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

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C-2010-089 PARNos. 1- 1A -1B, 2-2A-2B,, 3 New Horizon North Mine Page 33 of 60 U.S. Department of Agriculture, Soil Conservation Service Technical Release No. 60 "Earth Dams and Reservoirs", October, 1985. If any of the sediment ponds can qualify as having a Class B or Class C dam, please revise the permit application to demonstrate compliance with those Rules which apply to Class B or Class C dams. Alywnchx 2.05.3(4)-1 irtryi-evisedto ,vhow flicit till three j)onc1,v hcn7e ('Icts,,v A coin emhcnikmeilt art resolved in Dee-2011 resImnse. c) As required under Rule 4.05.9(8)(a) or (b), please revise the permit application after construction of the three sediment ponds to include the appropriate geotechnical demonstrations that the applicable factor of safety required under Rule 4.05.9(8)(a) or (b) had been achieved for each sediment pond embankment. APPenclix 2.r ,3 (41 -1 itws revised tol-n-ovklefin- 10-jbof-iricle embankment tol)s oil 4,111 Item resolved in Dec-2011 resi-jonse. e) The proposed sediment pond embankment heights, measured from the pond bottom to the emergency spillway bottom, are listed in Table 3 and shown on the cross sections, in Appendix 2.05,3(4)-1. The proposed embankment heights for ponds NHN-001 and NHN-003 are less than 10 feet but for pond NHN-002, the proposed embankment height is 11.5 feet. Rule 4.05.9(6) requires a foundation investigation for those pond embankments that exceed 10 feet in height. Please provide the foundation investigation required under Rule 4.05.9(6) or lower the height of the pond embankment for NHN- 002 to 10 feet or less. ,4p])eiit.li,y2.05.3(4)-lio,,a i,eiiseclaei-eqite,vtc?cI Ite lit resoli>edinl)ee-20-llrtslyonse. f) The certified pond cross sections in the Arcadis report in Appendix 2.05.3(4)-1 show that the pond embankment inslopes and outslopes for sediment ponds NHN-002 and NHN-003 are both 2H.1 V However, Rule 4.05.9(7)(e) requires that the combination of the inslope and outslope of a pond embankment not be steeper than 5H: IV unless a demonstration is provided to show that the steeper slopes will be stable. Please provide such a demonstration for ponds NHN-002 and NHN-003 or revise the ponds' embankment slopes accordingly. 177e 1�ond cles gn,5 in Aly)enclix 2, 05� 3(4)-1 were revi,5e(l alyn-oln-hitely. Itent resole ed i n Dec-20,11 resj)onse.