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<div>Even in karst areas, considerably thick soils can be found in accumulation</div><div>zones. Here, the degree of groundwater vulnerability depends</div><div>not only on the thickness, but also on the hydraulic conductivity and</div><div>retention properties of the soil cover. The hydraulic conductivity of</div><div>fine-grained karst soils from Slovakia, Croatia and Austria was studied</div><div>within several international research projects, by the application</div><div>of four different test methods. Results are discussed from different</div><div>points of view. Triaxial tests yielded a very broad interval between the</div><div>maximum and minimum hydraulic conductivity (from 5.83x10-7 m.s-1</div><div>to 3.50x10-11 m.s-1), therefore the mean value cannot be used in any</div><div>calculations. The consolidometer method gave lower values in general,</div><div>between 9.40x10-10 m.s-1 to 3.59x10-8 m.s-1. However, this method</div><div>overestimates the soil &ldquo;impermeability&rdquo;. Estimates based on grain</div><div>size are unsuitable, as fine-grained soils did not fulfil the random conditions&nbsp;of known formula. Finally, the &ldquo;in situ&rdquo; hydraulic conductivity</div><div>was measured using a Guelph permeameter. As expected, &ldquo;in situ&rdquo;</div><div>tests showed 100 to 1000-times higher kf than the laboratory tests.</div><div>This method best reflects the real conditions. Therefore, only this</div><div>type of data should be considered in any environmental modelling.</div><div>In a soil profile, hydraulic conductivity depends on the mineral composition,&nbsp;depth, secondary compaction, etc. The degree and duration</div><div>of saturation with water is very important for young soils containing</div><div>smectite. Their hydraulic conductivity might be very low when saturated</div><div>for long time, but also very high, when open desiccation cracks</div><div>occur. A very slight trend was found, but only in Slovak soils, showing</div><div>a decrease in the hydraulic conductivity with increasing content</div><div>of the clay fraction &lt;0.002 mm. These results should contribute to a</div><div>better estimate of the protective role of soils in groundwater vulnerability</div><div>maps.</div>