GROUNDWATER CONTAMINATION BY SANITARY LANDFILL AT OLUSOSUN (OJOTA) IN LAGOS STATE OF NIGERIA

Abstract

The study was an evaluation of the ground water contamination by the sanitary landfill at Olusosun (Ojota) in Jkeja Local Government area of Lagos State, Nigeria. The landfill at Olusosun (Ojota) has· been turned to open dump, due to the poor operation management. Wastes were buried without treating the bottom and sides of the trenches with sealant to control the leachate movement. Also wastes were left fallow for several months and not buried and whenever rain falls the wastes would be soaked, leading to production of leachate. The continuous generation of leachate without corresponding containment of leachate within the landfill in Olusosun (Ojota) constitute a major threat to the quality of groundwater and public health in Olusosun in Lagos state. Water samples were taken from wells around the dump site for a period of eight months and analyzed to determine the physical, chemical and biological characteristics. The results obtained were compared with WHO intemational standards on potable water. The average value for the parameters that reflects leachate pollution for the contaminated wells varied during the dry and wet season. The average BOD concentration of the contaminated wells at the dry season varies between 8.3mgll - 37.8mgll and wet season values varies between 8.3mg/l - 3 Irng/l. The zinc concentration at the dry season varied between I5.8mgll - 20.1mg/l and at the wet season it varies between 15.2mg/l - 21.1mg/1. The chloride concentration at the wet season varied between 368.6mgll - 709.4mg/1. The nitrate concentration at the wet season varied between 52.5mg/1 - 54.6mg/1. \Vells sited very close to the sanitary landfill had suffered contamination from the leachate of landfill and had concentration of some elements exceeding the maximum concentration limits. Some of these wells were sited on a reclaimed land,

formerly used for refuse dump. Some of this contamination are causing heritable genetic diseases, birth defect and sudden death. Data on hydrogeological features of Olusosun (Ojota) were collected from the Lagos State Ministry of Water Resources to determine the alternation of layers of sand bands, their thickness and identification of aquifer horizons. Structural and non-structural solutions to problems of contamination of wells at Olusosun (Ojota) are required to protect public health. These include the redesign of the landfill with underground protective membrane (bentonite, claysluny, bituminous felt) laid under the sanitary trenches, and the construction of a collection pit for the leachate. Control of leachate production discharge from the landfill, collection of the leachate with final treatment and or disposal. Formulate a policy on management strategies of municipal sanitary landfill, putting in place institutional and legal instruments for the management of sanitary landfill and environment. The decaying refuse is also raw material for a fertilizer company.