The objectives of this project are to 1) develop a reliable and cost-effective in situ method for assessing the extent and pathway of polyfluoroalkyl substances’ (aka “precursors,” denoted “PreFAS”) transformation under ambient field conditions by using in situ microcosms with the commercially available Bio-Trap® tool; 2) use the proposed in situ microcosm method and stable isotope probing (SIP) to document transformation pathways and indicative biomarkers of the biotransformation of four representative PreFAS compounds; and 3) study the environmental factors that may affect in situ PreFAS transformation such as groundwater geochemistry, nutrient availability, and microbial augmentation, among others.

This study proposes to use Bio-Trap® and SIP to conduct in situ microcosm tests to evaluate the transformation extent and pathways of four representative PreFAS in groundwater at aqueous film-forming foam (AFFF)-impacted site field conditions. The technical approach involves four tasks:

• Task 1 Method Development: An in situ microcosm assembly method will be developed for evaluating PreFAS transformation. Each assembly will include four in situ microcosm units representing four natural and engineered conditions: control, monitored natural attenuation, bio-stimulation, and bio-augmentation units. Each of the four selected PreFAS compounds will be loaded into the Bio-Trap®. A total of four assemblies will be prepared, one PreFAS per assembly.
• Task 2 Site Selection: A Department of Defense (DoD) AFFF-impacted site will be identified where in situ microcosms will be deployed.
• Task 3 Deployment of In Situ Microcosm Assemblies: In situ microcosm assemblies will be installed in four existing groundwater monitoring wells. The assemblies and associated samplers will be retrieved at the end of an eight-week deployment period.
• Task 4 Assessment of PreFAS Transformation and Microbial Species Involved: Groundwater and microbial samples collected through the in situ microcosms will be analyzed for PreFAS and potential transformation products, geochemical indicators, the SIP, and the in situ microbial groups enriched during the biotransformation process. These data will be used to address the basic research questions related to PreFAS transformation extent and pathways.

This research is expected to provide the following benefits:

• A low-cost and readily implementable method for documenting in situ PreFAS transformation would significantly enhance the ability to understand which transformation processes occur, the pathway and extent of transformation, and relevant terminal perfluoroalkyl acid transformation products.
• The technology developed via this project, if successful, will help to dramatically improve risk assessment and site management decisions at thousands of AFFF-impacted sites.
• The results of this work could have widespread applicability and promote follow-on field-based studies that would lead to a much better understanding of the transformation processes of a variety of PreFAS.

(Anticipated Project Completion - 2024)