Application of Darcy Tools and Advection– Dispersion Models to Predict the Spatial and Temporal Variations of Contaminants in Borehole Water: A Case Study of Attisa Kingdom, Yenagoa

This study integrated groundwater quality assessment with Darcy-based mass-flux analysis and the Advection– Dispersion Model (ADM) to investigate contaminant transport in the shallow, unconfined aquifer of Akaba-Attisa in the Niger Delta, Nigeria. Groundwater samples were collected from three boreholes (A–C) aligned along the inferred flow direction and analyzed for physicochemical parameters, major ions, nutrients, and trace metals using standard WHO and NSDWQ protocols. Numerical modelling was applied to quantify groundwater flow, contaminant fluxes, and dominant transport mechanisms. Results indicate a Ca–Mg–HCO₃ groundwater facies with increasing mineralisation and nitrate contamination toward the mid-gradient well (B), identified as the plume core. Computed groundwater velocity (0.37 m/day) reflects a slow but persistent flow regime typical of shallow aquifers. Darcy-based mass flux calculations show that conservative solutes such as nitrate, TDS, chloride, bicarbonate, and hardness exhibit the highest fluxes, with a consistent hierarchy of B less then C greater than A. ADM results further confirm that advective fluxes exceed dispersive fluxes by more than an order of magnitude for most parameters, supported by Peclet numbers greater than unity, indicating advection-dominated transport. Sensitivity analysis demonstrates that reasonable uncertainty in hydraulic conductivity, porosity, and dispersion coefficients does not alter the dominance of advection or the observed plume structure. Public health evaluation reveals nitrate exceedances at downgradient wells, implying sustained advective delivery and elevated chronic exposure risk. The combined Darcy– ADM framework provides a robust basis for linking groundwater flow dynamics with contaminant migration and health risk, offering a valuable tool for groundwater protection and management in shallow aquifer systems.