Vapor intrusion attenuation factors relative to subslab and source, reconsidered in light of background data

Abstract

The basis upon which recommended attenuation factors for vapor intrusion (VI) have been derived are reconsidered. By making a fitting curve to the plot showing the dependence of observed indoor air concentration (cin) on subslab concentration (css) for residences in EPA database, an analytical equation is obtained to identify the relationship among cin, css and the averaged background level. The new relationship indicates that subslab measurements may serve as a useful guide only if css is above 500 μg / m3. Otherwise, cin is independent of css, with a distribution in good agreements with other studies of background levels. Therefore, employing this screening value (500 μg / m3), new contaminant concentration attenuation factors are proposed for VI, and the values for groundwater-to-indoor and subslab-to-indoor air concentration attenuation factors are 0.004 and 0.02, respectively. The former is applied to examining the reported temporal variations of cin obtained during a long-term monitoring study. The results show that using this new groundwater-to-indoor air concentration attenuation factor also provides a reasonably conservative estimate of cin.

A Petroleum Vapor Intrusion Model Involving Upward Advective Soil Gas Flow Due to Methane Generation

“…Therefore when the traditional CST equation is used to predict short-term maximum indoor air concentrations, more conservative input parameters should be employed than those usually adopted to predict the health risks of petroleum products. Moreover, according to the statistical analysis of U.S. EPA’s VI database by EPA and other researchers, after minimizing the influences of background sources, the observed subslab-to-indoor air concentration attenuation factors varies from 1 to 10 −4 (34, 44). It should be noted that most datasets recorded in U.S. EPA’s VI database were obtained at sites contaminated by chlorinated chemicals, and in those cases there should be no upward advective soil gas flow that can increase the soil gas entry rate into the building (and the subslab-to-indoor air concentration attenuation factor).…”

Evaluation of site-specific lateral inclusion zone for vapor intrusion based on an analytical approach

“…AAMLPH can also be employed to estimate a conservative indoor air concentration C in by using a generic subslab-to-indoor air concentration attenuation factor ${\alpha }_{ss}^{\mathit{\text{in}}}$ as 0.02 [37–38]. Figure 6 shows sensitivity test of $\frac{1}{r}$ in predicting the maximum subslab soil gas concentration.…”

“…For example, 50 and 100 µ g / m 3 have been employed as the risk-based screening levels for soil vapor concentration of benzene [39]. Besides the risked-based screenings, a contribution-based screening was proposed recently to identify the dominant sources responsible for the indoor air contaminants [37]. It was reported that there is a greater likelihood that C in is determined by VI instead of background sources if C ss >500 ug / m 3 [37].…”

“…Besides the risked-based screenings, a contribution-based screening was proposed recently to identify the dominant sources responsible for the indoor air contaminants [37]. It was reported that there is a greater likelihood that C in is determined by VI instead of background sources if C ss >500 ug / m 3 [37]. In the present study, independent of contaminant types, 50 and 500 µ g / m 3 are chosen as the typical risk-based and contribution-based thresholds of C ss for chlorinated chemicals (CHCs), respectively.…”

Impacts of changes of indoor air pressure and air exchange rate in vapor intrusion scenarios

“…With the growing awareness of the problem, as evidenced by numerous studies of the problem in the past two years, e.g. (Beckley et al, 2014; Brusseau et al, 2013; Dawson, 2013; Goreham et al, 2014; Holton et al, 2015; Johnson et al, 2014; Johnston and Gibson, 2014; Jourabchi et al, 2013; Lowe et al, 2015; Marchant, 2014; Perron et al, 2013; Schumacher and Zimmerman, 2013; Verginelli and Baciocchi, 2014; Yao et al, 2013c; Yao et al, 2015), there remains a strong impetus to better quantitatively characterize vapor intrusion processes.…”