Groundwater Prospecting in Fractured Shale Aquifer Using an Integrated Suite of Geophysical Methods: a Case History from Presbyterian Church, Kpiri-Kpiri, Ebonyi State, SE Nigeria

Abstract

Groundwater has strategically remained valuable in Ebonyi state, SE Nigeria owing to the lack of surface water reservoir supply facilities maintenance culture and inconsistencies attributed to various limiting factors. But in the study area, groundwater exploration has always being critical since secondary features such as fractures control groundwater movement and occurrence. Intermittent water shortages which lower drilling success rates of water boreholes have also resulted from negligence to the application of geoscientific techniques. To study the groundwater potential and conditions in details, we applied an integrated suite of surface-geophysical methods to characterize the hydrogeology of fractured shale aquifer at the Presbyterian Church, Kpiri-Kpiri, Ebonyi state, SE Nigeria. First, an EM 34-3 electromagnetic anomalies were identified and determined as the location and lateral continuity of fractures and to identify the hydraulic properties of transmissive fractures in the region 180-300 meters (highest electrically conductive anomaly). Second, 3 Vertical Electrical Soundings (VES) using Schlumberger configuration with AB/2 spacing ranging from 3.5 m to 165 m were obtained with the main objective of determining the formation resistivities and depth to the aquifer. The last but not the least was the results of an Azimuthal Resistivity Survey (ARS) indicating from graphical interpretation of survey data that the mapped fractures trend generally in the northwest-southeast direction at the depths of 28.3, 40.0 and 50.0 m with the coefficient of anisotropy ranging from 1.15 to 1.55. Areas with low resistivity values were associated with the fracture zones inferring high secondary porosity and high electrical conductivity. This investigation illustrates the effectiveness of the use of combine geophysical methods for identification and evaluation of electrically conductive fracture zones.