DELINEATION OF SEDIMENTARY AND BASEMENT CONTACT ZONES WITHIN FELELE AND ENVIRONS,USING AN INTEGRATED VES AND VLF-EM NORTH –CENTRAL NIGERIA

ABSTRACT This study evaluates the groundwater potential of Felele, Southern Bida Basin, using an integrated geophysical approach of Vertical Electrical Sounding (VES) and Very Low Frequency Electromagnetic (VLF-EM) surveys. Fifteen (15)VES stations wereconducted with Schlumberger configuration at current electrodespacing up to 200 m, complemented by VLF profiles obtained with the ADMT 300 system. The subsurface lithologies consist of topsoil (18.8–495.5 Ωm; thickness 2,500 Ωm).Aquifers were delineated within weathered regolith (40–150 Ωm; 5–20 m thick), fractured basement zones (80–250 Ωm; 30–90 m depth), and sandstone layers (50–200 Ωm; 11.2–50.8 m depth). Geo-electrical curve types recorded includeA, K,AK, KQ, HK, and HA, reflecting the varying hydrostratigraphy. Integration of VES and VLF data delineated reliableaquiferzonesatVES2,9,11,12,and13,wherelow-resistivityunitscoincidedwithconductiveanomalies. Boreholetargets in these locations are recommended at depths of 30–90 m, with expectedyields of1–5 L/s. From literature-basedcalibrationwithintheSouthernBidaBasin,transmissivityvaluesrangefrom11.86–348.03m²/day, hydraulic conductivity from 2.32–47.99 m/day, and storativity between 0.0006–0.0093, confirming moderate to high groundwater potential. However, deeper layers (>120 m) exhibit reduced aquifer potential due to high resistivity (>1,000 Ωm), indicating limited storage. The findings emphasize the need for sustainable abstraction practices and demonstrate that integrating VES and VLF surveys provides a reliable framework for aquifer characterization and water resource development in basement terrains.