**6. Conclusions**

A completely revised hydrogeological conceptual model was proposed for the Thriassion Plain, West Attica, Greece. We suggest that the saline water hosted in the Neogene-Quaternary coastal aquifers is likely due to seawater entrapment prior Pleistocene-Holocene clay deposition. Due to that, any modern direct-seawater intrusion is precluded. Moreover, an almost stagnant zone is developed within the Pleistocene-Holocene sediments under the coastal area and the Eleusis Gulf seafloor. A minor quantity of groundwater is partly discharged as an upwards leakage through the clay strata, forming wetlands or swamps on the ground surface, whereas the major one moves very slowly southeast. Finally, coupling our data (chemical water analyses and aquifer types) with the existing stratigraphic ones (borehole data), we infer that the submarine fresh water possibly exists in the deeper aquifers beneath the seafloor of the Eleusis Gulf.

— — **Author Contributions:** Conceptualization, D.H.; methodology, D.H.; formal analysis, D.H.; investigation, D.H., P.M., G.K., and A.A.; resources, D.E.; data curation, P.M. and D.H.; writing—original draft preparation, D.H.; writing—review and editing, D.H., P.M., G.K., and A.A.; visualization, D.H.; supervision, D.H. and A.A.; and project administration, D.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no funding.

**Acknowledgments:** This study was accomplished at the expense of the Agricultural University of Athens.

**Conflicts of Interest:** The authors declare no conflict of interest.
