Hydrogeochemical assessment of groundwater of Igboora Area, Southwestern Nigeria

Abstract

The people of Igboora rely on groundwater for their domestic water supply. A hydrogeochemical study was carried out on twenty-seven  groundwater samples collected from various boreholes across the study area to determine the suitability of the groundwater for drinking purpose. The total dissolve solids (TDS), electrical conductivity (EC) and pH of the water were measured in the field directly, while the concentrations of major ions were done in the laboratory using flame photometry and spectrophotometry methods. The hydrogeochemical facies classes was done with piper plot and the likely enrichment source(s) of the chemical facies were interpreted with Gibbs plot in conjunction with correlation analysis. The results showed that the pH was between 5.0 and 6.7 at an average (av.) of 5.8; TDS ranged from 50 – 280 (av. 183) mg/L and EC was 110 – 560 (av. 373) μS/cm. The concentrations of the major cations in mg/L were: 5 – 105.5 Ca²⁺, 1 – 11.9 Mg²⁺, 0 - 95 Na⁺, 0 – 112 K⁺, while for anions the ranges were, 9 - 58 HCO₃ - , 6.8 – 28.8 CO₃ ^2-, 1.1 – 29.4 SO₄ ^2-, 2.9 – 26 Cl- and 16 – 90.5 for NO₃ -. From the mean values, the order of the cationic dominance was Ca²⁺ > K⁺ > Na⁺ > Mg²⁺ while that of anionic was NO₃ -> HCO₃ ^- > CO₃ ^2- > CI- > SO₄ ^2- . The hydrogeochemical facies in the groundwater was  mainly Ca-HCO3 type with minor occurrences of Na-HCO₃ and Ca- Na-HCO₃ types. Enrichment source of the cationic chemical facies was mainly rock dominated, while that of the anionic were from meteoric and biogenic sources. From the results of correlation analyses, the TDS has direct and positive relationships with most chemical constituents, indicating that the analysed ionic constituents dominated the dissolved solids in the groundwater. The groundwater can be said to be potable except that the water in the boreholes is slightly acidic and nitrate concentration exceeded recommended limit of 50 mg/L in many of the samples.