Journal of Earth Sciences and Geotechnical Engineering

Integrated Geophysical and Hydrogeochemical Studies of Shallow Aquifer Contamination in Osubi, Near Warri, Southern Nigeria

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• Abstract

  Integrated geophysical and hydrogeochemical studies of shallow aquifer contamination emanating from dumpsites in Osubi area, near Warri, Southern Nigeria has been carried out. This was with a view to mapping contaminant presence and its impact on groundwater in the area. Geophysical methods employed include the Spontaneous Potential (SP), adopting the Gradient and the Fixed Base array techniques, the Dipole-dipole array techniques, and the Electrical Resistivity, adopting the Vertical Electrical Sounding(VES) method. A total of Nine (9) VES stations were occupied across the dumpsite using the schlumberger configuration with electrode separation, AB/2 ranging from 40 to 225 m. Dipole-dipole profiling was carried out along two orthogonal traverse lines of length ranging from 50 to 250 m with electrode separation of 5 m. Spontaneous Potential profiling was also carried out with electrode spacing of 5 and 10 m. From the dumpsite area, water samples were collected from boreholes, hand dug wells, and swamps, close to and far away from the dumpsites for chemical analysis. All these measurements were carried out in both the rainy and dry seasons in order to establish the seasonal variation of the migration of leachate from the dumpsites. The geoelectric sections from the VES generated revealed three to four probable subsurface geoelectric units, which are the topsoil, clayey sand/sandy clay and sand. Around the dumpsites, the resistivity values from the VES and Dipole - dipole measurement to a depth of about 15 m varies from 18 to 400 ohm-m as against higher values of up to 2500 ohm-m outside the dumpsite area. Also, the spontaneous potential (SP) profiles show high positive potential of up to 500 mV outside the dumpsite area to as low as -450 mV around the dumpsite area in both seasons. The low potential and resistivity values around the dumpsite area could be the signature of the oxido-reduction phenomenon occurring at depth in the contaminated groundwater.