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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    ABSTRACT: This case study presents measurements of radon and moisture infiltration from soil gases into the basement of an unoccupied research house in Madison, Wisconsin, over two full years. The basement floor and exterior walls were constructed with preservative-treated lumber and plywood. In addition to continuous radon monitoring, measurements included building air tightness, indoor–outdoor pressure difference, indoor and outdoor temperature and relative humidity, wood moisture content, and tracer gas decay. A single-zone air infiltration model was calibrated based on tracer gas measurements. Soil moisture infiltration was determined by mass conservation after accounting for all other moisture flows: humidification, air exchange, diffusion through the above-grade building envelope, sorption in hygroscopic materials, and moisture removal by air conditioning. A moisture balance methodology used in previous work was validated and improved here by including two time scales in the sorption modeling. Active soil depressurization was applied and shown to reduce both radon and soil moisture infiltration. The stack effect is shown to correlate well with soil moisture infiltration but does not fully explain radon entry.
    Building and Environment 02/2015; 85. DOI:10.1016/j.buildenv.2014.12.008 · 3.34 Impact Factor
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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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    ABSTRACT: In this study, the development and partial validation are presented for an analytical approximation method for prediction of subslab contaminant concentrations in PVI. The method involves combining an analytic approximation to soil vapor transport with a piecewise first-order biodegradation model (together called the Analytic Approximation Method, including Biodegradation, AAMB), the result of which calculation provides an estimate of contaminant subslab concentrations, independent of building operation conditions. Comparisons with three-dimensional (3-D) simulations and another PVI screening tool, BioVapor, show that the AAMB is suitable for application in a scenario involving a building with an impermeable foundation surrounded by open ground surface, where the atmosphere is regarded as the primary oxygen source. Predictions from the AAMB can be used to determine the required vertical source-building separation, given a subslab screening concentration, allowing identification of buildings at risk for PVI. This equation shows that the "vertical screening distance" suggested by U.S. EPA is sufficient in most cases, as long as the total petroleum hydrocarbon (TPH) soil gas concentration at the vapor source does not exceed 50-100mg/L. When the TPH soil gas concentration of the vapor source approaches a typical limit, i.e. 400mg/L, the "vertical screening distance" required would be much greater.
    Journal of Hazardous Materials 05/2014; 279:336-347. DOI:10.1016/j.jhazmat.2014.05.065 · 4.53 Impact Factor
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    ABSTRACT: Those charged with the responsibility of estimating the risk posed by vapor intrusion (VI) processes have often looked to information contained in the U.S. Environmental Protection Agency (EPA)'s VI database for insight. Indoor air concentration attenuation factors have always been a key focus of this database, but the roles of different environmental factors in these attenuation processes are still unclear. This study aims to examine the influences of these factors in the context of the information in the VI database. The database shows that the attenuation factors vary over many orders of magnitude, and that no simple statistical fluctuation around any typical mean value exists. Thus far, no simple explanation of this phenomenon has been presented. This paper examines various possible contributing factors to the enormous range of observed values, looking at which ones can plausibly contribute to explaining them.
    Environmental Science & Technology 12/2012; 47(2). DOI:10.1021/es303441x · 5.33 Impact Factor
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