Integrated GIS–AHP and 2-D Electrical Resistivity Tomography for Environmental Assessment of Solid-Waste Dumpsites in Gombe Metropolis, Nigeria

Open dumping of municipal solid waste can expose surface water and groundwater to leachate, yet surface environmental constraints and subsurface conditions are often assessed separately. This study aimed to integrate the GIS-based Analytic Hierarchy Process (AHP) with two-dimensional electrical resistivity tomography (2-D ERT) to assess the environmental setting and potential subsurface contamination pathways of existing solid-waste dumpsites in Gombe Metropolis, northeastern Nigeria. Sixteen dumpsites were mapped, ten spatial criteria were weighted by AHP, and ten dumpsites were surveyed with Wenner–Schlumberger 2-D ERT profiles of 100 m and 5 m electrodes spacing. Distance from wells/boreholes (27.65%), distance from rivers (19.52%), geology (13.41%) and land use/land cover (10.84%) received the highest weights (consistency ratio = 0.0362). About 80.28% of the analysed area lies within 500 m of rivers/streams and 15.30% within 500 m of wells/boreholes. Very low resistivities (<10 Ωm) occurred at seven of the ten surveyed dumpsites, whereas Bypass Doma House was comparatively resistive (mostly >200 Ωm). Combining both lines of evidence, Bagadaza GRA Bypass, Biu Road WD2, Liji WD1 and Yalanguruza, where extensive low-resistivity zones lie within 500 m of mapped boreholes, emerged as the highest priorities for hydrochemical verification. The integrated framework shows that water-resource protection, lithological and structural pathways, and subsurface conductivity should be evaluated together when assessing urban dumpsites. Because low resistivity can also reflect clay-rich or saturated materials, the conductive zones indicate possible leachate influence rather than confirmed groundwater contamination. The final GIS-AHP suitability map was mapped and the suitability classes as the outcome of the weighted spatial analysis