Dewatering requirements of three open pits located in western Turkey and the impact of dewatering on groundwater resources were evaluated using a three-dimensional numerical groundwater flow model. The groundwater was modeled using MODFLOW software and the dewatering was simulated using the MODFLOW Drain Package. The drain cell configurations were determined by pit boundaries; invert elevations of drains corresponded to the bench elevations in the mining schedule, which varied dynamically among the three pits. Transient model runs were conducted for the 21 years of mine life to calculate the monthly dewatering rates. Simulation results indicate that the average groundwater inflow to the excavations is 3.64 L/s, excluding the effects of direct rainfall into the pits and surface water flow from the benches. Long term (80 years) simulations were conducted to predict the amount of drawdown at the water supply wells in the area. The results indicate that 21 years of mining will not significantly impact the water levels in these wells. However, natural discharge from the springs near the pits will be exhausted by the dewatering.