Reconnaissance of Per- and Polyfluoroalkyl Substances (PFAS) in Selected Groundwater and Surface Water Sites in McHenry County, Illinois, 2020

Data were collected at 19 groundwater monitoring wells and 3 surface water locations across McHenry County, Illinois, in 2020 by staff from the U.S. Geological Survey (USGS) Central Midwest Water Science Center. Quality control samples (2 blanks and 1 replicate) were also collected to assess data reliability and precision. Samples were submitted to the USGS National Water Quality Laboratory in Denver, Colorado, and were analyzed for per- and polyfluoroalkyl (PFAS) substances in late 2022 and results provided in April of 2023. PFAS were detected in 16 of the 19 groundwater monitoring wells and in all 3 surface water sites sampled.