Abstract
This study critically investigates the risk of hydrocarbon activities linked to exploration, extraction, transportation, storage, and oil-related waste disposal on groundwater quality in Niger Delta Region (NDR) of Nigeria. Using a multi-faceted approach involving geospatial risk mapping, in-situ contamination analysis, and groundwater flow modelling, the research provides a comprehensive evaluation of hydrocarbon contamination risks. A source-pathway-receptor (S- P-R) risk framework was developed, integrating 14 thematic layers such as spill volume, proximity to pipelines and wells, precipitation, and population density, to delineate contamination zones. Approximately 16% of the NDR was categorised as moderate to high risk, with high-risk zones predominantly spanning the central delta. Investigations in Rivers and Imo states, identified as hydrocarbon hotspots, revealed that hydrocarbon concentrations, including total petroleum hydrocarbons (TPH), total hydrocarbons (THC), extractable petroleum hydrocarbons (EPH), polycyclic aromatic hydrocarbons (PAHs), benzene- toluene-ethylbenzene-xylene (BTEX), and benzene, exceeded national and global permissible limits by several orders of magnitude. Elevated contamination levels were observed in southeastern areas of the area under focus (Imo and Rivers states), driven by the shallow water table, heterogeneous lithology, and highly porous subsurface materials, emphasizing the need for targeted remediation. Groundwater flow modelling using MODFLOW and MODPATH indicated that contamination from oil spills is spatially localised, with limited vertical migration in aquifers. Backward particle tracking showed that deep groundwater sources (~250 m) remain largely unaffected by shallow contamination, suggesting their viability for safe water abstraction in affected regions. The dissolved phase of hydrocarbon contaminants can be readily transported with groundwater without any visible physical indicators, yet it poses significant risks to human health due to its potential to contaminate water supplies. The dissolved phase can persist in the environment for extended periods and may accumulate in certain areas, leading to long-term contamination risks, altering water quality and impacting aquatic life. This can have devastating impacts on human health, particularly if groundwater is used for drinking or agricultural purposes. While the dissolved phase was not explicitly modelled, advective flow patterns suggest minimal risks to deeper aquifers. However, it is important to consider the potential impacts on shallower aquifers and surface water bodies, which may be more susceptible to contamination. These findings provide critical insights into the spatial and vertical extent of hydrocarbon contamination and highlight priority areas for remediation and groundwater protection. By advancing the understanding of light non-aqueous phase liquids (LNAPL) transport dynamics in deltaic aquifers and offering a structured risk assessment framework, this study contributes valuable tools for assessing groundwater contamination in oil-producing regions. The framework also has broader applicability for sustainably managing groundwater in similar hydrocarbon-rich, ecologically sensitive environments globally.Keywords: Risk assessment, source-pathway-receptor (S-P-R) model, Niger Delta, groundwater flow modelling, Light Non-Aqueous Phase Liquids (LNAPLs).
| Date of Award | 25 Apr 2025 |
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| Original language | English |
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| Supervisor | Mo Hoque (Supervisor) & Malcolm Whitworth (Supervisor) |