1996-02-06_REVISION - M1977493 (11)

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10(d) Mayflower decant system The Mayflower decant sidehill risers consists of two 30 -inch diameter pipes that decant water from the surface of the tailing pond into twin 42 -inch diameter pipes to the treatment discharge point at the base of 5 -Dam. The risers used to control water flow through the placement of bricks over the 30 -inch diameter pipe inlets. Historically, the decant system was used to convey water to the clearwater pond where pumps were in place to return water to the Climax milling and process facilities some 5 miles away. The water may still be directed into the clearwater pond at an energy dissipater structure and valving system at the clearwater intake. Under normal circumstances, water in the decant line is directed by pipe to Tenmile Creek around the east side of the Clearwater Pond where the water is treated to the target pH with sulfuric acid. The system is designed such that a problem in the acid delivery system controls alarms to affect valve closure and routing of treated water from the Tenmile pipe to the Clearwater Pond. The alarms also dial radio signals to security staff on site. Seepage from No. 5 dam is captured through a system of trenched and piped subdrains, backfilled with gravel, constructed beneath the toe of the dam and upstream for a distance of 1500 feet. Seepage in the impoundment infiltrates directly into either of the two concrete seep water settling ponds located at the toe of the dam just above the clearwater pond. These collection ponds are designed to allow all seepage to be collected in one pond while the other is being serviced. The collected seep water is allowed to flow into the clearwater pond where pumps return the water (flows averaging 600 gpm) to the north end of Mayflower Pond for mixing and treatment with other waters. The pumping of Mayflower seep water is discontinued during the snow melt bypass period. At this time, treated water from Mayflower Tailing Pond flowing through the decant lines at 6 and 7 risers is partially valved into the clearwater pond. Seep water then commingles with treated water. and is discharged to Tenmile Creek. The system is best understood by visitation of the treatment works. I will submit a diagram of the above described system upon request.