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Salinization of coastal aquifer systems constitutes a major threat for groundwater. Especially areas with high population density due to increasing tourist activity may face severe problems. In this study, the GALDIT method was applied in the north side of Rhodes Island, Greece, in order to assess groundwater vulnerability to seawater intrusion. Hydrogeological data were elaborated in geographical information systems (GIS), and appropriate thematic maps were produced. The final vulnerability map was obtained from the combination of the thematic maps using overlying techniques. Based on the application of the GALDIT method, a zone up to 1000 m from the shore is characterized by medium to high vulnerability, while medium vulnerability characterizes the eastern part of the study area. Overexploitation of the aquifer, due to the intense touristic activity in Ialysos area, constitutes the main reason for groundwater salinization due to seawater intrusion in the study area. Consequently, planning of proper groundwater management and systematic monitoring of the groundwater reserves are of the utmost importance in order to solve existing problems and prevent future issues of salinization.

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In this work, a sand filtration-activated carbon adsorption system was evaluated to remove the fungicide content of a biologically treated effluent. The purification process was mainly carried out in the activated carbon column, while sand filtration slightly contributed to the improvement of the pollutant parameters. The tertiary treatment system, which operated under the batch mode for 25 bed volumes, resulted in total and soluble COD removal efficiencies of 76.5 ± 1.5% and 88.2 ± 1.3%, respectively, detecting total COD concentrations below 50 mg/L in the permeate of the activated carbon column. A significant pH increase and a respective electrical conductivity (EC) decrease also occurred after activated carbon adsorption. The total and ammonium nitrogen significantly decreased, with determined concentrations of 2.44 ± 0.02 mg/L and 0.93 ± 0.19 mg/L, respectively, in the activated carbon permeate. Despite that, the initial imazalil concentration was greater than that of the fludioxonil in the biologically treated effluent (i.e., 41.26 ± 0.04 mg/L versus 7.35 ± 0.43 mg/L, respectively). The imazalil was completely removed after activated carbon adsorption, while a residual concentration of fludioxonil was detected. Activated carbon treatment significantly detoxified the biologically treated fungicide-containing effluent, increasing the germination index by 47% in the undiluted wastewater or by 68% after 1:1 v/v dilution.