Investigation of VOC Transport in Soil Vapors due to Wind Effects using Models and Measurement

For the past several years, vapor intrusion of volatile organic compounds (VOCs) that emanate from hazardous waste sites has been gaining attention due to adverse health effects and regulatory action. Most studies of VOC vapor intrusion suggest that diffusion is the dominant contaminant transport mechanism, while advection is only considered important near contaminant entry points (i.e. building cracks). This conceptual framework is accurate when above-ground surface features do not promote air flow into (or out of) the ground surface. Recent research related to air flow in the atmospheric boundary layer (ABL) due to wind effects around buildings suggests a need for better understanding how advective transport processes can impact contaminant profiles and vapor intrusion exposure risks. In this study, a numerical model using COMSOL Multiphysics was developed to account for parameters affecting the transport of VOCs from the subsurface into buildings by considering wind effects in the ABL. Model simulations are compared to preliminary laboratory and field data to evaluate the relative importance of wind induced pressure gradients, soil permeability, soil porosity, and soil effective diffusivity on vapor intrusion entry rates. The major goal of this research is to develop an improved conceptual understanding of the vapor intrusion process so that remediation efforts can be better designed and implemented.