Electromagnetic Imaging for Groundwater Prospecting in Basement Complex Terrain, Offa, Southwestern Nigeria

Groundwater potentials in Basement Complex rocks were accessed using the electromagnetic prospecting method. The electromagnetic curve and profile maps generated from the measured potential difference have been analyzed to access the groundwater potentials in the study area. The three traverses used in this research showed distinct vertical fractures indicated with ‘red-lines’ on both the profile and curve maps. The results obtained showed the potential borehole locations in ‘red-lines’ which were points of potential difference drop ranging from 0.00 mV to 0.54 mV. Out of all the potential probing points, P4, P6 and P10 were drilled. The yields of P4, P6 and P10 boreholes as calculated were 100 L/min, 166 L/min and 125 L/min, respectively. The study concluded that groundwater is usually accumulated within fractured basement and less dense rocks usually overburden materials as revealed by very low potential difference values obtained at all the drilled borehole locations. Among the drilled boreholes in the study area, P6 was the best in term of yield. For further studies, 3 different parallel profiles that are 1 m apart starting from the same initial point along the same traverse, should be employed for a better understanding in the continuity of the interpreted subsurface geologic structures at the same probing point. Thus, the idea of how extensive the geologic structures are, can be seen.