Assessment of Groundwater Pollution using Geophysical Norms and GIS as a Tool, a Case Study of Part of Ikeja, Lagos State, Nigeria West Africa

Abstract

GIS and Electrical resistivity method of geophysical methods has been combined for the assessment of groundwater potential in Ikeja Local Government of Lagos State, Nigeria. Ten (10) vertical electrical sounding was carried out using the High resolution Abem Terrameter Sas 4000 Earth resistivity Meter.Curve matching techniques and Win Resist software were used to process and iterate VES data; Auto CAD 2012 version was used to draw the geoelectric section using the depth of each lithology and was then imported into the Arc GIS to perform several queries. The study area is situated in Ikeja, Lagos state and falls within the south-western Nigeria. The groundwater regime of the selected location has been delineated into Good quality fresh water, Good quality water, Intermediate quality fresh water, and Poor quality fresh water. The resistivity of the vertical electrical sounding carried out in the study area varies from 15.6Ωm to 1440Ωm. Fourteen(14) Geoelectric layers were delineated from the study area includes the Topsoil, Sand, Clayey sand, Coarse sand, Sandy clay, Clay, Clay/sand intercalation, gravelly sand, sand stone, silty clay, fine sand, clay with intercalations of thin sand layer, and coarse sand/sandstone. The pollution plume was noticed in VES 1, 4, 5 and 9 and the effect was more pronounced in VES 9 because of the leachate effect from Olushosun Landfill characterized with sand having resistivity range from 27Ωm to 30Ωm.This signify that the groundwater has been polluted at the surface.