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May 1, 2008 <br />Mr. James R. Stark <br />Environmental Protection Specialist <br />Colorado Division of Reclamation, Mining and Safety <br />Department of Natural Resources <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203 <br />~~~®~'~~ <br />~ 5 ~o®~ <br />~~~ © ~~c~ <br />1'J" ` <br />,~,~r ~4 gild ,agie ~ <br />O ~~~~n9 <br />RE: Technical Revision No. 73, Hydrologic Curve Numbers for Sediment Pond Design, Colowyo <br />Coal Mine, Permit No. C-81-019. <br />Dear Mr. Stark, <br />Enclosed please find two copies of materials provided for Technical Revision No. 73. This change updates <br />the ""Methodologies and Assumptions for Sedimentation Pond Design Evaluations" provided in Volume 2D <br />in regard to future hydrologic designs. As we have previously discussed, we intend to introduce a range of <br />curve numbers for individual cover types to provide more flexibility while maintaining the previously <br />agreed upon values. <br />It should be noted that Volume 13, Exhibit 7, Item 20 contains similar text for the Methodologies and <br />Assumptions for Sediment Pond Design. However, we are not proposing to modify this text as this material <br />is specific to the existing designs used for the three South Taylor ponds. <br />Also included with the revision package are an application form, the public notice and an index sheet. If you <br />have any questions or require additional information, please feel free to contact me at (970) 824-1578. <br />Sincerely, <br />~- <br />Ryan Pawlowski <br />Environmental Engineer <br />Encl. 2 copies <br />Cc: file CF 1.1.2.62 <br />_~ __ __ <br />