Hydrogeological and hydrogeochemical monitoring in the Cumae archaeological site (Phlegraean Fields, southern Italy)

The Cumae archaeological site is extended along the Tyrrhenian coast of the Campania region (southern Italy), in the western sector of the Phlegraean Fields active volcanic field. It is the first Greek colony in mainland Italy, which was founded in the 8th century B.C., and occupied continuously until the 12th century A.D. A hydrogeological and hydrogeochemical monitoring from December 2013 to February 2015 on 13 wells (6 shallow wells and 7 deep wells), joined with 222Rn measurements in groundwater have been carried out, with a monthly frequency. The study was motivated by the frequent flooding of archaeological excavations due to the rise of groundwater level, which threatens the integrity of ancient Roman ruins and prevents the continuation of archaeological researches. Therefore, reconstructing a comprehensive hydrogeological model of the archaeological site was considered an important goal to achieve for designing mitigation measures. Hydrostratigraphic and hydrogeological data allowed recognizing a multi-layered volcanic-sedimentary aquifer system, formed by shallow unconfined and deep semi-confined aquifers. The groundwater flow was assessed being strongly controlled by vertical and lateral lithological heterogeneities of volcanic-sedimentary deposits, as well as by groundwater pumping and drainage channel system. The dominant hydrochemical facies were ClSO4NaK, HCO3CaMg and HCO3NaK types, which were found spatially and temporally variable due to: i) localised rise of deep and highly mineralized fluids through faults and fractured zones of the western edge of Campanian Ignimbrite caldera boundaries, as indicated by outstanding levels of F- and 222Rn; ii) freshwater-saltwater interactions, induced by groundwater exploitation.