Approximately 70% of the drinking water in Germany (BGR) and about 50% worldwide (IGREC 2011) are abstracted 2 from groundwater using filter wells. Their implementation and operation are major factors contributing to the costs of drinking water production. Within the joint research project ANTIOCKER , funded by the German Ministry of Research and Education, and coordinated at the Dept. of Applied Microbiology of the Technical University Berlin, the partners Berliner Wasserbetriebe (BWB) and the Berlin Centre of Competence for Water (KWB) focus on the efficient operation of drinking water abstraction wells. One major reason for inefficient wells is so-called well ageing, i.e. the increase in drawdown at constant discharge rate due to biological, chemical and / or physical processes in and around the well. In Berlin, approximately 80% of clogging deposits are described to be of biochemical nature involving iron-related bacteria. Previous studies, i.e. in the scope of the KWB research project WELLMA have revealed that such well ageing phenomena are determined by multiple correlated biological and chemical processes. For this reason, it is the sound understanding of the main processes and key parameters that will provide the basis for the systematic control of iron bacteria occurrence by an optimized well operation. A new approach to a large variety of data from well construction and maintenance of the Berlin drinking water wells focused on the determination of key parameters for monitoring and the identification of hidden variables for ageing by means of probabilistic statistics. Cumulative distribution plots are used to visualize large data amounts and frequency distribution plots filter correlations between e.g. maintenance events in the lifetime of a well and monitoring data. First results indicate that small changes in the discharge rate Q on a daily basis could be used to monitor the well performance on a much higher frequency than the currently used evaluation of the specific capacity. In addition, the electric conductivity proved to be a key variable for clogging. Both parameters are now being verified in field investigations and further data analyses within the research project ANTIOCKER and about 50% worldwide are abstracted 2 from groundwater using filter wells. Their implementation and operation are major factors contributing to the costs of drinking water production.

Until around 2004, the term riverbank filtration (RBF) or simply bank filtration (BF, a unified term for river and lake bank / bed filtration) was not commonly used in context to drinking water supply in India. The abundant recharge of traditional dug wells (used for drinking and irrigation) located near surface water bodies (mainly rivers but also some lakes) by very low-turbidity water via natural bank filtration during and after the monsoon has been recognised in India for a very long time. Induced bank filtration has been suggested in the 1970s to address the growing agricultural irrigation demand in the alluvial plains along the Ganga River by inducing recharge from surface water bodies during and after the monsoon (Chaturvedi and Srivastava 1979). Documented evidence till date suggests that induced bank filtration has been used in India for at least 56 years, although even older BF systems may exist. In Nainital, bank filtrate has been abstracted from Nainital Lake since 1956 (Kimothi et al. 2012). BF supplements existing surface and groundwater abstraction for drinking water supply in the cities of Ahmedabad (by the Sabarmati River), Delhi and Mathura (Yamuna) and Nainital (Nainital Lake); on the other hand in Haridwar and Patna (Ganga), and Medinipur and Kharagpur (Kangsabati), BF is used as an alternative to surface water abstraction and to supplement groundwater abstraction (Sandhu et al. 2012). Considering the continuously growing demand for drinking water in sufficient quantities, the emphasis at many BF sites has traditionally been on maximising the volumes of raw water abstracted. Furthermore, the results of a fact-finding study (Ray and Ojha 2005) on the use of BF for drinking water production in India on one hand confirmed that a number of river-side communities have been already using BF for a long time, but that on the other hand only scarce information on the hydrogeological conditions and water quality of these BF sites existed. Holistic investigations on water quality aspects and sustainability (qualitative and quantitative) of these existing BF sites began only after 2004. Water quality investigations conducted at the BF sites of Srinagar by the Alaknanda river (Ronghang et al. 2011), Haridwar and Nainital (Dash et al. 2008, 2010; Sandhu et al. 2011a), Delhi (Sprenger et al. 2008; Lorenzen et al. 2010) and Mathura (Singh et al. 2010; Kumar et al. 2012) and Patna (Sandhu et al. 2011b) showed that the main advantage of using BF in comparison to direct surface water abstraction lies in the removal of pathogens and turbidity. The surface water concentration of trace organic contaminants and their removal at the investigated sites has not been widely investigated, but has shown to be high at sites in Delhi and Mathura (Sprenger et al. 2008; Singh et al. 2010). For conventional treatment, high concentrations of organic contaminants requires high (40–60 mg/L) doses of chlorine prior to flocculation thus creating a greater risk for formation of carcinogenic disinfection by-products, as reported in Mathura (Singh et al. 2010; Kumar et al. 2012). In such situations BF is advantageous as a pre-treatment in order to reduce the necessary doses of chlorine prior to flocculation. Additional advantages of BF may also be seen during the monsoon season principally in the removal of turbidity and pathogens, as well as in the removal of color and dissolved organic carbon (DOC), UV absorbance, turbidity, total and thermotolerant coliform counts, endocrine disruptor compounds and organochlorine pesticides (Dash et al. 2008, 2010; Sandhu et al. 2011a; Thakur et al. 2009a, 2009b; Sprenger et al. 2011; Mutiyar et al. 2011). BF, however, does not present an absolute barrier to other substances of concern (e.g. ammonium) and some inorganic trace elements may even be mobilized. This has been observed in Delhi which has poor surface water quality (Sprenger et al. 2008), at which extensive post-treatment is applied to remove high levels of ammonium. The objective of this deliverable is to provide an overview of known BF schemes in urban areas of India where the abstraction of bank filtrate is intentional. The main water quality issues of concern are highlighted. Related published and unpublished data, as well as new data collected since the commencement of the Saph Pani project in October 2011, is presented for the BF schemes in Haridwar, Nainital, Srinagar (by the Alaknanda river in Uttarakhand), Delhi Mathura and Satpuli (by the Eastern Nayar river in Uttarakhand).

