APPLICATION OF ELECTRICAL RESISTIVITY METHOD FOR SUBSURFACE LITHOLOGICAL MAPPING AND IMAGING OF HEAVY METAL POLLUTION– A CASE STUDY OF DELTA STEEL COMPANY, IN OVWIAN ALADJA, SOUTH WEST NIGER DELTA
Abstract
The application of geophysical method in subsurface geological mapping has gained reference over the years. The geophysical methods especially electrical resistivity method has the capability to map and delineate lithology at varying depths. The aim of this project is to map the subsurface lithology of Ovwian-Aladja using vertical electrical sounding (VES) survey and also to determine the possible pollution plume in the study area using 2D ER/IP imaging survey. Four (4) 2D ERT/IP traverses identified as traverses-1, 2, 3 and 4 were acquired at the study site and six (6) VES data. Data processing and inversion was done using Res2Dinv software application for simultaneous inversion of the ER and IP data sets and Win-resist application for VES data iteration. The result of the VES interpretation revealed four (4) to five (5) geoelectric layers that are composed of lateritic soil, sandy soil, clay, sandy clay and clayey sand lithologies. 2D ERT/IP inversion showed low resistivity contaminant plume (resistivity of 1.23-8.87 Ωm) observed at depth of 6.38 m within the subsurface at electrode position 60 m and 80 m respectively in traverse-1, while in traverse-2 low resistivity contaminant plume (resistivity of 32.0-65.6 Ωm) was observed at depth of 3.75 m to 12.4 m 6.38 m within the subsurface at electrode position of 20 m, 60 m and 80 m respectively. The low resistivity is due to high electrical conductivity contained in the heavy metal effluents discharged into the environment. The purpose of the IP-chargeability data inverted alongside electrical resistivity data was to isolate the low resistivity anomalies from the contaminant plumes due to heavy metal from low resistivity clay Formations within the subsurface. The low resistivities correlated with low IP values. From the maximum depth delineated from 2D imaging (15.9 m), and correlating this to the subsurface geology of the study area; it is evident that groundwater pollution is inevitable. Therefore, environmental management of water quality in these areas should be given top priority in view of the pollution effect caused by the age long steel company activities in their factory.
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