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LJ <br />4. Free cyanide in dte form of cymtide gas is, of course, a lmzard to breathing, <br />particularly in closed spaces. According to MSHA personnel, ir+ some settings, <br />wind may cause /sigh concentratioru of cyanide gns to be iruroduced ro persons <br />or animals. However, in many outdoor servings, the gas Wray he dispersed to a <br />level that would be considered non-toxic. <br />Free cyanide in solution or arty of the weak acid dissociable cya-tide compounds <br />may also be hazardous if consumed. Animals, in particular, need to be protected <br />' from the hazards of drinking water containing HCN. <br />Battle Mountain ltas raised tl+e issue of the difJSculry of analyzing for free cyanide, <br />' and although we have yet to receive real proof of the acduracy of these <br />statements, the Division is inclined to believe that the statements bear some <br />consideration. <br />' Battle Mountain Gold (and the Division) should consider the utility and <br />practicality of analyzing for free cyanide. WAD cyanide ar+alysea should include <br />' both the free and weak acid dissocinble components of cyanide, qnd Burs a single <br />analysis may be more reasonable for bot)t analytical and regtrldtory purposes. <br />RESPONSE: BMR submitted a report to CMLRD on the evaluation of the cyanide chemistry <br />in the tailing samples from the San Luis project in May 1992 (A$CI report, May <br />1992). Data in the report indicate that free cyanide analyses (performed <br />' independently on four duplicate samples from the San Luis tailings facility) by <br />two different EPA-certified laboratories, were erroneous and could not be <br />representative of the free cyanide levels in the tailings system. Tl+e report, and <br />a subsequent memorandum detailing calculation methods (ASCI/CMLRD, June <br />1, 1992) showed the maximum theoretical free cyanide levelh that could be <br />' derived from the analyses. <br />The report and memorandum indicate that free cyanide analyses are not suitable <br />' for evaluating chemistry of the San Luis tailings system and than an appropriate <br />and specified WAD cyanide, which includes both free and WAD cyanide <br />components in this analysis, should be substituted along with apalysis of metal <br />' species present in the San Luis tailings solutions, which are known to form WAD <br />cyanide complexes with cyanide. Appropriate and specified methods would be <br />ASTM method "C" or APHA/AWWA Standard Methods, l7th $ciition, Method <br />' 4500-C only, modified to account for the nature of the tailings chemical matrix <br />and presence of sulfide, nitrate and thiocyanate. <br />' It should be noted that there are no EPA-approved methods for free cyanide or <br />WAD cyanide. Only total cyanide and cyanide amenable to dhlorination, the <br />' -3- <br /> <br /> <br />