information.
DuPont went on to settle various lawsuits that claimed it contaminated local environments with forever chemicals. The company has repeatedly denied wrongdoing.
Chemours was spun off from DuPont in 2015.
The Louisville Water 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.
In Chemours' responses to a lawsuit filed by a West Virginia environmental group, the company denied its discharges were 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."
PFAS removal will challenge water utilities
Under current federal environmental regulations, Chemours can release some chemicals into the Ohio River. But it has exceeded the legal limits repeatedly over several years, according to court filings and the EPA.
That's why the West Virginia Rivers Coalition filed its lawsuit in 2024.
The EPA took enforcement action 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 the 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 KFF Health News and NPR, citing ongoing litigation, except to point out that Louisville's "finished drinking water is safe for consumption," with PFAS levels below the EPA's regulatory limits, as stated on Louisville Water's website and in the annual water quality report from 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 Nick Hart, the water policy director for the Kentucky Waterways Alliance.
"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," he said, "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 such as PFAS from getting into a community's drinking water supply is easier and less costly compared with removing it on the back end, he added.
In Chemours' responses to the lawsuit, the company acknowledged that its violating its current permit but noted it's working with government regulators on an eventual fix.
The federal judge in the case, Joseph Goodwin, decided that wasn't fast enough.
In August, he ordered Chemours to immediately stop overpolluting. The company quickly filed an appeal.
The West Virginia Rivers Coalition declined to speak with KFF Health News and NPR but did point to its August news release on the judge's ruling.
"This is a victory for public health and the Ohio River," Autumn Crowe, the organization's deputy director, said in the statement. "The Court recognized what communities have known for years: Chemours has been polluting our water and ignoring its legal obligations."
In a court filing for the case, Goodmann said that elevated levels of GenX could make it more challenging for water utilities such as Louisville's to comply with federal rules for safe drinking water.
In regard to Chemours specifically, Goodmann told KFF Health News and 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."
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