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).

In the densely populated semi-arid territory around Delhi, the water demand is rising continuously, while the surface- and groundwater resources are threatened by contamination and overexploitation. This is a typical scenario in many newly industrialising and developing countries, where new approaches for a responsible resources management have to be found. Bank filtration holds a great potential, thus being a low tech method and benefiting from the storage and contaminant attenuation capacity of the natural soil/rock. For this study, three field sites have been constructed to investigate bank filtration in different environments in and around the megacity with a main focus on inorganic contaminants. Hydraulic heads, temperature gradients and hydrochemistry of surface water and groundwater were analysed in three different seasons. Depending on sitespecific conditions, distinct hydrogeological conditions were observed and both positive and negative effects on water quality were identified. Most concerning issues are the impact of anthropogenic ammonia, the mixing with ambient saline groundwater and the mobilisation of arsenic during the reductive dissolution of manganese- and iron(hydr)oxides. Positive aspects are the dilution of contaminants during the mixing of waters from different sources, the sorption of arsenic, denitrification, and the precipitation of fluoride under favourable conditions.

Submersible data loggers are widely used for groundwater monitoring, but their application often runs the risk of hardware and data loss through vandalism or theft. During a field study in India, the authors of this article experienced that well locks attract the attention of unauthorized persons and do not provide secure protection in unattended areas. To minimize the risk of losing data loggers, a cheap and simple solution has been invented to hide the instruments and associated attachments below the ground surface, inside observation wells. It relies on attaching the logger to a length of small-diameter pipe that is submerged at the bottom of the well, instead of attaching it to the top of the well. The small-diameter pipe with the logger is connected to a small bottle containing a magnet that floats on the water surface of the well and can be recovered using another bottle also with a magnet. A logger that is concealed in this way is difficult to detect and access without knowledge of the method and adequate removal tools. The system was tested and successfully applied for monitoring shallow

Bank filtration (BF) is a well established and proven natural water treatment technology, where surface water is infiltrated to an aquifer through river or lake banks. Improvement of water quality is achieved by a series of chemical, biological and physical processes during subsurface passage. This paper aims at identifying climate sensitive factors affecting bank filtration performance and assesses their relevance based on hypothetical 'drought' and 'flood' climate scenarios. The climate sensitive factors influencing water quantity and quality also have influence on substance removal parameters such as redox conditions and travel time. Droughts are found to promote anaerobic conditions during bank filtration passage, while flood events can drastically shorten travel time and cause breakthrough of pathogens, metals, suspended solids, DOC and organic micropollutants. The study revealed that only BF systems comprising an oxic to anoxic redox sequence ensure maximum removal efficiency. The storage capacity of the banks and availability of two source waters renders BF for drinking water supply less vulnerable than surface water or groundwater abstraction alone. Overall, BF is vulnerable to climate change although anthropogenic impacts are at least as important.

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.

The microbial degradation of pharmaceuticals found in surface water used for artificial recharge is strongly dependent on redox conditions of the subsurface. Furthermore the durability of production wells may decrease considerably with the presence of oxygen and ferrous iron due to the precipitation of trivalent iron oxides and subsequent clogging. Field measurements are presented for oxygen at a bank filtration site in Berlin, Germany, along with simplified calculations of different oxygen pathways into the groundwater. For a twodimensional vertical cross-section, oxygen input has been calculated for six scenarios related to different water management strategies. Calculations were carried out in order to assess the amount of oxygen input due to (1) the infiltration of oxic lake water, (2) air entrapment as a result of water table oscillations, (3) diffusive oxygen flux from soil air and (4) infiltrating rainwater. The results show that air entrapment and infiltrating lake water during winter constitute by far the most important mechanism of oxygen input. Oxygen input by percolating rainwater and by diffusive delivery of oxygen in the gas phase is negligible. The results exemplify the importance of well management as a determining factor for water oscillations and redox conditions during artificial recharge.