ATTENUATIVE CAPACITY OF COMPACTED THREE REDDISH BROWN TROPICAL SOILS

Three compacted reddish brown tropical soils from Ibadan, Southwestern Nigerian, West Africa, were investigated in the laboratory for their suitability as hydraulic barriers for waste containment structure. The key parameters evaluated was the impact of Municipal Solid Waste (MSW) landfill leachate on the geotechnical, mineralogical, long-term hydraulic conductivity and sorptive and diffusive properties of the soils. The effective diffusion coefficient D* value for Na⁺ (2.69 x 10^-10m²/s) in MP3 increased to a peak value in MP1 (3.48 x 10^-10m²/s) with corresponding decrease in tortuosity factor. It can be seen that Na⁺ Na⁺ (0.18) in MP3 increased to 0.29 in MP1. Also, K⁺, Mg²⁺ and Cl^- also follow the same trend. In all, Na cations were found to diffuse faster than other ions including the only anion Cl. The effective diffusion coefficients of the cations and anion were found to be in the order of Na⁺ < K⁺ < Mg²⁺ < Cl^-. This finding suggests that the soils would be effective hydraulic barriers against the migration of potential contaminants in landfill leachate. It was also found that the presence of kaolinite as the major mineral allowed sorption of the ions that are generally considered conservative in linear-leachate compatibility studies on soils from tropical regions.