Ground Water, 41(2): 142-155, 2003
Analysis of solute transport in flow fields influenced by preferential flow paths at the decimeter scale
Chunmiao Zheng and Steven M. Gorelick
Several recent studies at the Macrodispersion Experiment (MADE) site in Columbus, Mississippi, have indicated that the relative preferential flow paths and flow barriers resulting from decimeter-scale aquifer heterogeneities appear to have a dominant effect on plume-scale solute transport. Numerical experiments are thus conducted in this study to explore the key characteristics of solute transport in two-dimensional flow fields influenced by decimeter-scale preferential flow paths. A hypothetical but geologically plausible network of 10 cm wide channels of high hydraulic conductivity is used to represent the relative preferential flow paths embedded in an otherwise homogeneous aquifer. When the hydraulic conductivity in the channels is 100 times greater than that in the remaining portion of the aquifer, the calculated concentration distributions under three source configurations all exhibit highly asymmetrical, non-Gaussian patterns. These patterns, with peak concentrations close to the source and extensive spreading downgradient, resemble that observed at the MADE site tracer tests. When the contrast between the channel and nonchannel hydraulic conductivities is reduced to 30:1 from 100:1, the calculated mass distribution curve starts to approach a Gaussian pattern with the peak concentration near the central portion of the plume. Additional analysis based on a field-scale model demonstrates that the existence of decimeter-scale preferential flow paths can have potentially far-reaching implications for groundwater remediation. Failure to account for them in numerical simulation could lead to overestimation of the effectiveness of the remedial measure under consideration.
Click here to play an animation of solute transport
in a flow field influenced by dm-scale preferential
flow paths as simulated by MT3DMS.
Field work at the MADE site.
Decimeter-scale preferential flow paths from an
aquifer cross section adjacent to the MADE site.