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SUBSURFACE SOIL CONDITIONS BENEATH AND NEAR BUILDINGS AND THE POTENTIAL EFFECTS ON SOIL VAPOR INTRUSION
Citation:
TILLMAN, F. AND J. W. WEAVER. SUBSURFACE SOIL CONDITIONS BENEATH AND NEAR BUILDINGS AND THE POTENTIAL EFFECTS ON SOIL VAPOR INTRUSION. Presented at 18th Annual National Tanks Conference, Memphis, TN, March 20 - 22, 2006.
Impact/Purpose:
To assess quantitative and qualitative methodologies evaluation of vapor intrusion, including quantification of uncertainties, to be used in the decision making process.
Description:
Migration of volatile chemicals from the subsurface into overlying buildings is called vapor intrusion. Volatile organic chemicals in contaminated soils or groundwater can emit vapors that may migrate through subsurface soils and enter indoor air spaces of overlying buildings. The evaluation of contaminated sites for the potential for soil vapor intrusion routinely uses a 1-dimensional screening-level model known as the Johnson and Ettinger model. Unsaturated zone moisture content may vary between locations beneath a structure and outside the footprint of the building slab. These differences may have a large effect on vapor-phase transport in the unsaturated zone and vapor intrusion of soil gas into overlying buildings. Continued drying of sub-slab soils will provide increased pathways for vapor transport directly beneath a building. Sub-slab locations near the edge of a structure appear to respond to rainfall at land surface. Subsequently, vapor intrusion risk assessments based on outside-of-slab moisture content values may not be protective of exposures to organic vapors transported from below a building slab.