Hydrogeological and hydrogeochemical study of a volcanic-sedimentary coastal aquifer in the archaeological site of Cumae (Phlegraean Fields, southern Italy)

A hydrogeological and hydrogeochemical survey in the Cumae archaeological site (Phlegraean Fields, southern Italy) together with radon levels determination in groundwater have been carried out. The study was motivated by the fact that the site is often submerged by the outcrop of groundwater, threatening the integrity of ruins, and hence by the need to preserve such important archaeological park. The hydrostratigraphic and hydrogeological data revealed the presence of a multi-layered aquifer system, formed by a shallow unconfined and a deep semiconfined aquifer. The groundwater flow appeared to be strongly influenced by vertical and lateral lithological heterogeneity of volcanic-sedimentary deposits, as well as by groundwater pumping and drainage by surface micro-channel system. The dominant hydrochemical facies were Cl−-SO42−-, Na+-K+, HCO3−-Ca2+-Mg2+ and HCO3−Na+-K+ types. These facies were affected by: i) dissolution and chemical weathering, ion exchange with volcanic-sedimentary deposits, ii) localized rise along faults and fractured zones of deep magmatic fluids highly mineralized, with outstanding levels of F−, 6.4 mg L−1 in deep water and 3.3 mg L−1 in shallow water, and 222Rn, 31,500 Bq m−3 in deep water and 5400 Bq m−3 in shallow water; iii) freshwatersaltwater interactions, induced by groundwater pumping.