Subsurface passage as utilized during river bank filtration and artificial groundwater recharge has shown to be an effective barrier for multiple substances present in surface waters during drinking water production. Additionally it is widely used as polishing step after wastewater treatment. However, there are limitations concerning the removal of DOC and specific trace organics. The project ”OXIRED“ aims at assessing possibilities to overcome these limitations by combining subsurface passage with pre-oxidation by ozone. In the first phase of the project, laboratory-scale column experiments were conducted in order to quantify removal for different settings under varying conditions. In a previous study different combinations of advanced oxidation and subsurface passage were evaluated concerning their potential removal efficiency and practical implementation on the basis of existing, published experiences and theoretical considerations. Two different scenarios were identified as promising for experiments in laboratory-scale columns with surface water and sewage treatment plant effluent: (A) surface water - oxidation - groundwater recharge and (B) surface water - short bankfiltration - oxidation - groundwater recharge. The investigations were designed to lead to recommendations for the implementation of a combined system of subsurface passage and advanced oxidation in pilot scale experiments that will be carried out in the second phase of the project. Prior to column experiments, batch tests following the RCT-concept by Elovitz and von Gunten (1999) were carried out to characterize the reaction of ozone with the investigated water qualities [1]. Additional batch ozonation tests with subsequent analysis of biodegradable dissolved organic carbon (BDOC) were conducted in order to determine optimal ozone doses for DOC removal in column experiments. For laboratory-scale experiments a set of 8 soil columns (length: 1 m; diameter: 0.3 m) was operated at TUB to evaluate the effects of pre-ozonation of different source waters (secondary effluent, surface water, bank filtrate). Ozonation was conducted with gaseous ozone in a 13-L stirred tank reactor. Specific ozone doses of 0.7 mg O3/mg DOC0 and 0.9 mg O3/mg DOC0 were investigated. Trace organic compounds to be targeted were identified in a prior literature study on existing data on subsurface removal. Results from laboratory-scale soil column experiments led to recommend specific ozone doses (z) of 0.7 mg O3/mg DOC0 for the following technical- and pilot-scale applications. Removal of surface water DOC in the soil columns was increased from 22% without ozonation to 40% (z = 0.7) and 45% (z = 0.9) with preozonation and the DOC in the column effluent reached the level of tap water in Berlin within less than one week of retention time. At bank filtration and artificial recharge sites in Berlin similar removal rates were only observed within 3 - 6 months of retention [2]. The transformation of many trace compounds was efficient with specific ozone doses of 0.6-0.7 mg O3/mg DOC0. Realistic surface water concentrations of carbamazepine,sulfamethoxazole, diclofenac and bentazone were reduced below the limits of quantification (LOQ). The pesticides diuron and linuron were reduced close to LOQ. The substances MTBE, ETBE and atrazine were only partly transformed during ozonation. For efficient transformation of these substances, higher ozone doses or an optimisation of the oxidation process, for example as advanced oxidation process (AOP), should be considered. Operating a preceding bank filtration (scenario B) will enhance the transformation efficiency of MTBE and ETBE. With similar ozone consumption the transformation of MTBE and ETBE was increased by 27-31% and 28-33% of the original removal, respectively. Other investigated compounds were efficiently transformed during ozonation of surface water independently of the preceding bank filtration step. For the removal of bulk organic carbon only little improvement was observed for scenario B. Overall DOC removal increased from 45% with direct ozonation of surface water to up to 50% with a preceding soil column. Despite the presence of relevant bromide concentrations (~ 100 µg/L) formation of the oxidation by-product bromate was not observed (< 5 µg/L). However, this could also be a result of analytical problems, as later spiking tests showed. Formation of brominated organic compounds was also not observed. Adsorbable organic bromide (AOBr) even decreased by 50 - 60% for secondary effluent and 80 - 90% for surface water. The reduction of AOBr concentrations was accompanied by an increase of inorganic bromide by up to 40 µg/L during ozonation of surface water. In the two conducted in vitro genotoxicity tests (Ames test, micronucleus assay) no genotoxicity caused by ozonation of water samples was observed. Testing for cytotoxicity (glucose consumption rate, ROS generation) showed positive results in several samples. However, a systematic attribution of toxic effects to ozonation or subsequent soil passage was not possible. Reasons for cytotoxic effects were not evaluated within the scope of this project but it is assumed that they were caused by unknown cofactors. These results show that the objectives of enhanced removal of trace organics and DOC by combining ozonation and subsurface passage are well met. Further investigations need to confirm this for the pilot scale, especially taking into account the formation, retention and toxicity of oxidation by-products.

