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Title: Carbon dioxide-water-rock interaction and hydrogeochemical evolution of thermal and cold ground waters in Wonchi Crater Lake and Ambo- Woliso area.
Advisors: Seifu Kebede(Dr.)
Keywords: hydrogeochemical evolution
CO2-water-rock interaction
CO2-water-rock interaction
trace element mobility,
Wonchi Crater Lake
Copyright: May-2011
Date Added: 24-Jul-2012
Publisher: Addis Ababa University
Abstract: Isotopic and geochemical data are used to study the hydrogeochemical evolution of thermal and hypothermal ground waters and CO2-water-rock interaction of ground waters around Wonchi, Woliso and Ambo area. Geochemical data are classified by Q-mode hierarchical cluster analysis in to objective groups in order to identify ground waters that have the same hydrogeological and chemical nature so that to conduct inverse geochemical modeling. HCA classified the water in to two major groups of high and low TDS and six sub-groups. The waters in the classified subgroups are similar in chemical composition, geology and the depth in to shallow and deep aquifer. Hydrogeochemical evolution of ground waters of the study area is highly influenced by two regional structures like YTVL and Ambo-Wonchi-Butajira faults that cut across this region. Thermal and gaseous ground waters of the study area are particularly aligned along these structures. The CO2 influx to ground waters of the area is due to the deep seated faults that bring this gas from deep source of metamorphic decarbonation or mantle gas origin. The source of CO2 gas is suggested by using δ13C isotope indicates high values are in thermal and gaseous mineral waters of the region. High TDS thermal and gaseous ground waters are characterized by NaHCO3 in Wonchi and Woliso area while Ambo area is characterized by NaCaHCO3 type waters. Low TDS ground waters are suggested as shallow and cold ground waters of recharge area that undergone less water-rock interaction and characterized by δ18O enrichment and CaHCO3 and CaMgHCO3 water types except in some mixed ground waters. Stable isotope data indicates that thermal and gaseous ground waters are depleted in δ18O except in Wonchi area ground waters that shows δ18O enrichment due to hydraulic connection with Lake Wonchi. The effect of the influx of CO2 to ground waters of this region plays a major role in CO2-waterrock interaction to be significant and silicate hydrolysis like dissolution and precipitation of silicate minerals during ground water chemical evolution. Trace element mobility is observed in high TDS thermal and gaseous ground waters due to strong CO2-water-rock interaction. Heavy metals that are harmful to the human and environment like Sr, Ba, Mn,Fe and Al are observed in some thermal and mineral waters of the study area above the permissible concentration of WHO drinking water standard.
Description: A Thesis Submitted to the School of Graduate Studies of Addis Ababa University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Hydrogeology
URI: http://hdl.handle.net/123456789/3468
Appears in:Thesis - Earth Sciences

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