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<br />III IIIIIIIIIIIIIIII <br />999 <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Department of Naw ml Resources ~~~~~ <br />131 3 Sherman SL, Room 215 <br />Denver, Colorado 8020) <br />Phone. (30 41 866-3567 <br />FA X:13031 R32-AIU6 <br />DEPARTMENT OF <br />NATURAL <br />RESOURCE <br />February 22, 1994 a° Ru^,e, <br />v <br />Cuvr~nor <br />Mr. Murari P. Shrestha hen sa ~a aar <br />Assistant Manager of Engineering e'e`°"veDire"°' <br />Western Fuels - Utah Michael e. I°^ti <br />D iv is inn Dirednr <br />405 IIrban Street 7}305 <br />Lakewood, Colorado 80228 <br />RE: Second Preliminary Adequacy Review <br />Technical Revision TR-33 - Refuse Pile SA <br />Deserado Mine (C-81-018) <br />Dear Mr. Shrestha: <br />The Division has completed a second preliminary adequacy review of <br />the above referenced technical revision and has identified the <br />following concerns: <br />Hydrology <br />1) The Division calculated a curve number of 85 for the <br />undisturbed drainage as opposed to a curve number of 79 <br />as calculated by WFU. The determination of the curve <br />number was based on the soils map presented as Map 6 of <br />the permit application package. Most of the soils <br />indicated on the map fall within the D hydrologic soil <br />group according to Appendix B of the SEDCAD manual. The <br />vegetation type, according to Map 10 of the permit <br />application package is primarily Big Sagebrush with <br />Western Wheatgrass with 10-30~ cover. Therefore, the <br />Division selected the cover type from Table 2-2d of the <br />SEDCAD manual to be "Sagebrush with grass understory" <br />with poor (<30%) cover. The resulting curve number was <br />85. WFU should re-run the SEDCAD model for the <br />undisturbed drainage with a curve number of 85 or provide <br />justification for using a curve number of 79. <br />2) Although the channels are designed to be vegetated, the <br />vegetation will not be established immediately. <br />Therefore, to account for conditions prior to the <br />establishment of vegetation, the model should be run with <br />the ditches characterized as earthen channels. <br />