Successful predictions of the fate and transport of solutes during bank filtration and artificial groundwater recharge depends on the availability of accurate transport parameters. We expand the CXTFIT code (Toride et al., 1995) in order to improve the handling by pre- and post processing modules under Microsoft EXCEL. Inverse modelling results of column experiments with tracers, pharmaceutical residuals and algae toxins demonstrate the applicability of the advanced simulation tool.

In the course of the interdisciplinary research project NASRI (natural and artificial systems for recharge and infiltration) many investigations are currently being carried out to assess the risk of break through of persistent organic substances into raw water used for drinking water supply. One part of these studies is the determination of the transport behavior of pharmaceutical residues in test sand filters, so called enclosures, equipped with sampling points at various depths. Breakthrough curves were determined for carbamazepine, primidone (both antiepileptic drugs), clofibric acid (a metabolite of blood lipid lowering agents), diclofenac, ibuprofen (both analgesic drugs) and for chloride, used as a conservative tracer. Retardation coefficients and degradation rates were obtained by using the software Visual CXTFIT. Degradation rates between 0.7 h–1 and 1 h–1 were observed for ibuprofen whereas clofibric acid, primidone, carbamazepine and diclofenac showed no or very little degradation (lambda < 0.06 h–1).

To evaluate the potential hazard of a harmful substance on its pathway from a source to a sensitive site, it is important to know if degradation or reversible sorption is the dominant process. While, in case of degradation, mass is removed from the system, in the case of reversible sorption the transport is only retarded. A mathematical analytical concept is outlined, which can be applied to evaluate data from field experiments, from technical and semitechnical facilities and from the laboratory. The concept is exemplified on a series of enclosure experiments performed with phages within a project investigating processes during bank filtration. Results show that parameters are not constant in the experiments and indicate a significant influence of redox conditions on both retardation and deactivation rates. On the other hand, an influence of the clogging layer could not be detected.

The UBA’s experimental field on the outskirts of Berlin offers a unique possibility of simulating bank filtration, artificial recharge and slow sand filtration on a technical scale. The site consists of a storage reservoir (pond) with an adjacent artificial aquifer consisting of sand and gravel. Additionally the surface water can be conducted into 4 infiltration basins (two slow sand filters and two aquifer infiltration ponds). Three enclosures as well as large scale columns can be used for shorter and longer term simulation of groundwater transport. The whole site is separated from the surrounding aquifer by a layer of clay. A variety of physico-chemical parameters can be measured continuously and observed online. The travel times for the bank filtration passage determined by tracer experiments range from a few days to a maximum of 3 weeks. In the enclosures, infiltration ponds and large scale columns contact time can be varied between a few hours up to 3 months.

River bank or slow sand filtration is a major procedure for processing surface water to drinking water in central europe. In order to model the performance of river bank and slow sand filtration plants, we are studying the different mechanisms by which the elimination of pathogens is realized. An important question concerning the mode of action of slow sand filters and river bank filtration units is the role of the colmation layer or “schmutzdecke” on the elimination of human pathogens. The schmutzdecke is an organic layer which develops at the surface of the sand filter short after the onset of operation. We have inoculated a pilot plant for slow sand filtration with coliphages and determined their rate of breakthrough and their final elimination. In the first experiment, with a colmation layer still missing, the breakthrough of the coliphages in the 80 cm mighty sandy bed amounted to ca. 40 %. In contrast, less than 1 % of coliphages escaped from the filter as the same experiment was repeated two months later, when a substantial colmation layer had developed. Our preliminary conclusions are that the colmation layer is extremely efficient in eliminating of viruses.

Cyanobacteria proliferation and the potential health risk related with the release of the associated toxins have lead the local association EDEN to initiate a comprehensive study on cyanobacteria in the river Erdre. Within the consortium in charge of the project, the Berlin Centre of Competence for Water (KWB) realised lab-scale research in cooperation with the German Federal Environmental Agency (UBA), on the species Planktothrix agardhii which predominates in the river Erdre, and the associated toxin microcystin. The objective was to determine the influence of key factors such as nutrients (nitrogen, phosphorus), light, flow velocity and sediments on cyanobacteria growth and competition as well as microcystin release from the Planktothrix population in the river Erdre. Results from the lab-scale cultures proved that nutrient-limited conditions lead to a decrease of cyanobacteria biomass and may favour some genotypes with reduced needs among the Planktothrix population. Given the current state of scientific knowledge, no differences in competition between toxic and non-toxic Planktothrix strains can be established. Nutrient limitation favours microcystin release from cells, however the global decrease of cyanobacteria biomass induces a decrease of the total quantity of released toxin. These results can be applied in a water body where nutrients concentrations are very low (below 50 µg/L for total phosphorus). In the river Erdre, as long as external nutrients inputs remain considerable, light is the limiting factor. Internal nutrient recycling from the sediments is globally negligible in comparison with external inputs. Culture experiments in a flow simulation flume proved that flow velocity had substantial impact neither on Planktothrix growth nor on microcystin release. Only a short transition phase with negative effects was observed. Overwintering of Planktothrix in Erdre-sediments could be proved by the detection of a substantial population using fluorescence analysis. This inoculum should be large enough for initiation of Planktothrix development in the next vegetation period. However, the high adsorption capacities of the analysed sediments from the river Erdre allow to put aside a potential risk of microcystin release from sludge. While providing innovative results on the species Planktothrix agardhii, this project contributes to the comprehensive study initiated by the EDEN association in order to preserve the values associated with environment, health and tourism in the river Erdre.

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.