Groundwater investigation within the basement complex, North Central Nigeria, Using magnetic and resistivity method

Abstract

The research focuses on using an integrated approach to locate viable locations for sitting boreholes within the Bosso local government area of Niger State. An area within the basement complex in North Central Nigeria is enclosed by longitudes 6.25′ to 6.31′ and latitudes 9.35′ to 9.45′, with a total area of 16 by 8 km2. This work is central to employing both magnetic and electrical methods of exploration. The derivatives of residual magnetic intensity data for the area were employed to locate regions within the area that are fractured or faulted and could give access to the required underground water. This was followed by conducting Vertical Electrical Sounding (Schlumberger array) within two selected sites within the faulted area and one site outside the faulted area to serve as a control. First vertical derivative displayed lineaments labelled (A), (B), (C), (D), (F), and (G), which are mostly in the Northeast–Southwest (NE-SW) direction. Three sites were chosen for Vertical Electrical investigation for groundwater; sites A (on latitudes 9° 40′ 37.11″ to 9° 41′ 37.1″ N and longitudes 6° 29′ 52.64″ to 6° 30′ 51.56″ E) and B (latitudes 09° 40′ 37.17″ to 09° 41′ 37.15″ N and longitudes 06° 29′ 51.66″ to 06° 30′ 51.55″ E) are within the fractured zones and site C is outside the fractured zone which serves as a control. Thirty-six (36) VES points were sampled on each of the three sites measuring 500 by 500 m2. Result of Vertical Electrical Sounding carried out indicated three geologic layers comprised of topsoil, intermediate clay formation, and weathered/fractured or fresh basement. The depth of the basement at VES points within sites A and B varies from 25 to 48 m; these are within the faulted zone, while depth of overburden in site C used for control varies from 6 to 18 m. Hence, VES points located within sites A (1) and B (2) are viable for groundwater exploration; points A2, A5, B4, B5, C2, C4, D4, D5, E1, E3, and F4 are high conductivity zone which are prolific for groundwater potential. The depth range for aquifer potential zones is between 22.7 and 50.4 m. Result from site C equally shows two layers, more than 90% of the VES which are not viable for groundwater potential. This work thus recommends sitting of borehole within VES points on site A or B for good yield and authenticates the viability of integrated algorithms for groundwater exploration in the basement complex region.