Hydrogeochemical Characterization and Processes Controlling Groundwater Chemistry of Complex Volcanic Rock of Jimma Area, Ethiopia

The sustainable management of groundwater in the Jimma area is complicated by a lack of comprehensive studies on its chemical makeup and the geochemical processes influencing its hydrochemistry. This research aims to fill that gap by examining 51 groundwater samples from various sources, including deep groundwaters, shallow groundwaters, hand-dug well groundwaters, surface waters, and springs within the area primarily consisting of complex volcanic rocks. The goal is to describe the hydrogeochemical characteristics and determine the key processes affecting groundwater composition in this volcanic area. The study identifies clear patterns in cation and anion concentrations. For deep groundwaters, the average cation concentration is ranked as Na+ &gt: Ca2+ &gt: Mg2+ &gt: K+, while shallow groundwaters, hand-dug well groundwaters, surface waters, and springs show a ranking of Ca2+ &gt: Na+ &gt: Mg2+ &gt: K+. The major anions are typically ordered as HCO3&minus: &gt: NO3&minus: &gt: Cl&minus: &gt: SO42&minus:. The quantitative hydrogeochemical analysis indicates that the freshwater types in the region are primarily Ca-HCO3 and Ca-Mg-HCO3, with some highly mineralized Na-HCO&#8323: waters also detected. The weathering of silicate minerals mainly drives the geochemical processes affecting groundwater chemistry. An increase in mineralization, suggested by saturation indices, points to a longer residence time underground, with deep groundwaters exhibiting the highest saturation levels and springs the lowest. This mineralization is especially significant for Mg-silicates and carbonates. Stability diagrams for feldspar minerals further demonstrate groundwater evolution along flow paths, revealing that shallow systems are in equilibrium with minerals like gibbsite, whereas deeper systems achieve stability with albite, Ca-montmorillonite, and microcline. Higher CO2 levels (10&minus:1.5 to 100.5 atm), likely from mantle-magma degassing, add more HCO3&minus: to the deeper aquifers. This study offers the first thorough characterization of the groundwater composition in the Jimma area and provides important insights into the Jimma area&rsquo:s hydrogeochemical development, establishing a basis for enhanced groundwater management within this intricate volcanic aquifer system.