Large-scale dispersion was studied in an unconsolidated, sandy, glaciofluvial, river-recharged, and confined aquifer in Germany. Groundwater observation wells from a 3.5-km-long transect located in flow direction from the river Oder into a large lowland area (Oderbruch polder) were sampled for noble gases in order to date the groundwater with the tritium and helium (3H-3He) technique. The apparent 3H-3He ages of the groundwater increased from only a few months to >40 years along the flow path. Highest values for initial 3H (sum of 3H and its decay product tritiogenic helium, 3Hetri) were encountered in 2.6-km river distance. Concentrations of 4He in the water increased to 1.1 × 10-7 cm3 STP/g with distance from the river. The initial 3H data enabled an estimation of the longitudinal dispersivity with a simplified one-dimensional transport model. The best fit of modeled and measured initial H data was obtained using a dispersivity of 120 m. Deviations of modeled hydraulic ages and measured apparent 3H- 3He ages for older samples can be explained by dispersive mixing.

With increased computer performance and data-processing functionalities, there has been a tendency in the last few years to apply detailed hydrodynamic sewer modelling for long-term simulations, with long time series of rainfall. Although this is now fairly realistic for small networks, there is still a clear limit as to what can be done in the case of running bigger models for a long time, which need a lot more computational effort. Therefore, the idea has grown to investigate the possibilities of hybrid sewer modelling, a combination of conceptual and mechanistic modelling approaches to combine the advantages of both models, the speed of conceptual models and the accuracy of mechanistic models. Suggestions for hybrid model simplifications are presented in this paper within their application for two case studies.

Demonstrationsprojekt Berlin-Margaretenhöhe: Dezentrale Klärtechnik vor Ort erprobt und auf Wirtschaftlichkeit geprüft.

Managed aquifer recharge is gaining importance as a practice to bank and treat surface water for drinking water production. Neon (Ne) concentrations were analysed at four different recharge sites in and near Berlin, where groundwater is recharged directly from surface water courses, either by near-natural bank filtration, induced bank filtration or engineered basin recharge. Neon concentrations in excess of saturation (DNe) were used to identify excess air in the infiltrates. Excess air concentrations were around saturation at the near-natural bank filtration site, where river water infiltrates through a permeable river bed into a confined aquifer under completely saturated conditions. At two induced unconfined bank filtration sites, samples generally contained excess air (up to 60% DNe). Highest excess air concentrations (up to 81% DNe) were encountered at the engineered basin recharge site. The degree of water table fluctuations, the water saturation of the sediments in the infiltration zone and the presence of a confining layer affect the formation of excess air. Excess air can only be used to trace bank filtrate or artificially recharged water in a setting where the ambient groundwater in the near vicinity of production wells is not affected by large water-table fluctuations. Nevertheless, excess air concentrations provide valuable additional information on the type of recharge (saturated or unsaturated, degree of water table fluctuations).

The behaviour of residues of antibiotic drugs during bank filtration was studied at a field site in Berlin, Germany, where bank-filtered water is used for the production of drinking water. The neighbouring surface water used for bank filtration is under the influence of treated municipal wastewater. Seven out of 19 investigated antimicrobial residues were found in the surface water with median concentrations between 7 and 151 ng L¡1. Out of the seven analytes detected in the surface water only three (anhydroerythromycin, clindamycin and sulfamethoxazole) were found with median concentrations above their limits of quantitation in bank filtrate with a travel time of one month or less. With the exception of sulfamethoxazole, none of the 19 analytes were present in bank filtrate with a residence time larger than one month or in the water-supply well itself. Sulfamethoxazole found with a median concentration of 151 ng L¡1 in the surface water was the most persistent of all antimicrobial residues. Nevertheless, it was also removed by more than 98% and only found with a median concentration of 2 ng L¡1 in the water-supply well. The degradation of clindamycin and sulfamethoxazole appear to be redox-dependent. Clindamycin was eliminated more effi­ciently under oxic infiltration conditions while sulfamethoxazole was eliminated more rapidly under anoxic infiltration conditions. A slight preference for an improved degradation under oxic (clarithromycin and roxithromycin) or anoxic (anhydroerythromycin) conditions was also observed for the macrolide antibiotics. Nevertheless, all macrolides were readily removable by bank filtration both under oxic and anoxic conditions.