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Keywords:

  • Volatile organic compounds;
  • Exposure;
  • Indoor air;
  • Soil moisture;
  • Transport

Abstract

Two finite-source models that calculate volatilization of contaminants from soil to indoor air were used to study the effect of soil moisture on indoor air concentrations and inhaled doses, using a representative model volatile organic chemical. A hypothetical scenario was used that assumed that subsurface contaminant diffuses through a layer of clean soil and is then swept into the building interior via advection. Both models simulated depletion of source contaminant via volatilization and degradation. One was an analytical model adapted from the behavior assessment model of Jury et al., which could be used to calculate time-dependent volatilization rates (and indoor air concentrations) as a function of constant soil moisture contents and steady-state moisture advection. The second model, the Integrated Moisture Plus Contaminant Transport (IMPACT) model, had the additional capability of simulating daily and seasonal variations in soil moisture behavior from actual daily temperature and rainfall data. Predicted indoor air concentrations and inhaled doses for the model contaminant varied by up to seven orders of magnitude, depending on the soil moisture conditions and whether or not contaminant degradation was considered. Over extended time periods, inhaled doses predicted under conditions of daily and seasonal variations in soil moisture were in general agreement with those predicted using average soil moistures or average moisture fluxes, suggesting that simplified treatment of soil moisture behavior may be adequate if accurate soil moisture data are available.