The development of diffusive equilibrium, high-resolution passive samplers to measure perfluoroalkyl substances (PFAS) in groundwater.

Per- and poly-fluoroalkyl substances (PFAS) are a group of anthropogenic, highly recalcitrant organic compounds consisting of thousands of individual species that are of increasing importance as groundwater contaminants. In-situ measurements of PFAS would be useful to better understand vertical profiles and mobility, contamination in partially saturated media, and to reduce sampling artifacts associated with groundwater collection and analysis. Diffusive equilibrium, high-resolution passive samplers (HRPPs) can be directly driven (>10 m) in sediments or groundwater. The samplers equilibrate with porewater through diffusion across the sampler membrane, providing high spatial resolution (sample every 20 cm) porewater concentrations of dissolved species. The objective of this study was to develop an HRPP to measure PFAS in contaminated groundwater and saturated media. To achieve this objective, a screening study was conducted to demonstrate quantitative measurement of selected PFAS as well as the kinetics of uptake into a sampler using both nylon and stainless steel membranes. Utilizing the results of the screening study, a prototype sampler was demonstrated in a laboratory flow box. Over a deployment period of 28 days, concentrations of several perfluoroalkyl carboxylic acids (PFCAs), a perfluoroalkyl sulfonate (PFSA), and a precursor PFAS reached equilibrium with porewater (sampler concentration >90 percent of porewater concentration). Application of these samplers could provide improved understanding of the behavior of PFAS in saturated or partially saturated groundwater systems and allow better assessment of fate and transport in the subsurface. Reliable subsurface site characterization will yield robust site assessments, conceptual models, and improve remediation designs as well as increase confidence in post remedial assessments at PFAS-impacted locations.