HR: 1340h
AN: H23A-1123    [Abstracts]
TI: Evaluating Electric Resistance Tomographs of a Controlled Infiltration Event in a Complex Vadose Regime Using Stochastic Models
AU: * Carle, S
EM: carle1@LLNL.gov
AF: Lawrence Livermore National Laboratory, PO Box 808 , Livermore, CA 94551 United States
AU: Carrigan, C R
EM: carrigan1@LLNL.gov
AF: Lawrence Livermore National Laboratory, PO Box 808 , Livermore, CA 94551 United States
AB: Linking field observations to field-scale models of subsurface flow and transport processes remains a challenge, particularly in the vadose zone. The LLNL Vadose Zone Observatory (VZO) experiments gathered Electrical Resistance Tomography (ERT) data to remotely monitor the infiltration process of water and brine from near-surface to an 18-m deep water table over several days. ERT observations suggested, surprisingly, that infiltration might rapidly reach the water table within only hours, which is a concern where the vadose zone has been assumed to act as a barrier to contaminants. To better understand this behavior, we are integrating several LLNL 3-D computer models (listed in parenthesis below) together to investigate the combined complexity of geologic heterogeneity (TSIM), variably saturated flow and transport (NUFT), flow of electrical current due to ERT (ParFlow), and ERT inversion (MultiBH). This integrated simulation approach, involving stochastic models, permits linkage between the ERT observations and 3-D flow and transport process models. While our simulations compare reasonably to some types of monitoring data (e.g. gypsum blocks), they do not exhibit rapid infiltration to the water table as indicated by the ERT inversions based on field data. The models indicate that strong preferential pathways, such as fracturing or vertically oriented sand lenses, may be required to explain the rapid communication between the infiltration point and the water table. Alternatively, recent bench-scale lab experiments involving resistivity measurements of plumes infiltrating a partially saturated sand-filled test section performed as part of this project (Parekh, et al., 2004, Rensselaer Polytechnic Institute) suggest the existence of air-water interfacial conduction processes strongly decreasing the formation resistivity in the unsaturated zone (see also R. Knight, Geophys., 56, p. 2139-2147, 1991) that are not simply associated with a resistivity decrease resulting from the downward migration of a brine tracer. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1869 Stochastic processes
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting