HYDROGEOCHEMICAL AND ISOTOPIC ANALYSES OF GROUNDWATER IN THE COASTAL AREA OF BALIKPAPAN, EAST KALIMANTAN PROVINCE

• Main Author: Irsyadulhaq
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/82880
• Institution: Institut Teknologi Bandung

The research area encompasses the coastal region of Balikpapan City, which has a total population of approximately 733,000, with an estimated groundwater use for domestic purposes of about 70%. As the buffer zone for Nusantara (IKN), the future population of Balikpapan is expected to increase, which could result in intensified groundwater use as well as alteration in groundwater quality. This study examines hydrogeochemical and isotopic characteristics of groundwater, identifies the occurrence and causes of seawater intrusion in the study area, and reconstructs a conceptual hydrogeological model using data comprising groundwater samples, lithology, seismic, groundwater levels, and sea tides. The findings reveal that the Total Dissolved Solids (TDS) of groundwater range between 141 to 11,023 mg/l, the pH varies from 4.49 to 9.29, and the groundwater facies consist of mixed cation-HCO3, Na-Cl, Na-HCO3, Na-mixed anion, and Na-Cl. The isotopic composition of 18O and 2H indicates the evolution of groundwater isotopic characteristics through evaporation and water-rock interaction. Seawater intrusion is observed in one groundwater sample (point M-2.1) within an aquifer at depths of 30 – 33 meters; it is interpreted to occur naturally. The mixing ratio analysis of this groundwater sample shows a composition of approximately 60% freshwater and 40% seawater. The conceptual hydrogeological model of the study area suggests the interbedding of sandstones and claystones or aquifers and aquitards, where the aquifer at depths of 30 to 33 m at point M-2.1 is interpreted to be connected to the sea.