Forever chemicals have been detected in many sources of groundwater nationwide. (zimmytws/Shutterstock)
In a nutshell
- A new USGS study estimates that 71-95 million Americans rely on groundwater containing detectable levels of PFAS, also known as “forever chemicals”, before any treatment. These synthetic compounds have been linked to cancer, fertility issues, and other health risks.
- The study’s predictive model shows PFAS contamination is widespread, particularly in urban areas, shallow groundwater sources, and regions with sandy or clay-heavy soils. States like Florida, California, Massachusetts, Michigan, and North Carolina have some of the highest affected populations.
- While many public water systems treat PFAS, private well owners often don’t have access to testing or treatment. The USGS released an interactive map to help people understand regional contamination risks, and the EPA now regulates six types of PFAS in drinking water.
PEMBROKE, N.H. — An invisible contamination problem has been brewing in America’s underground water supplies for decades. New research from the U.S. Geological Survey has finally mapped its extent, showing that between 71 and 95 million Americans rely on groundwater containing detectable levels of “forever chemicals,” synthetic compounds linked to cancer, fertility issues, and other health problems.
This research, published in Science, includes a first-of-its-kind map that comes as public awareness about these contaminants grows. Despite mounting health concerns, we’ve had major blind spots in understanding how widespread this contamination truly is, especially for small towns and rural homes with private wells.
“This study’s findings indicate widespread PFAS contamination in groundwater that is used for public and private drinking water supplies in the U.S.,” says lead study author Andrea Tokranov, a USGS research hydrologist, in a statement. “This new predictive model can help prioritize areas for future sampling to help ensure people aren’t unknowingly drinking contaminated water. This is especially important for private well users, who may not have information on water quality in their region and may not have the same access to testing and treatment that public water suppliers do.”
What Are “Forever Chemicals” and Why Should You Care?
PFAS (per- and polyfluoroalkyl substances) earned their “forever chemicals” nickname because they hardly break down in the environment. These synthetic chemicals have been around since the 1930s and show up everywhere, from non-stick pans and waterproof jackets to fast-food wrappers and firefighting foam. Their widespread use has led to environmental contamination, with drinking water being a major concern.
The USGS scientists collected groundwater samples from wells across the country between 2019 and 2022. These samples were taken before any treatment and tested for 24 different types of PFAS. The results? At least one type of PFAS turned up in 37% of the samples.
The team then built a computer model to estimate where PFAS likely contaminates groundwater across the Lower 48 states. They looked at factors like urban development, well depth, soil type, septic systems, and distance from potential PFAS sources like airports or factories.
The Surprising Scope of the Problem
When applied nationwide, the model revealed contamination on a massive scale. The affected areas cover roughly 5.5-13% of public water supply zones and 7.2-15% of areas served by private wells across the contiguous United States.
These affected areas are home to millions of Americans. About 50-66% of people who rely on groundwater for drinking, whether from a utility or private well, may be consuming water with detectable PFAS before any treatment.
Florida and California had the highest number of people affected through public water (9.5-13 million), while Massachusetts had the highest percentage of its population at risk (86-98%). For private wells, Michigan, Florida, North Carolina, Pennsylvania, New York, and Ohio topped the list.
The USGS has published an interactive, online map so you can check the probability estimates for your region. Just remember, these results are meant for regional understanding, not individual household assessment. Also, these estimates show where PFAS might exist before any treatment, and many public water systems already test and treat for these chemicals.
Where “Forever Chemicals” Most Often Lurk
Urban areas, places with shallow groundwater, and densely populated regions had stronger connections to PFAS detections. Public and private wells were evaluated separately because they typically draw water from different depths. Public wells usually reach deeper underground than private wells.
Soil type also played a surprising role. Sandy soils generally had higher PFAS levels, probably because chemicals move through sand more easily. Medium-clay soils seemed to block PFAS better. But oddly, very clay-heavy soils showed increased contamination, possibly because clay-rich soils can crack, creating channels for chemicals to reach groundwater.
The most commonly found compounds were ones you might recognize from news headlines: PFBS, PFOS, and PFOA—all now regulated in drinking water by the EPA.
What This Means for Your Health and Community
The EPA recently set legal limits for six types of PFAS in drinking water. While many public water suppliers have started monitoring and treating these chemicals, such treatment can be expensive and difficult for small or low-income communities. People with private wells, who rarely test or treat their water, face even greater risks.
In Connecticut, for example, groundwater feeding private wells for 67 to 87% of well users could contain PFAS. If you’re worried about your water, you can explore treatment options through EPA guidance or by contacting state officials or your water supplier.
PFAS contamination zones may continue to expand over time as polluted water filters down through aquifers, given how extensively these chemicals have been found in air, rain, soil, and many other environmental samples.
This study gives us a powerful new tool for tackling “forever chemicals” in America’s drinking water. But it also raises an unsettling question: With over 12,000 types of PFAS out there, and this study only testing for 24 common ones, what else might be flowing from your tap that we haven’t even measured yet?
Paper Summary
Methodology
The USGS scientists collected samples from three types of well networks spanning major aquifer systems across the country. These included public supply wells, observation wells in urban and agricultural areas, and domestic wells. They analyzed the samples for 24 different PFAS compounds and built a predictive model using a technique called eXtreme Gradient Boosting. The model incorporated 25 potential PFAS sources and various environmental factors to predict contamination probabilities for each 1 km × 1 km grid cell across the contiguous United States.
Results
The model predicts that between 71 million and 95 million Americans rely on groundwater with detectable PFAS concentrations—approximately 50-66% of all people who use groundwater for drinking. For public water supplies, Florida and California had the highest affected populations, while Massachusetts had the highest percentage of its population at risk (86-98%). For domestic wells, Michigan, Florida, North Carolina, Pennsylvania, New York, and Ohio had the most people potentially affected. The model correctly predicted PFAS occurrence in about two-thirds of cases when tested against independent datasets.
Limitations
The model predicts PFAS in untreated groundwater, so it may overestimate actual exposure since many public water systems already test for and treat these chemicals. It works best for regional trends rather than predicting contamination at specific locations, and users should not interpret results for individual households. The study tested for only 24 of the over 12,000 existing PFAS compounds, potentially underestimating total PFAS contamination. Additionally, well depths were unknown for some validation datasets, which affected comparison accuracy.
Discussion and Takeaways
This research provides the first national estimate of how many Americans potentially drink PFAS-contaminated groundwater. The findings highlight environmental justice concerns, as removing PFAS from drinking water is expensive and often beyond the means of poorer communities. Private well owners, who typically don’t have regular water testing or treatment, face particularly high risks. The model provides a valuable tool for prioritizing areas for testing and directing limited resources toward communities at highest risk. Urban land use, well depth, and soil clay content were identified as the strongest predictors of PFAS contamination.
Funding and Disclosures
This research was supported by the USGS National Water Quality Program, USGS Ecosystems Mission Area Environmental Health Program, and California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment Program. The authors declared no competing interests, and all data and model files were made publicly available as a USGS data release.
Publication Information
The study, “Predictions of groundwater PFAS occurrence at drinking water supply depths in the United States,” was published in the journal Science (Volume 386, pages 748-755) in November 2024. Andrea K. Tokranov of the U.S. Geological Survey led the research team, which included 11 co-authors from various USGS offices across the United States.
