|dc.description.abstracteng||This PhD thesis investigates the application of isotope techniques in groundwater aquifers, with the main focus on systematic variations of the Strontium (Sr) isotopes and chemical composition including fractionation patterns of rare earth elements (REE).
This thesis is subdivided into five chapters. After the introduction, in the second chapter (chapter 2), an attempt is made to assess the efficiency of the Aquifer Storage and Recovery Project (ASR) by using isotope tracers, such as strontium and stable isotope and to prove the suitability of natural tracers to follow up the artificial recharge process. The results showed that the change in 87Sr/86Sr ratios could be observed during an artificial recharge due to the different isotopic fingerprint of surface water and groundwater. However, the flow direction of the injected water cannot be clearly interpreted because of the limited number of monitoring wells, small distance between each monitoring well and the short duration of injection. In chapter 3, the investigation of variations of the isotopic and chemical composition as well as fractionation patterns of rare earth elements (REE) of three different aquifers at Äspö Hard Rock Laboratory has been carried out over five years. The aims of this study are to identify the possible end-members of groundwater composition and to increase understanding about groundwater evolution of paleo-groundwater in this area as well as the effect of tunnel building on internal mixing of groundwater and chemical change. The Sr-data and REE patterns show especially the long-term groundwater-rock interaction and δ18O values indicate the presence of glacial meltwater in the deep aquifer. Significant chemical changes caused by internal mixing processes or present microbial activity were not observed during the five years of investigation. In chapter 4, we make an effort to clarify the hydrochemical behavior of the CO2-rich groundwaters and identify possible sources of their CO2 in Southern Thailand by analyses of major elements, REE and isotopic composition (3H, δ13C, 87Sr/86Sr). The results show that these CO2-rich groundwaters are characterized by high contents of HCO3-, SO42-, Cl-, Total Dissolved Solid (TDS), Ca2+, Mg2+, K+, Sr2+ and Ba2+. Upper continental crust (UCC) normalized REE patterns show a slight heavy REE (HREE) enrichment with high positive Eu anomalies and they show a specific high 87Sr/86Sr ratio of 0.726, The 3H amount indicates that
CO2-rich groundwaters are submodern groundwater, which were recharged before 1950s; whereas non-CO2-rich groundwaters in the same area show higher amount of 3H (1.50-1.57 TU), which indicates mixing of submodern and modern groundwater. While the δ13C values indicate a deep seated mantel source for CO2. In the future, the attempt is made to combine isotope techniques and modeling techniques together to optimize isotope data as a powerful forecasting tool for a better groundwater management.||de