Abstract
Firefighting training activities (FTAs) over the last half-century have utilized aqueous film forming foam, a solution that contains per- and polyfluoroalkyl substances (PFAS). Human exposure to PFAS has been linked with adverse effects on human health. Consequently, leaching of PFAS from aqueous film forming foam (AFFF) to the aquifers below FTAs is an area of growing concern. One method for understanding PFAS leaching through the vadose zone is through numerical computer modeling. However, computational modeling of PFAS transport in the vadose zone is still a developing field, and no two-dimensional models of PFAS transport have been validated against real-world data.
In this thesis, I present a two-dimensional PFAS transport model developed using the HYDRUS 2D software and calibrated against data from a firefighting training site in Killingworth, Connecticut. This calibrated model is then adapted to explore the effects of additional water percolation during FTAs, limiting PFOS influx to only occur during FTAs, changing the climate to that of a more arid region, and introducing single and multiple sources of heterogeneity in the soil. The application of additional percolation during FTAs was found to increase the total concentration of PFOS leached but did not change the shape of the contamination plume. Restricting PFOS influx to only occur during FTAs was found to decrease the total concentration of PFOS, but similarly did not affect the plume. Imposition of an arid climate was found to both drastically decrease the rate of transport and drastically decrease the total concentration of PFOS leached. Lastly, the introduction of blocks of higher hydraulic conductivity and greater sorption loamy sand was found to accelerate the transport of the tracer while capturing a large portion of the PFOS and slowing the rate at which it reaches the aquifer. Together, these model variants and their findings illustrate the usefulness of a calibrated 2-dimensional model in exploring varying PFAS transport scenarios and provide the basis for future research in AFFF application periods, climate dependent PFAS leaching, and leaching in heterogeneous soils.