Hydrogeophysical Investigation and Aquifer Evaluation of the Formations in Nsukka Area, Southeastern Nigeria

Abstract

The study targeted the aquiferous Ajali Sandstone and Nsukka Formations that underlies the Nsukka metropolis and its environs (within Latitudes 6 o 80 1 N and 6 o 89 1 N; Longitudes 7 o 21 1 E and 7 o 30 1 E), covering an area of about 210 square kilometres. Thirty four (34) cross array Vertical Electrical Sounding (using the Schlumberger electrode configuration) and records from four (4) selected boreholes have been used to investigate the subsurface distribution of electrical resistivity and to delineate hydraulic properties of aquifers in Nsukka area, Southeastern, Nigeria.The electrical surveys of the area show high values of permeability, ranging from 0.0075 to 0.015cm 2 , hydraulic conductivity, ranging from 8.29 to 16.64m/s, transmissivity, between 455.87 and 1002.48m 2 s -1 , and specific yield, ranging from 2.35 to 4.76m 3 . A tie with the results of borehole logs analysis reveals the presence of at least four layers of contrasting hydraulic conductivity. Analyses, however, suggests that the Nsukka Formation (which overlies the Ajali Sandstone) is thick and poorly conductive while the Ajali Sandstone unit is homogenous and anisotropic and has higher conductivity (especially beyond the depth of 100 m), suggesting a prolific water-bearing formation at such depth and beyond. The Ajali Sandstone aquifer in the area is thick and prolific. The distribution of major geological units, well log data, static water level data were shown to have influence on the groundwater occurrence and flow pattern in the area.