Characterization of Dominant Hydrogeochemical Processes in Groundwater in Onitsha Area, Southeastern Nigeria

The characterization of the dominant hydrogeochemical processes in groundwater in Onitsha area, southeastern Nigeria was carried out. This is to identify the dominant mechanisms responsible for the evolution and the chemical composition of the water sources. A total of fifteen (15) groundwater samples were collected from different locations in the study area in August 2022 and these samples were subjected to chemical analysis using standard methods. The results indicated that the water quality parameters were within the World Health Organization acceptable limits for drinking quality although turbidity in six of the samples exceeded the guideline values. The hydrochemical facies were determined using various plots. Piper diagrams indicated that Ca2+ - Mg2+ - Cl- – SO42- was the dominant facies with Ca2+ and Cl- as the dominant ions. The Durov diagram indicate recharge water in limestone and sandstone aquifers and influenced by important ion exchange reactions. However, the Gibbs plots mainly plotted in the rock dominance zone indicating that the major processes controlling water chemistry in the study area were water-rock interaction and dissolution of rock minerals. The ionic ratio plots were employed to determine the mechanisms and reactions prevalent in the study area that influenced the water chemistry. Na/Cl plot indicated that the excess of Cl- over Na+ was balanced by Ca2+ and Mg2+ while the depletion of Na+ with respect to Clindicated ion exchange reaction which could be attributed to silicate weathering confirming the Na/Cl plot conclusions. The relative abundance of anionic facies shows that Cl- + SO42- were more abundant than HCO3- and the plot of Ca2+ + Mg2+ ions against HCO3- ions depict samples with excess Ca2+ + Mg2+. However, Ca2+ +Mg/HCO3 ratio was less than one (<1) and indicated fresh recharge water.