HR: 1330h
AN: H13B-15    [Abstracts]
TI: Influence of the Air-Entry Pressure Ratio in Bimodal, Heterogeneous Unsaturated Zones
AU: * Holt, R M
EM: rmholt@olemiss.edu
AF: University of Mississippi, Department of Geology and Geological Engineering, 118 Carrier Hall, Oxford, MS 38677 United States
AU: Baker, K E
EM: Kristine.Baker@inl.gov
AF: Idaho National Laboratory, P.O. Box 1625 MS 2107, Idaho Falls, ID 83415-2107 United States
AU: Schafer, A L
EM: nsa@inel.gov
AF: Idaho National Laboratory, P.O. Box 1625 MS 2107, Idaho Falls, ID 83415-2107 United States
AB: The unsaturated zone at the Idaho National Laboratory (INL) displays bimodal heterogeneity with high air-entry pressure (AEP) sedimentary interbeds intercalated with variably fractured, low AEP basalt flows. While most past work has focused on understanding flow and transport in the basalt flows, the influence of the sedimentary interbeds is beginning to become recognized. Recent studies suggest that sedimentary interbeds may control large-scale vadose zone flow and transport behavior at the INL. We investigate the influence of high AEP interbeds (e.g., sedimentary) within a low AEP medium (e.g., basalt) using a macroscopic invasion percolation (MIP) model that includes the effects of capillary, gravity, and viscous forces. The MIP model is parameterized with spanning pressures derived from pressure-saturation curves for the low and high AEP media and hydraulic conductivities derived from a capillaric model. The MIP model is used in a series of Monte Carlo simulations to define transport pathways that interconnect a source at the land surface to a water table at depth. We find that the air-entry ratio (high AEP/low AEP) strongly influences transport pathways. At small air-entry ratios, transport pathways are short and largely vertical. As the air-entry ratio increases, transport pathways become increasingly complex reflecting the spatial distribution of interbeds. Above a critical air-entry ratio, transport pathways stabilize and become insensitive to the distribution of properties within the low AEP medium (e.g., basalt). Our results suggest that detailed characterization of INL basalts may not be required to define transport pathways through the INL unsaturated zone.
DE: 1832 Groundwater transport
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2005 Joint Assembly