Model Based Raw Water Quality Management – Manganese Mobilization Induced by Bank Filtration

Abstract

AbstractIn many countries bank filtration is used as the first step of drinking water treatment. River water percolates the riverbed and aquifer sediments which serve as a natural filter removing substances like nitrate, particular and dissolved organic matter and trace elements. Raw water quality, therefore, depends on both river water quality as well as hydrogeochemical processes within the sediment. Exemplified by the case study of Auf dem Grind, Well II (Düsseldorf, Germany), the geohydraulic and hydrogeochemical processes of a catchment area that is strongly influenced by bank filtration were investigated. Raw water extracted from Well II showed significantly elevated manganese concentrations compared to river water and to raw water from other wells in the catchment area. A reactive transport model was developed for retracing the measured raw water quality. Retrospective modeling revealed the principles of long and midterm changes in raw water quality, especially fluctuations in manganese concentrations. Based on the model‐scenario, the effects of varying river water qualities and/or agricultural fertilization practices can be predicted. The quantitative understanding of coupled hydrogeochemical and hydraulic processes enables the development of sustainable strategies optimizing raw water quality, e. g. with regard to a cost effective water treatment.