Effect of multiple contaminant migration on diffusion and adsorption of some domestic waste contaminants in a natural clayey soil

Abstract

This paper describes laboratory model tests involving the placement of domestic landfill leachate on top of a layer of saturated undisturbed clayey soil and allowing chemical constituents to migrate into the soil by diffusion only. During the testing period (15 days), samples from the overlying leachate were regularly collected and analyzed for the chemical constituents of interest (i.e., Cl−, Na+, K+, Mg++, and Ca++). At the end of the test, the soil layer was sectioned to determine the pore-water and adsorbed concentration variations with depth for each species. Mathematical model POLLUTE was then used to back-figure both the diffusion coefficient (D) and the adsorption term (ρK). The measured diffusion coefficients at a temperature of 10 °C were determined to be [Formula: see text], [Formula: see text], and [Formula: see text]. The corresponding adsorption terms were [Formula: see text], [Formula: see text], and [Formula: see text].Ca++ and Mg++, originally predominant on the clay exchange sites, were heavily desorbed to accommodate the adsorption of migrating Na+, K+, and possibly NH4+, causing hardness halo effects that the model could not fit. This behaviour corresponds to that commonly observed at domestic waste sites in southern Ontario.The importance of multiple contaminant migration on diffusion rates was assessed by comparing the leachate models with similar models using a variety of single salts dissolved in distilled water as the source solutions. For the single-salt models, all species considered, including Ca++ and Mg++, behaved in a way that could be described by conventional Fickian theory. A comparison of the diffusion and adsorption parameters obtained from the two types of models indicated that for both Na+ and K+, the measured D and ρK from the leachate models were 20 and 60% lower, respectively, than the values obtained from the single-salt models. For Cl−, the diffusion coefficient obtained from the leachate models was 25% higher than that obtained from the single-salt models.For the Sarnia grey soil used, both D and ρK are significantly influenced by the types and amounts of co-diffusing species present in the initial source solutions. Laboratory tests conducted to determine diffusion parameters for use in design should be run with soils and source solutions chemically identical to those expected in the field. Key words: domestic waste leachate, multiple contaminant migration, clayey soil, diffusion, adsorption, laboratory study.

Molecular Structure Effects on Diffusion of Cations in Clays

“…Under these conditions, predicted times for pollutant breaching a clay barrier are several hundred years. Field trials, however, have shown that some small molecules do not adhere to this behavior and move rapidly through soils (Johnson et al 1989;Goodall and Quigley 1977;Quigley et al 1987;Barone et al 1989;Crooks and Quigley 1989). As a result the mode of diffusive transport of solutes through clay films is of interest.…”

Geo-Environmental Site Investigation for Municipal Solid Waste Disposal Sites

“…Estimates of pollutant transport parameters based on laboratory tests such as column, diffusion and batch equilibrium tests are also important in the more detailed phases of geoenvironmental investigations (Freeze & Cherry, 1979;Rowe et al, 1988;Barone et al, 1989;Shackelford & Daniel, 1991;Yong et al, 1992;Shackelford, 1993;ong, 2001). These laboratory tests can be conducted with the objective of a better interpretation of the in-situ test results, and for a numerical modeling performance, using a good conceptual model definition for the problem.…”

Properties of a Lateritic Red Soil for Pollutant Containment

“…Diffusion tests followed the procedure described by Barone, et al [1]. The specimens were compacted directly in the moulds, and saturated by capillarity and seepage.…”