PERMFILE131162

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 5/4/2007
• Doc Name: South Taylor Erosion Control And Sedimentation Plan
• Section_Exhibit Name: Exhibit 07 Item 20 -ST
• Media Type: D
• Archive: Yes

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Exhibit 7, Item 20, Table 4
COLOWYO COAL COMPANY
SEDIMENTATION POND SUMMARY PROPOSED PLAN -SOUTH TAYLOR MINE PLAN
SECTION 28 SECTION 21 WEST TAYLOR
POND POND POND
WATERSHED AREA (acres):
Disturbed 27.8 33.4 53.6
Postmining Topsoiled and Seetled 24.1 68.5 78.9
Untlisturbed 137.8 178.0 182.0
1-2 Year Reclamation 782.3 255.4 207.8
3+Year Reclamation 0.0 0.0 94.9
Total Area Draining [o Pond 371.96 535.28 611,2
Excluded 39.7 63.5 132,4
Total Watershed Area 411.70 598.77 743.53
POND PARAMETERS: 3.0
Upstream Toe Elevation Original Ground 7058.0 6989.0 7456.0
Principal Spillway Invert Elevation 7071.0 6982.0 7471.0
Emergency Spiliv2y Invert Elevation 7077.0 6988.0 7476.0
Top of Embankment 7082.0 6993.0 7481.0
Storage Volume Below Emergency Spillway Invert (acft) 8.31 74.05 5.64
Storage Volume Below Principal Spillway Invert (ac-ff) 4.62 6.37 2.90
Storage Volume Below Lowest Spillway Perforation (ac-ft) 2.46 5.44 1.77
Principal Spillway Parameters:
Type Perforated Riser Perforted Riser Perforated Riser
Riser Diameter (in) 18.0 1 B.0 18.0
Riser Height (ft) 16.0 18.0 16.0
Barrel Diameter (in) 18.0 18.0 1 B.0
Elevation of Lowest Perforation(s) (ft) 7066.0 6978.0 7468.0
Size of Perforation(s) (in) 3.0 3.0 3.0
Number of Perforations per Elevation 2.0 2.0 2.0
Emergency Spillway Parameters:
Type Trapezoidal Trapezoidal Trapezoidal
Diameter (in) N!A N/A N/A
Bottom Width (ft) 30.0 30.0 30.0
Crest Length (ft) 30.0 30.0 30.0
Side Slopes'i H:1V (ft) 2.0 2.0 2.0
HYDROLOGICINYDRAULIC PARAMETERS:
Base Flow Rates (cfs) O.DO 0.00 0.00
10-Year, 24-Hour Storm Event:
Precipitation (in) 1.80 1.80 1.80
Runof( Volume (ac-f[) 3.51 4.72 5.19
Principal Spillway Peak Discharge (cfs) 1.79 2.09 10,83
Emergency Spillway Peak Discharge (cfs) 0.00 0.00 0.00
Peak Surface Water Stage Elevation (ft) 7070.68 6982.07 7472.63
50 % of PMP, 6-Hour Storm Even[:
Precipitation (in) 4.20 4.20 4.20
Runoff Volume (ac-ft) 25.15 39.22 45.51
Principal Spillway Peak Discharge (cfs) 24.07 25.53 25.53
Emergency Spillway Peak Discharge (cfs) 225.19 461.29 770.39
Peak Surface Water Stage Elevation {ft) 7079.24 6990.73 7479.51
Pond Freeboard (ft) 2.76 2.27 1.49
SEDIMENT LOADING PARAMETERS (10-Year, 24-Hour Eve nt):
Storm Predicted Peak Sediment Concentration (mg/p 276,801 499,358 135,418
Storm Predictetl Sediment Supply (tans) 736.8 2381.4 527.9
Storm Predicted Peak Settlable Concentration (ml/0 57.88 183.24 0.0
Available Sediment Storage Volume (ac-ft) 0.29 0.94 0.21
Based on Average Annual R of 10.0 for "x" years: 1.0 1.0 1.0
Revision Date: 3/29/07
Exh. 7-20-7 Revision No.: PR-02