Determination of extent of contamination using electrical resistivity method in a basement complex terrain, Southwestern Nigeria

Abstract

Geophysical investigation involving the use of the electrical resistivity method was carried out to determine the extent of contamination at a waste  management site in Obafemi Awolowo University Teaching Hospital Complex (OAUTHC), Ile-Ife, Osun State Southwest Nigeria. As a result, 1D and 2D  imaging techniques of the electrical resistivity method of prospecting were adopted involving Vertical Electrical Sounding (VES) and dipole-dipole  profiling, respectively, using Schlumberger and dipole-dipole electrode configurations. VES and dipole-dipole data were acquired at five (5) locations and  along three (3) traverses, respectively, and interpreted quantitatively using a partial curve matching technique and computer-assisted 1-D forward  modelling and inversion. A maximum of four (4) main geoelectric layers, namely: topsoil, weathered layer, fractured rock and fresh basement rock, were  delineated in the area. The topsoil and weathered layer resistivities and thicknesses vary from 58–61 Ωm, 0.4–1.2 m, and 17–289 Ωm, 3.5–13.2 m,  respectively. The fractured rock has a resistivity of about 400 Ωm with a thickness of > 15 m; the fresh bedrock's resistivity was >2,000 Ωm. Therefore, a  relatively low resistivity of less than 20 Ωm observed within the study area accounted for the impacted zone. In conclusion, the landfill site had been  impacted by the leachates in the area up to a maximum depth of about 8.0 m. The southeastern part of the area was most impacted.