Vapor intrusion in urban settings: effect of foundation features and source location

In many urban settings, groundwater contains volatile organic compounds, such as tricholoroethene, tetrachloroethene, benzene, etc., at concentrations that are at or slightly below non-potable groundwater standards. Some non-potable groundwater standards do not protect against human health risks that might result from vapor intrusion. Vapor intrusion is a process by which vapor phase contaminants present in the subsurface migrate through the soil and ultimately enter a building through foundation cracks. The end result is a decrease in air quality within the building. Predicting whether or not vapor intrusion will occur at rates sufficient to cause health risks is extremely difficult and depends on many factors. In many cities, a wide-range of property uses take place over a relatively small area. For instance, schools, commercial buildings and residential buildings may all reside within a few city blocks. Most conceptual site models assume the ground surface is open to the atmosphere (i.e. green space); however the effect that an impervious surface (e.g. paving) may have on vapor transport rates is not routinely considered. Using a 3-D computational fluid dynamics model, we are investigating how the presence of impervious surfaces affects vapor intrusion rates. To complement our modeling efforts, we are in the initial stages of conducting a field study in a neighborhood where vapor intrusion is occurring.