HR: 0800h
AN: H31A-05    [Abstracts]
TI: Effects of Soil Moisture Dynamics on NAPL Spill Zone Architecture in Two-Dimensional and Three-Dimensional Heterogeneous Porous Media
AU: * Yoon, H
EM: hyoon3@uiuc.edu
AF: University of Illinois at Urbana-Champaign, Newmark Civil Engineering Lab 205 N Mathews Ave, Urbana, IL 61801, United States
AU: Valocchi, A J
EM: valocchi@uiuc.edu
AF: University of Illinois at Urbana-Champaign, Newmark Civil Engineering Lab 205 N Mathews Ave, Urbana, IL 61801, United States
AU: Werth, C J
EM: werth@uiuc.edu
AF: University of Illinois at Urbana-Champaign, Newmark Civil Engineering Lab 205 N Mathews Ave, Urbana, IL 61801, United States
AB: NAPL distribution in the vadose zone is controlled by the spatial distribution of water saturation and soil permeability, the NAPL spill scenario, water infiltration events, and vapor transport. The effects of these processes in two-dimensional and three-dimensional heterogeneous porous media were investigated using the three-phase flow simulator, Subsurface Transport Over Multiphase Phases (STOMP). A 3-D heterogeneous field with five stratigraphic layers was assumed and a 2-D vertical cross-section along the center of the 3-D field was used for the 2-D simulations. The conceptual model of the soil heterogeneity was based upon the stratigraphy at the Hanford carbon tetrachloride (CT) spill site. Co-disposal of NAPL with large volumes of wastewater was considered, as also occurred at the Hanford CT site. The same NAPL and water infiltration rates were used in 2- D and 3-D simulations. The form and location of NAPL were most strongly influenced by spill area (i.e., CT infiltration rate), high water discharge rates and NAPL evaporation to the atmosphere. The front of NAPL reached the groundwater table faster in 3-D than in 2-D. However, the fraction of total CT mass that reached the groundwater table was higher in 2-D than in 3-D. The difference between 2-D and 3-D simulations can be primarily attributed to the following factors. First, water saturation in the low permeability layer was lower in 3-D than in 2-D because the water plume spread out more evenly due to the additional horizontal direction in the 3D case. Hence, the NAPL front can penetrate through the low permeability layer due to the increased NAPL relative permeability and less capillary barrier effect in the low permeability layer, while in the 2-D case the water saturation in the low permeability layer was close to one during vertical migration of the wastewater plume. Second, the effect of density-driven vapor transport in 3-D was more significant than in 2-D, mainly due to the presence of the additional horizontal direction for vapor transport in 3-D. Hence, more CT mass moved out of the NAPL source zone in the 3-D simulation, resulting in a lower fraction of the total NAPL mass in groundwater. These simulations indicate that the 2-D simulation for organic compounds with high vapor pressure need to be compared with the 3-D simulation, in particular, under simultaneous water infiltration scenarios. The effect of variability in the permeability field and quantitative analysis of dimensionality on NAPL distribution will be further exploited through stochastic modeling.
DE: 1835 Hydrogeophysics
DE: 1838 Infiltration
DE: 1866 Soil moisture
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: 2007 Joint Assembly