1989-12-18_REVISION - M1988112 (8)

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18. The pond cross-section shown on Figure C-8 will be used for the leak detection sump. provided in Appendix J state that an 8-inch clarify. indicates a 6-inch PVC pipe The construction details pipe will be used. Please 19. What effect will the additional 80 cfs diverted to the north by the east diversion ditch have on the drainageway receiving this flow? Are any channel improvements proposed for this north drainage to insure stable conditions during the 100-year, 24-hour storm runoff event? 20. How was the SCS curve number of 70 derived? What soil and vegetation conditions were assumed in the derivation? 21. A velocity of 4.5 fps will result in the south diversion dit<:h 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. 22. Section H-H' on Figure C-10 shows the 48-inch culvert doom drain to be buried. What will be the minimum and maximum fill depths placed on the pipe? Are anti-seep collars considered necessary for this advert? 23. 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 elevaticon of the tailings. Figure D.6-2 is title "Borrow tdap." Please provide the missing reference on PMF elevations. 24. Please commit to reporting of hydrologic data to the Division as required in the approved permit. 25. Pseudostatic factors of safety of less than 1.25 are unacceptable for embankment slopes. Please provide further design specificatiions which would provide for a minimum factor of safety of 1.25 under pseudostatic conditions. The minimum acceptable factor of safety of 1.25 for embankment slopes is recommended because this would help ensure a more stable condition during the life of the facility. The U.S. Etureau of Mines and Canmet guidelines for tailings disposal facility designs both indicate that 1.25 is a prudent design criteria for pseudostatic conditions. 26. Please provide a sliding wedge stability analysis for the main embankment at Phase 2, Raise 1 and Phase 2, Raise 2. 27. Please revise the stability analysis summary in Figure D.6-12 to include the VLDPE instead of the material type 1 as foundation material. 28. Please provide a stability analysis of Waste Rock Disposal Area D, similar to those provided for the other waste rock facilitie<.~ in the approved application. -3-