Reaction of subsurface coastal aquifers to climate and land use changes inGreece: modelling of groundwater refreshening patterns under natural recharge conditions

This paper studies the multicomponent ion exchange process and freshening t ime under natural recharge conditions for three coastal aquifers in Greece. Due to over-pumping and the dry years of 1980-1990 decline in groundwater quality has been observed in most of the Greek coastal aquifers. This decli ne is caused by a lack of reliable water resource management, water abstrac tion from great depths, and seawater intrusion resulting in a rise of the f resh/salt water interface (salinisation process) due to a negative water ba lance. The reverse phenomenon, which should lead to groundwater freshening, is a long process. The freshening process shows chromatographic patterns t hat are due to chemical reactions such as calcite dissolution and cation ex change, and simultaneously occurring transport and dispersion processes. Us ing the geochemical simulation codes PHREEQE and PHREEQM (Parkhurst et al., US Geol. Surv. Water Resour. Invest., 80-96 (1980) 210; Appelo and Postma, Geochemistry, Groundwater and Pollution (1994)), these patterns were analy sed and the above-mentioned processes were simulated for carefully selected aquifers in Peloponnesus and Crete (Greece). Aquifers of the Quaternary ba sin of Glafkos in Peloponnesus, the Neogene formations in Gouves, Crete, an d the carbonate aquifer of Malia. Crete, were examined as representative ex amples of Greek coastal aquifer salinisation. The results show that when pu mping was discontinued, the time required for freshening under natural cond itions of the former two aquifers is long and varies between 8000 and 10,00 0 years. The Malia aquifer on the other hand, has a freshening time of 15 y ears. Freshening time was shown to depend mainly on cation exchange capacit ies and the recharge rate of the aquifers. (C) 2001 Elsevier Science B.V. A ll rights reserved.