1992-04-07_REVISION - M1988112 (2)

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Battle Mountain Gold Permit M-88-112 Technical Revision No. TR-004 - Treatment of Excess Free Cyanide Stipulations Stipulation No. 1 The Division considers it urgent that Battle Mountain Gold (BMG) commence cyanide detoxification of the tailings slurry in its San Luis Project tailings impoundment. BMG has reported free cyanide levels of 170 ppm and weak acid dissociable cyanide levels of 210 ppm in the tailings pond as of January 30, 1992. In the interest of rapidly commencing remedial activities the Division believes that the application of "Cytox" chemicals is an acceptable methodology for Battle Mountain Gold to apply to decrease the observed cyanide levels. However, the Division is not, at this time, approving the proposed BMG tailings pond remedial plan target cyanide concentrations of: Less than 30 ppm free cyanide in the tailings ponds (available to waterfowl). Less than 40 ppm true WAD cyanide in the tailings ponds. Less than 40 ppm total WAD (true WAD plus Free cyanide) cyanide in the tailings ponds, under the following formula: True WAD + 1.3 Free CN 40 ppm The Division is concerned that these proposed active tailings pond permissible cyanide levels are approximately 9 times the required final reclaim@d tailings cyanide concentrations, contained in the approved BMG permit. The (division assumes that BMG is now proposing to differentiate between the cyanide concentration limitations to be applied to the active tailings pond and to the final reclaimed tailings. No such differentiation was included within the original approved permit application. The amended constructlon of the tailings area was approved by the Division relying upon BMG's representation that "The (treated slurry tailings) data shows total cyanide values of 4.4 ppm and weak acid dissociable cyanide values of 3.8 ppm." (BATTLE MOUNTAIN RESOURCES, SAN LUIS PROJECT, CMLRD ADEQUACY LETTER RESPONSES, Page 1 of 28) Further, the rationale relied upon by BMG in its approved permit characterizes the tailings as impermeable. It fs this impermeability that BMG suggests will preclude the mobilization of toxic tailings parameters. If the tailings achieve the projected low permeability, the Division is concerned that 8MG will be unable to affect detoxification of the tailings. Before the Division can approve the requested active tailings pond permissible cyanide levels, BMG will need to provide additional information in support of its proposal. BMG should submit additional information, including at a minimum: (1) Clarification of BMG's proposal, differentiating between the active tailings pond and reclaimed tailings phases.