Development of a Comprehensive Environmental Chemistry Framework for Risk-Based Land Management in Post-Remediation Oil-Impacted Sites in the Niger Delta

Post-remediation management of oil-impacted land in the Niger Delta lacks a scientifically grounded risk-based framework that integrates chemical residual risk with land use planning, ecological recovery assessment, and long-term monitoring design. This dissertation develops an original, comprehensive environmental chemistry framework for risk-based land management in post-remediation sites across Bayelsa, Rivers, and Delta States. Fourteen sites that had undergone remediation under the Hydrocarbon Pollution Remediation Project were characterised by extensive soil and pore water chemical analysis including petroleum hydrocarbon fingerprinting, polycyclic aromatic hydrocarbon speciation, metal speciation, and residual contamination mapping by portable X-ray fluorescence and cone penetrometer technology deployed in a systematic grid. Ecological soil screening levels were derived from toxicity reference values for endemic Niger Delta soil organisms, filling a critical gap in site-specific risk criteria. Human health risk assessment incorporated exposure factors for subsistence farmer, resident, and worker scenarios. A probabilistic Monte Carlo risk model with spatially referenced outputs was developed for each site type. Post-remediation ecological recovery trajectories were quantified using soil microbial community diversity indices and earthworm bioassays as biological endpoints integrated with chemical data. Results reveal that eleven of fourteen sites contain residual PAH concentrations that, while within current NNPC remediation target levels, exceed derived ecological soil screening levels for sensitive invertebrate species. A revised tiered remediation target framework based on land use and ecological sensitivity zones is proposed as an original regulatory contribution. Keywords: post-remediation, risk-based management, Niger Delta, petroleum hydrocarbons, environmental framework