The goal of this project is to synthesize the relevant findings from SERDP & ESTCP-funded research on the fate and transport of per- and polyfluoroalkyl substances (PFAS) in the vadose zone into a coherent body of knowledge that can be readily interpreted by consultants, remedial project managers, and regulators. Current and impending federal regulations on the cleanup and treatment of PFAS will require that relevant stakeholders understand the fundamental research conducted on vadose zone transport processes. The primary objectives of this project are to 1) identify and gather a group of leading experts in vadose zone transport of PFAS for a consensus-building workshop, and 2) translate the key findings of the workshop into information deliverables (i.e., fact sheets, handbooks, videos) and in-person presentations (i.e., webinars and a workshop).

The project will begin with identifying a coalition of suitable experts willing to participate in discussions of relevant PFAS fate and transport processes in the vadose zone. The coalition will be comprised of representatives from academia, consulting, regulators, site managers, and SERDP & ESTCP. A one-to-two-day breakout meeting will be held in Spring 2026. Relevant discussion topics will be selected by the moderators before the meeting and forwarded to the group of experts for approval and input before the workshop. Based on the feedback, a series of questionnaires will be developed for the experts to fill out prior to the workshop. The workshop will utilize the Delphi method for consensus building, which consists of a series of evolving questionnaires formulated to eliminate processes where there are disagreements and come to a consensus on relevant topics. Once consensus on a selection of topics has been reached, the workshop will conclude, and the moderators will begin the work of synthesizing findings into written and presentation formats.

Most PFAS source zones – particularly source zones impacted with aqueous film-forming foam – are in the vadose zone. Vadose zone processes are distinct from saturated groundwater transport processes and are often highly transient. Current approaches have proven ineffective for managing and understanding PFAS source zones. By developing consensus on the key processes affecting PFAS fate and transport in the vadose zone, a succinct body of literature can be created that can be readily interpreted by environmental practitioners. This will be coupled with practical recommendations for PFAS remedial investigations and emerging management strategies. An improved understanding of vadose zone processes by relevant environmental practitioners will lead to improved remedial designs for PFAS-impacted source zones, ultimately strengthening the operational readiness and capability of warfighters. (Anticipated Project Completion - 2026)