Mathematical analysis and flux-based radius of influence for radon/VOC vapor intrusion mitigation systems

Subslab Depressurization Versus Subslab Ventilation: Insights from Recent Research

“…This spreadsheet analysis and interpretation can be performed in real-time during field data collection which enables data adequacy to be addressed efficiently. The model assumptions and application to subslab gas flow are described in McAlary et al 2018, 2020and ESTCP ER-201322 2019 Mass removal rates are another option for SSV performance monitoring. The mass removal rate is simply the product of the volumetric flow rate in the extraction pipe(s) and the concentrations of VOCs or radon in the extracted vapor.…”

“…Consider the two-layer conceptual model for flow in response to gas extraction beneath a floor (see Figure 1) and assume for the sake of comparison there are two buildings with conditions summarized in Table 1. The model formulation and assumptions are described in McAlary et al 2010, 2018, 2020and ESTCP ER-201322 (2019. Also assume:…”

“…Figure 3 shows the calculated profiles of velocity vs. radial distance for the two cases and Figure 4 shows the calculated profiles of travel time vs. radial distance from the suction points (see McAlary et al 2020 4 to 6 inches thick (10-15 cm) in building codes, but the thickness of the active flow zone (b) for Case 2 could be much more than the assumed value. Velocity and travel time depend on the gas conductivity (K), not the transmissivity (T), and since T = Kb by definition, the velocity and travel time would decrease in direct proportion to any increase in the thickness of the active flow zone.…”

A Review of Recent Vapor Intrusion Modeling Work

“…McAlary et al (2018) presented a fluid model to calculate building-specific attenuation factors using subslab flow and vacuum measurements, building pressure, and building ventilation rates. Later, McAlary et al (2020) developed a mathematical model to assess the radius of influence for subslab venting systems based on mass flux instead of static vacuum distribution. In summary, those studies provide some alternatives to estimate indoor air concentration based on more site-specific parameters, which may not be easily characterized in site investigations.…”

Simplified Approach for Calculating Building‐Specific Attenuation Factors and Vapor Intrusion Mitigation System Flux‐Based Radius of Influence

“…Alternative methods for evaluating the ROI of mitigation systems have been developed including a flux-balance approach and subslab velocity and travel time (McAlary et al 2020). The conceptual diagram of the flux-balanced ROI is shown in Figure 1.…”