The study aims at validating the point-of-use investigations on long-term gravity-driven ultrafiltration for a scaled-up system, which could produce drinking water for a community of 100-200 inhabitants using natural surface water. Eawag, KWB and Opalium conceived a membrane-based small-scale system (SSS) which can operate without crossflow, backflush, aeration or chemical cleaning. Equipped with a biosand filter as pretreatment, it is designed to be robust, energy-sufficient (gravity-driven) and run with restricted chemical intervention (only residual chlorine). The containerised unit (10’) requires to be fed with raw water at a 2 m-height (energy-equivalent to ~8Wh/m3). As sole operational requirement, the membrane reactor is simply to be drained (i.e. emptied) on daily to weekly basis to superficially remove the material retained by the membrane and accumulated in the module. Otherwise, the system, which is only driven by a 40 cm differential pressure head (i.e. 40 mbar), is totally self-determined and autonomous. This report details the validation tests performed at Veolia Water Research Center in Annet-sur-Marne (France) from January to August 2009 : the gravity-driven UF compact unit showed promising results in regards to flux stabilization and flow capacity. Although early investigations take place in winter, an initial flux stabilization to 2.5 lmh is observed, which is below the reference results from the Eawag lab tests (i.e. 7-10 lmh, at 20 ± 2°C). However, the “scaled-up” system can benefit from a weekly drainage which seems to enhance the flux to 4-5 lmh, and thereby, the unit is to produce more than 4 m3/d, which is consistent with the design target of 5 m3/d. Moreover, the increase of the drainage frequency (to 3 times/week) along with warmer temperatures – leading to a better membrane permeability and biological activity - contribute to a further enhancement to 5-7 lmh. This is particularly relevant for South Africa, for which decentralized water supply is a burning issue and where the unit is to be further tested from November 2009. The investigations also highlighted the critical performance of the biosand filter as pretreatment. More than the UF step – whose membrane integrity was confirmed with bacterial analyses, the pretreatment step needed more frequent (i.e. monthly) O&M requirements. Therefore, the pretreatment necessity will be further assessed in South Africa where high turbidity peaks could represent an extra challenge for the unit.

The assessment of methods for the diagnosis and distinction of well ageing types and processes with the aim to recommend methods and tools for further fieldwork was part of work package 1 of the preparatory phase WellMa1. Therefore, field tests were carried out at selected well sites with a variety of methods covering standard monitoring methods to assess the constructive state of a well (TV inspections, borehole geophysical methods) and its performance (pump tests) as well as methods aiming at a better process understanding such as the hydrochemical and microbiological analysis of the raw water and clogging deposits. Altogether ten methods were applied at 21 different wells of the Berliner Wasserbetriebe (BWB) covering (i) exposure of object slides during operation and rest periods for microbiological investigations, (ii) BART with test kits for iron-related bacteria (IRB) and slime-forming bacteria (SLYM), (iii) water sampling for the investigation of pristine groundwater organisms, (iv) online measurements of chemical parameters O2, Eh, pH and T and water sampling for chemical analyses (main cations and anions), (v) TV inspections, (vi) three-step pumping tests, (vii) borehole geophysics with Gamma-Gamma-Density scan (GG.D), NeutronNeutron log (NN), Flowmeter (Flow) and Packer-Flowmeter measurement and (ix) Particle countings. The assessment and comparison should originally be completed by a horizontally directed core sampling from different depths from the screen sections of three of the chosen wells. Due to technical difficulties, this was not achieved during this phase of the project. The investigations led to a development and refinement of the methods and approaches. Because of their limited accessibility to the different parts of a well, a combination of methods is always necessary. Especially for the indirect methods like borehole geophysics, an initial assessment of the well condition directly subsequent to construction is essential to provide a basis for the assessment of the well performance development. Generally, the applied standard monitoring methods and diagnosis tools provided the expected identification of a performance deterioration and evidence for the presence of starting materials for clogging processes such as iron, oxygen, iron-related bacteria and particles. Room for improvement could be identified with regard to the reliability, information value and comparability of the tested methods, e.g. by a stepwise combination and extension of the methods to determine the interacting processes from the composition of the deposits. Further investigations should aim at method validation, especially for well monitoring during routine operation (e.g. use of delta h, development of standards for Qs-measurements and TV inspections), and further method development for the ongoing project with scientific investigations to obtain deeper process understanding, e.g. investigating shares of deposits resulting from the different processes (chemical, biological, physical) and relations between the rate of clogging or the location of deposits to well characteristics and site conditions to separate the different well ageing processes. This will then lead to the identification of key parameters that may be influenced to slow down well ageing and keep the well performance and water quality at an optimum.

