DELINEATION OF AQUIFEROUS ZONES USING GEOPHYSICAL METHODS AND CONTAMINANT FLOW DIRECTION -A case study of dumpsite at Cassidy, Okokomaiko, LASU-Badagry Expressway, Lagos State, Nigeria

Abstract

Introduction: Cassidy area, of Okokomaiko, Ojo, Lagos State, is a rapidly developing area with attendant growing population arising from the presence of University, financial institutions and popularly known Alaba market. Unfortunately, water supply by the water corporation is not readily available. The inhabitants only rely on the surface water and groundwater extracted from hand dug wells and boreholes. Aims: The study is to map the aquiferous zone and establish the groundwater flow direction, with a view to averting subsurface contamination emanated from dumpsite within the area. Materials and Methods: Twenty five (25) Vertical Electrical Sounding (VES) using Schlumberger electrode array, four (4) Electrical Resistivity imaging using Wenner Electrode Array were acquired at four different traverses. Manual groundwater flow direction was also conducted. Results: The identified unconfined aquifer was sand/sandy clay which is overlain by peat/clay soil that is loose and may allow downward migration of the contaminant plumes to deep groundwater. However, the confined aquifer observed to occur approximately at depth 18 m. The electrical resistivity distribution observed decreases upward, south and north. This implies increase in conductivity in such directions and as such indicating the contaminant could be more concentrated near-surface, north and south. Conclusion: The implication of the results obtained with respect to vulnerability to groundwater pollution is that the southern section of the aquifer is more susceptible to receive transported contaminants from the northern part of the study area. The study suggests the potential borehole should be sited in the north-eastern direction with the aid of geophysical survey.