Study on the Mine Drainage System of The Pit Nusa in Lhoknga, Aceh Besar, Aceh

Mine drainage management is a crucial aspect of mining operations, ensuring safety, efficiency, and sustainability. Poor water control may lead to operational disturbances, slope instability, and long-term environmental risks. Although studies on mine drainage exist, research focusing on integrated hydrological and hydrogeological analysis for both operational and post-mining conditions in the Lhoknga mining area, Aceh, remains limited. This study aims to design an effective mine drainage system that supports mining safety and minimizes environmental impacts. The research employed a combination of primary and secondary data, including rainfall records, groundwater measurements, hydraulic conductivity tests, infiltration rates, and topographic data. Hydrological analysis was conducted to calculate design rainfall, rainfall intensity, and runoff using the Gumbel distribution, Mononobe equation, and Rational method. Hydrogeological modeling applied Darcy’s Law, utilizing finite-difference numerical simulation, to evaluate groundwater flow and pit inflow. Water balance components were also analyzed, encompassing rainfall, evapotranspiration (using the Thornthwaite method), infiltration, runoff, and groundwater contribution. The results established a 30-year return period design rainfall of 57.5 mm/day, yielding an intensity of 7.91 mm/hour. The water balance analysis revealed that surface runoff is the dominant component, accounting for 70.33% of total precipitation. The hydrogeological model (R2=0.8) accurately predicted the formation of a cone of depression post-mining, with an estimated groundwater table drawdown of 5-15 meters. The primary contribution is a detailed technical drainage plan specifying designs for open channels and sumps for the mine drainage system. The plan necessitates a combination of open-channel drainage and a pumping system for the Northern Pit, while the Southern Pit can initially rely on gravity drainage.