WELLMA-1, WP 1.2 includes a statistical analysis of Berlin and French well data. The aim is to identify parameters by which the extent of iron related clogging can be assessed and which can be used for grouping the wells for further investigations. The data analysis is based on data on well construction, water chemistry and well operation for about 615 wells in Berlin and 47 in France. The approach is first to do a descriptive analysis of the datasets. It shows amongst others that the French data are not extensive enough to be included in further statistical analysis. They were therefore interpreted individually and added as annex to the report. In the second step, a reliable indicator for iron related clogging in the Berlin wells is identified. This is done by testing the significance of differences in parameters recommended by BWB (Qs, number of H2O2-treatments and results of TV-camera inspections) that indicate either intense clogging or no clogging. The analysis of the reduced dataset reveals that TV-camera inspections are the most reliable cloggingindicator for the Berlin wells for statistical analysis with the current database. Thirdly, the relation of all available constructional, hydro-chemical and operational parameters is checked for four different stages of clogging indicated by the TV-camera inspections. It can be stated that most wells reveal increasing clogging with increasing well age and decreasing depth of the first filter. Clogged wells are characterized often by lower iron and higher manganese and nitrate concentrations, a higher mean total discharge and more operating hours than wells without clogging indication. Finally, the clogging indicator is evaluated by a multiple linear regression. For this, the dependent variable clogging is linked to the ten variables, which are obviously related to clogging processes. Although all comprised parameters are partly related to the clogging intensity of the wells, only well age, depth of the first filter, iron and manganese concentrations as well as operating hours and total discharge have an explanatory value for clogging. However, their total explanatory value of 20% of the variance in clogging is low. Either the most relevant parameters to identify clogging are missing or the selected parameters reveal too much data variability. This can be due to temporal and depth oriented variations what could not be included in the recent analysis. Measurements in mixed raw water cannot characterize all processes involved in iron related clogging. Therefore, several recommendations of well operation and monitoring are given to improve the explanatory power of the data. The most important ones are the development of a more detailed matrix for the evaluation of well condition by TV-camera inspections and an improvement of measurements of specific capacity Qs by constant discharge rates and fully documented initial step pumping tests. Groups of wells that would be useful for more detailed field investigations and further data analysis are: (i) wells with different depth of the first filter, (ii) wells with significant differences in mean discharges (and similar construction and number of switchings), (iii) wells with different amounts of switchings, (iv) wells with similar number of switchings but different filter lengths or pump capacities and (v) wells of different age, but otherwise same construction and operational characteristics.

