One- and Three-Dimensional Soil Transportation Models for Volatiles Migrating from Soils to House Interiors

Abstract

Two models are presented for the transient migration of a volatile organic compound (VOC) from soil to the interor of a house with a crawl space. The migration in the house is taken as one-dimensional (1D) and coupled to a soil transportation model with diffusion, leaching and VOC degradation. The diffusion is either vertical, providing a 1D model, or three-dimensional (3D) axisymmetric, providing a 3D model. The initial subsurface VOC deposition is assumed to be a finite layer extending over the footprint of the house in the 1D case or as a cylinder of arbitrary radius in the 3D case. Using data for benzene as the VOC, comparisons are made for results from the two models for VOC concentrations in soil, crawl space and dwelling space as well as the cumulative dwelling space concentration used in human health assessment, for a wide range of soil parameters and subsurface sizes of the initial VOC cylinder. In all cases the values from the 1D transport model were slightly higher than those for the 3D model. The analysis uses Laplace transforms with numerical inversions. For the 3D soil transport model, different soil surface flux boundary conditions underneath and outside the house give rise to novel dual integral equations.