Investigation of the Effect of Highway Runoff along Lagos-Badagry Expressway Using Electrical Resistivity Tomography and Physiochemical Methods

Abstract

Geophysical and physiochemical investigations were carried out along Lagos-Badagry Expressway, Southwest, Nigeria on three locations dominated by highway runoff, with a view to monitoring the effect of highway runoff on nearby groundwater. The locations were: Iyana Isashi, Iyana Era and Agbara. An overview of the subsurface resistivity distribution was achieved employing Vertical Electrical Sounding (VES) using Schlumberger array and Two-dimensional (2D) resistivity imaging (Wenner array). The ABEM Terrameter SAS 1000 was used for both VES and 2D resistivity surveys and the data were analysed using IPI2win and RES2DINV, respectively. The VES results showed up to four geoelectric layers consisting of sand, clayey sand, clay and sandy soils. The resistivity at Agbara was found varying from 3.52 Ωm - 11 Ωm. This low resistivity value showed a high level of infiltration of highway runoff into the subsurface, thereby causing contamination of the groundwater. Iyana Isashi and Iyana Era have a relatively moderate resistivity values ranging from 103 Ωm to 178 Ωm. Physiochemical analysis of groundwater samples collected at the study locations revealed high electrical conductivity, total dissolved solids and pH values. The results of the borehole sample taken at 32 m away from the profile point at Agbara produced higher values of electrical conductivity and total dissolved solids than those of other locations, hence validating the electrical resistivity surveys, indicating that the groundwater sample from the survey point at Agbara is contaminated.