Application of Oxygen-18 and Deuterium Isotopes to Determine the Groundwater Recharge Area of Dumoga Area, Bolaang Mongondow Regency, North Sulawesi Province

The Dumoga area, which includes the districts of Dumoga, West Dumoga, East Dumoga, Central Dumoga, South-east Dumoga, and North Dumoga in Bolaang Mongondow Regency, North Sulawesi Province, is an agricultural area that relies on groundwater for agricultural irrigation. To ensure the sustainability of the groundwater resources, it is crucial to protect the recharge areas. This study aimed to determine the locations of groundwater recharge areas in the Dumoga region using stable isotopes, specifically oxygen-18 (18O) and deuterium (D). Measurements of groundwater levels (GWL) were conducted to understand the direction and flow of groundwater, while measurements of electrical conductivity (EC) and groundwater temperature served as supporting parameters to assess the groundwater conditions in the research area. The findings revealed that the groundwater in the Dumoga region originates from the surrounding hills, with estimated recharge areas in surronding hills ranging in elevation from 326 meters above sea level (masl) to 462 masl.