Abstract
Background and aim:
Groundwater resources in rapidly urbanizing areas are increasingly threatened by improper waste disposal. This study assessed groundwater contamination around the Angwan Gwandara dumpsite in Garaku, Kokona Local Government Area, Nasarawa State, Nigeria. The aim was to evaluate subsurface resistivity variations, identify aquifer systems, and determine contamination risks.
Methods:
Vertical Electrical Sounding surveys were conducted using Schlumberger and Wenner electrode configurations. Resistivity data were processed with IPI2WIN inversion software to delineate subsurface lithology and aquifer zones. Groundwater samples were collected from seven sources located 0.5–2 km from the dumpsite during the dry season. Samples were analyzed for physicochemical parameters (pH, electrical conductivity, turbidity, chloride, nitrate, sodium, calcium, and selected heavy metals) using standard hydrochemical techniques.
Results:
Geophysical interpretation revealed three to five subsurface layers dominated by weathered and fractured basement formations that serve as the main aquifers. Some zones exhibited low resistivity values (10–100 Ωm), suggesting saturated and potentially contaminated formations. Hydrochemical results showed pH values ranging from 6.06 to 7.25, generally within permissible limits. However, electrical conductivity values (240–3500 µS/cm) exceeded recommended standards at several locations. Elevated nitrate, turbidity, and calcium levels were also observed, particularly in shallow wells located closer to the dumpsite.
Conclusion:
Weathered and fractured basement formations facilitate contaminant migration, increasing the vulnerability of shallow aquifers to dumpsite leachate infiltration. Integrating electrical resistivity and hydrochemical analyses effectively identified groundwater contamination risks. Improved waste management practices, regular groundwater monitoring, and public health interventions are recommended to safeguard groundwater resources.

Key words: Vertical Electrical Sounding; Groundwater contamination; Pollution; Resistivity inversion; Dumpsite pollution