The use of Vertical Electrical Sounding (VES) to investigate the extent of groundwater contamination and lithology delineation at a dumpsite in Aluu Community, Rivers State

Abstract

Vertical electrical sounding (VES), an electrical method of geophysical exploration, using the Schlumberger array has been applied in an attempt to check the vertical extent of penetration of contaminated leachate from a waste dumpsite in Aluu community of Rivers State. Lithology delineation has also been interpreted from the VES result. Data were acquired in a single VES run with AB extending 100 m and maximum MN = 6 m. The acquisition was done using Ohmega Resistivity Meter (Series No. 0138), a product of Allied Association Geophysical Ltd. The result of the survey interpreted by IP2win software shows a characteristic KH curve type. Four layers of known thicknesses 0.43 m, 0.55 m, 2.7 m and 14.9 m were identified; a fifth layer which is suspected to be an onset of clean aquifer at a depth of 18.6m was also identified. The chemical make-up of leachate from waste dumps generally increases hardness and conductivity of groundwater. The VES result shows a sharp drop of resistivity value from 115 Ωm and 405 Ωm for the first two thin layers to resistivity values of 119 Ωm and 182 Ωm for layer three and four respectively, being an indication of an aquiferous zone with different levels of contamination. According to our results from this geophysical survey (VES), one must drill to about a depth of 20 m to be sure of a getting a portable drinking water in the area of study. However, from the result, there is no clear evidence of thick clay inter-beds to act as seal; hence, the aquifer zone of the area is still at risk of further contaminant penetration.

Keywords: Vertical Electrical Sounding, Aquifer, Groundwater, Resistivity, Lithology