1995-08-11_REVISION - M1977493 (9)

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. Details of this treatment system have been discussed earlier and are found in Appendices E and H. As with the Robinson and Ten Mile impoundments, the Mayflower impoundment is both a potential source of contamination and a critical EPF. As a potential source, the Mayflower impoundment contains tailing material which, like all Climax tailing, is considered potentially acid producing. It should be noted, however, that the long-term use of this impoundment strictly as a water treatment facility has served to add significant amounts of lime to the impoundment. Another source of potential contamination is seepage emanating from the toe of No. 5 Dam. Analyses indicate that seep water is slightly acidic with elevated sulfates and metals (Appendix G). As an EPF, the Mayflower tailing impoundment including the No. 5 Dam is crucial. The impoundment acts as the water treatment system for all Climax process water, mine water, and seepage waters. It also is the third and last line of defense for containment of any potentially contaminated materials or designated chemicals which may be released up-gradient of the impoundment. In addition, the Mayflower impoundment contains, mixes and treats acidic waters from several historic mines and smelter sites (Kimberly-Wilfley Group, Colonel Sellers and others) as well as non-point run-off waters which contact mine wastes within a large portion of the historic Ten Mile Mining District. Mayflower Seepwater Collection and Return System: The seepwater collection and return system below the Mayflower tailing impoundment is one of the most important EPFs at the Climax Mine. Although it has been discussed previously in some detail as part of the Climax water treatment and discharge system EPF, it is discussed again here as a specific EPF. This system serves both to collect and contain all seepage and to lower the phreatic line in the tailing impoundment and dam. Briefly, a system of trenched and piped subdrains, backfilled with clean gravel, is present under the impoundment and dam. These collection drains are routed to two concrete ponds which collect all seep water. Collected seepage is pumped back by vertical turbine pumps to the water pool on the tailing impoundment where it mixes with and is diluted by treated water. This pump station is located at the clear water pond below the tailing impoundment. Its operation is crucial in keeping seep water from entering Ten Mile Creek except during periods of snow-melt by-pass as authorized by CPDS Permit conditions. Should this pumping system fail, water within the Mayflower pool can be contained and controlled by blocking the riser in the decant system until the system is serviced and brought back into operation. Seepage can be contained within the 5 million gallon clear water pond system. Treated Water' H Control Station: The final EPF prior to discharge of treated water from the Climax system is the pH control station. This EPF is located at the Mayflower pump station. 27