2014-11-13_PERMIT FILE - C2010089A

• Permit No: C2010089A
• IBM Index Class Name: PERMIT FILE
• Doc Date: 11/13/2014
• Doc Name: ARCADIS Report on Sediment Control
• Section_Exhibit Name: Appendix 2.05.3‎(4)‎-1
• Media Type: D
• Archive: Yes

Table 2: Pipe Invert and Slope
Pond Name
Pipe Length
(ft)
Pipe Inlet Invert
(ft)
Pipe Outlet Invert
(ft)
Pipe Slope o
NHN -001
69
5676.6
5675.0
2.3
NHN -002
75 5676.0
5675.0
1.3
NHN -003
82
5686.0
5680.0
7.3
Sedimentation Pond Configuration
In order to minimize short circuiting, it is general practice to specify a minimum length -to -width ratio of 2:1. Larger
ratios up to 5:1 are recommended to promote the performance. Due to the location restraints for each pond,
length -to -width ratios are not ideal, particularly for pond NHN -002. Gated principal spillways, as designed for all
three ponds, prevent short circuiting.
The principal spillway pipe invert for all 3 ponds is placed above the sediment storage elevation. To account for
the uneven settling of sediment in the ponds, where more sedimentation occurs where the ditches enter the
ponds, the principal spillway is positioned away from the ditch entrances for each pond. This is a particular
concern due to the length -to -width ration of Ponds NHN -001 and NHN -002. Pond NHN -002 was placed with a
principal spillway 150 feet south of the NHN -002 North ditch entrance into the pond in order to account for the
uneven sedimentation in the pond.
Pond Design
The sedimentation ponds are designed, constructed and maintained to:
a. Provide storage for the runoff or inflow entering the ponds as a result of a 10 -year, 24 -hour precipitation
event and to meet all applicable State and Federal regulations for all effluent limitations before discharge
from the permit area. The characteristics of the mine site, reclamation procedures, and on site sediment
control practices are also considered in the design.
b. The sedimentation pond was designed to provide adequate sediment storage volume in compliance with
DRMS regulations.
c. An appropriate non - clogging dewatering device will be installed to maintain a 10 -year, 24 -hour storage
volume.
d. Appropriate combinations of principal and emergency spillways to safely discharge the runoff from a 25-
year, 24 -hour precipitation or larger event, as required by DRMS regulations.
All 3 ponds have a 10 foot wide top embankment and a 10 foot embankment height, per Rule 4.05.9(6). For Pond
NHN -001, the inslopes and outslopes are 3H:1V, and both Ponds NHN -002 and NHN -003 are 2.5H:1V, which
M.