Dr. Zack Munger, Ph.D., P.G.

Vadose Soil PFOS Leaching Evaluation to Support Groundwater Remediation Strategy at a Fire Training Facility in Florida

Dr. Zack Munger, Ph.D., P.G., Project Manager, Geosyntec Consultants

Leaching through the vadose zone is a key consideration for developing effective soil and groundwater remedial strategies at PFAS-impacted sites . Desktop evaluation of soil leaching is a tool that has been accepted by regulators for demonstrating whether soil excavation is an effective strategy for groundwater remediation.    At a fire training facility in Florida, site assessment revealed a large, shallow groundwater plume (35 acres) attributed to a former AFFF use area currently containing relatively low concentrations of PFOS in the vadose zone. While the concentrations were below the FDEP’s Provisional Soil Cleanup Target Level (SCTL) for PFOS based on residential direct exposure, they do exceed FDEP’s Provisional Leachability Criteria (L-SCTL) indicating the soil within the former AFFF use are may be acting as a source to groundwater.    Geosyntec developed a 1-dimensional PFAS leaching model to evaluate the potential reduction of PFOS in groundwater using different soil excavation scenarios  . The scenarios included simulating soil leaching for 1) the baseline condition without excavation, 2) the excavation of all soil with impacts greater than Florida’s Provisional L-SCTL, and 3) the excavation of soil with concentrations greater than 5x the Provisional L-SCTL. The infiltration rate of the model was calibrated to infiltration rate measurements collected at the site. PFAS leaching in the model considered the effects of partitioning to organic carbon and adsorption to the air-water interface. The results of the evaluation will support the remedial strategy decisions for the site by providing an estimate of peak soil leachate PFOS concentrations under baseline conditions and potential reductions of leachate PFOS concentrations under the simulated excavation scenarios.    This presentation will review the historical site data, objectives of and inputs to the model, model assumptions, results, and potential implications for a remedy application at the site.

Dr. Munger is a Geologist with more than 8 years of experience as an environmental consultant and 6 years of experience as a research hydrogeologist. His professional experience includes PFAS and non-PFAS contaminated site assessment; remedial action design/implementation; hydrogeologic investigations, multi-media field sampling of sub-slab vapors, soil, sediment, surface water, and groundwater; and data visualization and analysis via python and geographic information systems. He currently manages state-owned PFAS sites with involvement from the initial preliminary investigations through remedial design.