Simulating the effect of slab features on vapor intrusion of crack entry

School of Engineering, Brown University, Providence RI02912.
Building and Environment (Impact Factor: 3.34). 01/2013; 59:417-425. DOI: 10.1016/j.buildenv.2012.09.007
Source: PubMed


In vapor intrusion screening models, a most widely employed assumption in simulating the entry of contaminant into a building is that of a crack in the building foundation slab. Some modelers employed a perimeter crack hypothesis while others chose not to identify the crack type. However, few studies have systematically investigated the influence on vapor intrusion predictions of slab crack features, such as the shape and distribution of slab cracks and related to this overall building foundation footprint size. In this paper, predictions from a three-dimensional model of vapor intrusion are used to compare the contaminant mass flow rates into buildings with different foundation slab crack features. The simulations show that the contaminant mass flow rate into the building does not change much for different assumed slab crack shapes and locations, and the foundation footprint size does not play a significant role in determining contaminant mass flow rate through a unit area of crack. Moreover, the simulation helped reveal the distribution of subslab contaminant soil vapor concentration beneath the foundation, and the results suggest that in most cases involving no biodegradation, the variation in subslab concentration should not exceed an order of magnitude, and is often significantly less than this.

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    • "Similar wind effects were documented in the case study by Keskikuru et al. [13]. There is still significant interest in understanding the variety of factors which influence vapor intrusion, as reflected for example in the recent study of crack entry by Yao et al. [14]. Although the case study described here provides further data that could help confirm mechanisms for radon entry, the focus is on soil moisture infiltration. "
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    • "The choice to focus on a perimeter subslab concentration is somewhat arbitrary, but it reflects the common approach in VI modeling assuming a perimeter foundation crack as the foundation entry breach through which contaminants enter. A recent paper has shown that the assumption regarding the nature of this foundation entry breach is not critical to the analysis [19]. It has also been shown in a recent study [12] that the depth under open ground at which the concentration approaches that of the subslab perimeter is d f d s 0.5 , where d f ([L]) and d s ([L]) are the depth of building foundation and source, respectively. "
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