Saltwater Intrusion Appraisal of Shallow Aquifer in Burutu Area of the Western Niger Delta with 2D Electrical Resistivity Tomography

Abstract

The area is faced with endemic groundwater quality problems arising from abandoned shallow and deep boreholes. The abandonment of shallow boreholes is presumed to have been caused by saltwater intrusion from the ocean. The objective of this paper is to examine if saltwater is responsible for groundwater degradation associated with shallow groundwater aquifer. To achieve this, a multi-electrodes ABEM SAS 4000 Terrameter was used in the acquisition of 2D electrical resistivity tomography data. Inverse models which estimate actual subsurface geologic resistivity was generated from RES2DINV software and subsequently geologic information were construed from them. The interpretation of the various profiles returned resistivity values which contrasted the existence of saltwater in the pore spaces of groundwater aquifer media in the area under investigation. Resistivity images of values ranged from 2.34Ωm to 70 Ωm where interpreted as clays, greater than 70-90Ωm as fine sand and 90Ωm and above where interpret as medium sand. The evidence revealed by the 2D electrical resistivity tomography investigation combined with geochemistry of groundwater from literature suggested that abandonment of shallow boreholes are probably not related to saltwater intrusion. The study has established that poor groundwater quality being experienced is not caused by saltwater intrusion rather by iron which cannot be separately distinguished from groundwater by resistivity technique. 

Key Word: 2D electrical resistivity tomography, Burutu, Saltwater intrusion, shallow aquifer, western Niger Delta, groundwater quality