2011-03-21_PERMIT FILE - C2009087 (5)

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Creek Mine — Sump Design Report Spillways: The Upper and Lower Sumps were designed with both a principal and emergency spillway in accordance with Rule 4.05.9(2)(b). Map 2.05.3 -E2.D, Upper Sump, and Map 2.05.3 -E2.E, Lower Sump, show spillway locations and specifications. The principal spillways will be standard corrugated metal pipe drop inlet type with a trash rack as shown on Maps E2 -D and E2 -E. The invert elevations are listed above. Peak water levels for inflow from the 10 -year, 24 -hour storm event are less than the invert elevations. These calculations indicate that in accordance with Rule 4.05.9(2)(b), there is no discharge through the emergency spillway as a result of the 10 -year, 24 -hour storm event. The calculated 25 -year, 24 -hour event peak discharge from the Upper Sump is 6.98 cfs (see Addendum 2.05.3- E2.E -1, Emergency Spillway Channel Designs). The spillway invert is at elevation 6773.5 feet, while the peak stage in the SEDCAD demonstration is at 6773.1 feet. The top of the embankment is at 6775 feet. Both the spillway crest and outslope will be protected with rock riprap. Sage Creek Coal Company adds an additional 3- inches to the SEDCAD model recommended D50 size. The D50 for the Upper Sump spillway crest is 3.75 inches and 6 inches for the outslope channel. The calculated 25 -year, 24 -hour event peak discharge from the Lower Sump is 25.3 cfs (see Addendum 2.05.3- E2.E -1, Emergency Spillway Channel Designs). The spillway invert is at elevation 6655 feet, while the peak stage in the SEDCAD demonstration is at 6654.8 feet. The top of the embankment is at 6657 feet. Both the spillway crest and outslope will be protected with rock riprap. Sage Creek Coal Company adds an additional 3- inches to the SEDCAD model recommended D50 size. The D50 for the Upper Sump spillway crest is 4.5 inches and 9 inches for the outslope channel. The designs presented in Addendum 2.05.3 - E2.E-1, Emergency Spillway Channel Designs, indicate that the emergency spillways maintain the necessary freeboard specified in Rule 4.05.9(7)(d). 5.0 SUMMARY The capacities of the two sumps are attributed to embankment construction and interior incising. Since the sumps will not be permitted as CDPS structures, there will be no effluent limits and Rule 4.05.2(7) is not applicable. Both the principal and emergency spillways have been designed to assure compliance with the requirements of Rule 4.05.9. The embankments were designed to be stable and provide adequate freeboard and, therefore, the structures comply with the appropriate rules and regulations for a sedimentation structure. Sage Creek Coal Company will periodically inspect the structures for sediment storage, structural integrity and hazardous conditions. Maintenance or remedial work will be performed in accordance with the approved mine permits. TRO1 -10 2.05.3 -E2.E4 2/11