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In this study, the variable nature of the dispersion coefficients of some typical contaminant ions is evaluated through experiments with leaching columns. Three clay soils were used: a natural clay soil (60% clay content) obtained near an operating landfill site, and laboratory-prepared kaolinite and illite clay soils. Sufficient quantities of the contaminant leachate obtained from the nearby operating municipal solid-waste landfill site were used for all the leaching tests. The ions chosen for evaluation in this paper were chloride, potassium, magnesium, and calcium ions.
The comparisons between predicted profiles using constant and variable dispersion coefficients with actual experimental concentration profiles indicate clearly that the use of variable coefficients provides for better correlation with experimental information. This is not surprising, since the varying concentration profiles (with pore volume penetration) reflect physico-chemical interactions which result in accumulation/retention processes measured in terms of the profiles. As the data show, the variable processes obviously will control transport and retention of the contaminant ions. The modeling thereof for transport will be reflected through the corresponding variable dispersion coefficients.
hydrodynamic migration, chemico-osmotic, leaching, dispersion-convection, diffusion-advection, dispersion coefficients, contaminant, seepage velocity, hydraulic conductivity
William Scott Professor of Civil Engineering and Applied Mechanics, and Director, Geotechnical Research Centre, McGill University, Montreal, Quebec
Project coordinator, Conestoga-Rovers & Assoc, Ltd., Waterloo,