An Analytical Modeling Framework For Determining Site-Specific Soil Screening Levels For Pfas
Presenter: Jacob Smith1
Co-Author(s): -
Advisor(s): Dr. Bo Guo
1Department of Hydrology and Atmospheric Sciences, University of Arizona
Vadose zones at contamination sites have accumulated a significant amount of per- and polyfluoroalkyl substances (PFAS). The long-term risks of PFAS leaching downward to contaminate the groundwater underneath may require remediation of the contaminated soils. The development of soil screening levels (SSLs) in support of determining soil remediation standards often involves backward calculations starting from a given maximum contaminant level (MCL) in groundwater. EPA's current soil-screening methodologies and frameworks were developed for non-PFAS contaminants. However, it has been widely demonstrated that the surface-active properties of PFAS lead to unique leaching and mass discharge behaviors from the vadose zone to groundwater. It is anticipated that the current soil-screening methodologies will not be applicable to PFAS. To address this critical gap, the present work aims to develop an analytical modeling framework accounting for PFAS-specific transport processes that can be used for determining site-specific SSLs for PFAS at contamination sites. Specifically, we couple a process-based analytical model for PFAS leaching in the vadose zone and a dilution factor model in the groundwater to provide an integrated framework. We demonstrate the applicability of the new modeling framework by considering two typical types of contamination sites---AFFF-impacted sites and agricultural lands that receive PFAS-impacted biosolids.