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C , J Memo to Steve Renner - 2 - l~ January 4, 1989 On Page D-31, the statement is made that the tests showed low potential for acid production with almost no acid neutralization potential. The lab reports in Appendix F indicate a significant potential for acid production and excess of acid-producing potential over neutralization potential. The preliminary results from the humidity-cell test indicate acid production to be evident. What mitigation measures are proposed to limit the possible adverse impacts of acidic leachate from the tailings? 6. As proposed, the tailings will be disposed of behind a berm constructed in the South Waste Rock Disposal Facility. A method of combining waste rock and tailing by layering the two is described in the mine plan. Was consideration given to modeling the effluent from the camb~ned waste rock/tailings in a separate leachability test? Could a humidity-cell test be run on this material as well? If not, how can the geochemical characterization data be interpreted to project effluent quality from this combined disposal area? D.7 - Heap Leach Facilities Description 7. Solutions are described as to be pumped to and from the mill in pressure-tested welded pipe. Although the pipelines are not shown, a facility pipeline corridor is noted on Exhibit C-10. a. As this area can potentially come into contact with concentrated cyanide solution, the pipeline corrider should be lined with HDPE. A design should be submitted including the details at: the haul road crossing and mill building entrance location. b. Back-pressure valves are suggested for inclusion as b. safety feature in the solution pipelines. c. Will the barren solution pipeline run from the mill t.o the barren pond or will the pipeline run from the mill directly to the top of the heap at any point in time? D.7.4.1 -Pad Area 8. The pad solution collection trench shown on Exhibit C-8 does not appear to be the same as the series of collection trenches constructed through Stages ]-6 as shown on the figures in this section. Please clarify. 9. As the pad will be built in stages, as-built certification:: should be submitted at the completion of each stage. In particular, test results on liner seaming and collection channel connections between stages should be presented. What reporting commitments will be made in this regard?