Isotopic and geochemical data are used to study the hydrogeochemical evolution of thermal andrnhypothermal ground waters and CO2-water-rock interaction of ground waters around Wonchi,rnWoliso and Ambo area. Geochemical data are classified by Q-mode hierarchical cluster analysisrnin to objective groups in order to identify ground waters that have the same hydrogeological andrnchemical nature so that to conduct inverse geochemical modeling. HCA classified the water inrnto two major groups of high and low TDS and six sub-groups. The waters in the classifiedrnsubgroups are similar in chemical composition, geology and the depth in to shallow and deeprnaquifer.rnHydrogeochemical evolution of ground waters of the study area is highly influenced by twornregional structures like YTVL and Ambo-Wonchi-Butajira faults that cut across this region.rnThermal and gaseous ground waters of the study area are particularly aligned along thesernstructures. The CO2 influx to ground waters of the area is due to the deep seated faults that bringrnthis gas from deep source of metamorphic decarbonation or mantle gas origin. The source ofrnCO2 gas is suggested by using Î´13C isotope indicates high values are in thermal and gaseousrnmineral waters of the region. High TDS thermal and gaseous ground waters are characterized byrnNaHCO3 in Wonchi and Woliso area while Ambo area is characterized by NaCaHCO3 typernwaters. Low TDS ground waters are suggested as shallow and cold ground waters of rechargernarea that undergone less water-rock interaction and characterized by Î´18O enrichment andrnCaHCO3 and CaMgHCO3 water types except in some mixed ground waters. Stable isotope datarnindicates that thermal and gaseous ground waters are depleted in Î´18O except in Wonchi arearnground waters that shows Î´18O enrichment due to hydraulic connection with Lake Wonchi.rnThe effect of the influx of CO2 to ground waters of this region plays a major role in CO2-waterrockrninteraction to be significant and silicate hydrolysis like dissolution and precipitation ofrnsilicate minerals during ground water chemical evolution. Trace element mobility is observed inrnhigh TDS thermal and gaseous ground waters due to strong CO2-water-rock interaction. Heavyrnmetals that are harmful to the human and environment like Sr, Ba, Mn,Fe and Al are observed inrnsome thermal and mineral waters of the study area above the permissible concentration of WHOrndrinking water standard.rnKey words: hydrogeochemical evolution, thermal, gaseous, CO2-water-rock interaction, tracernelement mobility, Ambo, Woliso, Wonchi Crater Lake