DESIGN OF AN ENGINEERED LANDFILL NEAR IGBATORO DUMP SITE, AKURE, NIGERIA.

Abstract

This work focuses on providing a design for an engineered landfill in Akure with a view to encouraging a shift from Open Dumping which despite its apparent defects has remained the method of waste disposal in Nigeria. Geology, Topography and other criteria listed by the United Nations Environmental Programme(UNEP) in 2005 were considered in the choice of suitable location for the landfill. Strength, permeability and consistency tests were carried out on soil samples collected from the proposed site and borrow pit to determine their suitability as liner. The waste generation potential of Akure and the landfill’s attendant leachate and landfill gas emission potential were estimated. As a result, the landfill volume requirements,the leachate collection requirements and the landfill gas extraction wells spacing was determined. Also provided is the landfill perimeter drain and environmental monitors.The proposed site falls under an area a past research considered suitable for landfill siting. The cumulative waste generation potential of Akure over the design life is 5.89× 106m3 and will require a landfill with a dimension of 935m by 905m by 10mto collect it. The geotechnical tests revealed the proposed site will not yield under landfill loadings while the hydraulic conductivity and consistency properties of the borrow pit soil are suitable for a liner. The work thus recommends for bottom and side liners 1m thick borrow pit material found below depth 3.0m with coefficient of permeability (k) in the range 10-6to 10-8cm/s. The capping recommended comprises a 1.5m thick composite system. The peak leachate generation potential of the landfill is 1.76 × 10-6 m/min and thus will require a 150mm Ø High Density Polyethylene (HDPE) pipe with a minimum of a 12.78mm Ø perforation per linear metre for effective discharge. The landfill gas emission potential of the landfill is 85.58 Mg/yr. while the extraction wells have as radius of influence 58m. The landfill perimeter drainage channel provided is of 0.6m width and 0.5m depth. Finally, the design provides five groundwater well monitors (1 up gradient, 4 downside gradient) and 8 landfill gas monitors (one within the landfill, seven around the landfill) to monitor against leachate and landfill gas migration from the landfill body.