Differentiating groundwater recharge flowpaths in fault-controlled karstic aquifers (Gran Sasso range, Central Italy): Structural, hydrochemical and isotopic investigations on the highway tunnel drainage

Study region: The Gran Sasso karst aquifer is one of the largest aquifers of Central Italy and a key drinking water resource. The system (similar to 1000 km & sup2;) is composed of fractured/karstified carbonate rocks influenced by a complex tectonic framework of thrusts and normal faults. Two parallel motorway tunnels (tapping similar to 1.5 m(3)/s of groundwater for drinking purposes) provide a unique opportunity to observe flow conditions several kilometers below the ground. Study focus: This study assesses the recharge mechanisms and flow dynamics of the fractured/ karstified carbonate Gran Sasso aquifer using a multidisciplinary approach to improve drinking water withdrawal management and to contribute to the knowledge of recharge mechanisms in carbonate aquifers. It integrates a new characterization of the lithological/structural setting with discharge measurements, geochemical (major/trace elements) and isotopic data (delta & sup1;O-8, delta & sup2;H, H-3 and Sr-87/Sr-86) collected from 27 drainage points along the tunnels. New hydrological insights for the region: Results reveal four overlapped recharge mechanisms, from fast to slow pathways, all interacting to varying degrees with the Meso-Cenozoic aquifer and with Quaternary deposits. Structural/lithological variability of permeability control recharge heterogeneity. At the basin scale, different recharge mechanisms produce homogeneous groundwater characteristics. At the local tunnel scale, infiltration heterogeneity could generate significant vulnerability with critical implication for protection and management. These findings enhance understanding of the Gran Sasso aquifer's dynamics and provide a reference model for fault-controlled fractured/karst systems.