SUMMARY
Chianciano thermal basin in Tuscany belongs to a great structure that extends, from San Casciano Bagni to Rapolano,orientated SSE-NNW. Several springs are located in this thermal field: Acqua Santa, Macerina, Casuccini andSillene well. They are located close to the contact between the lower complex of the «Tuscan series» (Triassiclimestones and dolomites) and Pliocene formations (sands and clayey sands, clays and silty clays). According tothe groundwater flow scheme, the former formations represent the geothermal reservoir and, where they outcrop,the recharge areas. Thermalized fluids rise through direct faults, having an apennine orientation. In order to locatea new production well, electrical tomography and TDEM prospection were performed. Geophysical interpretationled to the construction of 1D imaged and 2D sections showing the main tectonic features. The different electricalbehaviour of the hydrogeological units disclosed a fault located near the old Sillene well; this tectonic featurecaused the uplifting of Triassic formations towards the north-east. A new production well was located close tothe fault in the uplifted sector with excellent results as it captured the thermal aquifer at a depth of 30 m with adischarge up to 70 l/s.