Mapping the Concentration and Pathway of Leachate Plumes of Major Dumpsites in Makurdi Metropolis, North Central Nigeria using an Integrated Approach

This study assesses the extent, depth, and contamination levels of leachate migration beneath major dumpsites in Makurdi Metropolis through an integrated geo-electrical and hydro-chemical investigation. Vertical Electrical Sounding (VES) surveys were conducted around the dumpsites to characterize subsurface resistivity variations and determine leachate penetration depth, while groundwater samples were analyzed for major heavy metals including Pb, Cd, Cr, Ni, Cu, Zn, Fe, Mn, As, Hg, and Se. Resistivity values ranged widely from 1.2 to 58,000 Ω·m, indicating varied lithologic units and differing contamination intensities. Resistivity values below 20 Ω·m marked highly conductive, leachate-saturated zones representing severe contamination, whereas 20–50 Ω·m indicated moderate impact. Dumpsites such as Water Board, Naka Road, and Aliade Road exhibited extensive low-resistivity zones with leachate infiltration reaching depths of up to 92 m, signaling deep subsurface contamination and significant risk to underlying aquifers. Conversely, sites like Best Brain Academy and City-Bay Park showed high resistivity (>100 Ω·m), suggestive of clean sands or unpolluted bedrock. Hydro-chemical analyses corroborated the geophysical results, revealing elevated concentrations of heavy metals near the dumpsites. Iron (Fe) and Manganese (Mn) recorded mean values far above WHO (2017) permissible limits, while Lead (Pb) and Cadmium (Cd) also exceeded recommended thresholds, posing serious public health concerns. Areas such as North-Bank, Gboko Road, and NKST Yaiko showed the highest contamination indices, aligning with the mapped low-resistivity leachate zones. A Leachate Penetration Depth Map revealed a dominant southwest–northeast migration direction, consistent with natural groundwater flow patterns and influenced by topography and subsurface permeability. Overall, the findings demonstrate that most dumpsites in Makurdi are significant sources of groundwater pollution, with deep and laterally extensive leachate plumes. The study highlights the urgent need for engineered landfill liners, effective leachate control systems, and continuous groundwater monitoring to safeguard public health and ensure environmental sustainability.