Reactive multicomponent transport modeling was used to investigate and quantify the factors that affect redox zonation and the fate of the pharmaceutical residue phenazone during artificial recharge of groundwater at an infiltration site in Berlin, Germany. The calibrated model and the corresponding sensitivity analysis demonstrated that temporal and spatial redox zonation at the study site was driven by seasonally changing, temperature-dependent organic matter degradation rates. Breakthrough of phenazone at monitoring wells occurred primarily during the warmer summer months, when anaerobic conditions developed. Assuming a redoxsensitive phenazone degradation behavior the model results provided an excellent agreement between simulated and measured phenazone concentrations. Therefore, the fate of phenazone was shown to be indirectly controlled by the infiltration water temperature through its effect on the aquifer’s redox conditions. Other factors such as variable residence times appeared to be of less importance.

The redox conditions below an artificial recharge pond in Berlin were largely dependent on seasonal temperature changes of 0-24 °C in the infiltrate. Aerobic conditions prevailed in winter, when temperatures were low, while anaerobic conditions were reached below the pond when temperatures exceeded 14 °C. In contrast to temperature changes, cyclic changes between saturated or unsaturated conditions below the pond had only a minor effect on the redox conditions. However, the intrusion of gaseous oxygen during unsaturated conditions caused a temporary reinforced increase in oxidation of particulate organic matter. The effect of variable redox conditions on the behaviour of a number of pharmaceutically active compounds, namely carbamazepine, phenazone and several phenazone-type PhACs, was investigated. Phenazone is redox sensitive and was generally fully degraded before reaching the first groundwater well, as long as oxygen was present. When conditions turned anaerobic, phenazone was not fully eliminated. 1-Acetyl-1-methyl-2-dimethyl-oxymoyl-2-phenylhydrazide (AMDOPH) and carbamazepine are very persistent drug residues. However, results suggest that AMDOPH may be slightly degradable under aerobic conditions too, but further studies will be needed to verify this statement.

The spatial and temporal evolution of the seepage water chemistry below an artificial recharge pond was investigated to identify the impact of dynamic changes in water saturation and seasonal temperature variations. Geochemical analysis of the pond water, suction cup water and groundwater showed that during summer, nitrate and manganese reducing conditions dominate as long as saturated conditions prevail. Iron and sulphate reduction occur only locally. When the sediment below the pond becomes unsaturated, atmospheric oxygen penetrates from the pond margins leading to re-oxidation of previously formed sulphide minerals and enhanced mineralisation of sedimentary particulate organic carbon. The latter promotes the dissolution of calcite. During winter, both the saturated and the unsaturated stage were characterised by aerobic conditions. Thereby, nitrification of sedimentary bound nitrogen could now be observed because nitrate is not immediately consumed, as is the case during summer. This suggests that nitrification below the pond might be less affected by seasonal temperature changes than nitrate reduction.

Artificial recharge of groundwater is often used to either purify partially treated wastewater or to enhance the quality of surface water by percolation through a variably saturated zone. In many cases, the most substantial purification process within the infiltration water is the redox-dependent biodegradation of organic substances. The present study was aimed at understanding the spatial and temporal distribution of the redox reactions that develop below an artificial recharge pond near Lake Tegel, Germany. At this site, like at many artificial recharge sites, the hydraulic regime immediately below the pond is characterised by cyclic changes between saturated and unsaturated conditions. These changes, which occur during each operational cycle, result from the repeated formation of a clogging layer at the pond bottom. Regular hydrogeochemical analyses of groundwater and seepage water in combination with continuous hydraulic measurements indicate that NO3 - and Mn-reducing conditions dominate beneath the pond as long as water-saturated conditions prevail. Manganese-, Fe- and SO24 -reducing conditions are confined to a narrow zone directly below the clogging layer and in zones of lower hydraulic conductivity. The formation of the clogging layer leads to a steady decrease of the infiltration rate, which ultimatively causes a shift to unsaturated conditions below the clogging layer. Atmospheric O2 then starts to penetrate from the pond fringes into this region, leading to: (i) the re-oxidation of the previously formed sulphide minerals and (ii) the enhanced mineralisation of sedimentary particulate organic C. The mineralisation of sedimentary particulate organic C leads to an increased H2CO3 production and subsequent dissolution of calcite.

Bank filtration and artificial ground water recharge are important, effective, and cheap techniques for surface water treatment and removal of microbes, as well as inorganic, and some organic, contaminants. Nevertheless, physical, chemical, and biological processes of the removal of impurities are not understood sufficiently. A research project titled Natural and Artificial Systems for Recharge and Infiltration attempts to provide more clarity in the processes affecting the removal of these contaminants. The project focuses on the fate and transport of selected emerging contaminants during bank filtration at two transects in Berlin, Germany. Several detections of pharmaceutically active compounds (PhACs) in ground water samples from bank filtration sites in Germany led to furthering research on the removal of these compounds during bank filtration. In this study, six PhACs including the analgesic drugs diclofenac and propyphenazone, the antiepileptic drugs carbamazepine and primidone, and the drug metabolites clofibric acid and 1-acetyl–1-methyl–2-dimethyloxamoyl– 2-phenylhydrazide were found to leach from the contaminated streams and lakes into the ground water. These compounds were also detected at low concentrations in receiving public supply wells. Bank filtration either decreased the concentrations by dilution (e.g., for carbamazepine and primidone) and partial removal (e.g., for diclofenac), or totally removed PhACs (e.g., bezafibrate, indomethacine, antibiotics, and estrogens). Several PhACs, such as carbamazepine and especially primidone, were readily transported during bank filtration. They are thought to be good indicators for evaluating whether surface water is impacted by contamination from municipal sewage effluent or whether contamination associated with sewage effluent can be transported into ground water at ground water recharge sites.

In Berlin, 70 % of the drinkinq water is derived from bank filtrate or artificially recharged water. Because the surface water system contains elevated proportions of secondary treated municipal sewage, a number of sewage indicators from various sources can be detected in the bank filtrate. An artificial recharge site and a bank filtration site in Berlin Tegel are introduced and compared in terms of their hydrogeological and hydrochemical properties. Because of a permanent clogging layer and the geological properties, travel times are slower at the BF site and the hydrochemical conditions are more reducing. First estimates for the reaction rate constants of oxygen and nitrate are obtained with exponential data fitting. Some of the effects of the different redox conditions on minor substances such as drug residues are highlighted.

Induced by well abstraction, surface water infiltrates into Berlin aquifers and is used for drinking water production. A major advantage of bank filtration is the capability of the subsurface to remove contaminants and save natural groundwater resources. Since a large proportion of the surface water in Berlin originates from treated effluents released by wastewater treatment plants, certain wastewater residues can be traced into the groundwater. A powerful tool to characterise bank filtration systems is the use of wastewater indicators and additional environmental tracers to estimate flow velocities and proportions of bank filtrate in the abstraction wells prior to reactive transport evaluations. Examples for tracer applications at the Berlin system are introduced in this paper. In addition, an overview on results of various studies conducted on contaminant transport and removal during underground passage of the bank filtrate in Berlin is given.