Dewatering behavior of perched aquifer in waste dumpsite using deep well system in the Mae Moh Mine, Thailand

• Perched water seepage and a weak foundation were primary causes of the 2018 large-scale failure. • Evaluated deep well dewatering performance in perched aquifers to enhance slope stability in waste dumpsites. • PP achieves faster water level reductions than SP and a broader effective range. • Increased influence of pumping cycles (N) lowers water recovery levels due to reduced aquifer recharge. • Developed predictive equations for ΔVr and Tr to optimize pumping cycles and improve dewatering efficiency. A large-scale failure occurred at west dumpsite of Mae Moh Mine, Thailand due to perched water seepage and inadequate drainage in the weak foundation. This study evaluated deep well dewatering to reduce the perched water table and hence improve its slope stability. A dewatering system with Single Well Pumping (SP) and Parallel Well Pumping (PP) operations was installed in the failure zone. PP outperformed SP, achieving faster perched piezometric level reductions with a broader effective range. Increasing pumping cycles (N) reduced recovery levels and inflow rates due to aquifer recharge limitations, emphasizing importance of managing N to sustain dewatering efficiency. Under SP and PP operations, the measured recovery volume change (ΔVr) at various time (Tr) could be represented by hyperbolic relationship. Mae Moh Mine has extended this innovation to the real-world practice by implementing the dewatering system in the failed dumpsite to stabilize its slope stability.