2008-12-04_PERMIT FILE - C1994082 (39)

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• In some instances, mining will cause the drainage area to change during the lice of the sedimentation structure. When the pit moves into the watershed, runoff is intercepted by the pit. In these cases, a conservative procedure was used; the structure was analyzed for the largest anticipated disturbance drainage area that will contribute runoff to the structure. It was estimated that this condition would occur if all of the proposed mining area is disturbed and the area is in different phases of mining and reclamation. In addition, the structure was conservatively designed to include adequate capacity for sediment storage and to treat the runoff from a 10-year, 24-hour precipitation event. Finally, the design conservatively assumed the principal spillway is clogged during the 25-year, 24-hour precipitation event and provides for maintenance of adequate freeboard to prevent overtopping of the embankment, The SEDCAD output for the pond as-built conditions are presented in Addendum 13-20- A, 13-20-B and 13-20-C. Summary The capacity of Sedimentation Pond 013 is attributed partially to the embankment and partially to the pond excavation. During passage of the 10-year, 24-hour storm the pond is designed to effectively treat the runoff and will not discharge flow through the emergency spillway. In addition, the emergency spillway was designed and constructed to safely discharge the 25-year, 24-hour storm event. • The embankment was constructed to be stable and provide adequate freeboard. Therefore, based on the design, this structure complies with the appropriate regulations for a sedimentation structure. Seneca Coal Company will periodically inspect the structure for sediment storage, structural integrity and hazardous conditions. Maintenance and remedial work will be performed in accordance with the approved mine permit. Construction Summary In accordance with Rule 4, Part 4.05.9114) of the Rules and Regulations of the Colorado Mined Land Reclamation Board pursuant to the Colorado Surface Coal Mining Reclamation Act 34-33-001 et seq., I, John Pellicer, state that during construction of Sedimentation Pond 013 inspections were conducted by MWH personnel under my supervision. Seneca Coal Company constructed Pond 013 under the supervision of Mr. Roy Karo, Reclamation Manager, and Mr. Dan Allen, Surveyor. Mr. Karo and Mr. Allen ensured that all work was performed in accordance with the design and the specifications. Mr. Mike Ross (MWH(, under my supervision, inspected the structure on a regular basis to verify compaction and to make sure that the embankment was being constructed in accordance with Rule 4, Part 4.05. 91141. Mr. Roy Karo (Seneca) and/or Mr. Jay James (formally with MWH( were also on the • TR-26 2 Revised 09/04