Geoelectrical Prospecting for Regolith Aquifer in Kundu, Zungeru Sheet 163, Nigeria

Abstract

This work employed surface geological mapping, surface fracture density and permeability mapping, in combination with Vertical Electrical Sounding (YES), Spontaneous Potential (SP) and Induced Polarisation (IP) sounding to delineate places within Kundu where hand-dug wells would produce water from regolith. Such places should be potential groundwater convergence zones which combine appreciable regolith thickness with resistivity and IP values that indicate low clay content and groundwater saturation. Regolith in this work is defined as the interval from soil's top to the first fresh basement surface. The soundings were conducted at fifty-one stations, using ABEM SAS 4000 device and Schlumberger array with maximum electrode spacing of 200 m. Topographic depression within the first fresh basement surface was identified within longitudes 6°8'34.0S"E - 6°9'00''E and latitudes 9°49'15"N -9°49'26.04"N. The depression constitutes a potential groundwater convergence zone within the regolith. Regolith thickness in this zone ranges from 10 to 20 m. The apparent resistivity values (150 to 450 Ωm) and IP values (lower than 10 ms) indicate groundwater occurrence and very low clay content within regolith aquifer in the zone. Significant surface fracture density (0.045-0.065 m-1) and surface fracture permeability (20-80 m2) characterise outcrops in immediate neighbourhood of regolith in the zone. Mosaic map of regolith base elevation, IP, SP and resistivity values was produced. The map reveals that regolith topographic and electrical attributes indicate high productive potential within SSE to SE (defined by longitudes 6°8'34.8"E; 6°9'0"E and latitudes 9°49'15"N; 9°49'25"N) of the study area. Hand-dug wells commonly produce water from regolith in such zones in basement terrains. Inhabitants of Kundu may dig wells manually into the delineated groundwater convergence zone within SSE to SE of the study area to obtain water from the regolith aquifer.