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Slope Failure at Buckhorn Mine

On May 12, 2011, a large slope failure below the Buckhorn Mine sent a wall of mud and large trees flowing down Gold Bowl Creek. Just below the mine facilities and one of the treated mine water discharge areas, the side hill of Gold Bowl Creek gave way, sending mud cascading thousands of feet, uprooting large trees and scouring the creek drainage of all vegetation 12-15 feet high.

 “Given the pattern of instability in the Gold Bowl drainage, this incident should not come as a complete surprise,” stated David Kliegman, Director of OHA.

According to Geology, by Chernicoff and Whitney, third edition (2002), blasting that accompanies mining, quarrying, and road construction can trigger mass movement. Vibration from these activities can force apart grains of loose sediment, eliminating the friction between them. Sometimes human activity, such as mining, may combine with natural factors to increase the chance of mass movement.

Melting of this year’s large snowpack and spring rains are filling the Buckhorn Mine with water faster than it can be pumped out and treated.

This spring, an estimated 400 gallons per minute (gpm) were entering the mine. At full capacity the new and improved reverse osmosis treatment system can process 285 gpm.

Gold Bowl Creek drainage has experienced slope failure before, but nothing close to this level of devastation. Geology text describes mass movements as the “most easily predicted of all geological hazards.” Early warning can be achieved by simply searching for evidence of past mass-movement events.

 
 The first incident inthe Gold Bowl drainage happened before the mine went into production. In June 2007, Kinross was issued a Notice of Violation (NOV, No. 4504) when mud overtopped a silt fence in the headwaters of Gold Bowl Creek.  In October 2008, the discharge of treated mine water caused slope instability, which eroded into Gold Bowl Creek. After many large trees fell down on the same slope below the mine facilities, in July 2009 Ecology issued an administrative order (No. 6965) requiring an assessment of the slope stability below the Gold Bowl discharge point (002). Ecology accepted the Kinross Slope Stability Assessment and plan in November 2009. On June 15, 2010, Ecology issued NOV 7858 for a large slope failure below the infiltration gallery in the headwaters of Nicholson Creek, which is downstream from Gold Bowl Creek.

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