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• III IIIIIIIIIIIIIIII • DATE: April 21, 1992 TO: Larry Oehler FROM: Allen Sorenson ~/ `~ RE: Input From Other Agencies Regarding Cyanide Levels in Mill Ef~luent SOUTH CAROLINA I spoke with Craig Kennedy of South Carolina Land Resources and t~ Birgit McDade the Industrial and Agricultural waste Division of the Depa tment of Health and Environmental Control. The Ridgeway Mine in S. Caroli a is a Vat Leach precious metal operation with a lined tailings impoundment, similar to the San Louie Project, The ridgeway tailings impoundment utilize a mat drain, much like the San Louie sub-drain, to limit the amount of head ap lied to the liner. One difference between the two mines, ie that the Ridgewa Project hoe a French Drain under the tailings impoundment to alleviate any pr enure from ground water that may develop under the impoundment. This French Drain also serves as a leak detection system and is monitored once per week. South Carolina does not require the mine operator to maintain any specific maximum levels of cyanide in the tailings pound. The levels in t e pond have been between 25 and 50ppm free CY through-out the life of the min however, the operator anticipates an increase in CY levels as they deplete the oxidized ore and move into sulfide ore. Bird mortality at the pond since ovember of 1988 at this eight stands at 335 birds, mostly shore birds, but m et of these deaths have been attributed to causes other than cyanide, althoug there is no hard data on cause of death. The tailings pond is monitored once per day at the return water i take barge, and once per day at the mill discharge point. The numbers from m 11 discharge monitoring are from 40 to 80ppm free CY. The French Drain under he impoundment is monitored once per week. In 3.5 years of operatio there has been no cyanide detected from the French Drain. Poet reclamation monitoring of tailing impoundment discharge will,be required by the Dept. of Health and Environmental Control. The discharge ~i12 be required to meet drinking water standard for total CY. Ferro-Sulfate was used at this site for approximately one year ofIoperation to detoxify the tailings. The operator was experiencing difficulty with tail deposition of the treated material, and discontinued use of the t eatment. At present the tails are deposited un-treated.