Environmental Engineering Design of a Sanitary Landfill for Onitsha Metropolitan Area, Anambra State

This study presents a professional engineering design concept for a sanitary landfill facility to serve the Onitsha Metropolitan Area in Anambra State, South East Nigeria. Onitsha, one of Nigeria's most commercially active cities, currently disposes of its municipal solid waste at an uncontrolled dumpsite that lacks leachate management infrastructure, environmental monitoring, and operational controls, generating significant groundwater contamination and greenhouse gas emission risks. The design study encompasses site selection assessment, waste volume projections, facility capacity design, liner system specification, leachate collection and treatment design, landfill gas management design, and a closure and aftercare plan. Site selection followed the NESREA siting criteria for solid waste disposal facilities, evaluating four candidate sites on geological, hydrogeological, traffic access, community proximity, and land acquisition criteria. The recommended site is in a low-permeability clay-dominated formation at least two kilometres from the nearest residential area, with appropriate buffer distances. The facility is designed for a twenty-year operational lifespan with a double liner system comprising a high-density polyethylene geomembrane over a compacted clay liner. Leachate is collected by a drainage blanket and treated in an on-site biological treatment unit. Landfill gas is collected from an active extraction system and flared with a future option for power generation. The design incorporates a daily cover protocol using inert material and an environmental monitoring programme for groundwater, surface water, and gas. Keywords: sanitary landfill design, solid waste disposal, leachate management, landfill gas, Onitsha.