INVESTIGATION OF ATMOSPHERIC EFFECTS ON VAPOR INTRUSION PROCESSES USING MODELLING APPROACHES

Most people in the United States (US) spend considerable amount of time indoors—about 90% of their time as compared to outdoors, which makes the US population vulnerable to adverse health effects of indoor air contaminants. Volatile organic compound (VOC) concentrations are well-known to be higher in indoor air than outdoor air. One source of VOC concentrations in indoor air that has gained considerable attention in public health and environmental regulatory communities is vapor intrusion. Vapor intrusion is the process by which subsurface vapors enter indoor spaces from contaminated soil and groundwater. It has been documented to cause indoor air contamination within hundreds of thousands of communities across the US. Vapor intrusion is well-known to be difficult to characterize because indoor air concentrations exhibit considerable temporal and spatial variability in homes throughout impacted communities. Unexplained variations in field data have not been systematically investigated using theoretical fate and transport processes. This study incorporates the use of numerical models to better understand processes that influence spatial and temporal variability in field data. The overall research hypothesis is that variability in indoor air VOC concentrations can be (partially) explained by variations in building air exchange rate (AER) and pressure differentials between indoor spaces and outdoor spaces. Neither AER nor pressure differentials are currently calculated by existing vapor intrusion numerical models. To date, most vapor intrusion models have focused on subsurface fate and transport processes; however, there is a need to understand the role of aboveground processes in the context of vapor intrusion exposure risks, which are commonly measured as indoor air VOC concentrations. Recent field studies identify these parameters as potentially important and their important role within the broader field of indoor air quality sciences has been well-documented, but more research is needed to investigate these parameters within the specific context of vapor intrusion. To test the overall hypothesis, the dissertation research developed a new vapor intrusion modeling technique that combines subsurface fate and transport modeling with building science approaches for modeling driving forces, such as wind and stack effects. The modeling results are compared with field data measurements from actual vapor intrusion sites and confirms that the research is relevant to not only academic researchers, but also policy decision makers