ASSESSMENT OF THE LEVEL OF ENVIRONMENTAL POLLUTION DUE TO LEACHATE MIGRATION FROM THE CLOSED MALLAM SCC WASTE DISPOSAL SITE, ACCRA - GHANA

ABSTRACT

The closed Mallam State Construction Corporation (SCC) waste disposal site is one of the many unengineered and improperly decommissioned municipal solid waste (MSW) landfills in Accra, Ghana. The site served as a landfill site for the Accra Metropolitan Assembly (A.M.A) for 7 years and received variety of solid waste from the A.M.A and other neighbouring municipal assemblies. Leachate management plans were, however, not implemented. Untreated leachate from the waste disposal site flows through the human settlements around the waste disposal site and enter into nearby surface water (Bawere Stream). The site was closed in 2001 after several agitations from the people living around, coupled with the fact that it was full to its maximum. The waste disposal site was not properly decommissioned prior to its closure. As a result, untreated leachate from the site still flows through the human settlements and enter the Bawere Stream. The research was carried out to assess the level of contamination of surface water, soil and groundwater due to leachate migration from the closed waste disposal site with emphasis on major ions (Na+, K+, Ca2+, Mg2+, Cl-, HCO3- , SO42-, NO3-, and PO43- ) and trace elements (Fe, Pb, Cd, Cr, Mn, As, Zn, Hg, Cu and Co). Major ions were measured using conventional methods. Trace element concentrations were determined using Atomic Absorption Spectrometry. Stable isotopic composition (δ 18O and δ 2H) of the surface water, soil and groundwater were determined using the Liquid-Water Stable Isotope Analyzer (Off - Axis Integrated Cavity Output Spectroscopy via laser absorption). Results showed high level of contamination of the surface water. The mean concentrations of Na+, K+, Fe, Pb, Cd and Mn (388 mg/L, 53 mg/L, 0.046 mg/L, 0.229 mg/L and 0.234 mg/L respectively) in the surface water were above the maximum permissible limit of the WHO (1996) guideline for drinking water. The mean δ 18O and δ 2H values of the surface water were -1.59 o/oo vrs VSMOW and -10.79 o/oo vrs VSMOW

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respectively. Porosity of the soil in and around the closed waste disposal site decreased with depth while the volumetric water content increased with depth. Trace element contamination of the soil was low. However, elevated concentrations of most of the trace elements were observed near the ground surface between 0 and 60 cm depths of the profiles. The level of contamination of the groundwater was high. The mean concentrations of Na+, Fe, Cd and Mn (330 mg/L, 1.178 mg/L, 0.040 mg/L and 0.157 mg/L respectively) in the groundwater were above the maximum permissible limit of the WHO (1996) guideline for drinking water. It is recommended that the closed Mallam SCC waste disposal site should be properly decommissioned and future waste disposal sites in Ghana should be properly engineered to minimize surface water and groundwater contamination due to leachate migration.