Groundwater which infiltrated in recharge areas discharges in the forms of evapotranspiration, baseflow to streams, groundwater abstraction and eventually flows into the sea. This study characterized radon-222 concentration and electrical conductivity (EC) in coastal groundwater discharge, well groundwater, Ilkwang Stream water, and seawater in the coastal area of Busan Metropolitan City and subsequently estimated groundwater discharge rate to the sea. The median value of Rn-222 concentration is highest in well groundwater (18.36 Bq/L), and then decreases in the order of coastal groundwater discharge (15.92 Bq/L), Ilkwang Stream water (1.408 Bq/L), and seawater (0.030 Bq/L). The relationship between Rn-222 concentration and EC values is relatively strong in well groundwater and then in seawater. However, the relationship is not visible between coastal groundwater discharge and Ilkwang Stream water. The groundwater discharge rate to the sea is estimated as 3,130 m 3 /day by using radon mass budget model and 16,788 m 3 /day by using Darcy's law.

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Saltwater intrusion in coastal regions can be detected by using numerous geochemical constituents in groundwater. However, insufficient numbers of groundwater data can often make us difficult to interpret saltwater intrusion. Probability statistics technique enables statistical prediction using a limited numbers of water quality data for a wider range and can make to effectively evaluate saltwater intrusion through a characterized distribution of probability. This study evaluated saltwater intrusion by applying probability statistics to the chemical constituents in groundwater, coastal discharge, and stream water in the coastal areas of Busan City. By the result of the study, it is proven that Na + , Mg 2+ , K + , SO 4 2− , and Cl − , abundantly contained in seawater, are valuable indicators for evaluating saltwater intrusion. On the other hand, it is judged that Si 4+ , NO 3 − , Fe 2+ , and PO 4 3− , showing similar probability distribution in groundwater, coastal discharge, and stream water, are not appropriate indicators for the detection of saltwater intrusion.