Eine optimierte Abwasserbehandlung führte seit den 1990er Jahren zu stark abnehmenden, kontinuierlich aus Punktquellen in die Vorfluter eingeleiteten Nährstofffrachten (HEINZMANN, 1998, SENSTADT, 2001), wodurch sich die Wasserqualität der aufnehmenden Gewässer Berlins merklich verbesserte. Episodische Belastungen durch Mischwasserentlastungen stellen jedoch weiterhin eine bedeutende Ursache einer herabgesetzten Wasser- und Sedimentqualität und eine der wichtigsten Managementaufgaben für die Berliner Stadtspree und der Kanäle dar (vgl. LESZINSKI ET AL., 2006, RIECHEL 2009). Hinsichtlich des von der EU-WRRL geforderten guten ökologischen und chemischen Zustandes der Binnengewässer bzw. des guten ökologischen Potenzials für stark veränderte und künstliche Gewässer, stellt die Lebensraumfunktion für die aquatischen Lebensgemeinschaften der Berliner Gewässer das wesentliche gewässerinterne Schutzziel dar. Neben dem erheblichem ökologischen Gefährdungspotenzial, das insbesondere von extremen Ereignissen der Mischwasserentlastung ausgeht, reduzieren vorrangig hydromorphologische Defizite (Stauhaltung, Uferbefestigung, Sohleintiefung, etc.) die Lebensraumqualität für die aquatischen Lebensgemeinschaften. Aufgrund der Schifffahrtsnutzung der Berliner Spree und der Kanäle stellen Wellenschlag und Sunk- und Schwalleffekte während Schiffspassagen eine zusätzliche, bedeutende Belastung dar (vgl. LESZINSKI ET AL., 2006). Wie in der Studie „Immissionsorientierte Bewertung von Mischwasserentlastungen in Tieflandflüssen“ (LESZINSKI ET AL., 2007) dargelegt, liegen die in Laboruntersuchungen ermittelten Ansprüche bzw. Toleranzen hinsichtlich der Wasserqualität für die Fischarten und Arten wirbelloser Bodenorganismen der Berliner Spree und der Kanäle in einem vergleichbaren Bereich (JACOB ET AL., 1984, LAMMERSEN, 1997). Die Herleitung von Gütestandards hinsichtlich der Wasserqualität für die Fischfauna schließt somit den Schutz der Lebensgemeinschaft der wirbellosen Bodenorganismen mit ein. Ebenso besteht bei beiden Organismengruppen ein grundsätzlicher, vergleichbarer funktioneller Zusammenhang zwischen der Ausprägung der Lebensgemeinschaft und der hydromorphologischen und strukturellen Lebensraumausstattung des Gewässers (z.B. SHELDON, 1968, KARR & SCHLOSSER, 1978, MINSHALL, 1984; MINSHALL & ROBINSON, 1998, TANIGUCHI & TOKESHI, 2004). So korrelieren Artenzahl und Diversität beider Organismengruppen höchst signifikant negativ mit dem Ausbaugrad der Ufer. Als Resultat der verschiedenen Belastungen findet sich in der Berliner Stadtspree eine extreme Dominanz von wenigen sehr anspruchslosen, toleranten Arten. Folglich sind Verbesserungen des ökologischen Zustandes und des Besiedlungspotenzials für wirbellose Bodenorganismen und Fische neben der Reduzierung der negativen Auswirkungen der Mischwasserentlastung, vorrangig durch Aufwertung der Uferstrukturen zu erreichen. Strukturelle Aufwertungen der Ufer müssen zusätzlich die hydrodynamische Belastung durch den schiffsinduzierten Wellenschlag berücksichtigen, um einerseits das Besiedlungspotenzial zu erhöhen, andererseits die Ufer vor Erosion zu schützen. Die vorliegende Studie gibt Hinweise auf die Möglichkeiten und Grenzen einer Revitalisierung der Berliner Stadtspree und der Kanäle am Beispiel der Fischfauna, indem sie die wesentlichen Belastungen und deren Auswirkungen skizziert. Potenzielle Maßnahmen zur Aufwertung der Uferstruktur sollten aufgrund der oben angesprochenen sehr ähnlichen Wirkmechanismen zwischenUmweltausprägungen und Zusammensetzung der Lebensgemeinschaften beiden, wirbellosen Bodenorganismen und Fischen, zu Gute kommen. Zur Beurteilung möglicher struktureller Maßnahmen wird zunächst davon ausgegangen, dass die negativen Auswirkungen der Mischwasserentlastung derart minimiert werden können, dass sie keine akute Beeinträchtigung der Wasserqualität und der aquatischen Lebensgemeinschaften mehr verursacht. Des Weiteren soll beurteilt werden, ob durch solche Maßnahmen ein Lebensraum für Fischarten geschaffen werden kann, die höhere Ansprüche an die Sauerstoffbedingungen im Gewässer haben als die aktuelle Lebensgemeinschaft.

