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Abstract:Berlin relies on induced bank filtration from a broad-scale, lake-type surface water system. Because the surface water contains treated sewage, wastewater residues are present in surface water and groundwater. Multiple environmental tracers, including tritium and helium isotopes ( 3 H, 3 He, 4 He), stable isotopes (υ 18 O and υ 2 H) and a number of persistent sewage indicators, such as chloride, boron and a selection of pharmaceutical residues (phenazone-type analgesics and their metabolites, carbamazepine and anthropogenic gadolinium, Gd excess ), were used to estimate travel times from the surface water to individual production and observation wells at two sites. The study revealed a strong vertical age stratification throughout the upper aquifer, with travel times varying from a few months to several decades in greater depth. Whereas the shallow bank filtrate is characterized by the reflection of the time-variant tracer input concentrations and young 3 H/ 3 He ages, the deeper, older bank filtrate displays no tracer seasonality, 3 H/ 3 He ages of a few years to decades and strongly deviating concentrations of several pharmaceutical residues, reflecting concentrations of the source surface water over time. The phenazone-type pharmaceuticals persist in the aquatic environments for decades. Bank filtration in Berlin is only possible at the sandy lakeshores. In greater water depth, impermeable lacustrine sapropels inhibit infiltration. The young bank filtrate originates from the nearest shore, whereas the older bank filtrate infiltrates at more distant shores. This paper illustrates the importance of using multiple tracer methods, capable of resolving a broad range of residence times, to gain a comprehensive understanding of time-scales and infiltration characteristics in a bank filtration system.

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Highlights:removal of trace organics and sum parameters during bank filtration late data aggregation removal kinetics: redox conditions, temporal removal, threshold concentration, residual concentration, site specifics, large database Abstract Managed aquifer recharge (MAR) provides efficient removal for many organic compounds and sum parameters. However, observed in situ removal efficiencies tend to scatter and can not be predicted easily. In this paper, a method is introduced which allows to identify and eliminate biased samples and to quantify simultaneously the impact of (i) redox conditions (ii) kinetics (iii) residual threshold values below which no removal occurs and (iv) field site specifics. It enables to rule out spurious correlations between these factors and therefore improves the predictive power. The method is applied to an extensive database from three MAR field sites which was compiled in the NASRI project -2005. Removal characteristics for 38 organic parameters are obtained, of which 9 are analysed independently in 2 different laboratories. Out of these parameters, mainly pharmaceutically active compounds (PhAC) but also sum parameters and industrial chemicals, four compounds are shown to be readily removable whereas six are persistent. All partly removable compounds show a redox dependency and most of them reveal either kinetic dependencies or residual threshold values, which are determined. Differing removal efficiencies at different field sites can usually be explained by characteristics (i) to (iii).