Integrated Geophysical Characterization of a Dumpsite and Leachate Plume Migration in Enugu South Local Government Area

Unmanaged open dumpsites in rapidly urbanizing areas of southeastern Nigeria present significant groundwater contamination risks, particularly where leachate generation and subsurface migration are poorly understood. This study conducts an integrated geophysical investigation to characterize a dumpsite environment and trace leachate plume migration in Enugu South Local Government Area. Electrical resistivity tomography, induced polarization, and VLF-EM measurements were employed in a combined framework across three survey directions around the primary dumpsite. ERT data were collected using a 48-electrode system with the dipole-dipole array and inverted with RES3DINV for three-dimensional subsurface imaging. Induced polarization chargeability anomalies highlight zones of enhanced ionic concentration consistent with leachate infiltration. VLF-EM phase data confirm conductive pathways oriented in the direction of the regional groundwater flow. Subsurface resistivity values as low as 1.2 ohm-m in the near-surface horizon beneath and downgradient of the dumpsite are indicative of highly contaminated percolation zones. The leachate plume is traced to a lateral extent of approximately 180 m from the dumpsite boundary and to a vertical depth of 12 m. Intersection of the plume with shallow domestic hand-dug wells is inferred in two locations, posing direct public health implications. These findings inform remediation priority areas and contribute to the growing body of applied environmental geophysics literature in urban Nigeria. The study also advocates for regulatory geophysical monitoring of dump sites as a standard environmental management practice.

Keywords: leachate plume, electrical resistivity tomography, induced polarization, VLF-EM, environmental contamination