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

Yao, Yijun, Wu, Yun, Suuberg, Eric M., Provoost, Jeroen, shen, Rui, Ma, Jianqing, Liu, Jing
Journal of hazardous materials 2015 v.286 pp. 553-561
air, databases, equations, monitoring, screening, temporal variation, vapors
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 500μg/m3. Otherwise, cin is independent of css, with a distribution in good agreements with other studies of background levels. Therefore, employing this screening value (500μg/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.