Geophysical and geochemical assessments of the environmental impact of Abule-Egba landfill, southwestern Nigeria

Abstract

There have been reports of cases of groundwater contamination in the areas around the Abule-Egba landfill site, Lagos, Nigeria. Based on this, geophysical and geochemical investigations were carried out to ascertain the cause(s) of the pollution and the extent of its impact on surrounding soils and groundwater within the area. A total of eleven vertical electrical sounding were conducted on two profiles established within the landfill area. Electrical resistivity tomography was conducted using a dipole–dipole array. The investigation results showed that the anomalously low resistivity values (> 40 Ω-m) observed from the surface to the depth of about 13 m on the generated geosections are due to leachate pollution of the aquifer units. On the borehole logs, a sand formation which ordinarily should possess a moderately resistive property was found to correspond to all the low resistivity zones characterized by leachate pollution. Geochemical results as observed from the wells within the landfill site show higher concentration of ions such as nitrate which is a diagnostic of leachate solution, as confirmed from geophysical analysis.