The overall goal of this project is to assess the repeatability and representativeness of porewater concentrations of per- and polyfluoroalkyl substances (PFAS) in aqueous film-forming foam (AFFF) source areas using porous cup suction lysimeters, and to correlate potential variability in PFAS concentrations to site conditions. Use of lysimeter data from previous and ongoing site investigations will be a key component of this approach. Specific objectives include:

• Evaluation of temporal variability in PFAS porewater concentrations measured in lysimeters emplaced within AFFF source areas.
• Statistical determination of the extent to which factors such as climate, storm events, and geology/heterogeneity impact repeatability in lysimeter data.
• Evaluation of the local equilibrium assumption and sorption reversibility on PFAS porewater concentrations measured in field-deployed lysimeters.
• Development of key findings and recommendations for limitations on lysimeter data interpretation, the type of ancillary data (e.g., precipitation, soil moisture, geology) that is required to properly assess lysimeter data, and identification of additional tools/techniques that may be needed for data interpretation.

Collected porewater data will be evaluated with respect to corresponding climatic, seasonal, geologic, and precipitation/moisture data from a total of 12 AFFF-impacted source areas. Data acquisition from these 12 source areas will rely heavily upon available databases, site reports, field notes and logbooks, personal communications, and published papers. Open-source agroclimatological datasets will be utilized to provide ancillary data (e.g., precipitation data, climate data, etc.). Statistical tools (e.g., T-tests and/or analysis of co-variance) will then be applied to determine if temporal repeatability is associated with any of these factors. A correlation matrix will be created using PFAS porewater concentrations and all other agroclimatalogical data to identify the processes that are most correlated with PFAS porewater concentration for individual locations or subregions.

In addition, PFAS porewater concentrations in collected intact cores will be measured at the bench scale to determine equilibrium porewater concentrations. Comparisons of these equilibrium values to the field porewater values will provide insights into potential mechanisms controlling variation in PFAS concentrations measured in the field. Desorption testing with isotopic exchange will be performed to provide insight into the desorption kinetics. Finally, a representative site will be selected for temporal lysimeter monitoring for one year (12 sampling events), thus providing a unique high temporal resolution dataset to further assess repeatability.

This study will provide a robust evaluation of the lysimeter data being collected as part of ongoing source area investigations. A key result will be identifying when to expect temporal variation in lysimeter sampling (i.e., geological conditions, precipitation conditions, etc.). Another expected outcome of this project is recommendations on assessing the appropriateness of the lysimeter data and basic guidelines on how to perform an appropriate PFAS lysimeter sampling program. Together, this information can serve as an initial guide regarding how lysimeter data should be collected and interpreted. Overall, this is expected to provide improved monitoring approaches and more reliable and defensible field data, which will ultimately lead to more cost-effective PFAS treatment options that are protective of the warfighter and their communities around military installations. (Anticipated Project Completion - 2027)