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Water Res

Title:		Modeling capillary fringe effect on petroleum vapor intrusion from groundwater contamination
Author(s):		Yao Y; Mao F; Xiao Y; Luo J;
Address:		"MOE Key Lab of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, 310058, China; Research Center for Air Pollution and Health, Zhejiang University, Hangzhou, 310058, China; Institute of Environmental Health, Zhejiang University, Hangzhou, 310058, China. Electronic address: Yijun_Yao@zju.edu.cn. MOE Key Lab of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, 310058, China; Research Center for Air Pollution and Health, Zhejiang University, Hangzhou, 310058, China; Institute of Environmental Health, Zhejiang University, Hangzhou, 310058, China. School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA. Electronic address: jian.luo@ce.gatech.edu"
Journal Title:		Water Res
Year:		2019
Volume:		20181120
Issue:
Page Number:		111 - 119
DOI:		10.1016/j.watres.2018.11.038
ISSN/ISBN:		1879-2448 (Electronic) 0043-1354 (Linking)
Abstract:		"At contaminated sites, indoor inhalation of volatile organic compounds from groundwater contamination, known as vapor intrusion (VI), is an important exposure pathway to determine groundwater cleanup level. Based on empirical analysis, US EPA concluded that there is a low probability for vapors from fuel hydrocarbons dissolved in groundwater to induce indoor concentrations that exceed risk-based standards, and recommended 6 feet vertical building-source separation distance as the risk screening tool for such cases. In this study, we examine this recommendation by performing numerical modeling to investigate the detailed effects of the capillary fringe on petroleum vapor biodegradation and attenuation. First, the numerical model is validated by comparison with laboratory data and field measurements in US EPA's database. Then the verified model is used to simulate two scenarios involving the capillary fringe effect, one with a groundwater source at various depth and the other with a soil gas source located above the groundwater level. For a groundwater contaminant source, the capillary fringe plays a significant role in VI by controlling the soil moisture content and oxygen availability, thus affecting the soil gas concentration biodegradation and attenuation. Specifically, the capillary fringe effect can significantly decrease the indoor air concentration by decreasing upward diffusion rates of hydrocarbon, increasing the thickness of the aerobic zone, and enhancing aerobic biodegradation. As a result, it is highly unlikely for sources located at groundwater level to induce unacceptable vapor intrusion risks, supporting US EPA's recommendation. Moreover, the simulations suggest that the vertical smear zone of residual light non-aqueous liquid contamination, induced by temporal fluctuations of groundwater level, may lead to a potential threat to indoor air quality for a short vertical source-building separation distance, and thus requires more attention. The sensitivity test of the numerical model also indicates that it is the vertical separation distance between building foundation and the top of the smear zone instead of the smear zone thickness that should be given more attention during the investigation"
Keywords:		"Biodegradation, Environmental Gases *Groundwater *Petroleum Soil Capillary fringe Groundwater contamination Numerical simulations Petroleum vapor intrusion Smear zone;"
Notes:		"MedlineYao, Yijun Mao, Fang Xiao, Yuting Luo, Jian eng Research Support, Non-U.S. Gov't England 2018/12/06 Water Res. 2019 Mar 1; 150:111-119. doi: 10.1016/j.watres.2018.11.038. Epub 2018 Nov 20"