*ABSTRACT* Water is an aspect that is often becoming a problem in the mining industry. In a system of open pit mine, the water that comes from surface water and groundwater is collected into a temporary collecting pond which is commonly referred to as sump. This paper analyzes a case study of optimization of sump at an open pit coal mine in South Borneo. The design of sump often ignores the role of groundwater. It has quite an impact on the efficiency of the design of the sump and the number of pumps used during the dewatering process. The process of pumping on the open pit system considers the total amount of water that runs into the pond of water, not only surface water alone. Moreover, the interconnected drainage channels and culverts also play a role in the optimization of the open pit sump system. Analysis of hydrogeological decision has an enormous role in the sump optimization, including sump design, pump usage, and the total number of culverts on the system so that the open mine pit design, which has good technical and economic value, can be obtained. Keywords: mines hydrogeology, open pit mines, groundwater.