title: Measuring spatial variability of vapor flux to characterize vadose-zone VOC sources: flow-cell experiments.
abstract: A method termed vapor-phase tomography has recently been proposed to characterize the distribution of volatile organic contaminant mass in vadose-zone source areas, and to measure associated three-dimensional distributions of local contaminant mass discharge. The method is based on measuring the spatial variability of vapor flux, and thus inherent to its effectiveness is the premise that the magnitudes and temporal variability of vapor concentrations measured at different monitoring points within the interrogated area will be a function of the geospatial positions of the points relative to the source location. A series of flow-cell experiments was conducted to evaluate this premise. A well-defined source zone was created by injection and extraction of a non-reactive gas (SF6). Spatial and temporal concentration distributions obtained from the tests were compared to simulations produced with a mathematical model describing advective and diffusive transport. Tests were conducted to characterize both areal and vertical components of the application. Decreases in concentration over time were observed for monitoring points located on the opposite side of the source zone from the local-extraction point, whereas increases were observed for monitoring points located between the local-extraction point and the source zone. The results illustrate that comparison of temporal concentration profiles obtained at various monitoring points gives a general indication of the source location with respect to the extraction and monitoring points.
authors.affiliation: Soil, Water and Environmental Science Department, School of Earth and Environmental Sciences, University of Arizona, Tucson, AZ 85721, United States.
authors.forename: J
authors.initials: J
authors.lastname: Mainhagu
authors.affiliation: Soil, Water and Environmental Science Department, School of Earth and Environmental Sciences, University of Arizona, Tucson, AZ 85721, United States.
authors.forename: C
authors.initials: C
authors.lastname: Morrison
authors.affiliation: Energy and Environment Directorate, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99354, United States.
authors.forename: M
authors.initials: M
authors.lastname: Truex
authors.affiliation: Energy and Environment Directorate, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99354, United States.
authors.forename: M
authors.initials: M
authors.lastname: Oostrom
authors.affiliation: Soil, Water and Environmental Science Department, School of Earth and Environmental Sciences, University of Arizona, Tucson, AZ 85721, United States; Hydrology and Water Resources Department, School of Earth and Environmental Sciences, University of Arizona, Tucson, AZ 85721, United States.
authors.forename: M L
authors.initials: ML
authors.lastname: Brusseau
mesh_terms: D002849:Chromatography, Gas; D003198:Computer Simulation; D004784:Environmental Monitoring / Q000379:methods*; D008962:Models, Theoretical; D012989:Soil Pollutants / Q000032:analysis*; D055549:Volatile Organic Compounds / Q000032:analysis*
chemical_list: D012989:Soil Pollutants; D055549:Volatile Organic Compounds
keywords: Flow cell experiment; Source characterization; VOC; Vadose zone; Vapor phase tomography