2013-10-07_PERMIT FILE - C1981025A ‎(6)‎

• Permit No: C1981025A
• IBM Index Class Name: Permit File
• Doc Date: 10/7/2013
• Doc Name: Final Engineering Calculations
• Section_Exhibit Name: 4.0 Appendix 4-B
• Media Type: D
• Archive: Yes

• L0NGPOND.WK3
APPENDIX 4-B, VOLUME III
LONG POND & T-1 & T-2 DESIGN
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The long pond is the first pond in a series of three ponds
that treat the seepage from the No. 1 & No. 3 Mines. Treatment
is by areation and settlement and both are accomplished
passively.
The following calculation is presented to determine the
appropriate size of the principle and emergency spillways
for the long pond.
STORM EVENTS
10 YEAR 24 HOUR EVENT
25 YEAR 24 HOUR EVENT
100 YEAR 24 HOUR EVENT
1.8 INCHES
2.2 INCHES
2.4 INCHES
The run-off calculations presented below are calculated based
on the manual - Procedures for Determining Peak Flows in
Colorado - published by the Soil Conservation Service, March
1984.
The soil type for the area is Dollard, soil type C.
The drainage area above the long pond is broken into two
• areas based on slope and vegetative cover. The steep slope
above the long pond has ground cover of 20% to SOo. The
flatter slope near the pond has ground cover of about 80% based
on the 1991 vegetation survey.
Other Agricultural Lands:
Upper Watershed Condition Curve #
----------------------------------------------------
----------------------------------------------------
Pasture-grassland-range poor <50% 8G
Pasture-grassland-range fair 500-75% 79
Brush-weed-grass poor <50% 77
Brush-weed-grass fair 50a-75% 70
Curve Number Selected
78
Lower Watershed
----------------------------------------------------
----------------------------------------------------
Pasture-grassland-range good >75% 74
Brush-weed-grass good >75% 65
Curve Number Selected
70
• P-9-5
08-14-95