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

Description

The hydrogeological overview map of Lower Saxony 1 : 500 000 - Groundwater quality: Sulphate content shows the evaluation of a representative selection of sulphate 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 (GFS) or the limit value of the Drinking Water Ordinance (TVO) of 240 mg/l as well as the TVO value of 500 mg/l in case of geogen-related exceedance. Increased concentrations, which are clearly due to point-like anthropogenic entries (e.g. old landfills), are not reflected in this overview map. The sulphate contents are presented in depth stages 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. Very high sulfate concentrations are partly due to geogenous influences: The highest concentrations of sulfate are found in Lower Saxony in the area of coastal salinization (East Frisian coast and north of the Jade Gulf). There are also very high geogenous sulphate concentrations in the distribution area of gypsum-containing rocks (Upper Buntsandstein, Mittlerer Muschelkalk, Mittlerer Keuper, Zechstein), where sulphate concentrations of more than 1000 mg/l are reached in groundwater. The oxidation of sulfides (e.g. pyrite) also leads to high sulfate levels. Concentrations of 100 – 400 mg/l are reached in the northern area of Hanover. One reason for this is the oxidation of pyrite minerals from rocks of the Cretaceous period. Increased iron levels and low pH levels are further consequences of this reaction. Very low sulphate contents with substantially less than 10 mg/l are usually due to sulphate reduction, whereby organic material in the rock is often subject to oxidation processes in this reaction. The groundwater in the Holocene deposits east and southeast of the Jade Bay is largely altered by sulphate reduction.

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0 https://nibis.lbeg.de/net3/public/ogc.ashx?NodeId=647&Service=WMS&Request=GetCapabilities&

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