The Wellenberg area, central Switzerland, is under investigation for a potential low and intermediate level radioactive waste repository. The host rock, the Palfris marl, is bounded on the north by Cretaceous limestone units of the Drusberg nappe and is underlain by a sequence of Tertiary to Jurassic sediments (limestones, marls) of the Wissberg-Firrenband-Equivalent. Chemical and isotopic data on groundwaters and rocks show that three essentially independent groundwater flow regimes occur in the area: (1) groundwaters of the Palfris marl, (2) groundwaters of the limestone units of the Drusberg nappe, and (3) groundwaters of the Wissberg-Firrenband Equivalent.