Flow direction and velocity determination of dumpsite-induced groundwater contamination in part of Delta State, Nigeria

Abstract

Contaminant flow direction and velocity from dumpsite in Osubi, Okpe area of Delta State, Nigeria, have been determined. Two-dimensional resistivity imaging, employing the dipole–dipole electrical resistivity technique, and radial resistivity sounding were used for this study. Also, the Groundwater Vistas version 4 was also used for particle/contaminant tracking, to determine flow direction and velocity. The low resistivity of 52 to 130 Ω-m of the topsoil and the second layer to a depth of about 25 m may be an indication of the presence of leachate from the dumpsite. The flow direction across the study area is in the NE–SW direction, which is in agreement with the flow direction generated from the anisotropy polar diagrams from the radial sounding. The path contour lines show the model groundwater steady state head distribution of the hydrogeological system of the area. An approximate head gradient of about 0.0006 towards the south-west was then calculated using the model output head distributions for the area. Therefore, from the groundwater flow equation, the flow velocity was calculated using the head gradient, porosity and hydraulic conductivity to be 0.0169 m/day or 6.0 m/year. If advective flow is assumed, therefore the contaminant would flow at an average speed of 0.0178 m/day or 6.0 m/year.