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• Annual Update <br /> Sunnyside Mine Bulkheads <br /> Page 3 <br /> • Cement Creek Treatment <br /> Diversion and treatment of Cement Creek was active through part of the 1999-report <br /> year. The entire stream was diverted and treated during low flow conditions (March <br /> 1999 — April 1999) and until June 1, 1999, the quantity diverted and treated was <br /> regulated at the approximate capacity of the water treatment plant. On June 1, 1999 <br /> Sunnyside discontinued treatment until November 22, 1999 when treatment was <br /> restarted. From November 22, 1999 through March 31, 2000 the entire flow was <br /> diverted and treated. <br /> This treatment is a temporary measure to offset or balance any short-term impacts that <br /> may have resulted from implementation of the A List remediation projects or from <br /> effects of the mine pool. This purpose, based on stream monitoring, had expired and <br /> was discontinued for part of the 1999 report year. When zinc levels in Cement Creek <br /> above the American Tunnel treatment plant (CC-1) appeared to be elevated from past <br /> monitoring results and during the fall seep, spring and flowing adit monitoring session <br /> it was discovered that monitoring sites were flowing at above normal quantities (most <br /> notably the Mogul Level #1 adit (M-1)), treatment was restarted. This was a temporary <br /> measure taken to minimize any impacts on A-72 from the increased flows. Potential <br /> causes of the increased flows could be; above normal levels of precipitation; natural <br /> flow regimes being restored as the mine pool rises and groundwater flows travel <br /> around the Sunnyside Mine workings instead of draining through the American and <br /> Terry Tunnels; or a fracture connection exists between the Mogul workings and the <br /> Sunnyside Mine workings. Because of access conditions additional information to <br /> help determine the reason for the increased flows could not be gathered during the <br /> 1999 report year. Consequently, Sunnyside temporarily restarted diversion and <br /> treatment of Cement Creek. <br /> • Reporting <br /> SGC is current on all Consent Decree monitoring and reporting requirements. <br /> Mine Pool: <br /> The American Tunnel bulkhead valve was closed in September 1996 and the Terry <br /> Tunnel bulkhead valve was closed in July 1996. Since September 1996 the mine pool <br /> has been allowed to rise towards physical equilibrium. As of the end of the report year <br /> (March 30, 2000), the mine pool had reached approximately 11,624 feet MSL. <br />