HR: 1340h
AN: H23A-1419    [Abstracts]
TI: LNAPL Entrapment in the Partially-Saturated-Fringe Under Natural Imbibition
AU: Dunn, A
EM: adunn@nd.edu
AF: Department of Civil Engineering and Geological Sciences University of Notre Dame, 256 Fitzpatrick Hall, Notre Dame, IN 46530 United States
AU: * Silliman, S
EM: silliman.1@nd.edu
AF: Department of Civil Engineering and Geological Sciences University of Notre Dame, 256 Fitzpatrick Hall, Notre Dame, IN 46530 United States
AB: Prior studies have shown the potential for LNAPL entrapment in heterogeneous media due to capillary traps. In the present study, entrapment is studied experimentally and numerically for the region bounding the water table and under conditions of imbibition through a heterogeneous medium. The results are consistent with previous studies in demonstrating that entrapment can occur, but they differ in demonstrating that such entrapment may be temporary due to the presence of non-zero relative permeability to LNAPL within the fine sands that overlie the capillary trap. The degree of entrapment is also strongly dependent on the rate of imbibition, with minimal entrapment occurring at very low and very high rates of imbibition. Three process rates appear to dominate the degree of entrapment: (i) rate of imbibition (or rate of rise in the water table), (ii) the time required for the capillary fringe to reach approximate equilibrium at a new water table height, and (iii) the rate of 'leakage' of LNAPL out of the capillary traps due to residual saturation in the sands overlying the trap. Temporary entrapment of an LNAPL requires that the time required for reequilibration of the capillary fringe be relatively small compared both to the rate of imbibition and the rate of LNAPL leakage. Long-term leakage of entrapped LNAPL is dependent on the relative NAPL-permeability within the sands overlying the capillary trap.
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: Fall Meeting 2005