Multiscale Geophysical Characterization of Leachate and Gas Plumes in a Tropical Landfill Using Electrical Resistivity Tomography for Environmental Analysis and Diagnosis

Monitoring environmental risks in operational landfills that contain closed cells requires non-invasive techniques capable of accurately characterizing subsurface contaminant dynamics. Electrical Resistivity Tomography (ERT) was selected because it enables continuous imaging across capped cells without intrusive drilling, with high sensitivity to the strong conductivity/resistivity contrasts that differentiate leachate (very low resistivity) from landfill gas or dry waste (high resistivity). This study employed ERT to spatially characterize contaminant distribution in closed cells within a landfill system in the Caribbean region of Colombia. Fifteen geophysical survey lines were acquired using Wenner, Dipole–Dipole, and Gradient arrays and processed through 2D, 2.5D, and 3D inversion models. The results revealed extensive low-resistivity zones (<2.1 Ω·m) in the southeastern sector, interpreted as leachate accumulations, some reaching the surface. Conversely, high-resistivity anomalies (>154 Ω·m) were identified in the southwestern area, associated with potential biogas pockets. Although these high-resistivity volumes represent <1.1% of the total modeled volume, their location and depth may pose geoenvironmental risks due to internal pressure build-up and preferential migration pathways. Existing leachate and gas collection systems showed adequate performance, though targeted corrective actions are recommended. ERT proved to be a precise, scalable, and cost-effective method for mapping subsurface contamination, offering critical insights for post-closure landfill management in tropical settings.