Hydrochemical Characterization of Shallow Groundwater in Keffi, Central Nigeria

The study assesses the hydrochemical quality and properties of the shallow ground water in Keffi, Central Nigeria, in the Basement Complex terrain. 30 groundwater samples (25 boreholes and 5 hand dug wells) were taken and analyzed for physicochemical properties, major cations and anions using Atomic Absorption Spectrometry (AAS). Three lithological units underlain the study area: Biotite Rich-Granitic Gneiss (20%), Feldspathic Gneiss (35%) and Biotite Schist (45%) with pegmatite veins. Physical parameters showed that the pH range was 5.53-8.72 (mean 7.13), electrical conductivity was in the range of 30.8-260 μS/cm and TDS was 12-231 mg/L suggesting freshwater classification. The abundance of major cations is in the order: Ca²⁺ > Mg²⁺ > Na⁺ > K⁺; the major anions are present in the order: Cl⁻ > HCO₃⁻ > CO₃²⁻ > SO₄²⁻. Based on the Piper trilinear diagram, three types of water were identified: Mixed Ca-Mg-Cl type, Ca-Cl type and Ca-HCO₃ type. The hydrochemical process of rock-water interaction was the most prevalent (66.67% of samples) in Gibbs diagrams with silicate weathering as the main controls on major ion chemistry. Iron was found to be higher (>0.3 mg/L) than WHO/NSDWQ limits in 29 samples, which indicated a possible health concern. It suggests that groundwater quality monitoring and treatment prior to use should be conducted regularly in these impacted areas.