Being good stewards of water resources is a top priority for New Mexico mining companies. This is why they choose to work closely with local stakeholders on water projects to support operations, and also to help sustain communities beyond the life of mining operations.
New Mexico copper mining professionals work diligently to operate within all applicable New Mexico rules and standards. Specifically, they work to ensure compliance with the New Mexico Water Quality Act, which requires mines to have: 1) an operating plan, 2) a monitoring plan, 3) a contingency plan, 4) a closure plan and 5) a financial assurance plan. The Act is administrated by the New Mexico Environment Department (NMED).
Water management and reuse is a vital aspect of copper mining at every stage–before, during and after the mine closes. A large scale mining operation covers thousands of acres of land and must have sufficient water to process ore. In addition, federal and state laws govern water quality and discharges to ground and surface water. New Mexico’s operating copper mines employ environmental and reclamation experts working to ensure that the numerous federal and state surface, ground and storm water regulations are met and that water is used efficiently to support long term environmental and project development goals.
Surface copper mining creates an open pit, which is a collection area for precipitation that falls within the pit’s drainage area. The ground water and storm water collected in an open pit is an important source of process water during mine operation. An open pit that extends below the water table acts as a hydrologic sink collecting ground water from all directions. If the open pit is large enough, annual evaporation of water accumulating in the open pit can exceed annual inflow of ground water and precipitation, and the open pit is considered to be a “hydrologic evaporative sink.” A hydrologic evaporative sink will never discharge water contained in the open pit to surrounding ground water. The open pit at the Chino Mine is an example of a hydrologic evaporative sink. Open pit hydrologic containment can also be achieved by pumping to maintain the water level in the open pit below the groundwater table.
In addition to water collected in the open pit, water that comes in contact with mined materials is collected in detention ponds, reservoirs, tailing impoundments and interceptor wells and is recirculated for the copper extraction process. Rarely, if ever, does this water require treatment before reintroduction into the copper mining and extraction circuit. Water that has not come into contact with mined materials can be discharged off site to surface waters.
Groundwater pumping systems designed to control the discharge of groundwater also provide water that can be reused. Through groundwater pumping systems, potential impacts are contained and managed to meet the same groundwater protection objectives within a reasonable distance from the pit within the mine operation.
Copper mines in New Mexico plan for long-term treatment of water impacted by mining operations. A water treatment plan is an engineering document that describes the processes and methods that will be employed to collect impacted water, treat and discharge it safely after the mine is closed. This plan is updated with every closure plan renewal and includes both the capital costs to build the treatment plant and operate and maintain the plant for 100 years. This cost estimate is used to calculate the amount of financial assurance provided by the mine operator to the State for a default closure scenario. In New Mexico, thousands of acres of historic mine sites and facilities have been successfully reclaimed.
A detailed description of typical water management practices at copper mines that shows how water is recycled and conserved is illustrated by the video Water in Mining Operations, produced by Freeport-McMoRan Copper & Gold.
Water in Mining Operations