PERMFILE100539

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 9/2/2004
• Doc Name: Attachment 1 to 9
• Section_Exhibit Name: Exhibit 07 Prospect Pond 007A
• Media Type: D
• Archive: Yes

COLOWYO COAL COMPANY
007A-PROSPECT
SEDIMENTATION POND SUMMARY
ORIGINAL 1996 1998 2002 DIFFERENCE
CONFIGURATION STUDY STUDY DIFFERENCE STUDY 1998 TO 2002
WATERSHED AREA (acres):
Disturbetl 0.0 0.0 0.0 0.0
Postmining Topsoiled and Seeded 45.0 68.0 23.0 57.6 -10.5
Postmining Undisturbed 211.3 191.5 -19.8 198.2 6.7
1-2 Year Reclamation 59.4 178.3 118.9 227.1 48.8
3+Year Reclamation 465.6 312.9 -152.7 229.7 -83.2
Total Area 781.3 750.7 -30.6 712.5 -38.2
POND PARAMETERS:
Bottom Elevation 6735.7 6735.7 6735.7 0.0 6734.0 -1.7
Principal Spillway Invert Elevation 6750.3 6748.8 6750.3 1.5 6750.3 0.0
Emergency Spillway InveR Elevation 6751.6 6751.6 6751.6 0.0 6752.0 0.4
Top of Emhankment 6754.0 6754.0 6754.0 0.0 6755.0 1.0
Storage Volume Below Emergency Spillway (ao-ft) 5.26 5.26 5.30 0.04 6.1 0.8
Stooge Volume Below Principal Spillway (ao-ft) 4.81 3.65 4.52 0.87 5.1 0.6
Principal Spillway Parameters:
Type Drap Inlet Drop Inlet Pert. Riser Pert. Riser
Riser Diameter (in) 12.0 12.0 12.0 0.0 12.0 0.0
Riser Height (ff) 8.7 7.2 8.7 1.5 8.7 0.0
Barrel Diameter (in) 12.0 12.0 12.0 0.0 12.0 0.0
Elevation of Pertoration(s) (ff) N/A N/A 6744.0 6744.0
Size of Pertoration(s) (in) N/A N/A 4.0 4.0
Number of Perforations N/A N/A 2 2.0
Emergency SpilM1vay Parameters:
Type Trapezoidal Trapezoidal Trapezoidal Trapezoidal
Diameter (in) N/A N/A N/A N/A
Bottom Width (ft) 12.0 12.0 12.0 0.0 12.0 0.0
Length (ft) 20.0 20.0 20.0 0.0 20.0 0.0
Side Slopes'i H:1 V (8) 2.0 2.0 1.5 -0.5 1.5 0.0
HYDROLOGICfHYDRAULIO PARAMETERS:
Base Flow Rates (cfs) 2.00 0.03 -1.97 0.00 D.0
10-Year, 24-Hour Storm Event:
Precipitation (in) 1.8 1.8 0.0 1.8 0.0
Runoff Volume (ac-ft) 2.7 4.3 1.6 2.0 -2.4
Principal Spillway Peak Discharge (cfs) 6.0 2.0 -4.0 1.1 -0.9
Emergency Spillway Peak Discharge (cfs) 0.0 0.0 0.0 0.0 0.0
Peak Sudace Water Stage Elevation (ft) 6751.3 6749.5 -1.8 6745.7 -3.9
25-Near, 24-HOUr Storm Event:
Precipitation (in) 2.3 2.3 0.0 2.3 0.0
Runoff Volume (ao-ft) 5.4 8.3 2.9 6.3 -2.0
Principal Spillway Peak Discharge (cfs) 6.9 4.5 -2.4 2.4 -2.1
Emergency Spillway Peak Discharge (cfs) 9.8 3.0 -6.8 0.0 -3.0
Peak Surface Water Stage Elevation (ft) 6752.1 6751.8 -0.3 6750.7 -1.1
Pond Freeboam (ft) 1.9 2.2 0.3 4.4 2.1
SEDIMENT LOADING PARAMETERS:
Storm Predicted Peak Setllable Concentration (ml/I) 0.00 0.00 0.0 0.00 0.0
Predicted Annual Sediment Loading (ao-ft) 0.09 0.52 0.43 0.53 0.0
Available Sediment Storage Volume (ao-ft) 0.76 0.76 0.00 1.41 0.7
Maximum Sediment Storage Elevation (ft) 6741.6 6741.6 6741.6 0.0 6741.6 0.0
Predictetl Number of Stora a Years 8.4 1.5 -7.0 2.7 1.2
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