Deep welling in the Benedikt area has proven the existence of recently active hydrothermal system in pre-Tertiary basement composed of banded gneiss, marble and schist originating from a regionally metamorphosed sequence of clastic sediments. Two aquifers with very high fracture porosity were tapped—at depths between 1,485–1,530 and 1,848–1,857 m, where the welling stopped owing to a technical failure. The water temperature exceeds 90°C, while the yield of 100 l/s is limited only by the well performances. The Na-HCO 3 dominated water is classified as a CO 2 -rich healing mineral water suitable for drinking, bottling and balneology. The free degassing gas is almost pure CO 2 (99.9 %) and its δ 13 C composition indicates volcanic origin. The tapped water is relatively old, probably of Pleistocene age at least, and the planned exploitation must consider reinjection in order to protect this valuable natural resource from overexploitation. This recent hydrothermal system is characterised by dominating vertical circulation of waters and is superimposed on older, already inactive hydrothermal system(s), recognised by veins of either metal sulphides and quartz, or calcite. These vein minerals precipitated from hydrothermal fluids migrating from a deeper source towards the ancient surface through a fracture system, which is now self-sealed already. The distribution of metal sulphides indicates that the source might have been a deep-seated Neogene pluton genetically related to the tonalites and quartz diorites that outcrop in the Pohorje Mountains, or a subvolcanic-level volcanic body related to the Neogene volcanic activity in the Graz Basin.

In order to determine the origin and the propagation mechanisms of highly concentrated chloride brines within the Quaternary aquifer system in the southern part of the Upper Rhine Graben, a combined isotope (H, O, C) and hydrochemical analysis was carried out. Groundwater recharge in this area is a complex system, consisting of local precipitation, river bank filtration, lateral flow from the Graben borders and, to a minor extent, an old Pleistocene component. In some areas, groundwater consists of up to 90% of recent bank filtrate, reaching depths down to at least 100 m. The isotopic and hydrochemical results show, that the elevated chloride concentrations in the Quaternary aquifer mainly result from leaky settling basins charged by the French potash mines until the mid 1970s. Input of natural brines coming from tertiary salt diapirs is of only minor importance. While infiltrating, the anthropogenic brines were strongly diluted by local river bank filtrate of the Rhine. Nevertheless, maximum chloride concentrations nowadays still reach some 10,000 mg/l at the base of the aquifer at a depth of more than 100 m below surface. The main volume of the brines is stored in the less permeable lower part of the quaternary sediments (Breisgau-Formation) whereas only a minor part is transported northwards with the rapid convective groundwater flow. Brines undergoing only dilution preserve their hydrochemical characteristics (NaCl-type). In contrast, brines recirculated from the Breisgau-Formation show a northwards increasing alteration through ion exchange processes. Potassium and sodium may be fixed in the fine grained aquifer material while calcium is set free into the groundwater. After a flow distance of about 12 km, complex hydraulic interactions between groundwater and surface waters lead to the rise of strongly diluted and hydrochemically altered brines with chloride contents up to maximum 700 mg/l. The presented case study is an example for a detailed analysis of a multi-component groundwater mixing system using combined isotope and hydrochemical methods. Furthermore, cation exchange is shown as a major process affecting the hydrochemical evolution of the young groundwater in the southern Upper Rhine Graben which is locally strongly polluted by chloride as a consequence of former potash mining.

Die Entfernung der steroiden Hormone aus dem Wasserkreislauf ist zukünftig eine wichtige Aufgabe, besonders in dicht besiedelten und wasserarmen Gebieten. Das Einzugsgebiet, in dem die Stadt Prag mit 1,2 Millionen Einwohnern liegt, hat ein gut entwickeltes Entwässerungs- und Kläranlagensystem und ist damit der ideale Ort, um das Verhalten natürlicher und synthetischer Östrogene im Wasserkreislauf zu untersuchen. Es wurden die Konzentrationen an 17β-Estradiol, Estriol, Estron, 17α-Ethinylestradiol, Mestranol und Norethisteron in den Flüssen und Bächen sowie den Kläranlagen und in der Wasserversorgung der Stadt Prag gemessen. Die höchste Konzentration an Östrogenen wurde mit 466 ng/l im Abwasserzufluss der Hauptkläranlage Cisarsky von Prag gemessen. Das geklärte Abwasser dieser Anlage enthält immer noch zwischen 72 und 100 ng/l Gesamtöstrogen. Das Wasser der Moldau hat vor dem Eintritt in das Stadtgebiet von Prag weniger als 1 ng/l Gesamtöstrogene, im Stadtbereich steigen die Werte auf 3,8 ng/l an. In den Kläranlagen wird das natürliche Östrogen 17β-Estradiol zu Estron abgebaut. Der Nachweis von 17α-Ethinylestradiol in vielen Bächen im Prager Stadtbereich lässt einen diffusen Eintrag und eine hohe Stabilität dieses Hormons vermuten.