Approximately 71 to 95 million people in the lower 48 states (more than 20% of the nation’s population) may depend on groundwater containing detectable concentrations of perfluoroalkyl and polyfluoroalkyl substances, also known as PFAS, for their drinking water supply. . These findings are according to a U.S. Geological Survey study released Oct. 24.
Predictive modeling results can help the public, water providers, and regulators understand the potential for PFAS contamination, guide future studies, and inform strategic water resources planning.
USGS scientists are the first to report national estimates of the presence of PFAS in untreated groundwater that supplies water to public and private wells. This research also provides the first estimate of the number of people nationwide who are potentially affected by PFAS-contaminated groundwater.
Along with a scientific report, the USGS published an interactive map online so users can view estimates of the probability of occurrence of PFAS. Note that predictive results should be evaluated at the state, regional, and national scale rather than at the individual household level. The probability estimates correspond to the presence of PFAS in groundwater and do not take into account any subsequent actions taken by states, municipalities, or individuals to treat drinking water. The model does not include estimates of PFAS concentrations; Testing is the only way to confirm the presence of contaminants.
Exposure to certain PFAS can cause adverse health risks to people, according to the U.S. Environmental Protection Agency. PFAS are a group of synthetic chemicals used in a wide variety of common applications, from box liners to fast food and non-stick cookware to fire fighting foams and other purposes. PFAS are commonly called “permanent chemicals” because many of them do not break down easily and can build up over time, making them a problem for drinking water quality.
“The findings of this study indicate widespread PFAS contamination in groundwater used for public and private drinking water supplies in the U.S.,” said Andrea Tokranov, USGS research hydrologist and lead author of this study. . “This new predictive model can help prioritize areas for future sampling to help ensure that people do not unknowingly drink contaminated water. This is especially important for private well users, who may not have information about the quality of the water in their region and may not have the same access to testing and treatment that public water providers do.
The EPA has established legally enforceable levels, called maximum contaminant levels, for six types of PFAS in drinking water. The EPA regulates the public water supply, and some states have additional regulations for drinking water. Some homes use private water supplies, where residents are responsible for the maintenance, testing and treatment of their drinking water. Those interested in treatment processes and testing options can read the EPA’s guidance or contact their state officials or water supplier.
The states with the largest populations relying on public water supplies with potentially contaminated groundwater sources are Florida and California. As for private wells, Michigan, Florida, North Carolina, Pennsylvania, New York and Ohio have the largest populations that rely on potentially contaminated groundwater.
The study also presents data according to percentage of the population. In Massachusetts, for example, the source water of between 86% and 98% of people who rely on groundwater from public water supplies could be contaminated with PFAS. In Connecticut, the water source of between 67% and 87% of people who rely on groundwater from private wells could be affected. Details by state can be seen in Tables S6 to S8 of the report.
“To derive these estimates, the team analyzed 1,238 groundwater samples collected by USGS scientists and determined how factors such as urban development and well depth can affect the occurrence of PFAS,” Tokranov continued. “With that information, a detailed machine learning model was developed and used to identify which geographic areas have a higher likelihood of contamination. That information was combined with existing USGS research on the number of people in a given area who rely on groundwater to drink. to establish population estimates.”
Scientists present separate estimates for public and private wells because they typically receive water from different depths underground. Public wells that use groundwater as the primary water source are typically deeper than private wells.
There are more than 12,000 types of PFAS, and not all can be detected with current tests; The USGS study tested for the presence of 24 common types. USGS estimates consider the presence of at least one of those 24 types of PFAS. The most frequently detected compounds were perfluorobutane sulfonate known as PFBS, perfluorooctane sulfonate known as PFOS, and perfluorooctanoate known as PFOA.
This research provides a broad perspective for the 48 contiguous states and presents state-level estimates. The scientists did not analyze specific cities in detail or provide estimates on the types of PFAS present or PFAS concentrations.