As part of the PFAS Strategic Science Vision for the U.S. Geological Survey (“USGS”) and consistent with the National Defense Authorization Act for Fiscal Year 2020, which identified activities related to PFAS where USGS could provide support, the USGS undertook a study of PFAS in tap water from private and public supply wells across the U.S.  The results were recently published and indicate at least one PFAS was detected in 20% of private-well and 40% of the public-supply well samples. However, the proposed EPA MCL for PFOA and PFOS were exceeded in only 6.7% and 4.2% of the samples respectively.  The most frequently detected compounds were PFBS, PFHxS, and PFOA.  In areas where PFAS were detected, the study found the median PFAS concentrations were comparable between public supply well and private well samples.  Most of the detections were observed near urban areas and potential PFAS sources, including the Great Plains, Great Lakes, Eastern Seaboard, and Central/Southern California regions.

The study focused on tap water, noting that most studies to date have focused on samples from community water supplies, which do not account for distribution system factors, e.g., plumbing material with PFAS or sorption/degradation in the supply network.  The study also sought to obtain data on tap water from private wells noting that there is limited PFAS data available for private wells and that approximately 40 million people in the U.S. rely on private wells for drinking water.  To conduct the study, the USGS study analyzed 716 tap water samples collected from residences, businesses, and drinking-water treatment plants across the U.S. from 2016 to 2021. Sampling locations were categorized as low (e.g., National Park Service/US Fish and Wildlife Service sites), medium (residential and rural areas), and high (targeted samples near reported PFAS sources) impacted areas. The study tested for 32 individual PFAS compounds using a method developed by the USGS National Water Quality Laboratory.  As expected, sites classified as low impact had the lowest prevalence of PFAS compared to sites near known PFAS sources, whereas PFAS varied widely among sites classified as medium.  The report recommends further monitoring of tap water, particularly from private wells, underserved communities, and small community water supplies.