HR: 08:15h
AN: H41B-02    [Abstracts]
TI: Evaluation of Water Flow-Paths and Dispersivities in Three-Dimensional Heterogeneous Porous Media Based on Magnetic Resonance Imaging Experiments
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: Zhang, C
EM: czhang@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
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
AB: Tracer concentration breakthrough curves (BTCs) depend mainly upon the spatial distribution of hydraulic conductivity (K). Small-scale heterogeneity causes local velocity changes and local concentration gradients which can result in dispersive mixing. To examine the effects of heterogeneity and dispersion coefficients on tracer transport, we used a unique non-intrusive experimental method that measures BTCs from magnetic resonance imaging (MRI) signal intensity profiles at a voxel scale of 0.1875cm x 0.1875cm x 0.225cm in a three-dimensional flowcell (25cm x 8.8cm x 8.5cm) packed with a spatially correlated heterogeneous distributions of K at the 1cm3 scale. Predicted breakthrough profiles obtained with an integrated finite difference code (STOMP) were compared to experimental BTCs averaged over 0.25x0.25 cm2, 1x1 cm2, and the entire heterogeneous flow cell cross sections (8x8 cm2), all in 0.25 cm increments along the main flow direction (x). Different methods of assigning hydraulic conductivity (K) values to these sand fractions based on literature and measured values were tested. At the 0.06525cm2 and 1cm2 scales, the simulated BTCs matched the measured BTCs very well in the highest K sand along the central portion of the flowcell, but matching was poorer in the lower K regions. Root mean squared error (RMSE) values between measured and simulated BTCs were calculated; they were lowest for the flowcell cross-section scale, and increased with decreasing scales (1 cm2 and 0.0625 cm2). The difference is attributed to: (1) a reduction in local effective conductivity caused by the mixing of the coarse and fine sands, and (2) variability between the experimentally packed and the numerical heterogeneous permeability field. The impact of the dispersion coefficients upon the RMSE was also evaluated under the assumption that the ratio of longitudinal to transverse dispersivities equals ten; a minimum RMSE value was obtained when the longitudinal dispersivity was similar to the grain size. The effect of local-scale heterogeneity on differences between measured and predicted BTCs will be further exploited by inverse flow modeling using measured BTCs.
DE: 0925 Magnetic and electrical methods (5109)
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1847 Modeling
SC: Hydrology [H]
MN: 2007 Joint Assembly