Professional Application of EM and Resistivity Methods in Contamination Assessment in South West Nigeria

This study examines the professional application of electromagnetic and resistivity geophysical methods in soil and groundwater contamination assessment across South West Nigeria. Industrial and urban growth in the South West has created diverse contamination scenarios including petroleum hydrocarbon spills, heavy metal pollution from e-waste recycling, leachate from unlined landfills, and agricultural chemical contamination of shallow aquifers. Geophysical methods provide cost-effective spatial characterisation of contamination extents that chemical sampling alone cannot achieve at reasonable cost. This study reviews 25 contamination assessment projects conducted using EM and resistivity methods in Ogun, Oyo, Lagos, Osun, and Ondo States from 2018 to 2023. Method selection appropriateness, survey quality, interpretation accuracy, and regulatory reporting adequacy are assessed. Chemical validation data available for 14 of 25 projects are used to evaluate geophysical interpretation accuracy. Findings reveal that Geonics EM38 and EM31 instruments are the most commonly deployed tools for near-surface contamination mapping, used in 18 of 25 projects. Electrical resistivity profiling supplements EM in 10 projects. Method selection is appropriate in 68 percent of cases. Geophysical interpretation correctly predicts chemical contamination extent within 15 percent in 11 of 14 validated projects. However, quantitative conversion of conductivity anomalies to contaminant concentration is rarely attempted, limiting the utility of geophysical data for remediation design. The study concludes that professional EM-resistivity contamination assessment in South West Nigeria is technically competent but requires methodological standardisation and quantitative interpretation advancement to fully support regulatory decision-making.

Keywords: electromagnetic survey, resistivity, contamination assessment, South West Nigeria, professional practice.