HR: 16:45h
AN: H14B-04    [Abstracts]
TI: Correct Characterization of Passive Tracer Dispersion in Porous Columns: Experiments vs. Theory
AU: * Cortis, A
EM: andrea.cortis@weizmann.ac.il
AF: Weizmann Institute of Science, Dept. of Environmental Sciences and Energy Research, Rehovot, 76100 Israel
AU: Scher, H
EM: harvey.scher@weizmann.ac.il
AF: Weizmann Institute of Science, Dept. of Environmental Sciences and Energy Research, Rehovot, 76100 Israel
AU: Berkowitz, B
EM: brian.berkowitz@weizmann.ac.il
AF: Weizmann Institute of Science, Dept. of Environmental Sciences and Energy Research, Rehovot, 76100 Israel
AB: Breakthrough curves (BTC) of a passive tracer in macroscopically ``homogeneous'' granular materials (well-sorted, unconsolidated sands or glass beads) were measured in a series of column experiments. % In parallel, classical experiments on dispersion of a passive tracer in fully and partially saturated porous columns were re-examined. % All of these BTCs exhibit anomalous (non-Fickian) features: early and late arrival times are observed to differ systematically from theoretical predictions based on solution of the advective-dispersion equation (ADE) for uniform porous media. % We propose that even in these small-scale, ``homogeneous'' porous medium columns, subtle and residual pore-scale disorder effects can account for these observations. % In a Continuous Time Random Walk (CTRW) framework, we determined an ensemble-averaged distribution of particle transfer rates (based on a Master Equation for the local flux-averaged concentration) which accounts for these effects. % Solutions of the resulting CTRW transport equations yield BTCs that are in excellent agreement with the entire series of observations. % The CTRW formulation also specifies the dependence of the effective macroscopic parameters on measurable quantities. % The theoretical predictions are in excellent agreement with the observations. % It is critical to understand that as a consequence of our results, the ADE should not be taken as the starting point of any upscaling technique. % Our analyses demonstrate that existing measurements and interpretations of tracer dispersion experiments in laboratory experiments should be carefully re-considered in the framework of these recent advances in conceptual understanding and quantification. % These results have also important implications for modeling the transport of contaminants in large-scale, highly-heterogeneous, hydrogeological systems.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1869 Stochastic processes
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting