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Abstract:Studies on the hydrogeological conditions of the Mesogea basin in east Attica reveal that the aquifers developed on the post-alpine formations at the inner part of the coastal brackish zone exhibit positive hydraulic head. These Neogene and Quaternary deposits present high salt concentrations. Selected points were sampled (total 85: 51 wells and 34 boreholes) in order to obtain hydrogeological and hydrochemical data for a better understanding of the structure, operation and dynamics of the aquifer of the area. Statistical methods, R-mode factor analysis and scatter-plot diagrams were used for the hydrochemical analysis and presentation of the data. The groundwater resources are relatively weak and there is significant quality degradation due to the geological structure of the greater area, as well as the bad management of the aquifer and anthropogenic activities. Groundwater is characterized by high salt concentrations. Electrical conductivity values range between 260 and 6970 µS cm 1 . High salt concentrations at the coastal aquifers are due to sea intrusion, whereas they are attributed to the dissolution of minerals of the geological environment in the inland area. The groundwaters of the study area can be classified into five water types: Ca-HCO 3 , Mg-HCO 3 , Na-HCO 3 , Na-Cl and Mg-Cl. They are saturated in dolomite and calcite, whereas they are unsaturated in anhydrite. High ion concentrations, e.g. NO 3 (0-221 mg l 1 ), NH C 4 (0Ð01-1Ð88 mg l 1 ), PO 3 4 (0Ð01-6Ð75 mg l 1 ), as well as high heavy metals concentrations are attributed to anthropogenic impacts.

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