A conversation with Werner Käss (Germany) about his contributions to tracer hydrogeology and characterisation of mineral waters and spas

Every hydrogeologist dealing with tracer tests is aware of the textbook of Werner Käss (born 1924 in Stuttgart, Germany; Figs. 1 and 2) on Tracing Technique in Geohydrology, which was first published in German (Käss 1992), then translated into English (Käss 1998) and finally published as a second German edition (Käss 2004). There is probably no other hydrogeologic discipline where a single book has such unrivalled status as a unique standard reference, gathering all available knowledge. The book is internationally used for teaching, research and professional application, and is frequently cited. Many authors contributed (e.g. H. Behrens, H. Moser, H. D. Schulz, H. Hötzl), but Werner Käss acted as lead author and editor. However, he did far more than collect knowledge. He was, and still is, among those who developed and improved the techniques of water tracing, particularly in the field of fluorescent dye analysis, but also for the characterisation of contaminant transport. His achievements in the field of thermal and mineral water research are internationally less well known, but in Germany, he is also an authority in this field. A voluminous reference book on all German spas, which he edited together with his wife Hanna, was published in autumn 2008 (Käss and Käss 2008). Probably, there is no comparable oeuvre elsewhere. On 5 October 2008, the authors visited Werner Käss and Hanna in their home in Umkirch near Freiburg, Germany (Fig. 2), to talk about his life and research. The interview was held in German, but an English translation is available as electronic supplementary material (ESM). The most remarkable thing about Werner Käss, who retired from the State Geological Survey in Freiburg in 1989 and is already well into his 80s, is his indefatigable scientific curiosity and activity. We asked him when he did his last tracer test, and he confessed that he had just injected two tracers, borax and uranine, at the alluvial aquifer experimental site ‘Merdingen’ near his home in order to study borate transport in groundwater (Fig. 1). Sampling was still ongoing, and he did the analyses in his laboratory at home, where he has a spectral fluorometer, an atomic absorption spectrometer, and a spectral photometer. On many occasions, Werner Käss emphasises the important role of his wife Hanna, a trained nurse, for his achievements. She did all of the text processing for his books, and he characterises her as somebody who always thinks and contributes through many suggestions. Werner Käss comes from a time when science was less English-dominated than today. Therefore, most of his work was published in German-language journals (e.g. Steirische Beiträge zur Hydrogeologie) that were highly renowned at that time but have now lost their importance, while English-language journals now prevail. A significant part of his work was achieved in cooperation with colleagues from the Association of Tracer Hydrology (ATH), an international group mainly composed of researchers from Germany, Austria, Switzerland and Slovenia. This profile focuses on the achievements of Werner Käss in the field of tracer techniques, but also outlines other contributions to hydrogeology that are less known outside German-speaking regions such as his research on mineral water. N. Goldscheider ()) Centre of Hydrogeology (CHYN), University of Neuchâtel, Rue Emile-Argand 11, Neuchâtel, 2009, Switzerland e-mail: [email protected] Tel.: +41-32-7182645