**4. Materials and Methods**

Lithostratigraphic cross-sections from boreholes drilled in the Thriassion Plain during 1952–2007 by the Land Reclamation Service of Agricultural Ministry (LRSAM) were taken into consideration. Water samples from 45 wells were collected in June 2012. Electric Conductivity (EC) and pH were measured in situ on the head of the pumping column (HACH). The samples were analyzed in the laboratory of Mineralogy and Geology in the Agricultural University of Athens. The average analytical precision was better than 5%. Ion chromatography (Metrohm 732) was used for major component determination, and the method of titration was used in determination of HCO<sup>3</sup> <sup>−</sup>. Water level was measured carefully 2–5 times/year for a 15-year period from 1999–2014 in 48 wells. Additionally, pumping tests in 7 agricultural large-diameter wells were carried out in the Plio-Pleistocene deposits during the 2009–2012 time period.

## **5. Results and Discussion**

The study on the LRSAM data showed that the water level in most wells stood above the top of the aquifers as high as 1–5 m during the drillings phase. In addition, the monitoring of the water level, as well as the analysis and evaluation of the pumping test data, concluded that the larger part of the aquifers is confined and semi-confined. Hydrochemical data (Tables 1–3) of the onshore groundwater indicate that fresh groundwater is possibly hosted in the offshore submarine aquifers. The Pleistocene-Holocene clay layers occur very frequently in different depths from 0–170 m throughout the plain in alternations with gravel, sand, and conglomerates 2–10 m in thickness. This Pleistocene-Holocene sequence being partly of shallow marine, partly of terrestrial origin contains the coastal aquifers. Clay typically ranges from 0.5 m to 80 m in thickness.

Based on their hydrogeological and geological-lithostratigraphic characteristics, the aquifers are grouped into three hydrostratigraphic units (HSU): the Neogene-Quaternary unit, the Cretaceous, and the Triassic one. The first one is divided into the Plio-Pleistocene subunit, which is under confined conditions, and the Holocene-Pleistocene subunit, which is confined/semi-confined and locally unconfined.


**Table 1.**Hydrogeological and hydrochemical data from the wells of the Triassic HSU. TDS: total dissolved solids.

**Table 2.**Hydrogeological and hydrochemical data from the wells of the Cretaceous HSU.



**Table 3.**Hydrogeological and hydrochemical data from the wells of the Neogene-Quaternary HSU.


**Table 3.** *Cont.*
