Modelling Fate and Transport of Petroleum Hydrocarbons in the Coastal Aquifer System of the Niger Delta

This study develops and validates a numerical model of petroleum hydrocarbon fate and transport in the coastal aquifer system of the Niger Delta, addressing the lack of site-specific transport models that quantify the extent and rate of groundwater contamination from oil spills at field scale. The Niger Delta's multi-layered coastal aquifer system, characterised by interbedded sands and clays with variable permeability, presents a complex transport domain where dissolved hydrocarbon plumes and light non-aqueous phase liquid migration are influenced by tidal fluctuations, seasonal recharge variations, and biodegradation processes. A conceptual and numerical model was constructed using MODFLOW-USG for groundwater flow and RT3D for reactive transport, calibrated against aquifer test data and available historical water quality measurements from monitoring wells at two contaminated sites in Bayelsa and Delta States. The model incorporates first-order natural attenuation kinetics for benzene, toluene, ethylbenzene, and xylene compounds, with biodegradation rate constants estimated from microcosm laboratory experiments using aquifer material from the study sites. Sensitivity analysis evaluated the relative influence of aquifer hydraulic conductivity, recharge rate, and biodegradation rate on plume extent predictions. Model validation against an independent dataset from a third site shows satisfactory correspondence. Simulations indicate that undisturbed natural attenuation would require decades to decades to reduce concentrations to target levels at both case sites. The study provides a decision-support tool for remediation design and regulatory risk assessment. Keywords: fate and transport modelling, petroleum hydrocarbons, coastal aquifer, Niger Delta, groundwater remediation.