Abstract:
The present study concerns the results of a tracer test in the vadose zone of the Trebiciano Abyss in the Karst of Trieste, at the bottom of which the Timavo underground river flows. Two tracers were used: Uranine and Tinopal CBS-X, separately introduced in two dolines above the abyss, through artificial spills of water, simulating heavy rainy events. Inside the abyss, 350 m deep, four points were equipped in order to control and capture the percolation waters (S1, S2, S3, and S4), at different depths, where drainage is normally present. At each point daily sampling and flow measurements were carried out, at S2 at -250 m a fluorometer probe was also installed, to record the two tracers continuously. Refraction seismic survey characterized the epikarst, The Uranine was found at point S3 the same day as its injection, subsequently at point S2 (fluorometer probe recording). Tinopal CBS-X was found at point S2 the same day as its injection. The tracing test also proved, unmistakably, that in just a few hours, after a strong rainfall or an accidental spill the release of pollutants on the karst surface, infiltrating underground, is transferred further than 300 m of depth, flowing directly in the base flow with no chance of being stopped.