In the initial phase of the project "Organic Trace Substances Relevant for Drinking Water – Assessing their Elimination through Bank Filtration (TRACE)" the total herbicide glyphosate was classified as highly relevant for further investigations [Chorus & Wessel 2007]. Glyphosate is one of the most widely used and distributed herbicides in the world. Even though it has been on the market since 1974 its use increased with the expiry of the patent at the beginning of the 1990s, in the context of “soil conserving” agriculture (no ploughing) and with the introduction of glyphosate resistant, genetically manipulated cultures like corn, soy beans and cotton wool in 1997. To estimate the occurrence of glyphosate and its main metabolite AMPA in the surroundings of Berlin samples from 22 surface water sites were analysed within this study. In 5 samples the glyphosate concentration was above the European threshold for herbicides of 0.1 µg/L in drinking water. Up to 70 % of Berlin’s drinking water is produced via bank filtration and aquifer recharge characterized by comparatively low flow velocities (< 1 m/d), long contact times (3-6 months) and mainly anoxic redox conditions. To evaluate the potential of bank filtration to protect the drinking water from glyphosate contaminations an experimental study was conducted in the second phase of the TRACE project. Three enclosures at the UBA’s center for aquatic simulations were dosed with three different concentration levels (average concentration: 0.7, 3.5 and 11.6 µg/L) over a time period of 14 days. The effluent was sampled daily for 34 days. Glyphosate and AMPA were analysed applying the HPLC method according to the German Standard DIN 38407-22/2001. In parallel the applicability of the ELISA kit of the company Abraxis was tested without adequate results. The one-dimensional substance transport model VisualCXTFit was applied to obtain substance specific parameters of glyphosate and hydrodynamic parameters of the filter substrate from observed and measured breakthrough curves. The obtained results show that the breakthrough of glyphosate was retarded remarkably (retardation coefficient (R): 18.3 to 25) despite of the initially postulated low adsorption potential of the sandy filter substrate. Also a significant reduction, probably due to degradation was observed (1st order decay-rate (alpha): 0.069 to 0.092 d-1). In addition to the semi-technical scale enclosure experiments laboratory and lysemeter tests were carried out to investigate the processes responsible for glyphosate removal during subsurface passage. The laboratory experiments yielded a KF-value of 1.8998 mg*L*kg-1 and a Freundlich exponent of 0.4805, from which a retardation coefficient of 53.4 was calculated for a glyphosate concentration of 20 µg/L. Furthermore, delayed degradation under sub-oxic conditions could be observed. The lysemeter experiments ensured no glyphosate breakthrough in the effluent of a 2 m thick column of fine to medium sandy material within 7 months. The data obtained in this project prove that there is a potential of bank filtration to eliminate the herbicide glyphosate: Taking into account that glyphosate concentrations in surface water are highly variable a good protection of the drinking water source by bank filtration especially in respect to peak concentration is ensured. However, adsorption and degradation parameters obtained in the laboratory and semi-technical experiments vary significantly due to the difficulty to imitate natural conditions in the laboratory. Therefore the experimental study of the project TRACE emphasises the need to conduct semi-technical experiments in a near-natural environment to evaluate the risk of contamination.

The combination of advanced oxidation (e.g. ozonation) and subsurface passage could overcome known limitations of MAR techniques with respect to dissolved organic carbon (DOC) and trace organics removal. The objective of the OXIRED project is to assess possibilities and limitations as well as practicability and technical feasibility of different combinations of advanced oxidation and subsurface passage with respect to this topic. As part of the first project phase, existing data on subsurface removal of organic trace substances was evaluated in order to identify substances that should be targeted in laboratory and technical scale experiments. This report summarizes the outcomes of this evaluation.