Approximately 70% of the drinking water in Germany (BGR) and about 50% worldwide (IGREC 2011) are abstracted from groundwater using filter wells. Their implementation, operation and maintenance are major factors contributing to the costs of drinking water production. According to an international survey (Howsam, Misstear & Jones 1995 ), 40% of worldwide used water abstraction wells work inefficiently in terms of well performance or water quality. This implies high costs and a great potential for improvement, both for the (re-) construction of new wells (capital investment) and well operation (energy consumption, maintenance needs). The main reason for inefficient well performance is so-called well ageing, i.e. the decrease in performance due to biological, chemical and / or physical processes in and around the well. Dominant factors determining type, extension and location of deposits are the geology of the exploited aquifer together with the qualitative properties of the abstracted water, the well design (dimensions and materials), construction (drilling method) and operation. The project WellMa, initiated and financed by the Berliner Wasserbetriebe (BWB) and Veolia Eau, and coordinated at the Berlin Centre of Competence for Water (KWB), aimed at improving the efficiency of drinking water abstraction wells by identifying, evaluating and testing methods of well management including design, operation and maintenance to slow down well ageing. Set into relation to ranges, in which ageing processes are known to occur, the initial data of well sites were used to differentiate a low, medium or high potential for the occurrence of well ageing and to define the monitoring needs accordingly. Well ageing processes were distinguished into six types, each of them implying different pre-requisites and site conditions and leading to different monitoring and/ or maintenance requirements. For carbonate scaling, iron ochre formation, biofouling, corrosion, colmation and sand intake pre-requisites, triggers and threshold conditions were identified and implemented in a decision support system enabling well operators to prioritize the needs for monitoring, diagnosis or maintenance action taking into account the specific well and site characteristics.

Groundwater exploitation in India has increased rapidly over the last 50 years as reflected by the growth of the number of groundwater abstraction structures (from 3.9 million in 1951 to 18.5 million in 1990) and shallow tube wells (from 3000 in 1951 to 8.5 million in 1990) (Muralidharan, 1998; Singh & Singh, 2002).Today groundwater is the source for more than 85 % of India’s rural domestic water requirements, 50 % of urban water and more than 50 % of irrigation demand. The increase in demand in the last 50 years has led to declining water tables in many parts of the country. For example, 15% of the assessment units (Blocks/Mandals/Talukas) have groundwater extraction in excess of the net annual recharge (Central Ground Water Board, 2007). According to Rodell et al. (2009), the extent of groundwater depletion between 2002 and 2008 was 109 km3, which is about half the capacity of India’s total surface-water reservoirs.

