HR: 0800h
AN: H11B-0306    [Abstracts]
TI: Analysis Of Field-Scale Contaminant Transport Behavior Using Continuous Time Random Walk Theory
AU: * Lee, S
EM: sylee@ucdavis.edu
AF: University of California, Hydrologic Sciences, Davis, CA 95616 United States
AU: Ginn, T R
EM: trginn@ucdavis.edu
AF: University of California, Civil and Environmental Engineering, Davis, CA 95616 United States
AU: Fogg, G E
EM: gefogg@ucdavis.edu
AF: University of California, Hydrologic Sciences, Davis, CA 95616 United States
AB: Conservative solute transport across a spectrum of alluvial aquifer systems was evaluated using high-resolution numerical simulation and non-Fickian transport theory based on a continuous time random walk (CTRW) method. Numerical experiments with hydrofacies patterns that varied with respect to connectivity and geometry associated with various high-K (channel) fractions were conducted to simulate a variety of non-Fickian transport phenomena. In addition, effects of facies mean lengths and of conductivity contrast between high- and low-K (floodplain) materials on the transport behavior were examined in a separate experiment. Each simulated cumulative breakthrough curve was optimally fitted with the solution of cumulative first passage time distribution (CFPTD) formulation. The fitting parameter $\beta$ controlling dispersive transport in the CFPTD solution was used to characterize the simulated transport behavior. Our results showed that growth of $\beta$ values, indicating diminishing non-Fickian transport behavior, tends to occur as volumetric fractions of high-K material increases and the K contrast between low- and high- K materials decreases. However, no overall systematic change in the $\beta$ values according to the change only in channel mean length was observed. Importantly, significant variation of $\beta$ values among the equally probable realizations demonstrates that complex channel geometries and connectivity lead to transport behaviors that cannot necessarily be captured solely from $\beta$ values derived from statistics on K or velocity field. This suggests indirect estimation of $\beta$ from K or velocity distribution should be viewed with caution when there exists complex network of high-K materials. Fitting error between the numerically simulated breakthrough curve and best-fitted CFPTD curve increased with increasing non-Fickian behavior, although clearly smaller than with macroscopic advection-dispersion model. Overall, analyses of simulated transport behavior based on CTRW solutions were compatible with the ones based on other measures such as breakthrough curves, plume spatial moments, and dilution indices.
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting