The U.S. Geological Survey (USGS), in cooperation with the Miami Conservancy District, Dayton, Ohio, in 2019 and 2020 investigated concentrations of per- and polyfluoroalkyl substances (PFAS) in groundwater from the Great Miami buried-valley aquifer (GM-BVA) of southwestern Ohio. Data in this release include reporting limits and detection limits from PFAS analyses of groundwater and quality-control samples collected or prepared by this study, including sequential replicate samples of groundwater, equipment blanks and source-solution blanks prepared before or during groundwater sampling. The 23 wells used for sampling were identified and sampled previously by the USGS National Water-Quality Assessment Program to assess the occurrence of a variety of inorganic and organic contaminants in the GM-BVA. Wells where groundwater was sampled and quality-control samples were prepared were from parts of the GM-BVA in Butler, Champaign, Clark, Greene, Hamilton, Miami, Montgomery, Shelby and Warren Counties within the Great Miami River, Little Miami River, and Whitewater River Basins. Groundwater and quality-control samples were analyzed for PFAS using different adaptations of the EPA 537.1 method at a contract laboratory using one proprietary adaptation (method 1; Bureau Veritas, Mississauga, Ontario, Canada) and at a different contract laboratory using a slightly different proprietary adaptation (method 2; SGS North America Inc., Orlando, Florida. The groundwater sampling and analyses were done to inform the public and area stakeholders about concentrations of PFAS compounds in the GM-BVA.