Seawater Intrusion Mapping Using Hydrochemical Ionic Ratio Data: an Application in Northern Part of Jakarta Groundwater Basins, Indonesia

Groundwater is the most important freshwater source in Jakarta for household and industry use. Along with the massive growth of population and industry in Jakarta, it has lead to excessive groundwater extraction, and in the end, it causes other problems such as land subsidence and sea water intrusion. Unfortunately, the extend of the seawater intrusion in the coastal part of Jakarta groundwater basin has not explained well. The purpose of this research was to establish the map of seawater intrusion in the northern part of Jakarta groundwater basin. This study used five parameter ionic ratios to determine seawater intrusion. This approach has advantages in terms robustness of processing and data analysis but is still powerful in determining seawater intrusion in the Jakarta groundwater basin. Hydrochemical data were collected from dug wells and monitoring wells in order to characterize the hydrochemical facies of the study area. Eighty-eight (88) groundwater samples were taken from dug well and monitoring well. Some of the groundwater sample has Cl− concentrations > 2386 mg/L and EC value with (> 1000 μS/cm), suggesting seawater intrusion already occurred. This data has been confirmed with ionic ratio where area with seawater intrusion shows higher ratio than area that was not affected by the seawater intrusion. Ionic ratio criteria were overlay to create seawater intrusion map (SWIM). The most extreme salinization occurs in the northern, northwestern, and eastern sections of this study area. From 2015 to 2017, the pattern of seawater intrusion map varies greatly. This research shows that the use of ionic ratio method is efficient tools in mapping of seawater intrusion. Apart from that, this research will be a consideration for stakeholders in groundwater management, especially in the northern part of the Jakarta groundwater basin to conserve groundwater sustainability.