Geochemical characteristics of salinization-zones in the Coastal Aquifer Test Field (CAT-Field) in North-Germany

The geochemical characteristics of a near shore inland aquifer system have been investigated in the Coastal Aquifer Test Field (CAT-Field) between Bremerhaven and Cuxhaven in the Northern Part of Germany which is described by Kessels et al.(this issue). Groundwater and sediment samples from the aquifer were taken at different locations on the flank of a glacial channel at depths between 5 and 100 m. Analyses of groundwater samples were carried out to determine possible zones of salinization, their origin, and associated geochemical processes in the transition-zone between salt and fresh water. Samples of aquifer material were used for a simulation of these processes in column experiments. Their results were modeled, using the computer program PHREEQC [Parkhurst and Appelo, 1999], and compared with the geochemical field data. INTRODUCTION Motivation In the subsoil of Northwest Germany a system of glacigene channels can be found which were refilled at the end of the Elster ice age [Kuster, 1979]. In the CATField one of these channels can also be found. Because of its partly coarse filling, the region seems to be suitable and may be interesting for a future groundwater exploration. The determination of possible influences of the exploration due to saltwater upcoming, a typical problem of coastal regions, is the aim of the project. Therefore different geophysical investigations were carried out [Fulda, Kessels et al., subm.; Kessels, Fulda et al., subm.; Siemon, Sengpiel et al., subm.; Willert, Behain et al., subm.] with the aim of a characterization followed by modelization [Gräsle, Willert et al., subm.] of the multilayered aquifersystem. Besides the necessarily intensily hydraulic investigations, this publication contents aspects of the geochemical interactions of the sediments with the underlying saltwater. Location and geological setting of the investigation area For the investigations an Coastal Aquifer Test Field (CAT-Field) was determined, which is located between Bremerhaven and Cuxhaven in the northwestern part of Germany.