GRAND RAPIDS, Mich. (WOOD) — A new study by the U.S. Geological Survey found that more than 20% of the nation’s population relies on water sources that contain a detectable amount of PFAS — and Michigan is a hot spot.

The results of the USGS study were recently published in the academic journal Science. Using more than 1,200 groundwater samples, the researchers put together a predictive model to estimate the spread of PFAS contamination, factoring in things like well depth.

“If you have shallow groundwater, and you’re near an urban area, and there are (nearby) industries that use PFAS, then you’re (very likely to have a contaminated source),” USGS researcher Bruce Lindsey told Bridge Michigan.

The model estimated that anywhere from 71 million to 95 million Americans get their drinking water from a contaminated source. In Michigan, the number is between 2.3 million and 3.2 million — approximately 30% of the total population.

Of those residents, up to 1.8 million get their water from municipal systems, which are monitored regularly and generally treated to remove PFAS. However, up to 1.4 million people draw their water from unguarded private wells.

Andrea Tokranov is a research hydrologist for the USGS and co-author of the study. She says it’s no secret that the U.S. has widespread PFAS contamination, but a predictive model could help environmental officials focus on the hardest hit areas.

“This new predictive model can help prioritize areas for future sampling to help ensure people aren’t unknowingly drinking contaminated water,” Tokranov said in a statement. “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 suppliers do.”

Florida and California were found to have the most contaminated groundwater sources for municipal systems, while Michigan, Florida, North Carolina, Pennsylvania, New York and Ohio have the most contaminated private wells.

A map shows large swathes of Michigan with almost near certainty of widespread PFAS contamination, including the Detroit metro area, Grand Rapids, Kalamazoo and large stretches of the Lake Michigan shoreline, from Montague down through New Buffalo.

PFAS — or per- and polyfluoroalkyl substances — are a large group of compounds first developed in the 1940s and incorporated into all sorts of products for waterproofing and heat resistance. Decades later, research showed that PFAS compounds take a long time to break down organically and can build up in the human body, causing serious health problems, including cancer. According to the National Institute of Environmental Health Services, there are more than 15,000 known PFAS compounds.

The Environmental Working Group says there are now more than 5,000 confirmed PFAS-contaminated sites across the United States, including at least one in all 50 states, Washington D.C. and two American territories. As of last month, 329 have been identified in Michigan.