Geological and Geoelectrical Delineation of Aquifer Systems in Girinya, North Central Nigeria

Abstract

Inhabitants of Girinya are unable to access potable water supply. The existing five boreholes were initially productive only during rainy season. They are now totally unproductive. Only three of existing forty-five hand-dug wells yield water all year now. Thus it is expedient to identify areas where groundwater can be sustainably produced from hand-dug wells and boreholes. This was achieved by integrating surface lithological mapping, water level mapping, Vertical Electric Sounding (VES) and 2D geoelectrical tomography techniques. The VES data were interpreted using WINRESIST, while the 2D geoelectrical data were processed and interpreted using RES2DINV. The exposed lithofacies represent Patti Formation and Agbaja Formation. The sandstone facies of the Patti Formation constitutes the unconfined aquifer from which hand-dug wells produce water. The resistivity values and depth to base of the unconfined aquifer range from 48 – 227 Ωm, and 12 – 26 m respectively. The resistivity values support the unconfined aquifer’s high porosity (0.27- 0.42) and hydraulic conductivity (40.2 m/day). One major groundwater convergence zone and two subsidiary convergence zones were revealed. The confined aquifers are the deeper subsurface sandstone facies of the Patti Formation. The study reveals (i) that the bottom of hand-dug wells is generally shallower than the base of the unconfined aquifer, and (ii) that confined aquifers exist below 70 m. This information is beneficial to Girinya as they can now deepen hand-dug wells to depth below 26 m, and drill boreholes to depth below 70 m for sustainable water yield.