Anomalous CO2 contents in a shallow aquifer of the Mt.Amiata geothermal area, Italy

In the framework of a project funded by Seismic Service of the Tuscany Region, the Bagnore thermal spring (Mt.Amiata geothermal area) has been selected as a suitable site to identify possible hydrogeochemical anomalies related to seismic activity. Since 2004, the Bagnore spring (TWATER = 21.5°C) has been monitored in continuous (more than 8 ( 105 data available today) with an automatic station equipped for the measurement of temperature, pH, EC, Eh, and the dissolved content of CO2 and CH4. During the period 2004- 2012, 68 discrete sampling campaigns for the determination of selected chemical-physical parameters in situ (T, pH, EC, alkalinity), and chemical parameters in the laboratory (Na, K, Ca, Mg, Cl, SO4, NO3, B), have also been performed. From all these data, it emerges that the low salinity (240 mg/l) waters of the Bagnore spring belong to the Ca-SO4 chemical type, and are characterized by a background PCO2 value of about 0.04 bar.