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<br />bJe recommend that the waste rock out slopes be graded to an uninterrupted <br />3.5:1 slope, rather than the proposed overall 3:1 configuration. <br />Section E. 3.3 Heap Leach Facilities <br />Section E.3.3.1 Cyanide Neutralization <br />71. As the heap solution containment ponds are designed to contain operating <br />solutions from leaching one tenth of the entire heap, i.e. 70(1,000 tons <br />of the total 6,500,000 tons to be processed, or 6.3 acres plus storm <br />events, and 2 ft. of freeboard, please delineate the staging of the heap <br />rinsing for detoxification/reclamation. As one-tenth of the Heap will be <br />rinsed per each stage, and each rinsing stage is estimated to take 12 <br />months (1 year) it appears that a 10 year heap rinsing schedule is <br />requi red. <br />72. Hydrogen peroxide is recommended as a cyanide detoxicant due t:o its <br />oxidation potential and minimal impact upon the environment; the end <br />products of hydrogen peroxide decomposition are oxygen and wager. Use of <br />hypochlorite is not recommended as it is toxic to fish, requires a high <br />pH (approximately 11) thus requiring additional pH neutralization. <br />Sulfuric acid is not recommended for use, as it will solubili::e heavy <br />metals in the heap and will also require pH neutralization prior to final <br />detoxification of the heap effluent. Please commit to use of hydrogen <br />peroxide as the cyanide detoxicant to be used at this site. <br />73. Recirculation of pond solutions through the heap for cyanide oxidation <br />and pond volume depletion is not recommended, as salt accumulz.tion has <br />been observed in other processed heaps, believed to be caused by <br />continued evaporation of solution and resulting precipitation of the <br />salt(s) component. Please consider spraying pond solutions over the <br />ponds, or onto an evaporation field, such that the salts may tie collected <br />and disposed of. Fresh water, or an oxidizing solution made try using <br />fresh water, should be added to the system to rinse the heap of salts, <br />metals and cyanide. Please discuss. <br />74. The cycle of oxidizing the heap water followed by spraying to rinse the <br />leach pile should continue until the effluent draining from the leach <br />pile reaches a pH between 6.0 and 9.0 and free cyanide concentration of <br />0.2 ppm in consecutive sampling over a three to four week period. The <br />0.2 free cyanide concentration is recommended as this is the (:olorado <br />ground water standard. We feel that the alluvial/colluvi al cover <br />tributary to Culebra Creek would be the likely recipient of he+ap <br />effluent. Thus, the ground water standard would appear to be most <br />applicable. <br />75. Cyanide neutralization results of fresh water column leach tests were not <br />presented in Appendix I, as indicated in the Reclamation Plan (page <br />'c-12). Column leach tests conducted for reclamation/detoxific:ation <br />purposes should be analyzed for pH, electroconductivity, total and free <br />cyanide, and metals. Details of cyanide leaching process simulation and <br />detoxification methods, duration, and effluent characteristic: should be <br />presented to the Division for evaluation of reclamation feasii~ility and <br />reclamation cost calculations. <br />-1 3- <br />