Groundwater, surface-water, sediment, and associated quality-control samples were collected downgradient from a former fire training area and wastewater infiltration beds on Cape Cod, Massachusetts and analyzed for per- and polyfluoroalkyl substances (PFAS). Samples were collected between July 2016 and February 2019 following U.S. Geological Survey protocols. Field parameters reported include temperature, pH, specific conductance, and dissolved oxygen. Samples were analyzed for chloride, bromide, nitrate, sulfate, and dissolved organic carbon. PFAS samples were extracted using offline solid phase extraction and were analyzed for 24 PFAS at Harvard University using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Perfluoroalkyl acid (PFAA) precursor concentrations in aqueous samples were estimated from PFAA formation following application of the total oxidizable precursor assay. Methods for sample collection and chemical analysis are described in Savoie and others (2012) and Tokranov and others (2021). Savoie, J.G., LeBlanc, D.R., Fairchild, G.M., Smith, R.L., Kent, D.B., Barber, L.B., Repert, D.A., Hart, C.P., Keefe, S.H., and Parsons, L.A., 2012, Groundwater-quality data for a treated-wastewater plume near the Massachusetts Military Reservation, Ashumet Valley, Cape Cod, Massachusetts, 2006-08: U.S. Geological Survey Data Series 648, 11 p., 1 CD-ROM, http://pubs.usgs.gov/ds/648/. Tokranov, A.K., LeBlanc, D.R., Pickard, H.M., Ruyle, B.J., Barber, L.B., Hull, R.B., Sunderland, E.M., and Vecitis, C.D., 2021, Surface-water/groundwater boundaries affect seasonal PFAS concentrations and PFAA precursor transformations: Environmental Science: Processes and Impacts, https://doi.org/10.1039/D1EM00329A.