Simulation of Groundwater Fluxes during Open-pit Filling and under Steady State Pit Lake Conditions

A critical component in determining post-mining pit water quality is knowledge of groundwater fluxes, both as the pit fills and after steady state conditions have been reached. Simulations of the filling of an open pit in Crescent Valley, Nevada, were made to generate inputs for pit lake chemistry predictions. The simulations show that the water table recovery is most rapid immediately after pumping stops, when the hydraulic gradients are steepest. The maximum lateral extent of water table drawdown occurs several years after pumping stops because water continues to be derived from storage as the pit fills. Under steady state conditions, the lake stage is lower than the elevation of the water table in the pit area prior to mining, and groundwater flow is directed toward the pit lake, because evaporation from the lake surface causes it to act as a groundwater sink.