The T-He age dating method uses the ratio of the concentration of radioactive tritium (3H) derived from atmospheric nuclear bomb testing and its decay product Helium (3He) in the groundwater to determine a groundwater age, i.e. the time passed since the water had its last contact with the atmosphere. At the Free University of Berlin, hydraulic and hydrochemical processes accompanying bank-filtration are currently examined at two very different locations: In metropolitan Berlin and the rural Oderbruch polder region. The city of Berlin enhances bank-filtration through well galleries located adjacent to the surface water system. The spatial and temporal development of the bank filtrate is studied in cooperation with the Berlin Waterworks and the Berlin Centre of Competence for Water at several exemplary piezometer transects. The system generally behaves highly transient due to continuously changing pumping regimes. At the gallery Lake Wannsee, the well filter screens are pumping water from 3 different glacial sand layers separated by aquitards. The well water is a mixture of very old deeper groundwater, medium old water from the middle layer and very young bank-filtered water. The Oderbruch is located north-east of Berlin aside the river Oder. Intensive melioration activities in the past 250 years converted the former swamp into a fertile, agricultural region and lead to the permanent infiltration of river water into the shallow, confined aquifer. Compared to Berlin, the infiltration is a long-term, very stable process. The groundwater is getting older with increasing distance and travel-time from the river. The concentration of “stable” tritium (sum of 3H and tritiogenic 3He) increase from the river inland reflecting the decrease of 3He in the atmosphere from the early 60’s onwards. Peak concentrations are encountered in 2.1 km river distance whereas further inland (3.4 km river distance) old water which infiltrated prior to the nuclear bombing peak is encountered. In addition, the groundwater has a high radiogenic 4Heterr concentration which also indicates that the groundwater is more than a few decades old. Even further inland, in the central polder areas, the groundwater is unconfined and continuously recharged to some extend by percolating water infiltrating through shrinkage fissures in the overlying dried alluvial loam. The water is a mixture of young seepage water and very old bank filtrate, the resulting “mixed” T-He age is getting younger again. The T-He method was successfully applied to support estimated groundwater ages derived from tracer analysis (e.g. 2H, 18O, EDTA, Gd) at both locations. In the Oderbruch, the T-He ages were used to calibrate a flow model. The method also proved to be a very good indicator for the identification of mixing processes.

The occurrence and fate of pharmaceutically active compounds (PhACs) in the aquatic environment has been recognized as one of the emerging issues in environmental chemistry. In some investigations carried out in Austria, Brazil, Canada, Croatia, England, Germany, Greece, Italy, Spain, Switzerland, The Netherlands, and the U.S., more than 80 compounds, pharmaceuticals and several drug metabolites, have been detected in the aquatic environment. Several PhACs from various prescription classes have been found at concentrations up to the µg/l-level in sewage influent and effluent samples and also in several surface waters located downstream from municipal sewage treatment plants (STPs). The studies show that some PhACs originating from human therapy are not eliminated completely in the municipal STPs and are, thus, discharged as contaminants into the receiving waters. Under recharge conditions, polar PhACs such as clofibric acid, carbamazepine, primidone or iodinated contrast agents can leach through the subsoil and have also been detected in several groundwater samples in Germany. Positive findings of PhACs have, however, also been reported in groundwater contaminated by landfill leachates or manufacturing residues. To date, only in a few cases PhACs have also been detected at trace-levels in drinking water samples.

The present report characterizes the field sites Lake Tegel and Lake Wannsee as well as the artificial recharge site GWA Tegel in terms of their clogging layer, sedimentary, hydraulic and hydrochemical properties. As a result, a solid basis for the interpretation of specific compounds evaluated within NASRI and for subsequent modeling and quantification of the data is given. Major problems or difficulties where identified, in order to focus investigations on aspects not fully understood to date in the next project phase. The combination of different tracers enables the interpretation of the flow regime. With the help of T/He analysis, ages of different water bodies can be estimated. The analysis of tracer showing distinct seasonal variations is used to estimate travel times while water constituents which are either mainly present in the bank filtrate or the background water are used for mixing calculations. The proportions of treated wastewater in the surface water were estimated in front of the transects. The surface water composition varies largely both in time and space, which is a problem at Wannsee, where the surface water sampling point is not representative for the bank filtration input. Estimates for travel times of the bank filtrate to individual observation and production wells are given and vary between days and several months. The production wells are a mixture of bank filtrate and water from inland of the wells and deeper aquifers, proportions of bank filtrate are given where possible to differentiate between contaminant removal and dilution. They vary between < 20 and > 80 %. The new observation wells enable a vertical differentiation of the infiltrate. It becomes clear that at Tegel and Wannsee, there is a strong vertical succession towards larger proportions of considerably older bank filtrate with depth. At the Wannsee transect, the observation wells deeper than the lake do not reflect the surface water signal at all. It will be important to combine the new information with hydraulic information of existing flow models (mainly of the IGB “model” group). The evaluation of the redox conditions shows that redox successions proceed with depth rather than (only) in flow direction. In addition, the redox zoning (as characterised by the appearance or disappearance of redox sensitive species) is very transient. The zones are much wider in winter than in summer, in particular at the artificial recharge site GWA Tegel, probably due to temperature effects. This poses a challenge for the desired modelling and the interpretation of data from redoxsensitive substances.