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 ofthe textbook of Werner Kass (born 1924 in Stuttgart,Germany; Figs. 1 and 2)onTracing Technique inGeohydrology, which was first published in German (Kass1992), then translated into English (Kass 1998) and finallypublishedasasecondGermanedition(Kass2004).Thereisprobably no other hydrogeologic discipline where a singlebook has such unrivalled status as a unique standardreference, gathering all available knowledge. The book isinternationally used for teaching, research and professionalapplication, and is frequently cited. Many authors contrib-uted (e.g. H. Behrens, H. Moser, H. D. Schulz, H. Hotzl),but Werner Kass acted as lead author and editor. However,hedidfarmorethancollectknowledge.Hewas,andstillis,among those who developed and improved the techniquesof water tracing, particularly in the field of fluorescent dyeanalysis, but also for the characterisation of contaminanttransport.His achievements in the field of thermal and mineralwater research are internationally less well known, but inGermany, he is also an authority in this field. Avoluminous reference book on all German spas, whichhe edited together with his wife Hanna, was published inautumn 2008 (Kass and Kass 2008). Probably, there is nocomparable oeuvre elsewhere.On 5 October 2008, the authors visited Werner Kassand Hanna in their home in Umkirch near Freiburg,Germany (Fig. 2), to talk about his life and research. Theinterview was held in German, but an English translationis available as electronic supplementary material (ESM).The most remarkable thing about Werner Kass, whoretired from the State Geological Survey in Freiburg in1989 and is already well into his 80s, is his indefatigablescientific curiosity and activity. We asked him when he didhislasttracertest,andheconfessedthathehadjustinjectedtwo tracers, borax and uranine, at the alluvial aquiferexperimental site ‘Merdingen’ near his home in order tostudy borate transport in groundwater (Fig. 1). Samplingwas still ongoing, and he did the analyses in his laboratoryat home, where he has a spectral fluorometer, an atomicabsorption spectrometer, and a spectral photometer.On many occasions, Werner Kass emphasises theimportant role of his wife Hanna, a trained nurse, for hisachievements. She did all of the text processing for hisbooks, and he characterises her as somebody who alwaysthinks and contributes through many suggestions.Werner Kass comes from a time when science was lessEnglish-dominated than today. Therefore, most of hiswork was published in German-language journals (e.g.Steirische Beitrage zur Hydrogeologie) that were highlyrenowned at that time but have now lost their importance,while English-language journals now prevail. A signifi-cant part of his work was achieved in cooperation withcolleagues from the Association of Tracer Hydrology(ATH), an international group mainly composed ofresearchers from Germany, Austria, Switzerland andSlovenia. This profile focuses on the achievements ofWerner Kass in the field of tracer techniques, but alsooutlines other contributions to hydrogeology that are lessknown outside German-speaking regions such as hisresearch on mineral water.