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

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C -2010 -089 New Horizon North Mine PARNos. I- IA -IB, 2- 2A -2B, 3 Page 37 of 60 b) Referring to Table 3 of the Arcadis report in Appendix 2:05.3(4) -1, the invert of the primary discharge pipe elevation for each sediment pond is located just above the maximum sediment storage elevation. The Division is concerned that the sediment ponds may have sediment discharge problems due to this small elevation difference. The Sedcad manual, on page 64, recommends a minimum 2 foot difference between the top of the sediment level and the primary pipe invert. If the release is slow, 0.5 feet to 1.0 feet can be used. Please consider increasing the height between the top of the sediment storage level and the invert of the primary discharge pipe, allowing for the requirement mentioned in question number 9 of this section that the pond capacity between the primary discharge pipe and the emergency spillway must contain the runoff volume from a 10 year -24 hour event. he a�edcad deem ,,v reflect uteri the lrr°itiral -v di,vclrcrt°(,,,,c }l)il-)e irn,erls swre raived in elewiti n. Item r°es &ed in Dec-2011 resImnse. 13. Figures 1 -4 of Appendix 2.05:3(3) -1 show that the sediment pond primary discharge pipes will extend beyond the permit boundary. Please revise these figures to show that the discharge pipes will not extend past the permit boundary. Figures 1 -4 were revised. Item reso aed inAl(�1-2011 res ons e� However, the Division has two additional requests. a) It does not appear that the primary and emergency discharge structures for the three sediment ponds are shown on Map 2.05.3(3)-l. Please add these structures to the map since they are part of the surface water hydrology. lUal) 2.051 3(3)-1 w a v renumbered eiv it crlr 2.0 .3(4) -C cited i- ei,i,ved crl)l)i- olii°i(tteli.,. ftc =nz rk oli `d ire Dee -201 r°esl)oiisem_ b) In Table 2 on page 4 of the Arcadis report in Appendix 2.05.3(4) -1, a primary discharge pipe length of 247 feet is given for sediment pond NHN -002. However, referring to Figure 3 of the same report, the pipe length appears to be about 60 feet. Please clarify. Table 2 w a.5 r ei =i,ve(l %ent r °esotwd in Dee-2011 r °es ons ; 14. The submitted pond designs are based only on the 10 year -24 hour precipitation event. Please provide pond designs that also use the 25 year -24 hour precipitation event to show compliance with Rule 4.05.9(7)(d) regarding the minimum elevation difference of one foot between the design event water level flowing through the emergency spillway and the top of the embankment. Itene r °evolred in Il ay- 0 l rAes ions . 15; Please confirm that the three riser pipe diameters are different than the barrel diameters for each of the three sediment ponds. Rene resoh7ed in, lacy -2011 r°esllonve; 16. Please revise the permit text and pond drawings to show that anti - piping barriers will be used on the primary discharge pipes that go through the pond embankment, as required under Rule 4.05.9(2). Item resoh,ed in A1ta1 011 r°esImnse> 17. The Sedcad designs contain two runs for the "Collection Ditch Design for Pond NHN -002 South ". The first design run appears to have used parameters from the previous run for "Collection Ditch Design for Pond NHN -002 North ". Please eliminate the incorrect Sedcad design run for NHN -002 South. The first design run was removed. Item r °esoh,ed in 11hij -2011 msponse.