The hydrogeological and contaminant-transport properties of fractured Champlain Sea clay in Eastern Ontario. Part 2. Contaminant transport

Contaminant-migration characteristics of fractured Champlain Sea clay were evaluated through laboratory studies and parametric simulations. Two different laboratory diffusion experiments were performed on five unfractured Champlain Sea clay samples. One test involved the placement of a single salt solution (NaCl) in contact with a fully saturated undisturbed clay sample, thus allowing downward chemical migration throughout the sample by diffusion only. The second test involved the placement of deionized water in contact with the undisturbed saturated clay, thus allowing an upward chemical migration by diffusion only. At the termination of the test, the soil samples were sectioned to determine the pore-water and adsorbed concentrations as a function of depth. Diffusion coefficients and retardation factors were determined from plotted data.Simulated profiles were fitted to the field data by using one-dimensional analytical models that represented solute transport in both fractured and unfractured porous media. The fractured simulations using laboratory measured effective diffusion coefficients and retardation factors with advective parameters measured during field investigations provided the best fit. The effectiveness of fractured Champlain Sea clay to retard contaminants migration is significantly reduced when dealing with low- and non-reactive contaminants. Parametric analyses of four hypothetical cases indicate that landfill sites on these clays should be designed with an engineered liner and a leachate collection system.