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

The Hydrogeological Overview Map of Lower Saxony 1: 500 000 — Groundwater quality: Sulfate 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 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 240 mg/l and the TVO value of 500 mg/l in case of geogenic excess. Increased concentrations, which are clearly due to point-shaped anthropogenic entries (e.g. old landfills), are not reproduced in this overview map. Sulphate levels are 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. Very high sulphate concentrations are partly due to geogenic influences: The highest concentrations for sulphate are found in Lower Saxony in the area of coastal salinisation (East Frisian coast and north of the Jadebusen). Also very high geogenic sulfate concentrations are found in the distribution area of gypsum rocks (Oberer Buntsandstein, Middle Shell Lime, Middle Keuper, Zechstein), where sulphate concentrations of more than 1 000 mg/l are reached in groundwater. The oxidation of sulphides (e.g. pyrite) also leads to high sulphate levels. In the northern area of Hanover, concentrations of 100-400 mg/l are achieved. One reason for this is the oxidation of pyrite minerals from rocks of the Cretaceous period. Increased iron content and low pH levels are further consequences of this reaction. Very low sulphate levels with significantly less than 10 mg/l are mostly due to sulfate reduction, wherein this reaction is often subject to organic material in the rock oxidation processes. The groundwater in the holocene deposits east and southeast of the Jadebusen is largely altered by sulphate reduction.