**3. Regional Setting**

## *3.1. Geological Setting*

– The Thriassion Plain is located at the border between non-metamorphic and metamorphic rocks of Eastern Greece and Attica geotectonic units, respectively [34]. The geological structure (Figure 3) of the study area consists of: (1) a Palaeozoic volcano-sedimentary complex, 400–500-m thick, composed of: (a) clastic materials (arkoses, greywackes, shales in alternations with phyllites, conglomerate, and lenticular intercalations of limestone) and (b) basic-igneous volcanic rocks; (2) Mesozoic sediments consisting of: (a) Lower-Middle Triassic phyllites and sandstones with breccia-conglomerate intercalations; (b) volcanic rocks and tuffs; (c) Middle-Upper Triassic white carbonate, crystalline in places, comprising limestone, dolomitic limestone, and dolomite; (d) Upper Triassic black limestone, dolomitic limestone, and (e) Grey Cretaceous limestone; and (3) Cenozoic sediments of: (a) Neogene (Pliocene marls with lignite intercalations in places, clay, conglomerate, sandstone, and marly limestone); (b) Pleistocene deposits (clay, sand, gravel, and torrential fans of loosely and cohesive conglomerate); and (c) Holocene deposits (clay, loam, sand, and gravel) [35].

**Figure 3.** Geological map of the study area. The numbering is the wells id.

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