Hydrogeological Characterisation of the Rima Group Aquifer System in Sokoto State

The Rima Group sedimentary sequence in Sokoto State, North West Nigeria, hosts the principal regional aquifer supplying groundwater to Sokoto city and surrounding rural communities, yet systematic professional characterisation of its hydraulic parameters and water chemistry remains limited relative to the dependence placed on this resource. This study undertakes a hydrogeological characterisation of the Rima Group aquifer system through systematic borehole construction, pump testing, and hydrochemical sampling across the Sokoto Rima Basin. Twelve monitoring boreholes drilled to depths ranging from eighty to two hundred metres were pump tested using step-drawdown and constant rate pumping tests to determine transmissivity, storativity, and specific capacity. Aquifer test data were analysed using Theis and Cooper-Jacob methods, with results cross-validated using Hantush-Jacob methods where semi-confined conditions were identified. Groundwater samples collected from the monitoring boreholes and existing production boreholes were analysed for major ions, fluoride, nitrate, and selected trace elements. Hydrochemical facies were identified using Piper trilinear diagrams, and water quality was assessed against WHO and NSDWQ standards. Groundwater flow direction and recharge mechanisms were interpreted from potentiometric surface maps and stable isotope data. Findings directly support the Sokoto State Water Board's ongoing aquifer management plan and long-term safe yield determination. Keywords: Rima Group, aquifer, hydraulic testing, hydrochemistry, Sokoto State.