Depending on demand for copper, gold and molybdenum, the mine been in and out of operation since the late 1800s. With the increased demand place on the mine, one pit at the eastern end of the mining district needed to be widened and deepened over a 6-year period. The challenge of the open-pit expansion is that it would penetrate a large aquifer made up of highly permeable carbonate bedrock. This carbonate groundwater system contains a large volume of water in storage, receives substantial recharge from the Egan Range and serves as a source of spring discharge used for local potable water supply.
Delivering a Sustainable Water Management Plan
Our team completed a detailed hydrogeologic characterization of the carbonate aquifer to delineate its extent, defined the life-of-mine dewatering requirements, and developed the design of the open-pit dewatering operation, while meeting the mine’s water-supply demand and complying with environmental regulations for discharge of excess water.
The dewatering goal was to maintain groundwater levels below the pit floor before mining and throughout the life of the mine. Primary and secondary dewatering strategies were developed to achieve this goal. The primary dewatering strategy focused on reducing groundwater levels with high-capacity vertical pumping wells in permeable zones around the perimeter of the pit to dissipate pore pressure in the pit walls. The secondary dewatering strategy focused on depressurization of lower-permeability zones along the pit perimeter and inside the pit. A combination of active and passive measures, such as vertical in-pit wells and horizontal drains, was used to meet the pit slope design criteria.