1 Transport of colloidal and solute tracers in three different types of alpine karst aquifers – Examples from southern Germany and Slovenia N. Göppert 1 , Dr. N. Goldscheider 2 , Prof. Dr. H. Hötzl 1 Abstract In many alpine karst regions, bacteriological pollution resulting from agriculture is the most important problem in groundwater protection. Colloidal tracers like fluorescent polystyrene microspheres are used to evaluate the hygienic risk for groundwater resources. Different sizes of colloids may be used to simulate the fate and transport of different types of micro-organisms. For the field tracer tests, three different types of karst systems within the alpine fold belt have been selected: karst aquifers in carbonate conglomerates and limestones in southern Germany, and unsaturated fissured carbonates in Slovenia. Large parts of Tertiary gravel fans in the foreland of European alpine orogens are made of coarse-grained conglomerates, which mainly consist of carbonate components in a carbonatic matrix. These rocks are predisposed to karstification and show a large variety of karst phenomena like dolines, karren, karst springs and estavelles. Tracer tests with fluorescent dyes and particles show high flow velocities and travel distances of up to 8 km. The flow orientation reflects the geological structure. This demonstrates the need for special groundwater protection schemes that take into consideration the heterogeneity and anisotropy of this aquifer type. The Helvetic nappes form parts of he Northern Alps and mainly consist of Jurassic and Cretaceous carbonate rocks. During low-flow conditions, a comparative tracer test with fluorescent- dyes and microspheres was carried out in the Hölloch, Germany’s longest cave (9,343 m). The Association of Tracer Hydrologists (ATH) conducted a comparative tracer test in the Slovenian Dinarids in order to evaluate the behaviour of different tracers in the unsaturated zone of the fissured karst aquifer in Sinji Vrh. The behaviour of the tracers shows important differences, especially for solute and particle tracers. Therefore, the authors strongly recommend using particle tracers for the evaluation of hygienic risks to groundwater. Introduction In karst areas, pathogenic micro-organisms and solute contaminants can easily enter the subsurface, either diffusely through shallow soils or point-like via swallow holes. Inside the karst aquifer, the contaminants are rapidly transported over large distances in the conduit network, often without effective attenuation. Karst groundwater is thus highly vulnerable to contamination and therefore has special protection needs (Drew & Hötzl, 1999; Goldscheider, 2002; Zwahlen, 2004). Solute tracers, particularly fluorescent dyes like uranine, are commonly used to characterise the fate and transport of solute contaminants, while colloidal tracers are appropriate to simulate the transport of microorganisms and contaminants that are attached to suspended colloids. The analysis of fluorescent dyes with a luminescence spectrometer is a standard method whereas the analysis of particle tracers – such as fluorescent microspheres – is rather time- 1 Department of Applied Geology (AGK), Universität Karlsruhe (TH), Kaiserstr. 12, D - 76128 Karlsruhe, Germany; PH +49 721 6083329; FAX +49 721 606279 ; email: goeppert@agk.uka.de; PH +49 721 6083098; FAX +49 721 606279 ; email: hoetzl@agk.uka.de 2 Hydrogeology Centre (CHYN), University of Neuchatel, Rue Emille-Argand 11, CH – 2007 Neuchatel, Switzerland; PH +41 327 182645; FAX +41 327 182603 ; email: nico.goldscheider@unine.ch