1989-12-22_REVISION - M1988112 (3)

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Memo - Steve Renner -2- December 22, 1989 6. The results of the tailings geochemical test program have not be submitted as noted on page D-31. The results of the geochenical testing (Appendix F) should be provided. In addition, any modifications to the analytical testing or ore processing being modeled which would affect geochemical characteristics of the tailings between original permit approval and the amendment proposal should be discussed. This discussion should consider expected concentrations of cyanide, salts, metals, and acidity of both tailing solids and leachates. 7. The pond cross-section shown on Figure C-8 indicates a 6-inch PVC pipe will be used for the leak detection sump. The construction details provided in Appendix J state that an 8-inch pipe will be used. Please clarify. 8. What effect will the additional 80 cfs diverted to the nortYe by the east diversion ditch have on the drainageway receiving this flow? Are any channel improvements proposed for this north drainage tce insure stable conditions during the 100-year, 24-hour storm runoff event? 9. How was the SCS curve number of 70 derived? What soil and vegetation conditions were assumed in the derivation? 10. A velocity of 4.5 fps will result in the south diversion ditch under design conditions. A velocity of 3.1 fps will result in the east diversion ditch. Will any attempt be made to improve channel bottom conditions in these diversions and reduce possible sedimentation downstream? The Division recommends the diversions be seeded after construction for erosion control. 11. Section H-H' on Figure C-10 shows the 48-inch culvert downdrain to be buried. What will be the minimum and maximum fill depths placed on the pipe? Are anti-seep collars considered necessary for this culvert? 12. The text on page D-42 states that Figure D.6-2 shows the freeboard required to contain PMF inflows as a function of the elevation of the tailings. Figure D.6-2 is title "Borrow Map." Please provide the missing reference on PMF elevations. 13. The model assumes 50% of the tailings disposal area is under deposition at any point in time and thus 50% of the area will be evaporating. How many days will an area of tailings be dry and subject to wind erosion? What would be the maximum extent (acres) of area with moisture conditions conducive to wind erosion and resultant dust generation? What measures, aside from residual moisture, will be used for dust control? 14. The water balance calculations are referred to on pages D-73„ D-74, and 6-3 as being found in Appendix I. The apparent correct refer^ence is Appendix K. 15. The units for monthly shallow lake evaporation are referenced in Appendix K as "miles". The apparent correct reference would be inches.