PERMFILE102806

• Permit No: C1981032
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: Diversion Ditch and Sediment
• Section_Exhibit Name: CHAPTER C MINE OPEATION PLAN Appendix A
• Media Type: D
• Archive: No

DIVERSION DITCH AND SEDIMENT POND SIZE CALCULATIONS
The requirements of 30 CFR, Sec. 717.17(e) have been fulfilled in this design. To
'
more clearly show compliance, each paragraph will be addressed individually.
_
•
(e) (1) (i) The pond will be the first thing constructed in the disturbed area.
The two diversion ditches will be constructed simultaneously.
(ii) The pond will be immediately downstream of the disturbed area.
The drainage way is not perenial stream.
(iii) N/A
(2) (i) The sediment volume was determined using the U.S.L.E. and is for a
3 year period.
(ii) N/A
(3) The detention time for the 10 year - 24 hour storm is 24 hours. This
is accomplished by a manually operated gate that will be opened
only after the required detention time is achieved
(i) N/A
(ii) N/A
(iii) N/A
(iv) There were no calculations for detention time, merely not opening
the gate provides the required time.
(4) The dewatering device is a manually operated gate that will have an
invert elevation above the elevation of 3 ,years of sediment.
• (5) Shor t circuiting has been eliminated by using the gate.
(6) Effluent limitations of the NPDES discharge permit and OSM
reouTations wilt be met.
(7) The pond has been sized to detain the entire 10 year - 24 hour storm
without any outflow through the emergency spillway.
(8) The pond shall be cleaned cvhen the sediment accumulates to 60% of
the design volume (i.e. el. 7136.0')
(9) The emergency spillway was sized to carry the 100 year - 24 hour
storm: This was decided upon to insure safety for events greater
than the 25 year - 24 hour storm. Rip-Rap will be provided on the
crest of the spillway and the downstream face of the embankment
where high velocity flows are expected.
The crest elevation is 7138.46' end the elevation of the principle
outlet will be 7137.25.
(10) The heed, at the outlet, for the 100 year - 24 hour storm is 0.91 feet
and the elevation is 7139.37'.
The crest elevation of the pond is 7140.5, which results in a
freeboard of 1.13'.
(11) The embankment will be constructed 5% above the design height.
1 (i.e. 7141.0' at the center decreasing to 7140.5' et the catch point).
(12) The top width of the embankment will be ,9 feet for the
sedimentation pond.