HR: 0800h
AN: H31B-0372    [Abstracts]
TI: Effect of soil moisture dynamics on the DNAPL spill zone architecture in heterogeneous porous media
AU: * Yoon, H
EM: hyoon3@uiuc.edu
AF: Civil and Environmental Engineering University of Illinois at Urbana-Champaign, 205 N. Mathews, Urbana, IL 61801 United States
AU: Valocchi, A J
EM: valocchi@uiuc.edu
AF: Civil and Environmental Engineering University of Illinois at Urbana-Champaign, 205 N. Mathews, Urbana, IL 61801 United States
AU: Werth, C J
EM: werth@uiuc.edu
AF: Civil and Environmental Engineering University of Illinois at Urbana-Champaign, 205 N. Mathews, Urbana, IL 61801 United States
AB: The water saturation, infiltration events, and soil permeability in the vadose zone determine the amount, location, and form of NAPL that requires remediation. Lenhard et al. (2004) recently proposed a new permeability-liquid saturation-capillary pressure (k-S-P) model that considers three NAPL forms: free, residual, and trapped. In this new constitutive model, both trapped and residual NAPL saturations depend on water saturation and saturation path history. Both free and residual NAPL have direct access to the pore gas, but the latter is held immobile by capillary forces. Trapped NAPL is surrounded by water, consequently, it does not have direct access to pore gas and it is immobile. The form and location of NAPL are likely to impact the time scales of cleanup. We used the three-phase flow simulator (STOMP), which includes this new constitutive model, to distribute NAPL in heterogeneous porous media for different NAPL and water loading histories. A 2-D vertical cross-section with layered heterogeneity was assumed, and simulations were performed for two scenarios of high and low water infiltration rates. For the first scenario, the form and location of NAPL were strongly influenced by the high water recharge rates. Water saturation increased as the water infiltration front swept downward. Since the advancing front of NAPL migrated slower than that of water, NAPL occupied only large pore spaces due to high water saturation. As a result, both trapped and residual NAPL saturations were low. The effect of different heterogeneous patterns of permeability and NAPL spill event scenarios on NAPL distribution was overwhelmed by high water recharge rates. For the low infiltration rate scenario, the distribution of water content prior to a NAPL spill event had a significant impact on NAPL migration and distribution due to the formation of residual and trapped NAPL. For initially low water saturation cases, the NAPL front was followed by a water infiltration front, which results in the formation of trapped NAPL. For initially moderate water saturation cases, trapped NAPL saturation was very low and residual NAPL saturation was relatively high. For all cases simulated, use of the new constitutive model that allows the formation of residual and trapped NAPL increased the amount of NAPL retained in the vadose zone. Although total NAPL saturation in the vadose zone was similar, the trapped NAPL saturation was different depending on the water infiltration scenarios. These results indicate that soil permeability, NAPL spill scenario, and infiltration events must all be simultaneously accounted for to describe the NAPL distribution and to predict the efficiency of remediation actions.
DE: 1832 Groundwater transport
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting