Integrated Geophysical Investigation for Groundwater Potential Assessment in a Basement Complex Terrain of Asokoro Abuja Nigeria

Groundwater is a critical resource in Nigeria, particularly within the crystalline basement complex terrains that underlie much of the country, where its occurrence is constrained to secondary fractures and weathered layers. This study presents an integrated geophysical survey combining Vertical Electrical Sounding (VES) and Frequency-Domain Electromagnetic (FEM) methods to delineate aquifer zones and identify an optimal borehole drilling site at a property in Asokoro, Abuja. The VES data, acquired using a Schlumberger array, revealed varying geoelectric sequences: a promising three-layer QHK-type curve at VES 1 indicating a deep weathering profile and a fractured aquifer, an unfavorable AA-type curve at VES 2 suggesting massive impermeable bedrock, and a highly favorable HKH-type curve at VES 3 signifying a well-developed, water- saturated fracture zone. To overcome site constraints and map lateral continuity, an EM survey was conducted, confirming a low resistivity anomaly indicative of a saturated fractured zone at depths of 120-150 m. Interpretation of the integrated data suggests a moderately low groundwater yield potential, with the aquifer confined within fractured basement rock. It is recommended to drill at the identified point to a depth of 140-150 meters to tap into the identified fractured aquifer unit, which is expected to function as a natural reservoir.