HR: 1340h
AN: H33B-0471    [Abstracts]
TI: Influence of Air Entry Pressure and Degree of Sorting on Air Entrapment below the Water Table: Simulation Results
AU: * Dunn, A M
EM: adunn@nd.edu
AF: University of Notre Dame, 156 Fitzpatrick Hall Civil Engineering and Geological Sciences, Notre Dame, IN 46556 United States
AU: Silliman, S E
EM: silliman.1@nd.edu
AF: University of Notre Dame, 156 Fitzpatrick Hall Civil Engineering and Geological Sciences, Notre Dame, IN 46556 United States
AU: Tontcheva, P
EM: petia-pt@yahoo.com
AF: University of Illinois at Chicago, Department of Earth and Environmental Sciences, Chicago, IL 60625 United States
AB: Our previous experimental studies have shown that air can be entrapped below the water table during periods of a rising or fluctuating water table. This is particularly evident when the aquifer material consists of heterogeneous sediments containing discontinuous lenses of coarse material in an otherwise relatively uniform medium. In this study, TOUGH2 (a finite difference model) is applied to, and verified against, imbibition results from our prior laboratory experiments. The model is then used to extend these experimental results to the investigation of the impact of air entry pressure and degree of sorting (of the coarse sediment lenses) on the air entrapment that is likely to occur below the water table. Within TOUGH2, the van Genuchten expression for the saturation-capillary pressure relationship is utilized, as is the van Genuchten - Mualem expression for relative permeability. The numerical portion of this study is based on variation of two parameters within the pressure-saturation expression, Po and lambda. Po is related to the air entry pressure for the sediments (with increasing Po associated with higher air entry pressure). The second parameter, lambda, relates to the degree of sorting within the sediments (with higher lambda associated with greater sorting - more uniformity in grain size of the sediments). Based on the numerical results, it is observed that the volume of air entrapped below the water table increases as the difference in air entry pressure between the coarse lens and the surrounding sediment matrix increases. Further, the volume of entrapped air increases with an increase in the uniformity of grain size of the coarse sediment (i.e., the sediment in the coarse lens is increasingly well sorted). These results provide substantial insight into the factors that control the degree of air entrapment below the water table.
DE: 1829 Groundwater hydrology
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting