Repeated fire-fighter training at US military sites over decades had led to concentrations of perlfuorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) at or above the current US EPA health advisory level (70 ng/L).  However, PFOS and PFOA are but two of a number of per- and polyfluoroalkyl substances (PFASs) found at sites contaminated by aqueous film forming foams (AFFFs).  Precursor, which are PFAS that can degrade to dead-end, persistent PFASs including PFOS and PFOA are also found at these sites and have implications for the selection of PFAS analytical methods, site characterization, and remediation.