Multicomponent heterovalent chromatography in aquifers. Modelling salinization and freshening phenomena in field conditions

Analysis of hydrochemical data using diagrams and the geochemical transport model PHREEQC confirmed that for the Argos plain aquifer and for other heterogeneous confined alluvial coastal aquifers in Greece, the variation of water qualities along a flow path has basically a chromatographic origin due to seawater intrusion and freshening processes. Additionally, calcite precipitation, dolomite and gypsum dissolution take place. Intense fertilization and overexploitation of the area resulted in degradation of the groundwater quality by high amounts of nitrate ions and increased salinization. The main physical factor affecting groundwater quality in this area is the cation exchange capacity that is calculated to be 4.3 meq(100 gr)−1. Good adaptation of the transport model to the field data showed that the model can be used to predict the freshening process after an artificial recharge. Hence in a first stage for Cl−, there is a continuous decrease to the initial fresh water concentrations corresponding to about 1–1.5 pores volumes that should have been shifted through the aquifer, while for both cations Ca2+ and Mg2+ this decrease is even lower and leads to concentrations lower than that of the initial fresh water. Complete restoration of the aquifer requires a great amount of recharge water that should be transported through the aquifer and corresponds to 32 pores volumes.