Hydrogeological and hydrochemical setting of the thermo-mineral area of Mondragone (Campania, Italy)

This paper deals with thermo-mineral groundwater of the Mondragone plain (Campania, southern Italy) and the possibility to use this low enthalpy geothermal resource. In the NW sector of this plain, at the bottom of Mt. Pizzuto, near the sea, there are thermo-mineral waters (50 °C) of sodium-chloride type, sulfureous and rich in CO 2 whose recharge is from the Mt. Pizzuto groundwater body. In the SE sector of the plain, close to the calcareous Mt. Petrino, a 80 m deep well has intercepted, in the carbonate basement of the plain, thermo-mineral groundwater (33 °C), sulfureous and rich in CO2, as in the NW sector, but displaying a calcium-bicarbonate composition. The chemical and the isotopic analyses allowed to verify that these types of groundwater are due both to meteoric waters infiltration and to enrichment of endogenous CO2 and H2S, at fairly high temperature. In the Petrinum well, the gases involve “connate waters”, affecting upwards the groundwater body of Mt. Petrino. Moreover, the rising of the gases increases the dissolution of the carbonate aquifer, determining very high values of HCO3 ions in the thermo-mineral groundwater. In the case of Mt. Pizzuto, the upwelling gas intercepts also evaporitic formation and, probably, causes saltwater intrusion. The upwelling of the gases occurs along the major fault that crosses NE-SW the plain of Mondragone. Finally, the understanding of the mineralization patterns allowed to identify in the plain the best location for a geothermal exploration well.