Karst aquifers represent complex systems where groundwater flows at different velocities through a network of secondary porosity structures such as fractures and conduits. Their complexity comes from the interplay between geological and climatic factors, as well as human activities, like tapping springs and drilling tunnels, which can significantly change flowpaths and discharge regimes.
The Gran Sasso aquifer, one of the largest fractured and karstified aquifers in the central Apennines, offers a unique opportunity to study these phenomena thanks to the presence of drainage in highway tunnels, drilled in the 1970s. These tunnels tapped approximately 2 m³/s of groundwater directly under the preferential recharge zone, providing access to peculiar hydrogeochemical conditions within the aquifer. Recently, to obtain information about hydrodynamic aspects of the natural drainage and an updated hydrodynamic setup of groundwater flow related to recharge mechanisms, the structural characterisation of both surface and tunnels has been carried out, integrating hydrogeochemical and isotopic data from 27 drainage points along the tunnels.
The study reveals a complex mix of recharge mechanisms influenced by fractures and lithology permeability. Major ions show minimal variation, while isotopic results identify four distinct flowpaths. These include fast infiltration via fault zones, the arrival of old water into the tunnel drainage, representing the slow-flow aliquot, interaction with Quaternary deposits, and rapid groundwater movement through karst systems. The findings also highlight the role of Campo Imperatore's endorheic basin and fault zones in groundwater recharge dynamics. The Gran Sasso aquifer can be used as a model for understanding fractured-karst systems under climatic and tectonic conditions similar to those in the Mediterranean, offering insights into strategies for conserving high-quality drinking water in the context of climate change and anthropogenic pressure