2001-06-08_REPORT - M1977378 (2)

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Annual Update Sunnyside Mine Bulkheads Page 2 • Reference point (stream) monitoring Included in the Appendix (B -17) is a graph of dissolved zinc concentrations at the Consent Decree reference point (A -72) from January 1989 through May 2001. This period includes the reference data set (January 1989 through June 1996) and the Consent Decree monitoring data (June 1996 through May 2001). The gaps in the reference data set are apparent in this graph. Included in the Appendix (B -18) is the Consent Decree graph that compares dissolved zinc at the reference point (adjusted for flow classes) to pre - project quality. This graph is the basis for determining if water quality at the reference point has changed. 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.. Included in the Appendix (B -19) is a graph of dissolved zinc in the mainstem streams (Animas, Mineral and Cement) combined with the resultant levels of dissolved zinc at the reference point A -72. While the data is still limited, it covers some of the gaps in the A -72 data and shows the relative effect of the mainstem quality on water quality at A -72. What has become apparent is that the reference data set does not reflect conditions at A -72. With treatment of Cement Creek and implementation of the remediation projects, low flow dissolved zinc levels have not reached the level in the reference data set that represents pre- Consent Decree quality. With the time period that has elapsed, this could not happen if the data set reflects mean quality. • 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 believed that the implementation of the work plans for these projects had 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. By the end of the 1999 report year, all three projects had been completed. It is too early after completion to determine if their implementation has improved water quality.