Sulfate dynamics within the area of groundwater surface in a forested catchment area< Back

Abstract:
In many catchments in porous aquifers of Germany a rise of the sulfate concentration in the raw water is to be registered. Apart from other sources also a contribution of biological-chemical processes which lead to the oxidiation of reduced sulfur compounds (i.e. Pyrite) to sulfate have to be taken into consideration as a cause of this incident. In this context case study investigations were executed in the forested section of the catchment area of the water works of Bruchsal about sulfate-relevant transformations in the subsoil and their influence on groundwater quality. These were accompanied by batch and column experiments in the laboratory. From the signature of stable sulfure-isotopes (d34S) it could be seen that at least at one of the waterworks‘ wells sulfate in the raw water originated from the oxidation of Pyrite. At a marshy place in the intake area of this well, soil probes to a depth of 18 m were taken and examined in aerobe batch experiments. The probes from a narrow horizon of 1,5 m height from just below the groundwater table set free up to 1.300 mg sulfate per kg dry matter. Pyrite framboids could be detected microscopically. The results of further investigations showed that at another well groundwater coming down from the neighbouring limestone hills causes the high sulfate concentration of raw water. Apparently this water also reaches the vicinity of the well through drainage ditches, that pass close to the well. Further results of the extensive explorations are presented in a final report in detail.