HYDRAULIC CONDUCTIVITY CHARACTERISTICS OF LEACHATE - CONTAMINATEDLATERITIC SOIL

Abstract

Lateritic soil contamination due to the Leachate from Municipal Solid Waste is a major environmental problem. Landfill leachate is generated from liquids existing in the waste as it enters a landfill or from rainwater that passes through the waste within the facility. The properties and structure of a compacted liner can change with time due to changes in moisture content, capillary forces, and physico-chemical interactions with the liquid waste resulting in a reduction of the effectiveness of the liner as a barrier to contain solid and liquid waste. The changes in chemical characteristics of soils due to leachate contamination may be detrimental to the compacted soils/liner. To protect the groundwater from landfill contaminants, lateritic soil liners are widely used to impede the flow of leachate from municipal solid waste (Osinubi and Nwaiwu, 2005). A comprehensive laboratory analysis was carried out to determine the index properties, compaction characteristics and hydraulic conductivity of natural and contaminated lateritic soil. Contaminated samples were prepared by mixing the lateritic soil with varying percentage of leachate at step concentration of 0%, 25%, 50%, 75% and 100% to vary the degree of contamination. The effects of leachate on the Atterberg limit showed increase in liquid and plasticity index values with the increase in the leachate content, thus: Liquid Limit (WI) and plastic index (IP) at 0% is 51 and 23.08, at 25%(WI = 52.92, IP =26.48, at 50%( WI =53, IP =29.28), at 70% (WI =53.22, IP =32.17) at100 %( WI =54.2 and IP = 34.13). The hydraulic conductivity of the natural lateritic soil is 1.40 x 10-6cm/s and 1.30x10-7cm/s using BSL and BSH comparative efforts respectively at 0 day curing time. There is corresponding increase in the hydraulic conductivity of the lateritic soil with increase in the percentage contamination, thus: 25%( 4.75x10-6cm/s and 2.78x10-7cm/s ), 50%( 6.94x10-6cm/s and 4.52x10-6cm/s ), 75%( 7.90x10-6 cm/s and 6.10x10-7cm/s ) and finally 100%(5.44x10-6cm/s and 7.33x10-7cm/s) using BSL and BSH comparative Effort respectively. In conclusion, increase in percentage contamination of lateritic soil increases the hydraulic conductivity, liquid limit, plasticity index and optimum moisture content while maximum dry density decreases.