Per-and polyfluoroalkyl substances (PFASs) as key components in aqueous film forming foams (AFFF) have led to growing incidences of environmental contamination. The aim of this study was to investigate a novel diffusion based passive sampling device comprising of microporous polyethylene (PE) for the long-term time-integrative monitoring of PFASs in groundwater systems. PE passive samplers (PEs) were deployed for 83 d and calibrated at five AFFF impacted groundwater sites representing different PFASs concentration levels (ΣPFAS 0.001 to 0.1 ng mL−1). Grab samples were collected simultaneously. Linear accumulation of 12 PFASs (r2 ≥ 0.84) were observed in the PEs over 83 d and PFASs sampling rates were 2–5 mL d−1. Estimated mean half-times to equilibrium for PFASs ranged between 122 and 490 d. A separate validation study compared PEs and grab sampling during a 93 d field deployment, at seven groundwater sites near a fire fighting training ground. Seventeen PFASs were detected in PEs and fifteen in grab samples. PEs showed higher sensitivity for precursors (i.e. 4:2 FTS and FOSA). Time-weighted-average water concentrations across all validation sites for all PFASs determined from PEs were strongly correlated (r2 = 0.98) with grab samples, (within range 0.3–60 ng mL-1 PFOS). Results represent the first application of passive sampling technology for the quantitative assessment of PFASs in groundwater systems.