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

The Hydrogeological Overview Map of Lower Saxony 1: 500 000 — Groundwater quality: Iron content shows the evaluation of a representative selection of iron 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 classified taking into account the limit values of the Drinking Water Ordinance (TVO) of 0.2 mg/l. Increased concentrations, which are clearly due to point-shaped anthropogenic entries (e.g. old landfills), are not reproduced in this overview map. The iron 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 concentration of iron in groundwater is strongly influenced by pH and redox ratios. The highest iron content in Lower Saxony is achieved in acidic and/or greatly reduced water. On the other hand, high concentrations of carbonate and sulphide ions cause the precipitation of siderite or iron sulphides, thus limiting the solubility of iron. At high concentrations of dissolved organic carbon, large proportions of iron are also bound to organocomplexes. In general, the iron content in the solid rock equifers of the Lower Saxony mountain region is significantly lower than in quaternary loose rocks. Mesozoic limestones contain the lowest iron concentrations of 0.01 to a maximum of 0.1 mg/l. Higher values are observed in mesozoic sandstone. In the paleozoic rocks of the resin there are values in the range of 0.1-0.5 mg/l. The oxygen-containing groundwater in northern Lower Saxony (e.g. Lüneburg Heath) shows iron concentrations in the range of 0.1-1 mg/l. In rare cases, up to 2 mg/l are achieved. In the lowlands in northern Lower Saxony, the limit value of the TVO of 0.2 mg/l is often exceeded. Iron concentrations of 2-10 mg/l are often observed in ascending groundwater with longer flow paths. Also very high iron content between 10 and 40 mg/l can be found in groundwater, which is influenced by moors (e.g. Vehnemoor southwest of Oldenburg and Teufelsmoor north of Bremen). By contrast, iron-containing groundwaters in the north of Hanover (Isernhagen, Langenhagen) with concentrations of up to 40 mg/l are likely to be traced back to the oxidation of pyrite from lower chalk claystone.