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In some instant's, mining will cause the drainage area to change during the life of the • <br />sedimentation structure. When the pit moves Into the watershed, ru no Cf Ss lnt ercepted by <br />the pit. In these cases, a conservative procedure was used; [he structure was analyzed <br />for [he largest anticipated disturbed drainage area that will contribute runoff to the <br />structure. It was estimated that this condition will occur if all of the proposed mi ning <br />area is disturbed and the area Ss in different phases of mining and reclamation. In <br />addition, the structure was conservatively designed to include adequate ca pa city fot <br />sediment storage and [o treat the runoff from a 10-year, 24-hour precl pl tation event. <br />Finally, the de:aign conservatively assumed the principal spillway Is clogged during the <br />25-year, 24-hour precipitation event and provides for maintenance of adequate freeboard <br />to prevent ove copping of the embankment. The SEDCAD output for the pond as-built <br />conditions are Presented In Addend ums 13-12A-A, 13-12A-B, and 13-12A-C. <br />Summa [V <br />The capacity of Sedimentation Pond 012 is attributed partially to the embankment and , <br />partially to the pond excavation. During passage of the 10-year, 24-hour storm [he <br />spillway does not dlscha rge sediment downstream nor is there any El ow through the • <br />emergency spil lway. In addition, the spl Llway Ss .designed [o safely discharge [he 25- <br />year, 29-hour storm even[. <br />The embank men[ was constructed to be stable and provide adequate freeboard. Therefore, <br />based on [he design, this structure complies with the app roprla[e regulations for a <br />sedimentation structure. Seneca Coal Company will periodically inspect [he structure Cor <br />sediment storage, structural integrity, and hazardous conditions. Maintenance and <br />[erred ial work will be performed in accordance with the approved mine permit. <br />Construction Sumnar <br />In accordance with Rule 4, Part 4.05.6(101 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 seq., I Michael G. Altavilla, hereby certify that the construction of <br />Sedimentation Pond 012 was inspected and constructed under my supervision. The <br />construction of Pond 012 was supervtsed on site by Dan Allen, Surveyor and Roy Ka ro, <br />Peclama[ion Manager, a[ [he Yoa st Mine. Dan and Roy assured all work was performed in • <br />accordance with -he aes ign and [he specificaU ons. <br />13-12A-2 Re vi e:ed U3/00 <br />