The Aquisafe project aims at mitigation of diffuse pollution from agricultural sources to protect surface water resources. The first project phase (2007-2009) focused on the review of available information and preliminary tests regarding (i) most relevant contaminants, (ii) system-analytical tools to assess sources and pathways of diffuse agricultural pollution, (iii) the potential of mitigation zones, such as wetlands or riparian buffers, to reduce diffuse agricultural pollution of surface waters and (iv) experimental setups to simulate mitigation zones under controlled conditions. The present report deals with (i), providing information on trace substances, which enter surface water predominantly via diffuse sources in rural or semi-rural environments. In particular, it provides a priority list of relevant substances to aid planning of monitoring programs at waterworks, which abstract surface water from rural watersheds, for which information on substance use is sparse. As this ranking is limited to substances for which broad data sets are available from literature, it is compared to actual screening programs in predominantly rural catchments in Brittany (France) and Indiana (USA). The literature review identified pesticides as the dominant known diffuse contaminant group in rural and semi-rural settings (section 2.1). This is confirmed for the agriculturally dominated Ic Catchment in France and Upper White River Watershed in the USA, where pesticides were found to dominate the diffuse source compounds (section 3). Seven agricultural pesticides were detected in the Ic Catchment with AMPA and atrazine being the most common compounds, detected in 54 % and 41 % of all the samples, respectively. In the White River Basin 26 of the 38 detected compounds were pesticides making them the largest group of chemicals detected. Based on literature values on pesticide detection in surface waters in Germany, France and the USA, a priority list was established in section 2.2 of this report (see Table on page vi). Only seven substances were among the 20 most relevant pesticides, both in the USA and in Europe. Accordingly, US and European substances are distinguished in the priority list. Most frequently detected substances were atrazine, metolachlor and simazine for the USA, AMPA (metabolite of glyphosate), diuron and atrazine for France and diuron, atrazine and isoproturon for Germany. The importance of atrazine in Europe is interesting, since it was already banned at the time of the monitoring, indicating the high persistency of atrazine in groundwater. In some cases in Germany, concentrations in surface waters were found to follow typical seasonal application patterns, indicating illegal use (pers. Comm.. M. Bach). Although the list of substances in the USA and in Europe differ, there is an agreement to the fact that many of the pesticides applied in agriculture find their way into surface waters. The concentrations found are often beyond 0.1 µg/L. For the EU this level already corresponds to the drinking water limit. Thus, if surface water is used for drinking water production pesticides seem to be of high relevance. In finished drinking water, frequently-used Isoproturon and Bentazon were most frequently detected in Germany and France. The importance for drinking water production is emphasized by frequent detections above 0.1 µg/L in finished drinking water in nine waterworks in the US. Regarding drinking water regulation, the thresholds in the USA are substance-specific and generally more than one magnitude higher than 0.1 µg/L. As a result threshold exceedance was mainly found for Atrazine. In terms of treatability in water works, the priority list includes the efficiency of classical treatment (flocculation, filtration, ozonation) and of powdered activated carbon (PAC), which is often added in emergency situations. Particularly problematic are triazines (such as atrazine), phenoxy-type substances (such as 2,4-D and Mecoprop) and Anilides/Anilines (such as Metolachlor and Acetochlor). The pesticides found in the screenings are in good agreement with the priority list of most problematic pesticides for the US and Europe. AMPA and atrazine, the substances detected most frequently in the Ic catchment, as well as 2,4-D and dichlorprop, which were found in high concentrations > 0.1 µg/L in one sample are all included in the Europe top 20 of the priority list. Other substances on the list may not have been found because they were not measured, because of relatively high analytical detection limits of the screening or simply because they are not used in the basin, dominated by corn and wheat cultures. In the White River Basin, atrazine, acetochlor and simazine were detected at concentrations exceeding early warning levels utilized by several states in the United States, indicating their high relevance concerning drinking water production. They are also included in the US top 20 of the priority list. The priority list is a reliable basis for potentially problematic pesticides. It can thus be used as a starting point for monitoring programs in rural catchments, where no specific information on pesticide use are available. If looking for pesticides in surface water, it is important to take times of application of regarded pesticides into consideration, as shown by strong fluctuations in atrazine concentrations in the source water of a waterworks in Indiana (Figure 12 of this report). The screening results indicate that also other contaminants than pesticides may play a role in rural catchments. In the screening in the semi-rural catchments in Indiana, twelve of the detected 38 substances were not pesticides, but belonged to other groups, such as domestic use products, manufacturing additives or gasoline hydrocarbons. Of these twelve substances, seven were only found in one of the two catchments, showing a strong catchment-specific relationship. The findings indicate that other substances than pesticides may be of local importance, though in the case study all 12 substances were at least 50-fold below human health benchmarks (if defined). We conclude that the pesticide priority list given below is a good starting point for diffuse pollution screening even though it may possibly not be sufficient if major local influences, such as factories, large roads with stormwater discharges, CSO or specific local pesticide uses are present.

