Geoelectrical soil mapping for subsurface hydrocarbon contaminant characterization and remediation site zoning at Alode, Central Niger Delta, Nigeria Nurudeen Onomhoale Ahmed a , Nik Norsyahariati Nik Daud a,* , Ipoola Ajani Okunlola b a Department of Civil Engineering, Faculty of Engineering, Universiti Putra Malaysia (UPM), 43400, Serdang, Selangor, Malaysia b Chemical and Geological Sciences Department, Al-Hikmah University, 240281, Ilorin, Nigeria A R T I C L E INFO Keywords: Geoelectrical subsoil mapping Electrical resistivity tomography (ERT) Subsurface contamination delineation Remediation site zoning Alode community Niger delta Nigeria ABSTRACT Hydrocarbon impacts on subsurface environmental systems occur due to leaked buried pipelines, petroleum facilities sabotage and oil spills during exploration, production, and transportation. 2D geoelectric investigation was carried out on soils of hydrocarbon impacted site in Alode community, Eleme Local Government Area of Rivers State, Central Niger Delta, Nigeria. This was imperative due to the right-of-way spill along a sabotaged petroleum flow line that has been identified for remediation. This study employed a PASI 16 GL earth resistivity meter for Electrical Resistivity Tomography (ERT) with established 5 Wenner-4 electrode array survey lines consisting of 290 horizontal electrical profiles (HEP) probes. The survey was done in a grid format over 100 m lines at 1.5 m, 3 m, 6 m, 9 m, 12 m, and 15 m constant spacing to acquire high-resolution 2D geoelectric data. ERT data inversion was performed using GS RES2DINV and AGI Earth Imager software’s to generate 2D re- sistivity subsurface imageries to map and delineate the hydrocarbon contaminations. The results showed re- sistivity values from 600 Ω-m to above 3500 Ω-m denoted impacted areas, extending beyond the maximum target depth of 6 m, as pertinent for soil excavation procedure during ex-situ remediation within the locality. ERT profiles displayed evident spill geometries at lines 1, 2 and 3 with only significant presence from below 2 m at lines 4 and 5. The result confirms the horizontal direction and vertical trajectory of the spill through a porous medium-grained sandy layer, providing information for impacted area zoning, conducting risk assessments, and designing and implementing appropriate remediation actions. 1. Introduction The discovery of mineral oil in the Niger Delta and the production, processing and transport through buried petroleum pipelines has led to degradation of natural resources and the environment (Aaltonen and Osei, 2022). Often, contaminations by petroleum hydrocarbons occur through leaks and spills due to corrosion and sabotage of oil and gas facilities. Spills pollute the soil and groundwater systems with major impacts being environmental degradation, human health hazards, eco- nomic hardship, and social dislocation (George et al., 2023). It is crucial to assess areas of contamination, remediating and monitoring clean-ups and final quality evaluation of the remediated soil (Ahmed et al., 2019). Geoelectrical methods like electrical resistivity tomography or electrical resistivity imaging (ERT/ERI) technique is a widely adopted subsurface mapping method known for its straightforward principles and efficient data collection by measuring resistivity of the Earth’s surface using specific arrays to generate apparent-resistivity sounding curves, profiling data, or pseudo-sections (Hsin-Chang et al., 2016). These outputs qualitatively depict variations in subsurface resistivity, making ERI valuable in groundwater studies, civil engineering projects, and environmental investigations due to its simplicity and effectiveness (Hsin-Chang et al., 2016). ERT has been increasingly employed for contaminant plume delineation and monitoring in hydrocarbon contaminated sites. It detects changes in subsoil resistivity influenced by hydrocarbon contamination, which generally reduces the resistivity of affected soil layers (Tse and Eshiemomoh, 2016). Geophysical methods, including both surface and down-hole techniques, offer effective means for investigating subsurface hydrogeologic and geologic conditions. These methods have proven valuable in detecting contaminant plumes and locating buried waste materials (Benson, 1993; Che-Alota et al., * Corresponding author. E-mail address: niknor@upm.edu.my (N.N. Nik Daud). Contents lists available at ScienceDirect Physics and Chemistry of the Earth journal homepage: www.elsevier.com/locate/pce https://doi.org/10.1016/j.pce.2024.103726 Received 5 April 2024; Received in revised form 11 July 2024; Accepted 4 September 2024 Physics and Chemistry of the Earth 136 (2024) 103726 Available online 10 September 2024 1474-7065/© 2024 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.