HR: 1340h
AN: H23B-1306    [Abstracts]
TI: Numerical Assessment of Indoor Air Exposure Risk from Subsurface NAPL Contamination under Hydrologic Uncertainties
AU: Unger, A
EM: aunger@uwaterloo.ca
AF: Department of Earth and Environmental Sciences, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada
AU: * Yu, S
EM: s7yu@sciborg.uwaterloo.ca
AF: Department of Earth and Environmental Sciences, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada
AB: Understanding the risk of indoor air exposure to residual contaminants in the subsurface following the redevelopment of contaminated land redevelopment project is a central issue at many brownfield sites. In this study, we examine various mechanisms controlling vapor phase intrusion into the indoor air of a typical residential dwelling from a NAPL source located below the water table, and consequently assess the indoor air exposure risk under multiple hydrologic uncertainties. For this purpose, a multi-phase multi-component numerical model, CompFlow Bio is used to simulate the evolution of a TCE source zone and dissolved plume in a variably saturated heterogeneous aquifer, along with the transport of dissolved TCE upwards through the capillary fringe with subsequent migration of TCE vapors in the vadose zone subject to barometric pressure fluctuations. The TCE vapors then enter the basement of the residential dwelling through a crack in the foundation slab, driven by a slight vacuum within the basement relative to the ambient atmosphere as well as the barometric pressure fluctuations. Hydrologic uncertainties affecting the indoor air concentration of TCE include the vacuum in the basement, the aperture of the crack in the foundation slab, the heterogeneous permeability field, the thickness of the capillary fringe, barometric fluctuations, recharge rates and the location of the TCE source zone. CompFlow Bio is then used to determine the future concentration of TCE into the basement as a consequence of imperfect knowledge in the various hydrologic parameters, and to evaluate the effectiveness of alternative remedial and foundation design options to minimize the exposure risk to the indoor air conditional upon the available data collected at the site. The outcome of this approach is two-fold. First, the owner of the site can reasonably evaluate the future indoor air exposure risk following the redevelopment of a formerly contaminated site following remediation activities. Second, the owner/developer of the site can then effectively price the risk that some residential dwellings will exceed an indoor air exposure regulatory limit assuming that the owner/developer of the site takes immediate actions to repurchase the residential dwelling where the regulatory limit was exceeded. Consequently, appropriate financial products (such as insurance or building a contingency fund) can be developed to enable the owner/developer to effectively hedge their risk and ensure solvency.
DE: 1847 Modeling
DE: 1873 Uncertainty assessment (3275)
SC: Hydrology [H]
MN: 2007 Fall Meeting