Geoelectrical Investigation of the Groundwater Potential in Eti-Osa, Lagos State, Nigeria

Abstract

An electrical resistivity survey was conducted in Eti-Osa, Lagos State, Nigeria, to characterize the subsurface lithologic units, delineate the underlying aquifer, and assess groundwater potential. The study utilized an ABEM SAS 1000 terrameter for the data acquisition. Eight vertical electrical soundings were carried out using the Schlumberger electrode configuration. Data interpretation, both qualitative and quantitative, was presented through tables, charts, and sections. The interpreted geoelectric models revealed three to five layers with varying lithologies, including topsoil, sand, silty sand, sandy clay, silty clay, and clay. The first geoelectric layer, with resistivity values ranging from 8 Ωm to 320 Ωm, is relatively thin, with a thickness between 0.4 m and 3 m. The second layer exhibits thicknesses of 1.3 m to 15 m and resistivity variation between 1.5 Ωm to 185 Ωm. The third layer varies in thickness from 1 m to 36 m, with varying resistivity between 9 Ωm to 335 Ωm. The fourth geoelectric layer has a thickness range of 5 m to 20 m and resistivity values between 1.6 Ωm and 193 Ωm. The basement resistivity ranges from 3 Ωm to 361 Ωm. The study identified the sand layers, particularly at VES points 1, 2, 3, and 8, as the most promising for groundwater extraction. In contrast, VES points 4 and 5 are less favorable, and points 6 and 7 may yield lower-quality water. It is recommended that boreholes be drilled to depths greater than 20 meters at VES sites 1, 2, 3, and 8 for optimal water quantity and quality. However, sites 3 and 8 may be at risk of contamination due to shallower depths.