Hydrogeological overview map of Lower Saxony 1 : 500 000 - Groundwater quality: Chloride content

Description

The hydrogeological overview map of Lower Saxony 1 : 500 000 - Groundwater quality: Chloride content shows the evaluation of a representative selection of chloride concentrations from the laboratory database of the LBEG. The data collected over a period from 1967 to 2000 were averaged twice. In the case of groundwater measuring stations with multiple analyses, mean values of the available test results were calculated. In addition, the values of all sampling points within a radius of 2000 m were subjected to further averaging. The classification of the classes takes into account the de minimis threshold (JRC) or the limit value of the Drinking Water Ordinance (TVO) of 250 mg/l. Increased concentrations, which are clearly due to point-like anthropogenic entries (e.g. old landfills, mining heaps), are not reflected in this overview map. The chloride contents are shown in depth steps without reference to the local hydrogeological situation. The bar charts in the example shown on the right reflect results for depth levels up to 20 meters, over 20 to 50 meters, over 50 to 100 meters and over 100 to 200 meters. A comparison of values is therefore not permissible without taking into account the respective hydrogeological situation (e.g. hydrogeological floor construction) as well as the use of the data for detailed investigations. The lowest concentrations of chloride in Lower Saxony are found in the Harz and Solling at 5 – 10 mg/l and in the Lüneburg Heath at 10 – 30 mg/l. Levels above 50 mg/l cannot generally be explained by atmospheric input and enrichment by evapotranspiration and are usually due to geogenous or anthropogenic salinisation of groundwater. Very strong geogenically caused chloride salinization of groundwater is found in Lower Saxony, especially on the coast and in the estuary area of the Elbe, Weser and Ems (coastal salinization by seawater) with concentrations of 15,000 - 16,000 mg/l. Outside the areas of seawater salinization, the chloride levels near the coast are between 30 and 50 mg/l. Another cause of geogen-related salinization of the groundwater is the aeration of salt rocks in the subsoil. An example of this are increased chloride concentrations, which often occur in lowlands of rivers (e.g. Elbe near Lauenburg and Gorleben, Jeetzel, Wümme) and which are due to rising aeration waters of salt structures. Also near Hannover (Ronnenberg, Sarstedt), Salzgitter, Braunschweig (Wolfenbüttel; Asse) and in the Lower Saxony mountains, small-scale salinization is often found near salt domes. Increased chloride concentrations are also found in areas of the Lower Saxony mountain region where salinar sequences (Zechstein, Oberer Buntsandstein, Mittlerer Muschelkalk, Mittlerer Keuper, Münder-Mergel des Oberen-Jura) occur near the surface. North of Hanover, the influence of marine claystone deposits of the Lower Cretaceous leads to an increase in the chloride content to 50 - 100 mg/l in the small quaternary deposits.

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