Modelling and Analysis of Groundwater Contamination Transport in Ogoni Land Using Advection-Dispersion Equations

Petroleum hydrocarbon contamination of groundwater in Ogoniland, Rivers State, South South Nigeria, has been documented as one of the most severe environmental pollution cases in sub-Saharan Africa following decades of oil spills and inadequate remediation. This study develops a mathematical model of contaminant transport in the shallow alluvial aquifer system underlying Ogoniland using the advection-dispersion-reaction partial differential equation framework. Aquifer hydraulic properties including hydraulic conductivity, effective porosity, and dispersivity are characterised from borehole pump tests and tracer experiments conducted at three remediation sites. Total petroleum hydrocarbon concentrations in 48 monitoring wells, measured quarterly over two years, provide the model calibration and validation dataset. The advection-dispersion equation is solved numerically using the alternating direction implicit finite difference scheme implemented in Python. Model calibration is performed using the Levenberg-Marquardt optimisation algorithm minimising root mean square error between simulated and observed concentrations. The calibrated model achieves a Nash-Sutcliffe efficiency coefficient of 0.81, confirming adequate predictive skill. Contaminant plume extent projections under continued natural attenuation versus active bioremediation scenarios indicate that active treatment achieves regulatory cleanup standards 4.7 years earlier. The study provides a quantitative decision support framework for HYPREP remediation programme planning in Ogoniland. Keywords: contaminant transport, advection-dispersion equation, groundwater, Ogoniland, petroleum hydrocarbon.