Predicting Open Pit Mine Inflow and Recovery Depth in the Durvuljin soum, Zavkhan Province, Mongolia

Abstract

Increasingly, mine issues and water resources are being managed on a watershed basis, while addressing problems at the local mine scale. A good example of this developed when empirical and analytical modelling of the potential inflow to an open pit mine in the Durvuljin soum, a region in northwest Mongolia, indicated that inflow would be on the order of 0.3 to 10.5 L/s. In this study, the radius of influence due to open pit mining was estimated to be between 0.6 and 3 km. Based on simulated drawdown contours and transient pit inflow figures that captured the impact of mining and groundwater inflow rate variations over a period of time, it appeared that advanced dewatering will not be required at this mine, unless currently unknown major fractured structures are intercepted. In-pit basal sumps and pumps should be sufficient to remove water from the mine floor. However, an assessment of the final pit level is also crucial to planning the post-mining surface and groundwater quality/eco-system and mitigation requirements during recovery. Our post-mining water table recovery estimate indicated that inflow will exceed evaporation and that a shallow lake will likely form. While such solutions, which do not rely on complex numerical models nor excessive input data, are not appropriate for all hydrogeologic situations, they are relevant to the conditions encountered at most mine sites.