Freshening under natural conditions of coastal aquifers polluted from sea water intrusion

This paper deals with the cleaning up process (freshening), of coastal aquifers which have been polluted by the intrusion of sea water. This intrusion is due to a lack of reliable water resource management, over-pumping, and the great depth of water abstraction which causes a rise of the fresh/salt water interface. The freshening process shows chromatographic patterns which are due to chemical reactions such as calcite dissolution and cation exchange, and simultaneously occurring transport and dispersion processes. These characteristics were analysed and the above-mentioned processes were simulated for carefully selected aquifers in Peloponnesus and Crete (Greece) using the geochemical simulation codes Phreeqe and Phreeqm. Aquifers of the Quaternary basins of Glafkos in Achaia and Argos in Argolis, the Neogene aquifer of Gouves, Crete, and the carbonate aquifer of Malia, Crete, were examined as four typical examples of salinization. The results show that after pumping was discontinued the time required for freshening of the former three aquifers is long and varies between 8,000-12,000 years. The Malia aquifer on the other hand, has a freshening time of 16 years. Freshening time was proved to depend mainly on cation exchange capacities and the recharge rate of the aquifers.