Hydrogeology of Abuja FCT-Nigeria: A GIS Evaluation

Abstract

Groundwater has been recognized as playing a very important role in the development of Abuja FCT Nigeria's capital, as many private and government establishments depend solely on wells for their water needs. Exploitation of groundwater is delicate due to its potency to contamination and difficulty to remediate aquifers. This study is to evaluate the input of the rock formations to the groundwater solute chemistry and groundwater domestic quality using hydrogeochemical tools and physicochemical parameters: pH, EC, Temperature, TDS, Chloro-alkaline indices, Ionic ratios, Gibbs diagrams, Piper diagrams, Durov diagrams and water quality index. From physicochemical parameters: pH ranged from, 4.8 -7.9; EC, 13.4 -1634 µS/cm; Temperature, 26˚C -36.1˚C and TDS, 17.42 -1094.78 mg/L. The major ions fell below WHO acceptable limits. The sequences of abundance of major ions were, K + > Ca 2+ > Na + > Mg 2+ for cations and Cl − >anions. Borehole depths range from 19.5 -34.5 m with static water levels between 3 -12 m.a.m.s.l. Yields were between 3.2 -7.2 m 3 /Hr. Ionic ratios show ninety-five (95%) percent of the groundwater chemistry resulting from chemical weathering of rock-forming minerals through the dissolution of the host rock. The Chloro-alkaline indices: CAI 1 87.23% are positive indicating exchange of Na and K from water with Mg and Ca of the rocks and 12.77% are negative, indicating reverse softening of groundwater in rocks by infiltrating rainwater while CAI 2 85.11% are positive indicating exchange of Na and K from water with Mg and Ca of the rocks and 14.89% are negative, indicating reverse softening of groundwater in rocks by infiltrating rainwater. Thus chloro-alkaline indices indicate the dominance of alkaline earth elements over alkalis in majority of samples due to direct exchange of Ca 2+ and Mg 2+ from the aquifer matrix with Na + and K + from the groundwater. Gibbs How to cite this paper: Akoachere, R.A., diagram revealed groundwater ionic content was as a result of ion exchange from rock-weathering. Piper diagrams give three water types: 75% are CaH-CO 3 , 21.20% are of MgHCO 3 and 3.19% are of Na + KHCO 3 water types respectively. Piper diagrams also give three hydrogeochemical facies in Abuja FCT: 54.25% are of Ca-Mg-Cl-SO 4 , 42.56% are of Ca-Mg-HCO 3 and 3.19% are of Na-K-Cl-SO 4 hydrogeochemical facies respectively. Durov plot shows 20.21% are anion discriminate Ca dominant; mixed water and 63.83% had no dominant ion; simple dissolution. Water quality indices (WQI) values were between −220 -180, Total hardness (TH) values were between 0 -519.12. These WQI and TH values indicate that 69.2% and 47.37% of the groundwater respectively are suitable for domestic purpose. The groundwater in Abuja FCT is acidic to slightly alkaline in nature, soft to moderately hard and of low to high salinity. Major processes controlling the water quality are the weathering of the host rock through mineral dissolution, cation exchange and inverse cation exchange processes. Ion-exchange, simple dissolution and uncommon diss...