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Illl1llllllll!lllll <br />c~RUs <br />C Yampa Valley <br />Cyprus Yampa Valley Coal Corporation <br />29567 Routt County Road #27 <br />Oak Creek, Colorado 60467 <br />303-879.3800 <br />September 5, 1991 <br />Tony Waldron <br />Reclamation Specialist <br />Colorado Mined Iznd Reclamation Division <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203-2273 <br />Dear Mr. Waldron: <br />=~~~~~~F~~~ <br />SEP 1 0 1991 <br />Mined Land <br />Reclamation Division <br />Re: Minor Revision 91-ti4. Addition of Culvert D-4TB; Permit C-82-056 <br />In response to Mr. Gorham's letter of August 23, and subsequent conversations with Mr. Berry <br />and yourself, TCC is submitting the revised Sedcad sizing and page Ex. 8-11(b). <br />As discussed, the previous sizing was inaccurate in three respects: <br />1) a portion of the acreage was inadvertently left out; <br />2) a typographical error was carried through the calculation, compounding the <br />original acreage omission, and; <br />3) an incorrect curve number was mistakenly utilized, as the CN was taken from the <br />wrong column of a previously approved table. <br />The revised Sedcad run utilizes an area of 28.52 acres, the previously submitted time of <br />concentration, and a curve number of 80, as discussed with Mr. Berry. The curve number of <br />80 is based upon a soil group B pastureland in poor condition (approximately 25%-30% cover, <br />moderate runoff, moderate infiltration), and the highly fractured nature of the surface materials. <br />The revised culvert sizing calls fora 21 inch diameter culvert to be installed, and has been <br />enclosed for reference. <br />Page Ex. 8-11(b) has been revised accordingly and is enclosed. I sincerely apologize for any <br />inconvenience this may have caused, and assure you steps will be taken to prevent a recurrence. <br />Should you have any questions or further concerns, please contact me at your convenience. <br />Sincerely, . <br />j0 ;~~~~ i <br />Marcus A. Middleton <br />Environmental Specialist <br />MAM:dg <br />