Bank fillration provides an important drinking water source to the city of Berlin. 56% of the drinking water is derived from bank filtration (the remainder is 14% replenished groundwater and 30% natural groundwater) [1]. At most bank filtration sites, the surface water contains portions of sewage treatment plant effluent (Lake Tegel 10-30%, [2]). Due to water recycling, the introduction of effluent organic matter (EfON) and persistent trace pollutants in the drinking water may be a concern. The project "Organic Substances in Bank filtration and Groundwater Recharge Process Studies" at the Department for Water Quality Control (DWQC) at the Technical University of Berlin is part of the "Natural and Artificial Systems for Recharge and lnfiltration (NASRI)' - project of the Berlin Centre of Competence for Water [3]. The research objectives of this part of the project are to study the removal of bulk organics (dissolved organic carbon (DOC) and EfOM) and trace organics at three field sites with different characteristics. Since the processes during bank filtration are very complex, it is difficult to predict bulk organic composition in the bank filtrale or to estimate important factors of influence for the degradation of trace compounds. For instance, it was shown in previous studies, that iodinated x-ray contrast medias are deiodinated under teductive conditions. Therefore, a bank filtration under anoxic or even anaerobic conditions would provide the removal of these trace pollutants. In addition to lhe redox state, factors such as retention time, initial degradable carbon . concentration, soil properties and hydrogeologlcal conditions may affect the final concentration. In order to be able to prevent the intrusion of persistent pollutants into the drinking water, lhe factors of influence are studied for a few model compounds that represent groups of trace pollutants. This will provide a tool that can be merged with hydrogeological models and soil properties to predict the removal efficiency of a given field site. To fulfill these objectives this research is presently investating: (i) the differences in bulk organic composition and trace organic concentration related to bank filtration conditions at three different field sites in Berlin, (ii) the simulation of a bank filtration site with a 30m soil column (elimination of hydrogeological variables).

Bank filtration and artificial recharge provides an important drinking water source to the city of Berlin. Due to water recycling, the introduction of persistent trace pollutants (e.g. pharmaceuticals) in the drinking water may be a concern. The project “Organic Substances in Bank filtration and Groundwater Recharge - Process Studies” at the Technical University of Berlin is part of the “Natural and Artificial Systems for Recharge and Infiltration (NASRI)”-project of the Berlin Centre of Competence for Water. The research objectives of this part of the project are to study the removal of bulk and trace organics at different field sites with different characteristics in Berlin. In Berlin’s public drinking water supply nearly 70% of the 220 Mio m3 per year originate from bank filtration and groundwater recharge (~56% from bank filtration and ~14% from groundwater recharge (BWB 2003)). Since the 19th century Berlin has relied on bank filtration with retention times of several months to produce “new” ground water. A semi-closed urban water cycle has been created with the growth of the city. At some bank filtration sites the surface water is strongly influenced by highly treated domestic waste water effluent (e.g. 15-30% in Lake Tegel) (Ziegler et al. 2002). Despite this indirect potable reuse, the bank filtration system continues to provide high quality water which is distributed without chlorination. This unique situation in Berlin was an interesting field site for a research project of the Berlin Center of Competence for Water. Recently, the break through of organic trace pollutants in bank filtration systems has been studied in various research projects. Especially, since improved analytical methods can detect in ranges below 1µg/l. Since the processes during bank filtration are very complex, it is difficult to predict the fate of trace organics during bank filtration or to estimate important factors of influence for their degradation. In addition to redox state, factors such as retention time, initial degradable carbon concentration, soil properties and hydrogeological conditions may affect the final concentration. Many studies revealed positive findings of pharmaceuticals, pesticides or industrial chemicals (Hiemstra et al. 2003, Heberer et al. 2001, Verstraeten et al. 2002) in bank filtrate. Compounds like carbamazepine and clofibric acid were reported to be partly recalcitrant during underground transport (Stan and Linkerhäger 1994, Ternes et al. 2002). Furthermore, Ternes and Hirsch (2000) reported the occurrence of x-ray contrast media in surface waters and in surface water influenced groundwaters, where they constitute a major fraction of the adsorbable organic iodine (AOI). The contrast media were found to be very polar, persistent and difficult to remove in wastewater treatment (Jekel and Wischnack 2000). Hartig (2000) reported the break through of antibiotic sulfonamides from surface water to monitoring wells more than 50 m off the lake front (residence time~3 months). But in most of the reported cases the concentration in the bank filtrate is much lower than in the surface water. Since this concentration decline is not only due to dilution, long term bank filtration appears to have the capability to reduce trace organic pollutant concentrations. It would be of great practical value to classify the important trace organic pollutants by degradability during bank filtration and to evaluate the conditions that are favorable for the removal of certain compounds. This study begins to clarify these issues for a few trace organic pollutants. The factors of influence for degradation are studied for model compounds that represent groups of trace pollutants. Additionally, the infiltration process is characterized by several bulk-organic parameters. The goal of the study is to provide a tool that can be merged with hydrogeological models and soil properties to predict the removal efficiency of a given field site.

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.