2018-01-31_PERMIT FILE - C1981019A

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 1/31/2018
• Doc Name: South Taylor Erosion Control And Sedimentation Plan
• Section_Exhibit Name: Exhibit 07 Item 20 -ST
• Media Type: D
• Archive: Yes

Exhibit 7,Item 20,Table 4
COLOWYO COAL COMPANY
SEDIMENTATION POND SUMMARY PROPOSED PLAN-SOUTH TAYLOR MINE PLAN
SECTION 28 SECTION 21 WEST TAYLOR WEST TAYLOR
POND POND POND POND
Active Mining Post-mining
WATERSHED AREA(acres):
Disturbed 00 Sec.21 Pond 684 00
Postmining Topsoiled and Seeded 52.1 Not Constructed 00 747
Undisturbed 2799 805 219.1
1-2 Year Reclamation 69 5.3 156.7
3+Year Reclamation 00 00 3787
Total Area Draining to Pond 33890 1542 8292
Excluded 0.0 6749 00
Total Watershed Area 33890 82910 82920
POND PARAMETERS:
Upstream Toe Elevation Original Ground 70580 7456.0 7456.0
Principal Spillway Invert Elevation 7071 0 7471.0 7471.0
Emergency Spillway Invert Elevation 70770 74758 74758
Top of Embankment 70820 7481 0 7481 0
Storage Volume Below Emergency Spillway Invert(ac-ft) 831 5.64 5.64
Storage Volume Below Principal Spillway Invert(ac-ft) 365 290 2.90
Storage Volume Below Lowest Spillway Perforation(ac-ft) 1 67 1.77 1.77
Principal Spillway Parameters.
Type Perforated Riser Perforated Riser Perforated Riser
Riser Diameter(in) 18.0 18.0 180
Riser Height(ft) 66 10.5 10.5
Barrel Diameter(in) 180 18.0 180
Elevation of Lowest Perforation(s)(ft) 7064.5 7468.0 74680
Size of Perforation(s)(in) 30 30 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) 30.0 300 30.0
Side Slopes'z'H-1V(ft) 20 20 2.0
HYDROLOGIC/HYDRAULIC PARAMETERS:
Base Flow Rates(cfs) 000 0.00 000
10-Year,24-Hour Storm Event.
Precipitation(in) 1 80 1 80 1.80
Runoff Volume(ac-ft) 210 4.34 7.51
Principal Spillway Peak Discharge(cfs) 1 37 1.61 14.06
Emergency Spillway Peak Discharge(cfs) 000 0.00 000
Peak Surface Water Stage Elevation(ft) 706715 7471 16 747374
Spillway Design Storm 100 yr/24 hr 25 yr/24 hr 25 yr/24 hr
Precipitation(in) 2.70 2.30 230
Runoff Volume(ac-ft) 798 1.44 1654
Combined Princ and Emer Spillway Peak Discharge(cfs) 10.80 426 5557
Peak Surface Water Stage Elevation(ft) 7071.22 7471.41 747652
Pond Freeboard(ft) 1 1078 9.59 448
SEDIMENT LOADING PARAMETERS(10-Year,24-Hour Event):
Storm Predicted Peak Sediment Concentration(in,mg/1) 130,913 702,476 78,287
Storm Predicted Peak Settl Solids,(out,ml/1) 00 00 0.00
Predicted Annual Sediment Loading(ac-ft) 010 01 0.02
Max sediment storage elevation (ft) 706450 74680 74680
Available Sediment Storage Volume(ac-ft) 171 2.02 202
Predicted Number of years to max sed stor EI 171 161 83.9
Revision Date: 11/15/17
Exh. 7-20-2 Revision No.: TR-117