Seawater intrusion forms a significant environmental and hydrogeological phenomenon that raises significant risks for the sustainability and quality of coastal aquifer hydrosystems. The present review study critically examines the available methodologies for assessing aquifer susceptibility to seawater intrusion, including the GALDIT and SEAWAT models. The GALDIT model is a parametric model that uses six main hydrogeological parameters for assessing groundwater vulnerability to seawater intrusion. Numerous researchers have proposed improvements to GALDIT either by adding new variables such as well density, well pumping rates, and hydrochemical indicators, or by applying machine learning (ML), fuzzy logic, and optimization algorithms to improve spatial resolution and accuracy. The SEAWAT code can be used for simulating variable-density groundwater flow and solute transport and has been widely used to model the salinization process under different pumping and sea-level rise scenarios. The presented case studies show that the combination of GALDIT and SEAWAT offers a stronger and robust framework for both vulnerability zoning and dynamic flow and transport simulation. Recent SEAWAT studies show that paleo-salinization has a significant influence, highlighting the need to measure both the trapped saline water in confined layers and the lateral intrusion of seawater. The present review concludes that future efforts need to focus on hybrid modeling approaches, integration of hydrochemical and geophysical data, and the inclusion of anthropogenic and climate-associated factors to enhance the accuracy and applicability of seawater intrusion risk assessments in coastal areas.

In Greece, the geodynamics of karst hypothermal–mineral springs, in which often shallow fresh groundwater is intermixed, is not well known. This study aims to investigate the monthly hydrochemical variability of three karst hypothermal mineral springs in Greece named Kyllini (southern Greece), Agiasma (northern Greece), and Voskina (northern Greece). Hence, monthly samples were collected and an analysis of major and trace elements, ion ratios, and saturation indices was performed, as well as statistical analysis and cross correlation. Elevated concentrations of Ca²⁺, Mg²⁺, and HCO₃⁻ are present in all springs, indicating that the dissolution of calcite and dolomite constitutes the main water–rock interaction process. Additionally, the mobilization and transport of Mn, Fe, and As are favored by the negative ORP values. However, there are also differences between the three springs. The Kyllini spring is characterized by high salinity and dominated by Na–Cl–HCO₃ water, while the Agiasma spring exhibits a mixed water type with moderate salinity. The Voskina spring reflects a fresher, bicarbonate-dominated aquifer system with modest trace element mobilization. This study provides the first comprehensive monthly assessment of the hydrochemical response of karst hypothermal–mineral springs in Greece, offering new insights into seasonal geochemical dynamics.

The intrusion of seawater in coastal aquifers in Greece is a particularly widespread phenomenon. The coastline of Greece has a length of 15,147 km. Once groundwater resources are contaminated, remediation strategies are difficult, costly and time consuming. In this paper three coastal aquifer systems of Peloponnese are studied. Initially the main ions and cations were calculated for the three aquifers. According to the results from hydrochemical analyzes Na+,Mg2+, Ca2+, SO4-2, Cl- have high values and are affected by the intrusion of seawater into the coastal aquifers. It estimates the vulnerability of groundwater to the intrusion of seawater. Using Geographical Information Systems (GIS) software, maps are prepared for the presentation of each parameter of the GALDIT method. The main factors that affect the seawater intrusion are basically presented in the 6 letters of the acronym GALDIT. The analysis of each parameter is as follows: Groundwater occurrence (aquifer type: unconfined, confined, and leaky confined), Aquifer hydraulic conductivity, depth to groundwater Level above the sea, Distance from the shore (inland distance perpendicular from shoreline), Impact of existing status of sea water intrusion in the area and Thickness of the aquifer. The final map that emerged from the study of the three groundwater systems shows the vulnerability of seawater intrusion in Peloponnese. The maps show that the groundwater system of Larissos presents lower vulnerability to the seawater intrusion compared to the other two groundwater systems. This is because the occurrence of flysch in the northern part of the area acts as a barrier to the penetration of seawater.

Seawater intrusion into Greece’s coastal aquifers is a prevalent issue. The Greek coastline extends for 15,147 km. Once groundwater sources become contaminated, remediation methods are often challenging, costly, and protracted. This study focuses on three coastal aquifer systems in the Peloponnese region. Initially, the main ions and cations were determined for these aquifers. Hydrochemical analyses revealed elevated concentrations of Na⁺, Mg²⁺, Ca²⁺, SO₄²⁻, and Cl⁻, indicating a significant impact from seawater intrusion. The study evaluates the vulnerability of groundwater to this intrusion. Utilizing Geographical Information Systems (GIS) software (ArcGISPro), maps were created to illustrate each parameter of the GALDIT method. The acronym GALDIT encapsulates the main elements influencing seawater intrusion. Each parameter is analyzed as follows: Groundwater occurrence (including the following aquifer types: unconfined, confined, and leaky confined), Aquifer hydraulic conductivity, depth to groundwater Level above the sea, Distance from the shore (inland distance perpendicular from shoreline), Impact of existing status of sea water intrusion in the area, and Thickness of the aquifer. The final map that emerged from this study shows their vulnerability to seawater intrusion in Peloponnese. Notably, Larissos exhibits lower vulnerability in contrast to the seawater incursion in the other two groundwater systems.