Coastal fresh groundwater extending deep offshore from southern Sicily (Italy): assessment of the Ragusa Aquifer via petrophysical and 3D hydrogeological modelling

Sicily (Italy) is among the regions most vulnerable to drought, with conditions expected to worsen under climate change, underscoring the need for sustainable water management and the exploration of unconventional water resources. This study investigates the Ragusa Oligo-Miocene Formation, a karstified and fractured carbonate aquifer with medium to high porosity, which outcrops across the Hyblean Plateau in southern Sicily. The primary objective was to assess and quantify the potential presence of fresh groundwater in the deeper and offshore extension of this carbonate aquifer along the southeastern coast of Sicily, where it is sealed beneath more recent deposits. To reconstruct its subsurface structure, data from 90 deep oil and gas wells, both onshore and offshore, were analysed. Geophysical logs were examined using advanced petrophysical methods, while hydrogeological data from onshore wells were integrated to refine the understanding of the regional aquifer system. The results provide clear evidence of freshened groundwater within the Ragusa regional aquifer, extending deeper than previously known, onshore and continuing offshore up to 10 km from the coastline. A preliminary, conservative volumetric estimate suggests approximately 3 km3 of fresh groundwater preserved in the offshore region of the study area, at depths between 500 and 1200 m below sea level. This discovery demonstrates the untapped potential of unconventional groundwater in both the deep onshore and offshore areas of southeastern Sicily, offering an additional solution to water shortage problems, and has significant implications for other countries along Mediterranean coastlines.