Groundwater chemistry and ionic ratios in a western coastal aquifer of Buan, Korea: implication for seawater intrusion

Seawater intrusion was studied in a monitoring well field, located in western coastal area of Buan, Korea using groundwater chemistry and ionic ratios. Most of the study area is paddy fields apart from 200–2,500 m from the coast. The groundwaters affected by the seawater intrusion featured high levels of C1 and TDS, which are the simplest common indicators for the seawater influence. The TDS showed highly positive correlation with the other major parameters except for nitrate. High levels of NO3 at some monitoring wells indicated nitrate pollution of groundwaters due to anthropogenic origin such as septic effluents or chemical fertilizers. Based on the piper plot, it was inferred that the groundwater salinization occurred via mixing and cation exchange reaction between two end members (fresh or less affected groundwater and the seawater). Beside of the major chemical compositions, it was demonstrated that ionic ratios would be useful to delineate seawater intrusion and they include HCO3/Cl Na/Ca, Ca/Cl, Mg/Cl and Ca/SO4. Cluster analysis based on these ratios produced an equivalent result to that of using the major chemical compositions. Finally, to differentiate causes of the high salinity in groundwaters between anthropogenic origin (excessive groundwater use) and natural phenomenon (seawater intrusion wedge), consecutive monitoring of groundwater is required for multi-years.