Hybrid Wenner-Schlumberger Electrical Resistivity Investigation for Groundwater at Nasarawa State University Keffi, Keffi Sheet 208 NE, North-Central Nigeria.

Geological traversing at Nasarawa State University Keffi, part of Keffi Sheet 208NE, North-central Nigeria, revealed that the area is underlain by the Basement Complex rocks consisting of biotite gneiss, granitic gneiss and schist. The structural trends are mostly in NNW-SSE and NE-SW directions and foliation in the NE-SW direction. Surface geophysical investigation was conducted using the new hybrid Wenner-Schlumberger array, where fifty (50) stations were investigated along seven established profiles to determine the groundwater potential of the area. Six curve types were observed; HA, KA, QH, HAK and KHA; QHA-types has the highest frequency of occurrence while KA and HAK-types has the least. Results revealed that the top soil being the 1st layer with resistivity (62- 5800 Ωm) and thickness (1-2 m). Laterite is the 2nd layer with resistivity (20-5550 Ωm), and thickness (2-7 m). The weathered basement is the 3rd layer with resistivity (43-2080 Ωm) and thickness (5-20 m). The fractured basement is the 4thlayer in the five (5) geoelectric layer case with resistivity (115-1700 Ωm) and thickness (25-50 m); while the partially weathered/fractured basement forms the 4thlayer in the six (6) geoelectric layer case with resistivity (66-2059 Ωm) and thickness (10-30 m). The fresh basement forms the 5thlayer in the five (5) geoelectric layer case with resistivity (312-2170 Ωm), while the fractured basement forms the 5thlayer in the six (6) geoelectric layer case with resistivity (139-2800 Ωm), and thickness (10-50 m). The fresh basement forms the 6thlayer in the six (6) geoelectric layer case with resistivity (310-3800 Ωm). The depth to fresh basement or overburden thickness range from 29-79.5 m, which implies that the area is generally good for groundwater development, especially places with distinctive weathered and/or fractured layers thicknesses. Groundwater potentials were zoned into low, medium and high potentials for groundwater development. Wenner data extracted and interpreted have a good degree of correlation with the Schlumberger results, the structural trends observed on the geological structures and with existing geology