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For landfills construction, considering that there may not be a suitable soil in the area, bentonite clays are usually added to the insitu soils to decrease their permeability. Taking into consideration that the amount of contaminants in the landfill’s leachates are relatively high, the clay particles may adsorb many of the contaminants, changing the thickness of the clay particles, thus affecting their permeability.
Bentonite clays also due to their large surface area and high cation exchange capacities, have more potential to adsorb contaminants than the other soils. For example, leachates containing organic liquids such as heptane, methanol, benzene ethanol amine, and tetra chloro-ethylene may increase the permeability of the clayey soils up to thousand folds. Heavy metals such as arsenic, barium, cadmium, copper, and nickel also causes some changes in the permeability of the clays.
Based on the above-mentioned information, this research was carried out to assess the effect of a real leachate on the structure and the coefficient of permeability of a bentonitic soil. To accomplish this research, various geotechnical tests such as grain size distribution, unit density, permeability, X-ray diffraction analysis, and environmental tests were carried out on the soil samples with 2%, 4% and 6% bentonites, and the effect of water and a real landfill leachate on the samples were investigated.
The results of the above tests showed that the coefficient of permeabilities of 4% and 6% bentonite-soil mixes were lower than the U.S.EPA standards required for landfill liners. Moreover, the permeability of the above mixed decreased 2.3 x i03 and 4 x i05 times respectively, after mixing with bentonite clays