CALCULATION OF SOIL CLEANUP CRITERIA FOR CARCINOGENIC VOLATILE ORGANIC-COMPOUNDS AS CONTROLLED BY THE SOIL-TO-INDOOR AIR EXPOSURE PATHWAY

Two deterministic models that calculate volatilization of contaminants from soil were compared and used to calculate soil cleanup criteria f or carcinogenic volatile organic compounds so that acceptable total do ses would not be exceeded through the inhalation of indoor air. A hypo thetical scenario was used which assumed that subsurface contaminant d iffuses through a layer of clean soil and then is swept into the build ing interior via advection, where long-term inhalation of contaminant was assumed to occur. The first model was one of three recently descri bed by Little et al. It assumed a constant source concentration and in finite thickness for the contaminated soil zone, and resulted in a ste ady-state interior air concentration. The model was modified to allow for first-order decay of the contaminant source. The second model was adapted from the behavior assessment model of Jury et al. It calculate d time-dependent volatilization, simulated the depletion of source con taminant via both volatilization and degradation, and could be used wi th a contaminated zone of finite thickness. For a given chemical, the predicted total exposure (and the resulting cleanup criteria) varied b y up to seven orders of magnitude, depending on the model, whether a f inite or infinite contaminated soil layer thickness was used and wheth er degradation was considered. When calculating soil cleanup standards for volatile organic compounds in the part-per-million range or lower , it appears to be important to consider contaminant source depletion with time and the actual thickness of the contaminated soil layer.