SCALDI: An enhanced multi-criteria framework for groundwater vulnerability assessment in fractured ultramafic aquifers – application to the ophiolite nappe of Mantoudi (Central Euboea, Greece)

The sustainable development of hard rock aquifers is based on the consideration of fractured rocks as a natural resource and as a social and economic wealth, the use of which is linked to its quality. Therefore, these bodies of water should be used and protected with priority given to the self-regulation of ecosystems, in line with the Rio Agenda (1992). It is obvious that the criteria used in the assessment of vulnerability in the case of karstic or continuous (porous) medium cannot be applied to discontinuity medium systems. The assessment of intrinsic groundwater vulnerability in fractured hard-rock aquifers remains a methodological challenge due to structural heterogeneity and complex recharge mechanisms. Widely applied index-based methods (e.g. DRASTIC and related approaches) often seem not to adequately represent these complexities. This study presents SCALDI , an enhanced multi-criteria intrinsic vulnerability assessment framework specifically developed for fractured aquifers in Greece. The framework is applied to the ophiolite nappe of Mantoudi (Central Euboea, Greece), characterized by fractured ultramafic formations and structurally controlled groundwater flow. SCALDI integrates five key parameters: slope (S), soil cover (C), aquifer permeability and hydraulic behaviour (A), land use (L), and intersection degree of discontinuities (DI). Unlike conventional vulnerability indices that focus on isolated risk elements, SCALDI conceptualizes vulnerability as an emergent property of a complex territorial hydrogeological system, where geological, geomorphological, and anthropogenic factors interact dynamically. Sensitivity analysis demonstrates the dominant influence of structural parameters on vulnerability distribution. The proposed framework provides an adaptable tool for groundwater protection zoning in hard-rock terrains.