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1111111111111111111 <br /> 999 <br /> AL <br /> SVNNYSIDE GOLD CORPORATION <br /> AN ECISO DAY COMPANY <br /> P.O. Box 177 • Silverton, CO 81433 <br /> Phone (970) 387-5533 • Fax (970) 387-5310 <br /> Ms. Sarah Johnson May 11, 1999 <br /> CDPHE-Assessment Unit MAY 14 1999 <br /> Water Quality Control Division <br /> 4300 Cherry Creek Drive South ;,vision of Minerals&Geology <br /> Mail Code: WQCD-Au-B2 <br /> Denver, CO. 80246-1530 <br /> RE: Notification of Intention to Decrease Cement Creek Water Treatment <br /> Dear Ms. Johnson: <br /> This letter is submitted to provide notice of Sunnyside Gold Corporation's (SGC's) intent to <br /> decrease treatment of Cement Creek as provided for in section V.9.c. of the Consent Decree. <br /> The last of the mitigation projects on the Consent Decree A list was completed in October 1997. <br /> Treatment of Cement Creek,to the limits specified in the Consent Decree, has been continuous <br /> from August 1996 and will continue until the effective date for this treatment reduction <br /> notification, June 1, 1999. On June 1, 1999, SGC plans to suspend all diversion and treatment of <br /> Cement Creek surface flows. This suspension of treatment will continue through September <br /> 1999. In September, SGC will evaluate whether to resume treatment in October. <br /> Treatment of Cement Creek served the purpose of mitigating short term impacts, if any, to water <br /> quality resulting from remediation project construction. SGC's determination that Cement Creek <br /> water treatment is not needed to mitigate impacts at the reference point from these sources is <br /> based on the following analysis. <br /> Construction and post-construction activity on the A list projects would have the largest potential <br /> impact on water quality during periods of stormwater runoff and high groundwater. This occurs <br /> during the summer months. Reference point monitoring results for dissolved zinc are compared <br /> monthly to mean concentrations from a pre-activity data set for the Consent Decree. The <br /> comparison is reported as a normalized residual from the mean of the data set(graph attached). <br /> The June-September periods appear to have improved from 1996 to 1998 with no indication that <br /> water quality is being negatively affected by A list projects or bulkheading of the Sunnyside <br /> Mine. By using mass balance calculations,the normalized residual for June 1998 — September <br /> 1998 was recalculated using the overly conservative assumption that all dissolved zinc removed <br />