SOIL-TO-INDOOR AIR EXPOSURE MODELS FOR VOLATILE ORGANIC-COMPOUNDS - THE EFFECT OF SOIL-MOISTURE

Two finite-source models that calculate volatilization of contaminants from soil to indoor air were used to study the effect of soil moistur e on indoor air concentrations and inhaled doses, using a representati ve model volatile organic chemical. A hypothetical scenario was used t hat assumed that subsurface contaminant diffuses through a layer of cl ean soil and is then swept into the building interior via advection. B oth models simulated depletion of source contaminant via volatilizatio n and degradation. One was an analytical model adapted from the behavi or assessment model of Jury et al., which could be used to calculate t ime-dependent volatilization rates (and indoor air concentrations) as a function of constant soil moisture contents and steady-state moistur e advection. The second model, the Integrated Moisture Plus Contaminan t Transport (IMPACT) model, had the additional capability of simulatin g daily and seasonal variations in soil moisture behavior from actual daily temperature and rainfall data. Predicted indoor air concentratio ns and inhaled doses for the model contaminant varied by up to seven o rders of magnitude, depending on the soil moisture conditions and whet her or not contaminant degradation was considered. Over extended time periods, inhaled doses predicted under conditions of daily and seasona l variations in soil moisture were in general agreement with those pre dicted using average soil moistures or average moisture fluxes, sugges ting that simplified treatment of soil moisture behavior may be adequa te if accurate soil moisture data are available.