MAPPING OF SUBSURFACE CONTAMINATION ZONE USING 2-D ELECTRICAL RESISTIVITY IMAGING AND VES TECHNIQUE IN ORON, NIGER DELTA, NIGERIA

F. D. Eyenaka; E. A. Idiong; S. O. Uwak; A. A. Udo

doi:10.5281/zenodo.16743299

F. D. Eyenaka Department of Physics, College of Education, AfahaNsit, AkwaIbom State, Nigeria
E. A. Idiong Department of Physics, College of Education, AfahaNsit, AkwaIbom State, Nigeria
S. O. Uwak Department of Physics, College of Education, AfahaNsit, AkwaIbom State, Nigeria
A. A. Udo Department of Physics, Federal University of Kashere, Gombe State, Nigeria

DOI: https://doi.org/10.5281/zenodo.16743299

Keywords: Contaminated Zones, 2-D electrical resistivity tomography (ERT), vertical electrical sounding (VES), saltwater intrusion and coastal aquifer

Abstract

The integrated geophysical survey measurements carried out in the coastal part of AkwaIbom State specifically Oron Local Government Area located with latitude 4⁰42‘0‘‘ and 4⁰51‘0‘‘N of the equator and longitudes 8⁰12‘0‘‘ and 8⁰18‘0‘‘E of the Greenwich Meridian reveals the extent of aquifer intrusion by saltwater. The geophysical methods employed were 2-D electrical resistivity tomography (ERT) and vertical electrical sounding (VES) techniques using state of the art resistivity meter (IGIS-SSP-ATS-MRT model). The 2-D (ERT) and VES used Wenner and schlumberge electrode configurations respectively with maximum current electrode spacing ranging from 5 to 200m for the field measurement. A total of 8 ERT and 8 VES traverses were covered and the interpretation of resistivity thickness and depth to bottom layer showed that the lithologies are predominantly saline clay/saline clayey sand, medium to coarse sand, fine medium sand, and lateritic/gravelly sand with upper limit resistivity of about 29.15 Ωm for saline clay/saline clayey sand, 362 Ωm for fine medium sand and 68,380 Ωm for lateritic/gravelly sands. The DC resistivity surveys also reveals significant variations within the subsurface coastal sediments with AK curve type having the highest occurrence showing dominant trend of decreasing resistivity with depth. The apparent resistivity of the field data delineate the subsurface formation with evidence of fresh water aquifer at VES 3, 6,7 and 8. The low resistivity values of about 2.4 Ωm, 6.0 Ωm and 6.2 Ωm with thickness of about 1.3m, 2.1m and 0.7m and depth to bottom values of about 1.3m, 2.1m and 0.7m respectively. High resistivity recorded in VESs 7 and 8 were interpreted as lateritic/gravelly sand. Interpreted 2D geoelectrical models showed surface and subsurface aquifer intrusions with lowest electrical resistivity value of about 6.60 Ωm ERT results also showed both surface and subsurface intrusion within the aquifer system at some locations. Hence, the interface mapped showed saline intrusion which is as a result of both anthropogenic and natural factors within the study area.

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