1999-06-10_REPORT - M1977378 (2)

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1999 Annual Update Sunnyside Mine Bulkheads Page 2 • Reference point (stream) monitoring Included in the Appendix (B-16) is a graph that compares dissolved zinc at the reference point in the Consent Decree (A-72) to pre-project quality. It is difficult to make any definitive statements concerning the levels of dissolved zinc observed at the reference point due to the complex interplay of hydrology, geology, etc. but it appears that remediation projects have improved water quality during summer months and no impact that could be attributed to the bulkhead seals has been observed. • Remediation Projects SGC completed the Consent Decree A List of remediation projects within the two- year time period allowed for in the agreement. This was accomplished by October 1997. SGC added three projects to the Consent Decree B List (optional project list) during the 1998-report year. These three projects are water diversion projects in the vicinity of the Mayflower Mill complex and are named: Mayflower Mill — Upland Hydrological Control project; Tailings Pond No 4 Upland Groundwater Diversion Project, and Tailings Pond No 4 Surface Drainage Modification Project. SGC believes the implementation of the work plans for these projects has more potential to benefit stream quality than the projects on the original B List. SGC started implementation of the work plan for the Mayflower Facility — Upland Hydrological Control project during the 1998-report year and one drainage diversion was completed and operational by the end of the report year. • Cement Creek Treatment Diversion and treatment of Cement Creek was active throughout the 1998-report year The entire stream was diverted and treated during low flow conditions (August — April) and throughout the remaining months, the quantity diverted and treated was regulated at the approximate capacity of the water treatment plant. This treatment is a temporary measure to offset or balance any short-term impacts that may have resulted from implementation of the A List remediation projects. Its purpose, based on stream monitoring, has expired and will be discontinued during the 1999 report year Implementation of the B List projects is not expected to have any short-term negative impacts on stream water quality since they are exclusively water diversion projects and do not disturb mine waste material. • Reporting SGC is current on all Consent Decree monitoring and reporting requirements_