Deep groundwater exploration in an Alpine alluvial plain: first insights for sustainable water and geothermal resource management in the Aosta Valley

The severe drought experienced during the summer of 2022 in the Western Alps brought unprecedented attention to water availability issues in Alpine regions traditionally considered rich in water resources, such as the Aosta Valley (Western Alps, Italy). This event highlighted the vulnerability of mountain groundwater systems to climate-driven extremes and emphasized the need for a deeper and more robust understanding of groundwater availability, particularly in densely populated alluvial plains where water demand is concentrated.

The Aosta alluvial plain represents a strategic hydrogeological system, supporting drinking water supply, ecosystem services, and an increasing interest in low-enthalpy geothermal applications. Despite its importance, the deep structure of the aquifer system and the depth to bedrock beneath the plain remained largely unconstrained until recently, limiting the reliability of conceptual and quantitative groundwater models and the capacity to anticipate future water scarcity scenarios.

Within a regional-scale program (UE-FESR Project: “Geothermalp”) aimed at enhancing sustainable groundwater and geothermal resource management, an integrated deep exploration campaign was carried out, combining advanced geophysical investigations with deep continuous-core drilling. Geophysical surveys were employed to characterize the geometry of Quaternary deposits and to delineate the bedrock surface, providing a framework for the optimal positioning of two deep boreholes. The boreholes reached depths between approximately 300 and 350 m and, for the first time beneath the Aosta plain, intersected the crystalline bedrock, yielding unprecedented direct information on lithostratigraphy, hydrogeological properties, and groundwater occurrence at depth.

The integration of indirect geophysical data and direct borehole observations revealed a hydrogeological structure significantly more complex than previously assumed. Previously unknown deep groundwater bodies were identified, hosted within permeable sedimentary units and in structurally controlled zones near the alluvium–bedrock interface. Based on the first interpretations, these groundwater bodies appear to play a key role in the vertical connectivity of the aquifer system and in the redistribution of groundwater flow at depth, suggesting multi-level circulation patterns rather than a single shallow aquifer system.

The first results have important implications for sustainable groundwater management in Alpine environments. They provide a stronger scientific basis for assessing groundwater availability under increasing climatic stress, protecting deep groundwater resources from overexploitation, and evaluating the compatibility between drinking water supply, geothermal exploitation, and ecosystem preservation. More broadly, the study demonstrates how integrated deep investigations can substantially improve hydrogeological knowledge and support informed decision-making in mountain regions facing emerging water scarcity challenges.