Heuristic Model for Predicting the Intrusion Rate of Contaminant Vapors into Buildings

The intrusion into and subsequent accumulation of contaminant vapors in buildings and family dwellings is of concern for health and safety reasons. When preparing environmental and health risk assessments, one must be able to quantify this exposure pathway in order to decide if site-specific conditions correspond to unacceptable indoor contaminant vapor concentrations. For cases in which contaminated-site soil cleanup levels can be negotiated based on site-specific conditions, a related problem is the determination of residual contaminant levels below which associated adverse health effect risks are deemed negligible. Unfortunately, there are currently no accepted models for predicting vapor intrusion rates, and there is considerable debate over which transport mechanisms govern the process. This paper presents a heuristic model for screening-level calculations. It incorporates both convective and diffusive mechanisms, as well as contaminant soil, and building foundation properties. Sample calculations are presented for a range of parameter values to illustrate use of the model and the relative contributions of individual transport mechanisms.