資源・素材学会 年次大会

Groundwater is one of the important resources in Indonesia. It is commonly utilized for domestic water supply including drinking water, irrigation, municipalities, and industries. On the other hand, coal mines are widespread in Indonesia, especially in Kalimantan Island. Mining with an open-pit system (surface mining) is regarded as an activity that affects the environmental deterioration. One issue is the impact on groundwater, including a decrease in the quantity of groundwater. According to environmental regulations in Indonesia, each mining company is obliged to submit Environmental Impact Assessment (EIA) documents before starting production, in order to protect and manage the groundwater in mine areas. The objective of this study is to estimate the impact of coal mining on groundwater recharge using a water balance approach as a part of EIA. Water balances, before mining operation and during mining operation, should be evaluated based on natural hydrological conditions in the land around open pit coal mine area. Hydrologic data, such as precipitation (P) and temperature, combined with topography data, were collected to calculate the evaporation-transpiration (ET) and run off (Ro) value. Then, groundwater recharge (U) was determined by water balance equation (U=P–ET-R_o). The results of this study showed that groundwater recharge before mining operation was 1038.15 mm/annual, while the recharge during mining operation was estimated to be 947.5 mm/annual. Decreasing the recharge value during mining operation would influence the total amount of groundwater in the aquifer storage around the mine area. Therefore, open pit coal mine would give significant impacts on groundwater quantity.