Geochemistry of Natural Water Systems in Ugwulangwu, Ebonyi State, Nigeria

The study area is underlain by Albian (Asu River Group) and Turonian (Ezeaku Formation) sediments which consists of calcareous sandstones with subordinate silty shales and black carbonaceous shales respectively. The hydrogeochemistry of the groundwater and surface water system was evaluated by analysing 25 water samples drawn from 15 bore holes/ hand-dug wells and 10 surface waters locations. The analytical results showed that for both groundwaters and surface water bodies the pH range is from 5.50 to 8.0 which indicates mildly acidic to mildly alkaline environments. Both the groundwater and surface waters have low solute concentrations which suggest small residence time of recharge water in the rocks. For the groundwater samples, total hardness ranges from 20-160mg/l with most values being greater than 100mg/l which indicates waters that are moderately hard to hard. The surface waters are generally softer than the groundwater with total hardness being mostly under 100mg/l in the groundwater. In the groundwaters, cation concentrations are in the order Mg2+greater thanNa+greater than Ca+ while anions follow the order HCO3-greater thanCl-greater thanSO42- but for the surface waters, it is Na+ greater thanMg2+greater thanCa2+ and anions have the order, HCO3-greater thanCl-greater than SO42. The difference in cationic chemistry between groundwater and surface waters is attributed to cation exchange reactions in the aquifer. The average value of manganese in the groundwater is 105.85mg/l but only few surface water samples had manganese. The indication is that manganese carbonates are reacting with water to release pyrolusite (Mn O2) into the water. The application of ionic ratios to the interpretation of the geochemical analysis result showed that important processes such as dolomite dissolution, carbonate weathering and dissolution of ferromagnesian minerals and cation exchange are responsible for the chemical composition of the natural waters.