Abstract

The 2D Electrical Resistivity Imaging (ERI) and Vertical Electrical Sounding (VES) techniques were deployed for groundwater extraction at a school located in Oworoshoki, Kosofe, local government area, Lagos. This becomes necessary due to two failed existing hand dug wells within the school premises. 2D ERI data and thirty VES data were acquired along five profiles. The results revealed four to five geoelectric layers which correspond to the topsoil, clay, clayey sand, sandy clay and sand. The topsoil is characterized by resistivity values ranging from 42.5 to 3798.4 Ωm. The clay has resistivity values ranging from 7.9 to 48.1 Ωm. The sandy clay has resistivity values ranging from 21.0 to 59.0 m. The clayey sand in VES (16, 17 and 26) has resistivity values between 72.9 to 96.5 Ωm. The sand identified at the VES (1 to 18 and 22 to 30) has resistivity values of 116.7 to 1531.3 Ωm at the shallow layer which is suspected to be the seasonal aquifer where most of the existing hand dug wells were situated. The sand at the fourth to fifth layer across VES (1, 2, 3, 6, 7, 8, 11, 12 to 15, 18 and 25) with the resistivity values between 107.2 to 450.0 Ωm represents a good aquifer where groundwater could be tapped. The 2D resistivity structures were able to delineate the shallow aquifer thereby complementing the VES results. Hence, the study recommends that borehole could be sunk at depth range (39.5 to 90.3 m) in the study area.

Keywords: Groundwater, 2D Electrical resistivity imaging, Vertical electrical sounding, Aquifer, and Extraction