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

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 have been averaged twice. For groundwater measuring points with multiple analyses, mean values of the available test results were formed. In addition, the values of all sampling points in a radius of 2 000 m were subjected to further averaging. Classes are categorised taking into account the de minimis threshold (GFS) or the limit value of the Drinking Water Ordinance (TVO) of 250 mg/l. Increased concentrations that are clearly due to point-shaped anthropogenic entries (e.g. waste landfills, mining dumps) are not reproduced in this overview map. The chloride content is shown at depth levels without reference to the local hydrogeological situation. The rod diagrams in the example shown on the right reflect results for the depths 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 examinations. The lowest concentrations of chloride in Lower Saxony are found in the Harz and Solling with 5-10 mg/l and in the Lüneburg Heath with 10-30 mg/l. Contents above 50 mg/l cannot be explained by the atmospheric input and the enrichment by evapotranspiration in general and are usually due to geogenic or anthropogenic salinisation of the groundwater. Very strong geogenic chloride salinisation of groundwater is found in Lower Saxony mainly on the coast and in the estuary of Elbe, Weser and Ems (coast salinisation by sea water) with concentrations of 15,000-16.000 mg/l. Outside the areas of seawater salinisation, the chloride levels are between 30 and 50 mg/l. Another cause of geogenic salinisation of groundwater is the blueness of salt rocks in the underground. An example of this is increased concentrations of chloride, which often occur in lowlands of rivers (e.g. Elbe near Lauenburg and Gorleben, Jeetzel, Wümme) and which are due to ascending agglomeration waters of salt structures. Also near Hannover (Ronnenberg, Sarstedt), Salzgitter, Braunschweig (Wolfenbüttel; Asse) and in the Lower Saxony mountain country, small-scale salinisations are often found near salt sticks. In addition, increased concentrations of chloride are located in areas of the Lower Saxony mountain region where salinar sequences (Zechstein, Upper Bunt sandstone, Middle Shell limestone, Middle Keuper, Münder-Mergel of the Oberen-Jura) occur near the surface. North of Hanover, the influence of marine claystone deposits of the lower chalk leads to an increase in the chloride content to 50-100 mg/l in the low-power quaternary deposits.