Investigating the Role of Soil Texture in Vapor Intrusion from Groundwater Sources

Abstract

Soil texture is believed to play a significant role in the migration of subsurface volatile chemicals into buildings at contaminated sites, an exposure process known as vapor intrusion (VI). In this study, we investigated the role of soil texture in determining the attenuation of contaminant soil gas concentration from groundwater source to receptor building. We performed soil column experiments, numerical simulations, and statistical analysis of the USEPA’s VI database. The soil column experiments were conducted with commercial sand and soils with sand and sandy loam textures. Measured one-dimensional soil gas concentration profiles were compared with numerical predictions. Good agreement between experiments and model results supports the use of the classical multiphase chemical transport equation for simulating contaminant vapor transport from groundwater through the vadose zone. A full three-dimensional numerical model was then used to simulate typical VI scenarios with groundwater sources. Results indicate that, although soil particle texture can play a role in determining subslab-to-indoor air concentration attenuation, there is no obvious relationship between soil particle size and groundwater source-to-subslab except in the case of a shallow contaminant source. This conclusion is consistent with results reported in USEPA’s VI database, in which variation in soil particle size does not affect source-to-subslab attenuation factors but does influence subslab-to-indoor air concentration attenuation factors by an average of about 0.4 order of magnitude. This finding suggests that an appropriate focus of VI site investigation should include the shallow soil beneath the building foundation.

Three‐Dimensional Simulation of Land Drains as a Preferential Pathway for Vapor Intrusion into Buildings

“…Due to such complexity, a full 3‐D finite element model is used to study the influences of such a preferential pathway on both of these measures. The 3‐D numerical model applied here was developed with COMSOL Multiphysics and has been presented in previous publications (Bozkurt et al, 2009; Pennell et al, 2009; Yao et al, 2011, 2012, 2013a, 2013b, 2013c, 2015, 2017a, 2017b). The numerical model includes two modules, Darcy's law and chemical transport in porous media.…”

How Does the Periodic Groundwater Table Fluctuation Impact on Chlorinated Vapor Intrusion?

“…Governing Equations. A 2D numerical model is built to investigate the influence of groundwater table fluctuations on vapor intrusion using a finite element code COMSOL Multiphysics, which has been widely adopted in previous studies to solve the problem of vapor transport from the contaminant source to the dwelling through the building foundation crack (e.g., [30][31][32][33]). The development and use of this code to solve typical vapor intrusion problems have been described in detail in Pennell et al [30].…”

A Review of Recent Vapor Intrusion Modeling Work

“…To examine a more realistic VI scenario, Yao et al (2017b) used a 3D numerical model to investigate soil texture's role in determining the attenuation of contaminant soil gas concentration from groundwater source to receptor building. They found that, although soil particle texture can play a role in deciding subslab‐to‐indoor air concentration attenuation, there is no obvious relationship between soil particle size and groundwater source‐to‐subslab attenuation factor except in the case of a shallow contaminant source.…”