2012-01-13_APPLICATION CORRESPONDENCE - C2010089 (2)

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C -2010 -089 New Horizon North Mine PARNos. I- IA-1B, 2- 2A -2B, 3 Page 36 of 60 % s ` "z ), r 10. The three sediment ponds each use a gated drop inlet primary discharge structure However, the Sedcad program cannot model pond volumes, discharges and sedimentology for a gated pond to show compliance with Rule 4.05.6 and 4.05.9. The Sedcad designs that were submitted use an un- gated, self- dewatering drop inlet structure. As a consequence, the designs do not match the proposed construction and the designs may be confusing. For example, the Sedcad designs show that runoff from the 10 year -24 hour precipitation event will flow out ofthe emergency spillway, which is not allowed under Rule 4.059(2)(b). Please provide sediment pond designs that demonstrate that the gated sediment ponds will comply with Rules 4.05.6 and 4.05.9. The demonstration can rely on pond water and sediment storage volumes without the pond discharging and without sedimentology demonstrations. Its nt reso ed in Maj -2011 resj)onseB 11. In the first full paragraph on the fourth page of Appendix 2.05.3(3) -1, the first sentence states that an emergency spillway with a height that is one foot below the top of the pond embankment can be used. However, Rule 4.05.9(7)(d) requires that there be at least one foot difference in elevation between the 25 year -24 hour precipitation event water level flowing through the emergency spillway and the top of the embankment. For the safe of clarity, please revise this statement on the fourth page to reflect the rule requirement. Itein resoh,e in t tty -2011 r ]-yon 12: On the fourth page of Appendix 2.05.3(3) -1; it is recommended that modifications to sediment ponds NHN -001 and NHN -002 be used in order to avoid short circuiting. Please revise the text to describe which modifications will be used, especially for pond NHN -002. Also for pond NHN -002, please explain per Rule 4.05.6(7) why the spillway pipe could not be located more towards the middle of the pond since it is now positioned very close to the outlet of ditch NHN -002 North. In the renamed Appendix 2.05.3(4) -1, WFC stated that the gated primary discharge pond inlets would minimize short circuiting: WFC further explained that location constraints prohibited redesigning the ponds. Item r s l rl in 1(cy = -20] l r :vll nse. The Division, however, has additional questions concerning sediment in the ponds. a) In the last sentence of the 3rd complete paragraph on page 4 of the Arcadis report in Appendix 2.05.3(4) -1, the sediment storage elevations listed for the three sediment ponds don't match the sediment storage elevations presented in Table 3 on page 5. Please revise. t he i 3 ,