Preliminary Result of Sea Water Intrusion Identification Based on Electric Conductivity Mapping in Balikpapan Coastal Aquifer Area

Abstract As the population grows, there will inevitably be an increased demand for water to meet daily life needs, including groundwater usage. Excessive use of groundwater significantly impacts groundwater problems, such as seawater intrusion, where seawater moves inland and contaminates groundwater. This phenomenon commonly occurs in coastal areas. Balikpapan is one city potentially affected by seawater intrusion. In this city, most residents living along the coastal areas rely on groundwater from shallow and deep wells as their source of clean water. The significant increase in groundwater usage in these coastal areas facilitates the easy entry of seawater into groundwater aquifers. This research aimed to investigate early signs of seawater intrusion occurring in the coastal areas of Balikpapan. The investigation measured the electrical conductivity (EC) values of groundwater from 36 shallow wells and 9 deep wells distributed across the research site. The investigation results showed that out of these 45 wells, 21 had an EC value of <700 μS/cm, indicating fresh water; 21 had an EC value of 700 - 2,000 μS/cm, indicating slightly saline groundwater; 2 had an EC value of 2,000 - 10,000 μS/cm, indicating moderately saline groundwater; and 1 had an EC value of 10,000 - 20,000 μS/cm, indicating highly saline groundwater. The distribution of groundwater with high EC values is generally found in the northeastern coastal area of Balikpapan, associated with alluvial deposits with moderate to high aquifer productivity