Migration of leachate solutin through clay soil

The problem of domestic solid wastes buried in landfill sites is viewed from the aspect of leachate contamination and migration in the substrate. Generally, this occurs through the penetration of the contaminant into the liner material. This study assesses the efficiency of natural clay barriers as an expedient economic lining material.Various chemical constituents of the landfill leachate of an actual waste containment site at Lachenaie (35 km east of Montreal) were determined from samples collected from specially designed basins.In companion laboratory tests, these leachate samples were permeated through laboratory columns that contained the natural clay compacted at the optimum water content. The columns were constructed so as to permit simulation of slow, saturated, anaerobic flow of leachate through the clay lining surrounding the landfill and leachate basins. Leachates were permeated through the soil columns for periods of four to five months, during which effluents were collected periodically and analyzed for different chemical species and physical parameters. These chemical analyses measured changes in the concentration of: (a) cations (Na, K, Ca, and Mg), (b) anions (Cl, HCO$ sb3$, and CO$ sb3$), (c) total organic carbon (TOC), and (d) heavy metals (Fe, Zn, Pb, and Cu). The physical parameters measured included: (a) pH, and (b) specific conductivity.Subsequent to the leaching tests, the column contents were cut into six sections and analyzed to determine the distribution profiles of the adsorbed and retained contaminants at various time durations.Predictions, using a dispersion-convection model for concentration profile development for either adsorbed or retained contaminants, were compared with the experimentally determined profiles (both in leaching columns and landfill laboratory model).Another set of experiments was also conducted to evaluate the effect of some organic fluids on the geotechnical properties of different clay soils (natural clay and two reference clay soils: illite and kaolinite).The results from this study have demonstrated that the natural clay soil can be used to adequately contain the different contaminant species usually present in the leachate solutions. Furthermore, the data suggested that under favourable soil conditions, landfill leachates containing low levels of trace metals will not pose a substantial contamination threat to the subsurface environment, provided that a proper thickness of barrier is used. (Abstract shortened with permission of author.