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In some instances, mining will cause the drainage area to change during t.~e life of the <br />sedimentation st rvcture. when the pi[ moves into the watershed, runoff is int excepted by • <br />the pit. In these cases, a conservative procedure was used; the st ructux~e was analyzed <br />for the largest anticipated disturbed drainage area thac will contribute rvnoff to the <br />st rvccure. It was estimated chat this condition will occur if all of the E~ropoted mining <br />area is disturbed and the area is in different phases of mining and rex:l amat.icn. In <br />addition, the structure was conservatively designed to include adequate cap.city Eor <br />sediment storage and co treat the runoff from a 10-year. 24-hour precip it aticn event. <br />Finally, the design conservatively assumed the principal spillway is clogged during the <br />25-year, 24-hour precipitation event and provides for maintenance of adequate fze:eboard to <br />prevent overtopping of the embankment. The SBDCAD output for the pond as-bu.i It conditions <br />are presented in Addendums 13-5D-A, 13-SD-B, and 13-SD-C. <br />Summary <br />The capacity of Sedimentation Pond 015 is attributed partially to the embankment and <br />partially to the pond excavation. During passage of the 10-year, 24-hour storm the <br />spillway does not discharge sediment downstream nor is there any flow through the <br />emergency spillway. In addition, the spillway is designed to safely discharge the 25- • <br />year, 2a-hour storm event. <br />The embankment was constructed to be stable and provide adequate freeboard. Therefore, <br />based on the design, this structure complies with the appropriate regulations for a <br />sedimentation structure. Seneca Coal Company will periodically inspect the st ru~cture for <br />sediment storage, structural integrity, and hazardous conditions. Maintenance and <br />remedial work will be performed in accordance with [he approved mine permit. <br />Construction Summary <br />In accordance with Rule 4, Part 4.05.6(10) of the Rules and Regulations of: the Colorado <br />Mined Land Reclamation Board pursuant to the Colorado Surface Coal Mining Reclamation Act <br />34-33-101 et aeq., I, Michael G. Altavilla, hereby certify thaC the const ru.et ion of <br />Sedimentation Pond 015 was inspected and constructed under my super/ision. The <br />construction of Pond O1S was supervised on site by Dan A11en, Surveyor, and E:oy Raro. <br />Reclamation Manager, at the Yoast Mine. Dan and Roy assured all work was pert: ormed in <br />accordance with the design and the specifications. • <br />13-SD-2 04/00 <br />