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<br />70. Please illustrate final contours of the Waste rock piles A,B, and C on <br />Figure F-1, and indicate how the contours will correlate to the adjacent <br />natural topography. <br />Section E.3.3 Heap Leach Facilities <br />Section E.3.3.1 Cyanide Neutralization <br />71. As the heap solution contaimm~et ponds are designed to contain operating <br />solutuions from leaching one tenth of the entire heap, i.e. 700,000 tons of <br />the total 6,500,000 tons to be processed, or 6.3 acres plus storm events, and <br />2 ft. of freeboard, please delineate the staging of the heap rinsing for <br />detoxification/reclamation. As one-tenth of the heap will be able to be <br />rinsed per each stage, and each rinsing stage is estimated to take 12 months <br />(1 year) it appears that a 10 year heap rinsing schedule is required. <br />NOTE: STEVE: you will need to multiply the calculated heap neurtalization <br />costs by 10 to accurately reflect the cost of neutralizing the entire 6.5 <br />million ton heap. <br />72. Hydrogen peroxide is recommended as a cyanide detoxicant due to its <br />oxidation potential and minimal impact upon the environment; the end products <br />of hydrogen peroxide decomposition are oxygen and water. Use of Fypochlorite <br />is not recommended as it is toxic to fish, requires a high pH (approximately <br />11) to prevent the formation of cyanogen chloride, thereby requiring <br />additional pH neutralization. Sulfuric acid is not recommended for use, as it <br />will solubilize heavy metals in the heap and will also require pH <br />neutralization prior to final detoxification of the heap effluent. Please <br />commit to use of Hydrogen peroxide as a cyanide detoxicant. <br />NOTE: CAM review sulfuric acid and chlorination as cyanide oxidants. <br />73. Recirculation of pond solutions through the heap for cyanide oxidation <br />and pond volume depletion is not recommended, as salt accumulation has been <br />observed in other processed heaps, beleived to be caused by continued <br />evaporation of solution and resulting precipitation of the salt(s) component. <br />Pond solutions may be sprayed above the ponds, or other evaporation field, <br />such that the remaining salts may be collected. Fresh water, or an oxidizing <br />solution created using fresh water, should then be added to the system to <br />rinse the heap of salts, metals and cyanide. Please discuss. <br />74. Due to the proximity of the heap to the Rito Seco, the cycle of oxidizing <br />the water followed by spraying to rinse the leach pile should continue until <br />the effluent draining from the leach pile reaches a pH between 6.0 and 9.0 and <br />free cyanide concentration of less than ,OB~ppm in consecutive sampling oY,er <br />a three to four week period, t us, ac eiving a receiving stxea+a <br />standardsfor cyanide. ~~..tw,-~ <br />