PERMFILE56247

• Permit No: C1981038
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Volume 8 Surface Drainage - Stockpile Run-Off Calculations
• Media Type: D
• Archive: No

' _:~ RUNOFF AND SEDIMENTATION CALCULATIONS
EMERGENCY COAL STOCKPILE
File 077-353
December 17, 1979
• The drainage area of the emergency coal stockpile was surveyed by
conventional means and vas determined to be 4.78 acres. Runoff expectations
for a 10-year 24-hours storm were taken from work by Charles Leaf, P.E.
Detailed work may be found in "Colorado Westmoreland Inc., Orchard Valley
Mine, Modification of Underground Coal Mining and Reclamation Permit -
submitted June 18, 1979" Section 784, page 22. The previous work was done
for Westmoreland Canyon, and it was judged that the emergency coal pile was
in close enough vicinity to use similar values. Based on this information,
runoff amounts are:
0.04 acre-feet For disturbed lands
acre
0.01 acre-feet for undisturbed lands
acre
Expected runoff, assuming the entire area as disturbed, is
0.04 acre-feet X 4.78 acres 0.19 acre-feet
acre
Expected sediment volume is based on 30 CFR 817.46b(2). The volume required
may vary from 0.10 acre-feet to a minimum of 0.035 acre-feet. The
acre
• regulations state that to use the mini
measures are used to reduce sediment.
to use the minimum of 0.035 acre-feet.
acre
temporary nature of the pile and close
acre
num, sufficient sediment control
Colorado t7esimoreland Inc. proposes
This is based on the emergency,
monitoring of sediment levels.
The expected sediaent volume for the area is
0.035 acre-feet X 4.78 acres = 0.16 acre-feet.
acre
Total storage capacity adding the runoff and sediaent values is
0.19 acre-feet + 0.16 acre-feet = 0.35 acre-Feet.
The sedimentation pond would have a storage capacity of 0.22 acre-feet. An
additional 0.14 acre-feet is provided within the bermed area directly north
of the rail spur. This will provide 0.22 acre-feet + 0.14 acre-feet =
0.36 acre-feet.
As stated previously, the sedimentation pond will be closely monitored and
as per 30 CFR 817.46(h) the pond will be cleaned at the level shown on
stockpile area drawings attached.
. The runoff/sedimentation storage areas will be dewa[ered with a pump. The
dewatering will be after a runoff detention time of 24 hours, and will be
done in such a manner as [o minimize disturbance to surrounding areas.
All drawings, calculations, and surveying for this emergency stockpile area
has been directed by a registered professional engineer.