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.

Development and Application of a Three-Dimensional Finite Element Vapor Intrusion Model

“…An EPA document21 and other recent publications22,23 summarize some of the earlier models. It is generally acknowledged that 1-D models cannot capture the full range of effects that play a role in actual vapor intrusion scenarios, but they are useful because they can be more simply solved than full 3-D models.…”

Accuracy and Conservatism of Vapour Intrusion Algorithms for Contaminated Land Management

“…Screening-level algorithms need to predict close to reality (need to have high accuracy) so credible concentrations are calculated to underpin site assessment and remediation decisions (Robinson & Turczynowicz, 2005). On the other hand the derivation of SSV requires a sufficient level of conservatism to account for variation in sites, soil, buildings, residents, etc.…”

Exposure Assessment Modeling for Volatiles—Towards an Australian Indoor Vapor Intrusion Model

“…The review by Tillman and Weaver (2005) focussed on the lack of uncertainty analysis in the use of the JEM, the need for more field data and additional investigations into subsurface parameters such as moisture content that have major influences on predictions. The other review, in an automated uncertainty analysis that accounted for synergism across model input parameters identified the nonlinearity of the JEM equation and subsequent response to parameter variation (with a skew Waitz et al (1996) Australian CSIRO model Extension of BAM Markey and Anderssen (1996); Anderssen and Markey (1998); Robinson (1999aRobinson ( , 1999bRobinson ( , 2000Robinson ( , 2003; Robinson and Turczynowicz (2005) toward increased risk) and the limitations of a "one-at-a-time" uncertainty analysis (increased model uncertainty compared to grouped variable analysis). Of particular interest was the finding that the air exchange rate was ranked as "the single most sensitive input parameter of the model" (Weaver & Tillman, 2005, p. 31).…”

“…A recent paper (Robinson & Turczynowicz, 2005) examined the issue of conservatism due to lateral migration losses of VOC beneath a dwelling associated with one-dimensional modeling. This was undertaken by comparison with a threedimensional axisymmetric transportation model of transient migration of a VOC from soil to a crawl space house interior.…”