Hydrogeology of a Volcano-Sedimentary Multi-Aquifer System: The Skydra, Northern Greece, Case Study

Due to climate change, water scarcity, and overexploitation of aquifers, the sustainable management and protection of groundwater resources will be one of the main challenges in the future. Therefore, the knowledge of hydrogeological characteristics, which must be as robust as possible, becomes crucial for defining groundwater management plans. On the other hand, the earliest evidence of the fertile plains and abundant water resources of Skydra and its surroundings dates back to the Neolithic period (6500-3200 B.C.), confirming the area's current agricultural vocation and productivity. In this perspective, the aim of the present study is to define the conceptual hydrogeological model of a complex confined multi-aquifer system characterizing the volcano-sedimentary deposits of the Skydra area, northern Greece. In particular, the architecture of the hydrostratigraphic units, the hydraulic parameters, and the hydrodynamic behavior of the multi-aquifer system were analyzed. The geological, geomorphological, and structural evolution affecting the area has influenced the geometric and hydraulic characteristics of the aquifer, and consequently its productivity. The thickness of the multi-aquifer system varies between 25.0 and 94.5 m and the hydraulic conductivity, calculated through the analysis of data from 72 pumping tests, and the application of empirical method (42 wells), ranges between 2.2 <middle dot> 10-6 and 2.5 <middle dot> 10-3 m/s. Higher hydraulic conductivity values are calculated in areas where tuffaceous formations are fractured and/or interlayered with sandy layers; while lower values occur where tuffs present only primary porosity and are interspersed with frequent clay layers. In the central area, due to overexploitation of the aquifer, an annual piezometric level drop of approximately 6 m has been recorded. The information acquired could serve as the basis for the sustainable development of groundwater resources in the test area and could also be applied in other similar hydrogeological settings.