Abstract

An integrated geophysical investigation involving 2D-Wenner profiling, very low frequency electromagnetic, vertical electrical sounding (VES) and water quality analysis was conducted around Aule area within Akure the capital city of Ondo state southwestern Nigeria where there have been reported cases of groundwater contamination. Also hydrochemical analysis was carried out on five water samples in the area; two from boreholes and others from hand dug wells. Results of the investigation showed that the groundwater had been contaminated by hydrocarbon arising from a filling station in the area. The hydrocarbon contaminant plumes are characterized by relatively high resistivity values (> 200 Ω-m) and were delineated to a depth of about 10 m. Hydrochemical results showed that three of the sampled water have higher total dissolved solids (TDS) (>240 ppm) compared to the remaining water samples. The major ions identified includes (Na⁺, K⁺,Cl^-,Mg^2+,,Ca²⁺ and NO₃^-). The total dissolved solid (TDS) and electrical conductivity shows values not in agreement with WHO standards. Twelve (12) Vertical Electrical Sounding (VES) stations were occupied along three traverse lines trending NW-SE and N–S direction. The vertical electrical sounding results indicate maximum of four subsurface layers-Top soil, hydrocarbon contaminated clay, weathered layer and the fresh basement. The VLF-EM results assist in the delineation of non conductive zones which in most cases coincides with the hydrocarbon contaminated plumes delineated by the 2D-pseudo section obtained from modeling the results obtained from Wenner profiling. The contaminant plume has migrated to a significant depth thus posing an inherent danger to the inhabitant of the area.

Key words: Hydrochemical analysis, contaminant plumes, Wenner profiling