HU - Hydrogeology and Environment

Journal of the Dept. of Hydrogeology and Environment, University of Würzburg (ISSN 09309-3757)

Editorial office: BGI, Greisingstr. 8, 97074 Würzburg, GERMANY

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Vol. 12 (1996)


Vol. 12: 

Geogene Arsenkonzentrationen in Keupergrundwässern Frankens/Bayern.
[Natural Arsenic Concentrations in Groundwaters of the Frankonian Keuper/Bavaria (Germany)]

Gerold Heinrichs

In Franken/Bavaria, groundwater with natural arsenic concentrations from the Keuper sedimentary formation is used for drinking water. Detailed sampling of these arsenic groundwaters shows elevated arsenic concentrations in certain geographic areas apparently related to the geology and stratigraphy of the aquifers. Using water-chemical data in combination with geochemical investigations of drill cuttings from five wells, increased sedimentary arsenic concentrations in certain layers of Keuper were found, being suspect to increased arsenic concentrations of the groundwater. The arsenic containing rocks are compact sediments of terrestrial to fluvial-marine depositional environments in the border facies of the Frankonian Keuper. Source area is most likely the crystalline continental basement of the Bohemian mass in the southeast of the research area. In corresponding marine sediments of the Frankonian Keuper basin facies elevated arsenic concentrations in sediments and groundwaters are lacking. A correlation of tectonic elements and increased arsenic concentrations is prevalent in samples taken north of Nürnberg. Reasons for increased arsenic concentrations are regionally defined. To the south and southeast of Erlangen sedimentary arsenic dissolves into the groundwater. Arsenic occurs here within minor sulphide minerals in the clayey-silty layers (confining layers) between the Keuper and predominantly at the top (Feuerletten, Rhätholias). Oxygen enriched ground water from near surface aquifers may intensify the solution of sulfides by oxidation. Local occurrence of hydroxic arsenic compounds of higher mobility within the coarse-grained aquifer are the most likely reason for increased arsenic in groundwaters to the west and south west of the research area. Besides regional sedimentary arsenic, tectonic influences may also be effective at certain areas north of Nürnberg. From the river Pegnitz up to Bamberg, increased arsenic concentrations were locally measured within ground waters. Here, an intermixture of higher mineralized, arsenic containing deep ground waters from the Buntsandstein or solutions originating from joint fillings, previously mineralized, is the most likely source.

Paper language: german; german abstract

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