With the recognition that per- and polyfluoroalkyl substances (PFAS) and other emerging chemicals contaminate the subsurface and pose health risks, significant progress has been made through laboratory, field, and modeling research. This session invites papers on recent advancements that enhance models, improve site characterization, and address new challenges in meeting regulatory goals and policy development. Contributions to traditional contaminants are also welcome to benefit from lessons learned that will be of use to PFAS and other emerging contaminants.

Recent research on PFAS has raised concerns and led to stricter regulation in many countries. PFAS combines aqueous mobility, extreme recalcitrance and adverse health effects at very low concentrations which requires immediate actions to reduce their release and spreading, better understand their transport and associated risks, and remove them from the environment. The unique properties of PFAS also pose many additional challenges for groundwater management, risk assessment and remediation. Many processes in both the groundwater and vadose zones need to be better understood and there is an urgent need for improved remediation and mitigation methods.

PFAS have produced additional challenges to our basic knowledge and models of solute fate and transport in the subsurface. The problem of transport of dissolved chemicals in vadose zone soils and groundwater has previously been extensively studied in applications of soil physics and hazardous waste chemicals contaminating groundwater. However, most contaminant transport studies and models focus on single solutes, with all solutes assumed to behave, for the most part, independently (i.e., the dilute solution approximation). Recent research has studied the basic processes of retention and transformation of PFASs in unsaturated and saturated soils under much more complex conditions of flow conditions where water dynamics determine the rates and types, not just the transformation. In upscaling this knowledge from laboratory batch and column testing conducted under idealized homogeneous soil conditions, it is required to understand the behavior under conditions of natural heterogeneities and multi-dimensional flow. This session will have particular focus on complex contaminant transport phenomena and their upscaling from the laboratory to real field sites.