Water Management at Alaska's Operating Mines: Process water, groundwater, and runoff all managed with care.

Author:Anderson, Tasha
Position:SPECIAL SECTION Mining
 
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Mining operations in Alaska are held to high standards when safeguarding people and the environment. A crucial factor of environmental stewardship is managing water, which in Alaska is a significant endeavor considering both the ubiquity and volume of water in the state. Mines operating in Alaska are responsible not only for water directly related to their mining processes but are often required to monitor the quality of bodies of water near their facilities or activities. What each mine is responsible for in terms of water management is dependent on the mine's operations and location.

The Division of Water, part of the Alaska Department of Environmental Conservation, is tasked with improving and protecting the quality of Alaska's water. Specifically, the Alaska Pollutant Discharge Elimination System (APDES) program issues permits to authorize the appropriate discharge of water to the environment.

Fort Knox

Fort Knox, an open-pit gold mine north of Fairbanks that's been in operation since 1994, has a closed system for process water (water which cannot be classified as drinking water and is used in connection with technical plants and industry processes) and maintains an APDES permit to discharge extracted, non-contact, non-process groundwater from pit dewatering wells.

The mine processes ore onsite at a carbon-in-pulp mill; other onsite facilities include the tailings storage facility (TSF), constructed wetlands complex, freshwater reservoir, and the Walker Creek Valley heap leach facility.

Fort Knox operates as a zero-discharge facility, which is possible because the TSF and mill form a closed system for process water. Water that has been used at the carbon-in-pulp mill to process mined material is sent to the tailings facility as part of the tailings slurry, and water is pumped to the mill from the TSF decant pond (a structure that uses sedimentation to remove settleable matter and turbidity--aka cloudiness/haziness--from wastewater). In plain terms; none of this water is discharged to the environment.

According to the "Fort Knox Annual Activity Report for Reporting Year 2016" published in February 2017, the mine maintains dry conditions via a system of thirty-four dewatering wells (of which three are inactive) and four Fish Creek wells. For 2016 the average pumping rate from the dewatering system was 2,120 gallons per minute. The majority of that water, 70 percent, was pumped directly to tailing impoundment; 16 percent was pumped...

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