5
I:\11\82323\0100\0122 TM\Feb14\11382323 TM PreFeasibilityHydrologyHydraulicsRevE 13FEB14.docx
reinforced section. The ponds will require periodic maintenance and cleanout to ensure proper
functioning. The required freeboard storage of one foot is not included in these numbers.
Sediment Pond
Catchment
Area
(ac)
10-Year
Event Volume
(ac-ft)
1
Sediment
Storage Volume
(ac-ft)
2
Total
Pond Volume
(ac-ft)
3
Waste Rock Facility
Pond 1
104.5
14.5
8.7
23.2
Pond 2
143.8
19.9
12.0
31.9
Pond 3
211.7
29.3
17.6
46.9
Pit Pond
Environmental Flows
249.1
32.4
20.8
65
Pit Dewatering
-
4.4
7.4
PUG Plant
PUG Plant Pond
45.1
6.3
3.8
10.1
Notes:
1. In accordance with the Wyoming Department of Environmental Quality Water Quality Rules and Regulations, Chapter 11,
Section 31, the sediment ponds are sized to accommodate the 10-year 24-hour runoff event. The design storm event was
modeled using the Hydrologic Engineering Center's HEC-HMS program. Additionally, the ponds must be sized to
accommodate the expected sediment storage.
2. The annual volume of sediment generated was assumed to be equal to one inch of runoff from the entire catchment area. This
corresponds to 3,630 ft³/acre.
3. Total pond volume represents a neatline volume and does not include the required freeboard.
5.3 Haul Road Culvert Sizing
Estimated culvert sizes are summarized in the table below.
Culvert Designation
(See Figure 1)
Design Flow
(cfs)
Culvert Size
(in.)
Length
(ft)
No. of
Barrels
D1
70.4
36
450
2
D2
168.9
42
450
2