Managed aquifer recharge (MAR) provides efficient removal for many organic compounds and sum parameters. However, observed in situ removal efficiencies tend to scatter and cannot 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 (2002e2005, Berlin, Germany). 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).

The herbicide Glyphosate was detected in River Havel (Berlin, Germany) in concentrations between 0.1 and 2 µg/L (single maximum outlier: 5 µg/L). As the river indirectly acts as drinking water source for the city's 3.4 Mio inhabitants potential risks for drinking water production needed to be assessed. For this reason laboratory (sorption and degradation studies) and technical scale investigations (bank filtration and slow sand filter experiments) were carried out. Batch adsorption experiments with Glyphosate yielded a low KF of 1.89 (1/n = 0.48) for concentrations between 0.1 and 100 mg/L. Degradation experiments at 8 °C with oxygen limitation resulted in a decrease of Glyphosate concentrations in the liquid phase probably due to slow adsorption (half life: 30 days).During technical scale slow sand filter (SSF) experiments Glyphosate attenuation was 70-80% for constant inlet concentrations of 0.7, 3.5 and 11.6 µg/L, respectively. Relevant retardation of Glyphosate breakthrough was observed despite the low adsorption potential of the sandy filter substrate and the relatively high flow velocity. The VisualCXTFit model was applied with data from typical Berlin bank filtration sites to extrapolate the results to a realistic field setting and yielded sufficient attenuation within a few days of travel time. Experiments on an SSF planted with Phragmites australis and an unplanted SSF with mainly vertical flow conditions to which Glyphosate was continuously dosed showed that in the planted SSF Glyphosate retardation exceeds 54% compared to 14% retardation in the unplanted SSF. The results show that saturated subsurface passage has the potential to efficiently attenuate glyphosate, favorably with aerobic conditions, long travel times and the presence of planted riparian boundary buffer strips.

In the 2nd phase of the project (OXIRED 2), trials at lab and technical scale were conducted to validate the results for trace organic and DOC removal from OXIRED 1 and to gain a more reliable knowledge about oxidation by-product formation for surface water from Berlin. To assess the stability of the process, a pilot unit was operated at Lake Tegel. Moreover the effect of oxidation + MAR on toxicological parameters was investigated (s. D 1.1). To prepare a field study three sites in Germany were evaluated regarding their suitability including parameters such as aquifer depth and composition, source water quality and possibility of authorization (s. D 2.1). The results were that none of the sites (Hobrechtsfelde, Braunschweig WWTP or artificial recharge site in Görlitz) was identified as suitable. The current state-of-the-art for influencing the redox zonation in the subsurface was reviewed (D 3.1) and the options to assess the quantity, composition and activity of the microbial population in the soil samples were summarized (D 2.2). To investigate the dynamic of redox processes, short term column tests were conducted (D 3.2). On the basis of these results reactive flow and transport modelling was carried out (D 3.2 and 3.3). The aim of this report is to give a summary of the main results from OXIRED 2 and to identify promising opportunities for further experiments and transfer to field scale.

It was the aim of the EU funded research project TECHNEAU to investigate the relevance and feasibility of bank filtration (BF) plus post-treatment for newly industrialised and developing countries. Field studies at BF sites in Delhi (India) were supplemented by literature studies and modelling in order to investigate if this natural drinking water (pre-) treatment is a sustainable option to provide safe drinking water for countries like India. The results showed that especially for those substances that are of relevance in newly industrialised and developing countries subsurface passage can represent an efficient barrier. However, certain limiting factors for BF application also need to be considered: high ammonium levels in surface water, usually associated with high shares of poorly or un-treated sewage, will not be mitigated during subsurface passage and require extensive post-treatment. In order to support decision makers in the difficult task of assessing the feasibility of BF systems at a certain site a simple decision support system was developed. This simple tool enables to assess a range of abstraction rates and well locations for a specific field site that could fit with their needs (e.g. minimum required travel time or share of BF).