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ABSTRAK Dominicus Vincent
PUBLIC Irwan Sofiyan

PT. XYZ is a gold mine operating in North Sulawesi Province. PT. XYZ plans to build an underground mine under one of the currently active mine openings, namely pit ABC. The main problem that has occurred in pit ABC since mid-2016 is the presence of groundwater flow with a significant discharge (measured discharge in September 2020> 900 liters / second), and is hot water with a temperature of more than 70o C. Hydrogeological conditions are important to know regarding appropriate alternative treatments to overcome the problem of hot water with large discharge that comes out of pit ABC. This is a major factor in the consideration of underground mining. In this study, investigations were carried out by conducting pumping tests and hydrogeological modeling based on a conceptual model and then simulated in a numerical model as a planning approach in the underground mine planning of PT. XYZ. Based on field observations, study literature, and previous data, it can be concluded that the hydrogeological media and groundwater flow in the study area are mostly controlled by the fracture media system and high permeable zones. The results showed that the groundwater flow to the East and towards the center which is an open pit area, also found that the local aquifer has parameter values in the form of storativity, hydraulic conductivity and large transmissivity. In addition, the value of the water discharge that enters the underground mine is also a number that is not small even though it has been assisted by a pump. And thus this study aims to model and perform calculations for the sake of carrying out underground mining under an open pit mining PT. XYZ.