Groundwater Exploration Using Vertical Electrical Sounding And 2D Electrical Resistivity Tomography In Shale Formation: A Case Study Of Sabongida, Plateau State, North Central Nigeria

Abstract

Sabongida is characterized by lots of abortive boreholes which are often shallow as a result of the complex nature of shale formation in the area and limited application of integrated geophysical techniques before drilling of boreholes. The presence of shale formation in the area makes it extremely difficult to drill productive boreholes, while the existing hand dug wells are always shallow due to the difficulty in digging deeper wells, this and other factors motivated the choice of the study location for the purpose of proffering solutions to solve the perennial water problem in the area. Twenty-two (22) vertical electric soundings data (VES) using Schlumberger array with the aid of Ohms mega resistivity meter were conducted with electrode spread of AB/2 = 215 m and eleven (11) 2D electrical resistivity tomography data (ERT) using ADMT – 600 S - X equipment were acquired. ERT was conducted using 20 m as the length of each profile with 300 m in 10 profile lines and 400 m as the depth of probing. The result of the VES interpretation shows three to five geo-electric layers while the geo-electric section revealed the aquifers to consist of sandstones with varying thicknesses. Two groundwater potential zones were delineated as shelly sandstones and clayey sand. The different color band indicates the different layers within the ground as the soil resistivity varies, blue indicates low resistivity values, green - yellow indicates moderate resistivity values while high resistivity values are brown - red. The results from the 2D images indicate the low resistivity regions, suggesting aquifer is within the depths of 150 to 300 m. Thus, the recommended depths for drilling of productive boreholes are 180 to 210 m and 270 to 300 m in Sabongida.