Identifying the characteristics of groundwater flow in the Classical Karst area (Slovenia/Italy) by means of tracer tests

Abstract

Tracer tests are a widely used research method in karst hydrology. In the Classical Karst area on the border between Slovenia and Italy, they have a long history and for the most part they have been used to research the underground flow in the main karst conduits between the ponors and the springs. The results of the tracer test from 2013 presented in the article revealed new knowledge about the central part of the aquifer, less well researched to date, where the density of caves and the level of karstification are lower. Two tracers (uranine and amidorhodamine G) were used at two injection points (a research borehole in the central part of the aquifer and the karst surface at a distance of 2.5 km from a drinking water pumping station), and six springs, a pumping station, three boreholes and four karst caves were observed for tracer breakthrough for a full year after injection. The results were compared with findings from three other selected older tracer tests in which uranine was likewise used as a tracer but where hydrological conditions varied (very low, low and medium water levels), as did the methods of injecting tracer (in a sinking stream, in a fracture on the karst surface). The comparison showed how different modes of aquifer recharge and the heterogeneity of aquifer structure affect the characteristics of water flow and solute transport in complex karst aquifers.