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~~ ~~ <br />As discussed previously, the waste rock material shows very little <br />potential to cause a water quality concern. The same material which is <br />being used at the other four waste rock facilities will be placed at this <br />facility, along with the mill tailings. Waste rock will comprise about <br />75% of the material deposited. A humidity cell test was conducted on the <br />combined waste rock and mill tailings, to simulate anticipated site <br />conditions. The results of the humidity cell test indicate that this <br />combined material is neutral to slightly alkaline. In addition, no <br />sulfide reactivity occurred which would result in acid production. <br />Approximately half of the mined ore will be processed in the mill <br />facility. About 10 percent of the mill facility production will be run <br />through a carbon-in-leach circuit, which utilizes a sodium cyanide <br />solution. <br />After processing, this material will be rinsed until the free cyanide <br />content has been reduced to 0.2 parts per million (p pm ). Weekly <br />monitoring for cyanide content will occur at the point of deposition. <br />If, prior to deposition, the free cyanide content is greater• than 0.2 <br />ppm, the material will be returned to the mill for additioneil rinsing. <br />Material leaving the mill facility will be dewatered to a moisture <br />content of approximately 22%. The tailings and concentrated waste will <br />be fine grained and could present a potential dust hazard. It is thought <br />that the residual moisture content and combining this maternal with <br />coarse waste rock, will alleviate the dust problem. The Air Pollution <br />Control Division would regulate dust production from this site. <br />The South Waste Rock Disposal facility has been designed to ensure long <br />term structural stability in both static (normal) and pseuds>static <br />(earthquake loading) conditions. This engineering analysis has been <br />performed for both construction and reclaimed configurations. <br />At the mill facility, the pregnant solution, or gold-bearing sodium <br />cyanide solution, will be processed to extract the gold. Are emergency <br />pond, sized to contain 100,000 gallons of solution, is located at the <br />mill in case a solution carrying pipe ruptures. The mill itself is <br />designed so that knee-walls will be constructed (concrete or cinderblock) <br />to contain spills within the mill building. <br />Heap Leach Facility <br />Approximately half of the ore mined will be crushed to about 3/16 inch <br />and subjected to sodium cyanide solution for precious metals extraction <br />at the heap leach facility. The potential public health and safety <br />problems inherent in this type of heap leaching operation iinclude ground <br />and surface water quality degradation, structural stability of the heap, <br />human contact with the sodium cyanide solution bearing ponds, wind blown <br />solution and potential pond failure. <br />The heap leach facility is a 63 acre area, including the heap, barren <br />pond and pregnant pond. At its nearest point, the facility is located <br />about 4,600 feet south of the county road, 3,850 feet south of Rito Se co <br />and is approximately 680 feet higher in elevation than Rito Seco. The <br />heap and pond facilities are separated by a topographic divide from Rito <br />Seco. <br />-3- <br />