The overall objective of this project is to implement an innovative methodology for high resolution characterization of per- and polyfluoroalkyl substance (PFAS) source zones in the vadose zone and improve site conceptual models of PFAS fate and transport. The methodology will address a critical need for PFAS fate and transport assessment by incorporating geophysical tomography images of field-scale soil surface area (SSA) and air-water interfacial area (AWIA) into the tiered PFAS-LEACH models (developed in ESTCP Project ER21-5041) and validating against lysimeter-based PFAS porewater concentrations. Specific objectives include the following:

• Conduct a bench-scale study to confirm the relationship between the AWIA and SSA and water saturation for soils collected from two demonstration sites;
• Conduct pilot-scale field measurement of SSA and water saturation using electrical geophysical tomography and directly validate via laboratory measurements on soil cores and existing vadose zone monitoring systems (VZMS) at the demonstration sites;
• Estimate field-scale AWIA from tomographic imaging to indirectly validate estimated AWIA by comparing PFAS-LEACH model predictions against PFAS porewater concentrations obtained from the pre-existing VZMS at the sites;
• Assess the high-resolution and spatially continuous distributions of variable water saturation and SSA obtained by geophysical surveys to improve the PFAS source-zone site conceptual model. 

The project technology focuses on improved characterization of aqueous film-forming foam (AFFF) source zones that cause persistent PFAS groundwater plumes. This will be the first integrated demonstration and validation of three fully mature tools and technologies. Rapid, non-invasive, and cost-effective geophysical tomography data will permit three-dimensional reconstruction of the surface area and saturation distribution.  Established geophysical to soil property ‘pedophysical’ relationships, calibrated to specific soil texture parameters for a site, will translate field-scale SSA and water saturation images into field-scale AWIA images. Estimation of field-scale AWIA is required to parameterize PFAS-LEACH models, and thereby improve PFAS conceptual site models. PFAS-LEACH simulations that incorporate the field-scale AWIA will be validated against PFAS pore-water concentrations available from VZMS at the selected demonstration sites.

PFAS associated with the historical use of AFFF have been detected in soil, sediments, and groundwater. Many site investigations reveal that vadose zones serve as PFAS reservoirs that pose significant risk to groundwater resources. Cost-effective management of PFAS-impacted sites will require technologies that can collect high-resolution data to improve site conceptual models and provide critical input parameters to mechanistic models of PFAS fate and transport. This project will validate geophysics-based SSA and demonstrate a method for estimating the field-scale AWIA, which will significantly improve the accuracy of models such as PFAS-LEACH for predicting the fate and transport of PFAS in the vadose zone. High-resolution delineation of SSA and saturation across the site will enable strategic monitoring of zones with the greatest PFAS retention and deployment of lysimeters. This will produce more representative site investigations and risk assessments, strengthening mission readiness by protecting the health of both warfighters and surrounding communities. (Anticipated Project Completion - 2028)