Using The Electrical Resistivity Method to Investigate Soil Resistivity at Okokpon, Okada, Edo State, Nigeria

Abstract

Electrical resistivity surveying was used to characterize the shallow subsurface at the ELPS CS2 site in Okokpon, Okada, Edo State, and to assess the implications for buried metallic infrastructure. Measurements were acquired at six vertical electrical sounding (VES) stations with an ABEM SAS 1000 Terrameter, a 12 V battery, four electrodes, connecting cables, a measuring tape, and a GPS receiver. The Schlumberger array was used to inject current and measure the resulting potential difference. Apparent resistivity values were calculated and inverted to obtain layer resistivities to an investigated depth of approximately 10 m. The interpreted resistivity values ranged from 70.1 Ωm to 9708 Ωm. The lower values are consistent with clay-rich or moisture-retaining horizons, whereas the higher values indicate relatively dry lateritic, sandy, or gravelly materials. Surface and 5 m contour maps also reveal marked lateral variation, including comparatively conductive zones around ERT1, ERT3, and ERT6 and highly resistive zones around ERT4 and ERT5. Overall, the site is not dominated by highly conductive soil; therefore, the resistivity data alone do not indicate a general requirement for cathodic protection. This conclusion should, however, be verified with seasonal measurements and complementary soil-corrosivity parameters before final pipeline design.