Hydrogeochemical processes and groundwater evolution in complex aquifer systems of the Lower Awash Basin, Ethiopia

Study area North-eastern Ethiopia, Lower Awash Basin Study focus The study aims to investigate the processes influencing groundwater composition and evolution using ionic ratios, chemometrics, and inverse geochemical modeling based on major ion chemistry of 164 groundwater samples that were collected from hand-dug wells, springs, and boreholes New hydrogeological insights The Results from the Gibbs plot, Ca + Mg vs SO 4 +HCO 3, Ca/Na vs HCO 3 /Na vs Ca/Na vs Mg/Na, and Chloralkaline indices showed that rock water interaction, silicate weathering, cation exchange, and evaporation are the major geochemical processes that control the groundwater chemistry. Principal component analysis identified three components: PC-I and PC-II reflect geogenic processes, whereas PC-III indicates anthropogenic influences. Hierarchical cluster analysis grouped the groundwater samples in to two main clusters: cluster I represents fresh Ca-Mg-HCO₃ type from the recharge zone alongside a mixed water type from transition zone, while cluster II includes mineral-rich samples from the discharge zone (Na-HCO 3 and Na-Cl). Inverse geochemical modeling indicated that major geochemical process that affect groundwater chemistry and evolution are dissolution of primarily silicate minerals such as plagioclase, olivine, and pyroxene, along with the precipitation of calcite and clay minerals. This study addresses the gap in conventional hydrochemical approaches in the understanding of hydrogeochemical processes by employing a quantitative approach and contributes in the formulation of policies for sustainable groundwater resource management.