Assessment of Long-Term Groundwater Recovery Trajectories at Decommissioned Tin Mine Sites in Plateau State Using Hydrogeological Modelling

The hydrogeological legacy of extensive tin mining on the Jos Plateau continues to affect groundwater systems decades after decommissioning, and predictive modelling of groundwater recovery trajectories is needed to guide long-term water resource management. This study assesses long-term groundwater recovery trajectories at decommissioned tin mine sites in Plateau State using numerical hydrogeological modelling. A conceptual hydrogeological model was developed from borehole logs, water table monitoring data, geological maps, and recharge estimates for a representative 25-square-kilometre study area encompassing four decommissioned mine sites in the Barkin Ladi district. A transient finite-difference groundwater flow model was constructed in MODFLOW and calibrated against 24 months of observed water table data. Mine pit lake water budget and groundwater-surface water interaction were incorporated as model boundary conditions. Results indicate that groundwater levels in shallow aquifers adjacent to major open mine pits are still declining or at disequilibrium 30 years post-decommissioning, attributable to pit lake evaporative water losses. Recovery to pre-mining groundwater levels in affected sectors is projected to take an additional 15 to 40 years under current climatic and land use conditions. The study identifies four communities whose water supply boreholes are at risk of declining yields within ten years and recommends contingency water supply planning. Sensitivity analysis shows that pit backfilling would accelerate recovery by 12 to 18 years on average. Keywords: groundwater recovery, tin mining, Plateau State, hydrogeological modelling, MODFLOW.