Groundwater Flow and Its Isotopic Evolution in Deep Aquifer of Jakarta Groundwater Basin
Jakarta Groundwater Basin is the Quaternary basin and has three zones of the aquifer, where the deepest aquifer is confined aquifer (Aquifer III). Stable isotope 18O and 2H (Deuterium/D) in this research studied to see its evolution, particularly in this deep groundwater. Isotopic evolution is studied to determine the distribution patterns of distribution and factors that may control in the evolution process. The research method was sampling of groundwater from bore wells that tap water from the Aquifer III, and then tested for the content of stable isotope and its TDS. Analyses have been done by using primary data and some secondary data of stable isotope and TDS data. The results showed that the isotopic evolution occurs in the deep aquifer, influenced by the action of water on rock minerals along groundwater flow. In general, isotopic enrichment occurs in line with groundwater flow, where the content of the stable isotope is heavier toward the north. This isotope enrichment related to the isotopic fractionation processes, which may be occur because of the limestone that consists of the aquifer III and Tertiary limestone of Klapanunggal and Bojongmanik Formations. Increasing of TDS in deep groundwater is followed by increasing of the isotope δ18O content, but it is unclear followed by an increasing of δD. Increasing of isotope content of groundwater in the aquifer is influenced by the groundwater flow velocity, where the rapid flow may occurred in the central part of the research area indicated by contours that curve northward, especially on the δ18O distribution contour pattern.