Groundwater fauna as an indicator of surface water-groundwater interactions at a riverbank filtration site

The water quality of bank filtrate is strongly influenced by complex hydrological exchange processes. In particular, surface water coming into contact with groundwater is a potential hazard for drinking water quality. Therefore monitoring for surface water intrusion is required for assuring the quality of the raw water being used. The hydrological interactions of the Rhine bank filtration site at Flehe, Duesseldorf were analyzed hydro-chemically and faunistically and both approaches were compared. In addition, the degree of surface water influence was determined by using the fauna and the Groundwater-Fauna-Index (GFI) after Hahn (2006a). The fauna provided a more detailed impression of the hydrological situation of the study area than the water chemistry. By means of the fauna and the GFI, different groundwater types were identified, indicating different degrees of surface water intrusion. Thus, the fauna and the GFI are considered to be suitable measures for the assessment of the hydrological conditions as well as for the evaluation of the surface water impact on the groundwater and consequently are suitable for use in vulnerability assessment.