2016-10-28_PERMIT FILE - C2010089A ‎(22)‎

• Permit No: C2010089A
• IBM Index Class Name: Permit File
• Doc Date: 10/28/2016
• Doc Name: Pond NHN-002 & NHN-002 DItch Designs
• Section_Exhibit Name: Appendix 2.05.3‎(4)‎-8
• Media Type: D
• Archive: Yes

Pond NHN-002 & NHN-002 Ditch Designs
Introduction
Pond NHN-002 at the New Horizon North Mine is designed to capture and contain the runoff
from the 10 -YR, 24 -HR storm event as part of sediment control at the mine. This appendix
contains design specifications for Pond NHN-002 and its feeding ditches, NHN-002 North and
NHN-002 South. Included in these designs are the stormwater runoff values for the 10 -YR, 24 -
HR event that the ditches and pond must contain and control and the 25 -YR, 24 -HR event that
the pond must pass safely through its emergency spillway.
Stormwater Data
Pond NHN-002 is the sediment pond for the stormwater drainage watershed SW2 shown on Map
2.05.3(4)-1. Runoff from this area flows entirely to the ditches that feed Pond NHN-002 or the
pond itself. Map 2.05.3(4)-9 shows the breakdown of SW2 into sub -watersheds that each feed a
separate part of the Pond NHN-002 stormwater control system. SW2-A feeds NHN-002 South,
SW2-13 feeds the pond directly, and SW2-C feeds NHN-002 North. Table 2.05.3(4)-8-1 shows a
summary of the runoff values for each sub -watershed. This data can also be seen in SEDCAD
models located in this Appendix. In addition to the sub -watersheds, Pond NHN-002 also will
handle pit pumping, which can be seen in the Table 2.05.3(4)-8-1. The10-YR runoff and peak
flows are from SEDCAD Model 1 (As shown later in this Appendix); the 25 -YR peak flow is
from SEDCAD Model 2 (As shown later in this Appendix).
Table 2.05.3(4)-8-1 Summary of Sub -watershed Runoff Values
Sub -watershed
Area
10 -YR, 24 -HR
25 -YR, 24 -HR
Acreage
Peak
Discharge
(cfs)
Runoff
Volume
(ac -ft)
Peak
Discharge
(cfs)
Runoff
Volume
(ac -ft)
SWS2-A
15.20
14.73
1.41
SWS2-B
44.10
39.58
4.05
SWS2-C
26.60
26.89
2.50
Pit Pumping*
N/A
2.00
0.16
SWS2 Total
85.90
83.20
8.12
1 113.40
11.23
*Pit pumping is the same regardless of storm size
Sediment Pond Design
Pond NHN-002 can be seen on Map 2.05.3(4)-9, along with its associated ditches. Map
2.05.3(4)-9 also shows cross sections of the pond design along with design information for the
ditches. Pond NHN-002 will be fed by both direct drainage and its two ditches. Discharge from
Pond NHN-002 will be controlled via a gated pipe system that has been used with great success
at other similar sediment ponds. An 18 -inch diameter pipe with a pair of valved 6 -inch diameter
Appendix 2.05.3(4)-8 Page 1 April 2016 (PR -01)