The Aquisafe project aims at mitigation of diffuse pollution from agricultural sources to protect surface water resources. The first project phase (2007-2009) focused on the review of available information and preliminary tests regarding (i) most relevant contaminants, (ii) system-analytical tools to assess sources and pathways of diffuse agricultural pollution, (iii) the potential of mitigation zones, such as wetlands or riparian buffers, to reduce diffuse agricultural pollution of surface waters and (iv) experimental setups to simulate mitigation zones under controlled conditions. The present report deals with (iv) and evaluates the suitability of the technical scale experimental site at the UBA in Berlin, Marienfelde for simulating processes that impact the fate and transformation of nutrients in wetlands / riparian zones. A 3-month pilot investigation (Sep. to mid Nov. 2007) was conducted in order to assess the impact of vegetation on nitrate (NO3-) removal in slow-sand filters (SSFs) and identifying possible interference of glyphosate with N and C cycling processes in these systems. SSFs are engineered bio-reactors that can mitigate the transfer of a wide range of pollutants including nutrients and organic contaminants to water bodies. Two vertical-flow experimental SSFs (average area: 60 and 68 m2, depth: 0.8 and 1.2 m, respectively) at the UBA facilities in Berlin were used in this study: one unplanted and the other vegetated with Phragmites australis. The SSFs received water amended with nitrate (NO3-) and phosphate (PO4 -) without and with glyphosate (added for 2 weeks). Mineral N concentration at the mixing cell, SSF surface, 40 cm depth and at the SSF outlet was measured at least twice per week to calculate N removal rates. Physical water properties (pH, redox potential, temperature) and greenhouse gas emission (CO2, CH4 and N2O) were also monitored to gain insights into controlling processes. Results showed that N removal rates were several-fold higher in the vegetated than in the non-vegetated SSFs averaging 663 mg N m-2 d-1 (57 % of input) and 114 mg N m-2 d-1 (14 % of input), respectively. In both systems, most of the N removal occurred in the top 40 cm of the SSFs. Marked temporal variation in N removal rates was also detected with rates in general 3 times higher in late summer compared to mid/late autumn. In the latter period, a net release of N was observed in the non-vegetated SSF. The seasonal variation in N removal could be related to a lack of vegetation growth and thus plant N uptake, and may also reflect of the sensitivity of denitrification to climatic factors as suggested by strong (r2 > 0.77) linear relationships between weekly N removal rates and SSF water temperature. A clear impact of glyphosate addition on nitrate concentrations could not be observed. Denitrification, the process most responsible for the removal of nitrogen from waters and soils seems to be unaffected by the addition of glyphosate under the conditions in the experiment. The impact of glyphosate, if any, was probably much smaller compared to the strong influence of temperature on N dynamics in the SSFs. Difficulty of maintaining a constant concentration of glyphosate during dosing may have also contributed to this outcome. Nitrous oxide emission accounted for < 3 % of the total N removed was always lower in the vegetated (< 0.1 - 0.3 mg N2O-N m-2 d-1) than in the non-vegetated SSF (0.2 - 3.8 mg N2O-N m-2 d-1). Conversely, CH4 emission was always higher in the vegetated (range: +0.4 to +49.5 mg CH4-C m-2 d-1) than in the non-vegetated SSF (range: -2.1 to +1.32 mg CH4-C d-1). These results, in connection with much lower oxidation reduction potential readings in the vegetated filter, suggest that the reduction of N2O to N2 was important in the SSF systems and that N2 was the dominant N gas produced. Thus, N2 production must be quantified in order to establish N mass balance of SSF systems. The results show that technical-scale experiments can realistically simulate mitigation systems, while having control over contaminant loading, flow conditions and monitoring. Important lessons learnt for future applications are the following (i) Denitrifying conditions can be established in both SSF of the experimental site by adjusting to low flow conditions (0.23 m³/h) and dosing nitrate. (ii) Dosing of trace contaminants (in this case glyphosate) needs to be improved, but will remain difficult for the large amounts of water involved. The results underline the importance of measurements in the mixing cell. (iii) Since seasonal effects play an important role in mitigation zone performance, any experiments need to be done in parallel, rather than in succession to be able to compare the results.

