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Development of Ammonium Concentrations at a Riverbank Filtration Site in Delhi (India) – Water-Sediment Interactions from Infiltration to Production

Maike Gröschke1, Theresa Frommen2, Gesche Grützmacher3, Michael Schneider2
1 Kompetenzzentrum Wasser Berlin/ Freie Universität Berlin
2 Freie Universität Berlin
3 Kompetenzzentrum Wasser Berlin

O 6.8 in Groundwater, soil and surface water interactions

30.05.2014, 14:20-14:40, H19, NW II

The Yamuna River in Delhi is highly influenced by partially treated sewage water. At a field site in central Delhi, several large horizontal filter wells (Ranney wells) were constructed in the 1970s, pumping water from the alluvial aquifer. Due to losing stream conditions they may draw high shares of bank filtrate, although travel times from the river to the production wells were shown to be high (> 1.7 years). Influenced by monsoon-driven strong variations in precipitation and water level, the hydraulic and hydrochemical conditions in the alluvial aquifer are highly transient. Measured ammonium and dissolved oxygen (DO) concentrations in the river water vary between 2.5-20 mg/L NH4+ and 0.03-5.5 mg/L DO throughout the year as the Himalayan snow melt and the monsoon rains dilute the otherwise oxygen depleted and ammonium-rich river water during the summer months (May-September). Flood events regularly change the flow regime (travel distance and flow velocity) and fluctuating groundwater levels most likely lead to changing infiltration conditions throughout the year. After nearly 40 years of pumping, the ammonium plume has moved substantially far into the aquifer and ammonium concentrations of up to 27.5 mg/L were measured in the groundwater at a distance of 500 m to the river. In order to understand the dominating processes regarding the transport of ammonium along a main flow path (from infiltration to production well), column experiments with aquifer material were conducted. Nitrogen mass balances reveal that it will take over 25 years until ammonium depleted water reaches the first production well, once river water quality improves. A 1D reactive transport model with PHREEQC is constructed to take into account the highly varying source water and infiltration conditions. This will contribute to estimating future ammonium concentrations for different scenarios regarding the source water quality and well operation. This is necessary to evaluate the suitability for future drinking water production and to plan appropriate treatment options. 



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last modified 2013-11-01