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<br />18. The concentrates from the carbon-in-leach circuit should be rinsed to <br />reduce the level of free cyanide to~0.2 ppm. This concentration is the <br />Colorado ground water receiving standard for free cyanide and appears to <br />be most appropriate for the San Luis Project. It is our opinion that the <br />ground water standard is most appropriate because the potential for <br />post-reclamation effluent to flow to Culebra Creek is minimal. <br />Infiltration into the colluvial/alluvial materials would probably be the <br />most likely flow path for any effluent. ~ c: <br />r ~ 1.,ao . t C ~~.i~'s- <br />~~. <br />Section D.6.2.2 Geochemical Characteristics <br />19. The analyses presented in Appendix F indicates that the material was <br />ground to -10 mesh and thoroughly blended. The textural anal~~ses of the <br />tailing material presented in Appendix D indicated that appro>:imately 81~ <br />of the whole tailing were smaller than 200 mesh. The tailing analyses <br />conducted to determine resulting water quality may therefore not be <br />representative of the final tailing due to the variation in p«rticle <br />size. Please address. <br />20. Was the tailing material processed through the flotation and or the <br />carbon-in-leach circuit prior to analysis? If so, please describe the <br />processing methods, chemicals utilized, duration and rinsing methods. If <br />not, the simulation should be made, with actual expected ore ~:ize <br />represented, to predict the disposed tailing effluent water quality. <br />21. Please discuss what effect the dilute sulfuric acid used in tfie batch <br />tests have on the sulfate concentrations reported in the tail~ngs <br />analysis. Can these sulfate data be considered representative? <br />22. Results for cyanide analysis indicate free cyanide to be greater than <br />total cyanide for Tailings Sample Number 1. Please explain or correct. <br />23. On Page D-31, the statement is made that the tests showed tha- the <br />tailings exhibit low potential for acid production with almos*. no acid <br />neutralization potential. The lab reports in Appendix F indicate a <br />significant potential for acid production and excess of acid-~~roducing <br />potential over neutralization potential. The preliminary results from <br />the humidity-cell test indicate acid production to be evident, Please <br />provide the final humidity cell test data, and please describr~ mitigation <br />measures proposed to limit the possible adverse impacts of ac~dic <br />leachate from the tailings. <br />24. As proposed, the tailings will be disposed behind a berm constructed in <br />the South Waste Rock Disposal Facility. A method of combinin~I waste rock <br />and tailing by layering the two is described in the mine plan. Was <br />consideration given to modeling the effluent from the combined waste <br />rock/tailings in a separate leachability test? We would suggest that a <br />humidity cell test be run on this combined material. If this is not <br />done, an explanation as to how the geochemical characterizati~~n data can <br />be interpreted to project effluent quality from this combined disposal <br />area with a reasonable degree of certainty must be provided. <br />-4- <br />