GSI North America Inc.
Jeff is a contaminant hydrologist with over 20 years experience in the environmental industry and research. He is currently the Principal Investigator on a US DoD SERDP funded research project looking at the fate and transport of PFAS in the vadose zone environment.
Modeling PFAS Air-Water Interfacial Adsorption during Transport in Water-Unsaturated Porous Media
Per- and polyfluoroalkyl substances (PFAS) released at the ground surface, as a result of the use of aqueous film-forming foams (AFFF) for fire-fighting activities or leaks at storage locations, ultimately transport through the vadose zone prior to contacting the water table and forming groundwater plumes within an aquifer. Depending on the release location, the vertical thickness of the vadose zone can vary between a few feet and hundreds of feet. Many PFAS of current environmental interest, including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), entering the subsurface as either components of AFFF formulations or degradation products of PFAS precursor chemicals within AFFF formulations, are surface-active agents. Therefore, in addition to other potential retention mechanisms, considerable retention of PFAS can occur within the vadose zone due to the adsorption of these surface-active chemicals at air-water interfaces (AWI). Here, we report the results of physical experiments and mathematical modeling that were used to incorporate AWI adsorption as a retention process into the HYDRUS unsaturated flow and transport model. Model modifications included incorporating the dependence of adsorption on PFAS concentration, air-water interfacial area, and bulk pore-water ionic strength. Model validation methods will be presented as will the results of test simulations to demonstrate the abilities of the model to capture retention resulting from AWI adsorption under dynamic flow conditions.