by Miltiadis Nimfopoulos
Authors: S. Tzimourtas, G. Soulios, M.K. Nimfopoulos
Proceedings 4th Hydrogeological Congress, Geological Society of Greece, 514-524, November 14, 1997
The hydrogeological basin of Axios river is a tectonic trench delineated by two series of EW and NS trending faults.... more
The hydrogeological basin of Axios river is a tectonic trench delineated by two series of EW and NS trending faults. The W part of the basin is a local tectonic depression dominated by NS trending faults, like the main fault axis of Axioupolis-Agios Petros-Koufalia. The basin is composed of modern and Quaternary unconsolidated river beds which overlie Tertiary mixed marine-lacustrine marl-sandstone formations. The groundwater aquifers of the area include 1) the shallow or phreatic (0-25m depth), which is charged with water from the Axios river, 2) the intermediate (25-75m) and, 3) the deep aquifer (>75m). Evaluation of the geological, tectonic and chemical data points to the occurrence of brackish water (at 60-80m and at 120m depth), trapped into wide lenses of agglomerate beds. This water formed by the prevalence of alternating facies between marine and lacustrine conditions. High-Cl (up to 5000 ppm) and Na (up to 2280 ppm)-contents are accompanied by high-Mg (up to 250 ppm). Thus, it is concluded that the brackish water is a trapped seawater (connate) which undergoes a slow rejuvenation. There is no connection between Thermaikos gulf and these aquifers through deep faults because deep water drillholesin the southern part of the area (nearer to the sea) contain fresh water.
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