In deltaic areas with deep polders and in valleys or deltas with heavy groundwater exploitation, bank infiltration is a rapidly expanding mechanism of groundwater recharge. Rhine bank filtrate can be distinguished best from autochthonous groundwater in The Netherlands by way of its natural lower O18 content. Tritium is a good measure of the portion of water younger than 25 years, at least in well mixed Rhine bank filtrate. This portion carries the bulk of the contaminations originating from the Rhine, as evidenced by strong positive correlations between H3 and, e.g., halogenated hydrocarbons, taste and mutagenic activity according to the Ames test. The composition of Rhine bank filtrate is further governed by the redox level of the hydrogeochemical system, varying in The Netherlands from suboxic to anoxic with fermentation, and by the underground distance to the influent Rhine branch. Anoxic bank filtrate with strong SO4-reduction and CH4 > 1 mg/l exhibited a significantly different composition from anoxic bank filtrate without fermentation and without SO4-reduction. The following parameters are involved: HCO3, total dissolved solids, Di)2; KMnO4-consumption, NH4, siderite, baryte and vivianite saturation indices, I, total hardness, total PO4, Fe, dissolved organic carbon, Ba, pH, dichloroethane, Mo, VOCl, Mn, V, dichlorobenzene and 1,2-dichloroethane, in order of decreasing significance. A longer underground detention time or travel distance, leads to a small decrease in the share of bank filtrate, and a rather strong decrease in K, Li, F, temperature, Mo (only in anoxic, SO4-(meta)stable bank filtrate) , UV-extinction, AOCl, X7OCl and mutagenic activity. Coli bacteria and viruses could not be detected, even in samples from wells at 50 m distance from the Rhine, with a minimum travel time of 30 d. (Author 's abstract)
Water Resources Abstracts; Water pollution sources; Groundwater quality; Surface-groundwater relations; The Netherlands; Water quality; Geohydrology; Groundwater recharge; Rhine River; Groundwater pollution; Groundwater; Infiltration; Isotope studies; Glacial aquifers; Tritium; Oxygen isotopes; SW 3020:Sources and fate of pollution; SW 0840:Groundwater