A hydrogeological study to assess the geothermal potentiality of Suio Terme (central Italy)

The hydrogeological setting of a sector located between central and southern Apennines, along the contact between the Eastern Aurunci Mts. and the Roccamonfina volcano, has been studied. The area includes the hydrogeological interaction between sedimentary Mesozoic and Cenozoic sequences and Quaternary lava-flows and pyroclastic products. The research has been focused on the thermal water-springs and their distribution, in the Suio Terme area. By detailed reference data including geological and hydro-geochemical analysis, the conceptual hydrogeological model has been carried out. The Eastern Aurunci Mts. has been considered as an isolate hydrostructure, having two different flowpaths. A shallow one, showing cold water (T<20 °C) enriched in Ca+2 and HCO3 - ions, typical of carbonatic reservoirs. A second one connected with a deeper reservoir, showing hot waters (20<T<60 °C) enriched in SO4 -2, Na+ and K+ ions. In order to evaluate the geothermal potentiality of Suio reservoir, thermal-waters has been analyzed using the geo-thermometer method. The performed analysis allowed to estimate an average reservoir-temperature about 150°C. Sampled waters display positive correlation between the mineralization-rate and temperature values. Adding more, the spring distribution, their chemical features and the heat origin have been linked to the tectonic trends. It has been highlighted as the circuit-depth depends on the faultdisplacements. These elements control the reservoir position in the low-stand areas and the thickness of the impermeable seal. New geological and hydrogeological surveys have been carried out to build a new hydrogeological conceptual model. Then, a geophysical campaign (TDEM-Time Dependent Electromagnetic Method) has been performed for a fine-tuning of the geological setting. Numerical simulations have been used to test the proposed model.