PERMFILE133938

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 9/2/2004
• Doc Name: Attachment 1 to 9
• Section_Exhibit Name: Exhibit 7 Streeter Pond - 001A
• Media Type: D
• Archive: Yes

COLOWYO COAL COMPANY
001A-STREETER
SEDIMENTATION POND SUMMARY
ORIGINAL 1996 1998 2002 DIFFERENC
CONFIGURATION STUDY STUDY DIFFERENCE STUDY 1998 TO 2002
ATERSHED AREA (acres):
Disturbed 0.0 0.0 0.0 0.0
Postmining Topsoiled and Seeded 50.6 231.3 180.7 139.5 -91.8
Postmining Untlisturbetl 207.0 53.8 -153.2 117.8 64.0
i-2 Year Reclamation 23.0 79.4 56.4 335.0 255.6
3+Year Reclamation 845.5 843.3 -2.2 745.0 -98.3
Total Area 1126.1 1207.8 81.7 1337.2 129.4
POND PARAMETERS:
Bottom Elevation 6576.7 6576.7 6579.0 2.3 6578.0 -1.0
Principal Spillway Invert Elevation 6586.9 6586.7 6585.0 -1.7 6585.0 0.0
Emergency Spillway Invert Elevation 6588.0 6588.0 6588.0 0.0 6588.0 0.0
Top of Embankment 6590.0 6590.0 6591.0 1.0 6591.0 0.0
Stoage Volume Below Emergency Spillway (ac-ft) 11.08 11.08 11.17 0.09 11.2 0.0
Storage Volume Below Principal Spilfivay (ac-fl) 6.12 8.39 5.21 -3.18 5.2 0.0
Principal Spillway Parameters:
Type Drop Inlet Drop Inlet Perf. Riser Pert. Riser
Riser Diameter (in) 12.0 12.0 12.0 0.0 12.0 0.0
Riser Height (ft) 5.7 5.5 3.7 -1.8 3.7 0.0
Barrel Diameter (in) 18.0 24.0 18.0 -6.0 18.0 0.0
Elevation of Pertoration(s) (fl) N/A N/A 6583.0 6583.0
Size of Pertoration(s) (in) N/A N/A 4.0 4.0
Number of Pertoretions N/A N/A 2 2.0
Emergency Spillway Parameters:
Type Trapezoidal Trapezoidal Trepezoidal Trapezoidal
Diameter (in) N/A N/A N/A N/A
Bottom Width (ft) 20.0 20.0 20.0 0.0 20.0 0.0
Length (ft) 40.0 40.0 45.0 5.0 50.0 5.0
Side Slopes'z'H:tV (ft) 2.0 3.0 1.5 -1.5 1.5 0.0
HYDROLOGIC/HYDRAULIC PARAMETERS:
Base Flow Rates (cfs) 1.00 0.03 -0.97 0.15 0.1
10-Year, 24-Hour Storm Event:
Precipitation (in) 1.8 1.8 0.0 1.8 0.0
Runoff Volume (ac-fl) 3.1 13.7 10.6 5.0 -8.7
Principal Spillway Peak Discharge (ds) 3.7 6.5 2.8 3.1 -3.3
Emergency Spillway Peak Discharge (ds) 0.0 0.0 0.0 0.0 0.0
Peak Surtace Water Stage Elevation (ft) 6587.7 6587.9 0.2 6585.7 -22
25-Year, 24-Hour Storm Event:
Precipitation (in) 2.3 2.3 0.0 2.3 0.0
Runoff Volume (ac-ft) 7.1 23.3 16.2 15.1 -8.2
Principal Spillway Peak Discharge (cts) 4.5 7.6 3.1 6.6 -1.1
Emergency Spillway Peak Discharge (cfs) 3.6 29.7 26.1 1.0 -28.7
Peak Surface Water Stage Elevation (ft) 6588.1 6588.9 0.8 6588.0 -0.9
Pond Freeboard (ft) 1.9 2.1 0.2 3.0 0.9
SEDIMENT LOADING PARAMETERS:
Storm Predicted Peak Setllable Concentration (ml/I) 0.00 0.00 0.0 0.00 0.0
Predicted Annual Sediment Loading (ac-fl) 0.42 0.64 0.42 0.33 -0.5
Available Sediment Storage Volume (ac-fl) 1.27 0.90 -0.37 0.84 -0.1
Maximum Sediment Storage Elevation (ft) 6581.3 6581.3 6581.3 0.0 6581.3 0.0
' Predicted Number of Storage Vears 3.0 1.1 -2.0 2.5 1.5