Kebede, Seifu (PhD)Mengesha, Diriba2020-11-102023-11-092020-11-102023-11-092012-03-03http://10.90.10.223:4000/handle/123456789/23139The objective of this study was to assess geochemical evolution of groundwater from plateau to the rift floor in Shinile area and to identify geochemical processes responsible for evolution by analyzing hydrochemical data using conventional graphical methods and multivariate statistical methods. For this purpose water chemistry data of eighty seven water samples from the area are analyzed and interpreted. Q-mode Hierarchical cluster analysis (HCA) is used to classify the eighty seven water samples in to five distinct hydrochemical groups. The results of this analysis revealed that in general salinity and concentration of the groundwater increases from highland areas to the rift floor and water type in the study area evolves from Ca-HCO3 and Ca-Mg-HCO3 dominated type on the highlands to Na-HCO3 and Na-HCO3-SO4 dominated type on the escarpment to Mg-Ca-SO4-HCO3, Ca-Na-SO4 and Na-Cl-SO4 types on the rift floor following the direction of the ground water flow. Principal component analysis, another multivariate statistical method, is employed to analyze the water samples to identify geochemical processes that are responsible for the observed variation in hydrochemistry of the area. The first three principal components accounted for 72.85% of the total variance in the hydrochemistry. The first principal component which explained 46.99% of the observed variance most probably represents dissolution reactions of carbonates and evaporite sediments; the second principal component which explained 15.29% of the observed variance in hydrochemistry most probably represents silicate hydrolysis reaction and the third principal component which accounted for 10.58% of the variance in hydrochemistry most probably represents addition of contaminants to the ground water from anthropogenic sources based on their factor loadings for the different hydrochemical variables. The relationship among the major ion compositions of the water samples are also analyzed to determine if the geochemical processes suggested based on the PCA results are responsible for the observed variations in hydrochemistry of groundwater in the study area. The results of this analysis clearly indicated the occurrence of dissolution reaction of evaporite deposits and carbonate sediments as well as silicate hydrolysis reactions in the study area confirming the PCA results. Finally water quality of the study area is assessed from domestic use and agricultural point of view and distribution of fluoride and SAR of the area are mapped.enGroundwater EvolutionHydrogeochemical ProcessesHierarchical Cluster AnalysisHydrochemistryPrincipal Component AnalysisShinile AreaThesis