Integrated geotechnical and hydrogeophysical investigation of the Epe Wetland Dumpsite in Lagos State, Nigeria

Abstract

Integrated geotechnical and geophysical investigation of a wetland dumpsite in Epe, Lagos State, Nigeria, was carried out with a view to determining the hydraulic properties of the underlying formation for possible leachate transmission and subsequent subsoil pollution. Eleven boreholes were drilled, lithologically logged, sampled and analysed for hydraulic/hydrogeological parameters. Geophysical investigation involved 1-D Vertical Electrical Soundings (VES) (8 Nos.) and 2-D Dipole-Dipole profiling along five traverses. The survey area is underlain by fine-medium grained sands with coefficient of uniformity values of < 6. The fresh water saturated sandy formation is characterized by relatively high layer resistivity values (5681-9889 Ωm). The mean bulk density is 1.89±0.162 g/cm^-3 ; porosity: 37.84±8.42%; and permeability: 3.0 x 10^-4 ± 1.1 x 10^-4 cm/sec. The 2D images identify leachate impacted zone beneath the waste dump site and its periphery characterized by relatively low resistivity values (4 to 165 Ωm). The study concluded that the sandy nature of the subsoil and its moderate permeability aided subsoil and groundwater pollution by leachate to depths in excess of 15 m.

Keywords: Boreholes, Dumpsite, Hydraulic Property, Pollution Plume, Soil and Wetland