For water systems that had one or more detection of PFOS, PFOA or another contaminant, an average was calculated using the all samples collected. Samples with no detections were treated as zero when calculating the average, which in turn may skew the value lower when the contaminant is more common.
All locations represented on the map are approximate, and meant to visualize the general area of a contamination site or public water detection. Locations were mapped using the best available data preserved in official records, including data provided by tests of public drinking water systems, the Safe Drinking Water Information System, the Department of Defense report “Addressing Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoic Acid (PFOA),” and the Northeastern University Social Science Environmental Health Research Institute.
Levels listed are for the range of the total of all PFAS detected at the time of the tests and do not reflect whether a water system is treating the water to reduce levels.
Data on contaminated industrial and military sites was current as of March 2019.