An analytical model of vapor intrusion with fluctuated water table

Abstract

Intrusion of subsurface contaminants in vapor phase from groundwater into overlying buildings through cracks or other pathways poses potential risk to human health. Previous studies indicated that water table fluctuations may have significant impacts on vapor intrusion, resulting in fluctuated concentrations of indoor volatile organic compounds (VOCs). Analytical solutions for vapor intrusion processes are flexible tools in predicting VOC concentrations and assessing health risks of VOC-contaminated sites. However, an analytical solution considering the impacts of fluctuated water table is not available. In this study, an analytical model of the vapor intrusion with fluctuated water table was developed. The VOC transport in unsaturated zones was described by diffusion equation and the varying water table was treated as a moving boundary. The residual VOCs in the unsaturated zone induced by water table fluctuations were also considered and were described by a source term of the vapor diffusion. The analytical solution was tested with its numerical solution. The results indicate that the fluctuated water table affects the dynamics of VOCs mainly in two ways, changing the length of vapor migration path and delivering the residual VOCs into the unsaturated zone. The VOC concentration at the outlet varies inversely with the water table fluctuation owing to the release processes of the residual VOCs dominate. The analytical solution matches well to the laboratory experiment data in an existing study and could be a simple tool for the risk assessment of vapor intrusion when considering the impacts of water table fluctuations.