keywords: Coastal aquifer, Ogidigben, saltwater intrusion, 2D electrical resistivity tomography
The area under consideration is faced with absence of fresh groundwater for the people of the community, especially from shallow aquifers. Consequently a 2D electrical resistivity tomography (ERT) was employed to investigate the subsurface geology so as to ascertain why shallow aquifers are not harnessed by shallow dug and borehole wells. Interpreted 2DERT data revealed that profiles nearer the coast depicted significant thin lenses of freshwater zones and thick saltwater zones. Thickness of freshwater lenses varied from 4 m- through- 8 to 16 m. These lenses have thickness that increases with distance from the shoreline towards the land. The low resistivity images which characterized the uppermost layers of some of the profiles at seashore area (911 Night Club) suggest inundation and infiltration of saltwater into the groundwater aquifers caused by tide due to the proximity of the aquifer to the sea. The potentiality of saltwater intrusion into groundwater aquifer is more pronounced around the vicinity of the sea than inland areas. The interface between saltwater and freshwater is situated at 60 m depth below the surface. Consequent upon the identification of saltwater and freshwater zones, the paper suggests pumping optimization of freshwater lenses and management approach centered on continuous monitoring of groundwater quality and water levels.