Characterization of the Pit Lake Area for Sustainable Management at a Coal Mine in Central Kalimantan, Indonesia

Abstract A pit lake, formed at the end of mining activities, can potentially be sustainably utilized. Several mines in Indonesia have reached the end of post-mining, and some have been abandoned as voids that eventually become lakes. Pit lake planning needs to be conducted to ensure these lakes are useful and sustainable. One of the former mining areas that has become a pit lake is located in Central Kalimantan. The dimensions of the pit lake are 2,300 m long, 620 m wide, and approximately 68 m deep. The amount of water in the pit lake is estimated to be approximately 37.5 million m 3 . This research was conducted to determine the potential use of the pit lake by characterizing the factors affecting its sustainable use. Observations were carried out to comprehensively understand the characteristics of the pit lake area. Field measurements were carried out to assess water quality, while rock samples were taken to analyze their geochemistry. Measurements in the field indicated that the lake water pH was in the range of 5 to 6. Meanwhile, the area around the pit lake has several open areas where revegetation has failed, resulting in rock exposure around the pit lake area. Geochemical tests on 23 samples from around the pit lake area showed that 15 samples had pH values below 6. Mineralogical tests on 4 samples indicated the presence of secondary minerals generating acid mine drainage, such as jarosite. Based on the obtained results, efforts must continue for the long-term use of the pit lake, including the closure of open areas and water treatment, so that the water can be used for operational needs in the field.