Hydrogeological characterization of a geothermal system: the case 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 of exploitation of 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 of sodium-chloride type, sulfureous and rich in CO2 whose recharge is from the Mt. Pizzuto groundwater body which somehow floating on seawater. 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, 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 case of Mt. Pizzuto, the upwelling gas intercepts evaporitic formation and, probably, causes saltwater intrusion, with a peak from June to September. In the case of the Petrinum well, the gases involve "saline formation groundwater", 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. The upwelling of the gases occurs along the major fault that crosses NE-SW the plain of Mondragone at the southern edge of the Mt. Petrino. Finally, the understanding of the mineralization patterns allowed to identify in the plain the best location for a geothermal exploration well.