Hydrogeophysical Investigation of Fractured Shale Aquifers in Ikwo and Environs, South-Eastern Nigeria

Abstract

AbstractResults obtained from the interpretation of vertical electrical sounding (VES) were combined with geological data to determine the groundwater potential of the study area. The dominant lithology in the area is the shales of the Asu River group of Albian age. The tectonic activities that took place in Santonian times resulted in folding, uplift, and intense fracturing of the shales of the study area. The challenge lies on how to map the fracture zones in the shales in order to optimally exploit the groundwater resources in the area. Ten (10) vertical electrical soundings (VESs) with maximum current electrode (AB) spread of 300 m were acquired using the Schlumberger configuration. Four (4) of the soundings were carried out near existing boreholes for comparative purposes between the geological and geoelectric sections. Layer parameters (aquifer thickness, depth to water, transverse resistance, etc.) were obtained after data processing with the IP12 Win™ software. The derived layer parameters were combined with borehole logs and pumping test data from existing boreholes to estimate aquifer hydraulic parameters in other locations without boreholes. Results show that the depth to the fractured shale aquifer ranges from 22.1 to 54.9 m at Ekpelu (VES 9) and Ndufu Alike II (VES 2), respectively, while aquifer thicknesses vary from 19 m at Ndufu Alike I and II (VES 1 and VES 2) to 56.4 m at Amainyima (VES 10). Hydraulic conductivity varies between 0.0047 m/day at Ndufu Alike I (VES I) and 0.300 m/day at Onyikwa playground (VES 5), while transmissivity varies between 0.0893 m2/day at Ndufu Alike I (VES I) and 9.780 m2/day at Onyikwa Playground (VES 5).KeywordsAquifer parametersVertical electrical soundingFracturesGroundwater