MINING NEWS: Coeur Alaska lowers turbidity levels at Kensington mine near Juneau

Coeur Alaska has provided detailed information to the Alaska Department of Environmental Conservation on measures taken to control erosion at the Kensington mine near Juneau. The company was cited by DEC Nov. 10 for violating the turbidity standard due to sediment discharges into Johnson Creek from construction activities at the mill site, upper bridge and topsoil stockpile areas. The problems were caused by heavy rainfall.

Construction of the mine is also under scrutiny from the Corps of Engineers, which suspended its permit for the discharge of fill material into U.S. waters Nov. 22. Environmental groups have challenged the original issuance of this permit in a lawsuit that objects to Coeur’s plan to dump tailings into Lower Slate Lake. If the permit is still suspended next summer, it will hinder construction of the tailings dam. At present the suspension only affects the upgrading of a small portion of the mine’s access road, according to Luke Russell, Coeur d’Alene’s vice president for environmental services.

DEC re-inspected the construction site Dec. 2, collecting turbidity samples at three locations. State water quality standards require that turbidity increase no more than 5 NTU (Nephelometric Turbidity Units) above natural conditions. Readings taken downstream of all construction activity measured between 1.5 and 3.5 NTU above natural conditions.

Inspectors noted that a number of improvements had been made to the storm water systems, including diversion ditches and pipes for clean water, the construction of small ponds adjacent to the road to collect and treat muddy water, and the addition of more and larger ponds at the topsoil stockpile area. “We continue to implement our storm water management plan,” Russell told Mining News. “The rain in the last couple of months has been significantly above average. We had a plan in place, but we didn’t anticipate as heavy rain as we got.”

Since receiving the citation, Coeur Alaska has hired Washington-based GeoEngineers to provide technical guidance and design information to resolve the sediment discharge problem, and also Oregon-based Zeroday Enterprises to address the use of flocculants on site.

—Sarah Hurst