The Aquisafe project aims at mitigation of diffuse pollution from agricultural sources to protect surface water resources. The first project phase (2007-2009) focused on the review of available information and preliminary tests regarding (i) most relevant contaminants, (ii) system-analytical tools to assess sources and pathways of diffuse agricultural pollution, (iii) the potential of mitigation zones, such as wetlands or riparian buffers, to reduce diffuse agricultural pollution of surface waters and (iv) experimental setups to simulate mitigation zones under controlled conditions. The present report deals with (ii) and aims at identifying numerical modelling tools that can assess the origin of contaminants as well as the impact of different mitigation measures regarding water quality aspects on a catchment scale. In order to test the identified modelling tool in the further course of the Aquisafe project a case study was found in Brittany (France) in agreement with Veolia Eau: the small watershed of the river Ic. Due to intensive agricultural land use the nitrate concentration exceeds the threshold for surface water used for drinking water purpose (which is the main concern of Veolia Eau). Additionally, trace contaminants (pesticides) were detected in the surface water ever since measurements have been carried out. Therefore modelling shall mainly support the water supplier in actions aiming at reducing the nitrate concentration in the surface water. An additional task could later on be the application of the model in order to assess the effectiveness of mitigation measures against trace contamination. In order to choose the most appropriate model a model comparison was carried out using a three step approach. The first step was a screening of different information sources and resulted in the identification of 44 existing models. The second step was a pre-selection according to essential criteria in order to identify models that fulfil the basic requirements for a) the Ic nitrate issue and b) the Aquisafe trace contaminant issue. In a third step a multicriteria analysis was carried out using 6 additional criteria followed by a final recommendation. The essential criteria used for the pre-selection of the models were a) the inclusion of major hydrological processes, b) the inclusion of the nitrogen cycle (for the Ic nitrate issue) or the inclusion of trace contaminants (for the Aquisafe trace contaminant issue) c) the size of catchments that can be modelled, d) the temporal and spatial resolution and e) the possibility to include management options and/or mitigation measures. For the Ic nitrate issue this resulted in the selection of the models: HBV-NP, HSPF, SWIM, SWAT, WASMOD and Mike She. For the Aquisafe trace contaminant issue only four models remained after the pre-selection process: DRIPS, HSPF, SWAT and Mike She. Additional criteria were then applied and resulted in the recommendation to use the model SWAT for further investigations in both cases due to sufficient accuracy and included processes (full hydrological model with water quality simulation (nutrients and trace contaminants) as well as a wide range of successful applications (amongst others). This report presents a wide range of models with their capabilities and limits. It contains criteria which were identified with the stakeholders in order to choose the most appropriate model. The approach presented in this report shall support the decision process of selecting a model for a certain problem regarding water quality and includes only a recommendation. The final decision on which model shall be applied, will be taken in agreement with the stakeholders Veolia Eau and Goel’Eaux.