Understanding the processes of fate and transport for per- and polyfluoroalkyl substances (PFAS) in the environment is critical for the development of lines of evidence and benchmarks for assessing the effectiveness of PFAS remedies. Fate and transport processes relevant to PFAS are identified as a critical priority research need in the September 2017 Summary Report of the SERDP and ESTCP Workshop on Research and Demonstration Needs for Management of AFFF-Impacted Sites. The variety of PFAS present in Aqueous Film-Forming Foam (AFFF) product formulations and the natural variance of impacted sites complicates typical fate and transport evaluations. As a result, fate and transport processes for PFAS are a critical data gap for assessing the effectiveness of PFAS remedies. This data gap defines a need for a fate and transport evaluation approach that eliminates chemical unknowns and natural environmental variance.

The technical objective of this project is to utilize a scaled aquifer, where chemistry and aquifer conditions can be controlled, and an aggregation and analysis of data from numerous AFFF-impacted Department of Defense (DoD) sites along the east coast, to determine relevant factors controlling fate and transport of PFAS in the subsurface. The focus of this project is identification of relevant and quantifiable factors controlling fate and transport by analysis of aggregated and compiled data, minimizing site heterogeneity, taking advantage of the many AFFF-impacted sites where the principal investigators and co-performers are already working, and collecting and analyzing data from controlled testing of PFAS in a scaled aquifer, an approximately one-fifth scale physical aquifer at the US Army Corps of Engineers Scaled Aquifer Testing Facility. The technical questions to be answered by this project include: 1) What relevant and quantifiable fate and transport processes are identifiable from analysis of aggregated data (i.e., applicable to most sites and therefore important as a line of evidence in assessing a remedy)? 2) What relevant and quantifiable fate and transport processes (important from a remedy design and assessment perspective) are identifiable from analysis of data collected in a controlled environment where chemistry and natural variance can be limited?

Researchers will collect, aggregate, and analyze PFAS, geochemical, and physical data to identify relevant and quantifiable fate and transport processes. Task 1 includes collection and analysis of data from the scaled aquifer where relevant factors such as the effect of gravity and potential for vertical partitioning of PFAS under lateral flow conditions, sorption and transport attenuation of PFAS under continuous source conditions, differences in transverse dispersivity, initial effect of matrix diffusion and subsequent breakthrough curves in saturated soil for PFAS over time will be evaluated. Task 2 involves collection and aggregation of available data from numerous AFFF-impacted DoD sites where the principal investigators and co-performers are already working. A data driven analysis to determine common factors affecting fate and transport of PFAS will be performed. Simple statistics as well as machine learning and multivariate statistical analyses will be applied to identify common fate and transport factors of PFAS that can be used to design broadly applicable remedies for AFFF-impacted sites and evaluate remedy effectiveness. Task 3 includes data compilation and analysis, and final reporting.

This project is designed to resolve the critical data gap of relevant fate and transport processes for PFAS. Use of the controlled scaled aquifer will also allow an understanding of source depletion. The results will be extremely valuable to the DoD, other government agencies, and the private sector, as lines of evidence for evaluating remedy effectiveness, input for remedial design, or constraining parameters for groundwater flow and transport models in both the investigative and remedial phases. (Anticipated Project Completion - 2023)