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The U.S. Geological Survey (USGS) New England Water Science Center works with national programs and other partners on interpretive hydrologic science, such as determining the drivers of PFAS contamination in groundwater used for drinking-water supplies in the United States.

Map showing locations of aquifer systems and drinking-water well networks in the eastern U.S.
Map showing locations of aquifer systems and drinking-water well networks in the eastern United States. Wells shown with white symbols indicate that perfluoroalkyl and polyfluoroalkyl substances (PFAS) were not detected, and those shown with other colors indicate that PFAS were detected.

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are widely used in many of the products we use in everyday life. As a result, PFAS in the environment are widespread, and some PFAS are known or suspected to be associated with adverse human-health effects. Sources of water used for drinking-water supplies, particularly those sources from groundwater, are highly susceptible to contamination from PFAS. Groundwater supplies 35 percent of drinking water in the United States. Although there has been much discussion on the topic, knowledge of the factors that are related to the presence of PFAS in groundwater has been lacking. To address this need, USGS scientists analyzed more than 250 samples of groundwater used for drinking water in the eastern United States to evaluate the occurrence of PFAS in groundwater and built a model to identify potential factors related to PFAS occurrence. The data revealed that 60 percent of public-supply and 20 percent of domestic-supply wells contained PFAS. In addition, many samples with PFAS also contained tritium, chloride, sulfate, dissolved organic carbon, manganese, and iron. The interactions among these constituents and other features were examined to identify the most important factors related to PFAS occurrence in groundwater used for drinking water is described in a new report: Perfluoroalkyl and Polyfluoroalkyl Substances in Groundwater Used as a Source of Drinking Water in the Eastern United States.

Graph showing factors related to PFAS occurrence in public- and domestic-supply wells in the eastern U.S.
Graph showing factors related to the occurrence  of perfluoroalkyl and polyfluoroalkyl substances (PFAS) in public- and domestic-supply wells in the eastern United States. 
The presence of tritium, an indicator of modern, or recently recharged groundwater, was the strongest predictor or PFAS in wells.  Distance to the nearest fire training facility, dissolved organic carbon concentration, urban land use, the sum of all volatile organic compounds, sulfate, and chloride were also strong predictors.
Blue tick marks along the x-axes of the inset panels indicate the variable minimum, maximum, and deciles of the model training dataset. Dist., distance; DOC, dissolved organic carbon; Pct., percent; VOC, volatile organic compound; Ag., agriculture; Est. N, estimated nitrogen; Mft, manufacturing; FRS, facility registration service; Mfg, manufacturing; Prdts, products; TU, tritium unit; km, kilometer; mg/L, milligram per liter.
USGS Researcher Fills a Sample Container from a Dripping Spigot.
USGS Environmental Health Program Scientist sampling a public-supply well in Minneapolis/St Paul, MN, August 2019 (Photo credit, Shannon Meppelink, Central Midwest Water Science Center).

Relatively little is known about potential effects of complex PFAS mixtures in drinking-water sources on human health, but better understanding of the composition of those mixtures could help inform toxicity studies. The relatively common occurrence of multiple PFAS in the samples has implications for the sum of PFAS compounds (ΣPFAS) and the complexity of PFAS mixtures in well water. ΣPFAS strongly correlated with the number of PFAS detected in the samples (Spearman’s rho = 0.91; p < 0.001) (fig. 2C).  Networks NECBS, NECBD (both in New England), and SURF have relatively large fractions of samples containing >6 PFAS (37 to 54 percent) (fig. S2A). Not surprisingly, networks with the largest numbers of co-occurring PFAS (New England has the top two in this study) also have the largest numbers of unique PFAS mixtures relative to the number of samples in the networks (fig. S2B). In New England, in the shallow aquifer (NECBS), 68 percent of the samples contain combinations of two or more PFAS that are unique to that sample. Overall, three PFAS occur in ≥80 percent of the mixtures (perfluorooctanoate [PFOA] > perfluorobutanesulfonic acid [PFBS] > perfluorooctane sulfonate [PFOS]), but the dominant PFAS in mixtures vary between networks.

Broadly, USGS researchers found that groundwater affected by modern anthropogenic activity appears to be associated with PFAS, given significant relations between PFAS detections and variables such as tritium, urban land use, VOCs, and pharmaceuticals. Modeling indicates that it is possible to predict PFAS occurrence based on the hydrologic, geochemical, and geospatial explanatory variables investigated here.

For more information about this study or the report, contact Andrea Tokranov ( or Joseph Ayotte (

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