The mineral springs of the Scrajo spa (Sorrento peninsula, Italy): a case of “natural” seawater intrusion

This paper deals with the mineral springs feeding the Scrajo spa in the Sorrento peninsula southeast of Naples, approximately six km from Castellamare di Stabia, another spa location. The Scrajo mineral water is sulfureous, salt-bromine-iodic and CO2 - rich. The two hydromineral areas fall within the groundwater basin of Mt. Faito formed chiefly by limestones. Due to the high permeability of the limestones there is considerable rainwater infiltration which recharges a basal fresh groundwater resting on denser seawater. This groundwater body feeds the mineral springs of the Scrajo spa, the springs of Castellammare di Stabia and some submarine springs. All the data gathered for the Scrajo springs led to propose the following mineralisation scheme: • the basal fresh groundwater of Mt. Faito (on underlying seawater) receives endogenous contributions of CO2 and H2S which cause a “natural” seawater intrusion within the fresh groundwater; • the upwelling of gases would appear to occur via the major faults which bound Sorrento peninsula to the NW; • during the year the chemistry of the springs changes according to the different degree of seawater intrusion: the minimum occurs in June and the maximum in November. The close interaction between the sea and the Scrajo’s mineral waters (but also those of Castellammare di Stabia) highlights their particular vulnerability not only to over-extraction of groundwater but also to climate change. Finally, a hypothesis is presented explain the connection between the mineral waters rich in CO2 and H2S and the concentration of karst phenomena observed in the Scrajo area.