Multi-tracer tests to assess the impact of the new railway tunnels in Northern Tuscany, Italy, on ground and surface waters

High-speed railway tunnels in the Northern Apennines caused large-scale groundwater drainage of turbiditic sandstone units, resulting in the drying up of springs and stream baseflow. In order to better characterise the connections between the losing streams and the tunnels, multi-tracer tests were done at four catchments, one of which is presented here. Uranine was used for all experiments and proved to be the best tracer; lithium, sulforhodamine G and tinopal CBS-X were additionally used for some experiments. The results proved connections between the streams and water inlets in the tunnels, with maximum linear distances of 1.3 km, mainly along faults. The flowpath partly run across previous water divides, suggesting that the tunnels have entirely altered the natural drainage system. Although restoration of the natural situation is impossible as long as the tunnels continue to drain the aquifer, different technical measures for the maintenance of a minimum stream baseflow were evaluated.