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a <br />F • <br />The overburden blast sketch and narrative on page 2.05-29 has ' <br />;' been revised to correct a typographical error which showed a <br />7 ms delay instead of the`cbfrect`17 ms delay. The corrected <br />page is enclosed. <br />8. West Pit and Section 16 Sooil Fill <br />These concerns will be addressed in a separate letter. <br />Items 13, 15-22 Bonding Concerns <br />A meeting between the Division and Colowyo was held April 1, <br />1992, at the Division's office to address these concerns. <br />29. R1ArdD Designs <br />The appropriate riprap designs for the Prospect and West Pit <br />Ponds are included in Exhibit 7, Hydrology Information, Item <br />8, Design of Surface Runoff Control Structures, Permit <br />Revision, 1991. <br />30. Culverts and Ditches <br />All culverts and diversions with specific design criteria, or <br />to which performance standards apply, are included in the i~~,r-i., <br />Colowyo permit, exhibit 7 and on updated map numbers 11 and pp <br />12. Additionally, Colowyo is in the process of developing a I`";`~' <br />new map, Hydrology of Gossard and Mine Maintenance Areas, map ', <br />number 12A. The list of maps, table of contents has been ~ ~`~~'~~ <br />revised to reflect this, and this new map is referenced on ~}~,•.,, <br />maps 11 and 12. Map 12A will be sent to MLRD under a <br />separate letter upon completion. <br />Please direct your attention to Volume 3, item 4, Design of <br />Surface Runoff Control Structures prepared by Tipton and <br />Kalmbach. The first "ha._f inch" of this item 3 affords a <br />wealth of information on culverts and diversions and also <br />incudes macs and typical drawings. Additionally, direct your <br />attention to Volume 3, item 5, Drainage Plan for Colowyo Coal <br />Company Work Area, Tipton and Kalmbach. This section contains <br />additional calculation plus a work area drainage plan mav. <br />34. Justification- of Curve .Number and Unit HYdrograph Shape <br />Response <br />The curve number justification is fully explained in Exhibit <br />7, Hydrology Information, Item 8, Design of Surface Runoff <br />Control Structures, Permit Revision 1991. <br />The unit hydrograph shape response has been changed from a <br />"slow" response to a "medium" response. The modified <br />calculations are in Exhibit 7, Hydrology Information, Item 8, <br />"Design of Surface Runoff Control Structures, Permit Revision, <br />,tea, <br />