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~~~ ~~~~~~~I~~~~~~~~ i oo~oa~e:,2~„~ZOO' STAT~OF COLORADO <br />MINED LAND RECLAMATION DIVISION <br />Department of Natural Resources <br />• 7373 Sherman St., Room 275 <br />Denier, CG 80203 <br />303 866-3567 <br />Fa x: 303 832-8706 <br />OF' COr <br />~~~ ~ roQoo <br />w~ 7~~90 <br />r ~r i <br />x 18'16 ~ <br />Roy Romer, <br />Gaverna <br />Fred R. Ban[a, <br />Division Director <br />November 22, 1991 <br />Rockcastle Coal Company <br />C/0 Mr. Dean Massey <br />Parce] Mauro Hultin and Spaanstra <br />1801 California, Suite 3600 <br />Denver, Colorado 80202 <br />RE: Rockcastle Pit No. 4 submittal, October, 1991, File No. C-81-039 <br />Dear Mr. Massey <br />The staff has reviewed the October, 1991, submittal related to the Pit No. 4 <br />disturbance area. The Division's analysis of the bond necessary for <br />backsloping has been forwarded to you under separate cover in the bond release <br />adequacy letter. I evaluated the hydraulics on the revised Pond No. 4 and <br />the associated ditches. I find the pond adequately sized, but I am concerned <br />about its general configuration. I do have several questions about the <br />assumptions employed by the consultant. We would like you to pass this <br />information on to ACZ, but we will not require modifications of the design <br />calculations. <br />Methodology Concerns <br />A. The use of a CN of 47 for undisturbed sagebrush community is <br />not justified by either the hydrologic soil classifications or <br />the amount of cover found in the baseline studies. <br />B. The 1983 copy of 'Soils of Colorado' lists the soil erodability <br />value for the top 12" of Rockcastle soils as follows: <br />Coutis Fine Sandy Loam .20 <br />Winevada - Splitro Complex .41/.18 <br />Winevada Fine Sandy Loam .41 <br />Skylick .32 <br />Mr. Nettleton has indicated in telephone conversations that <br />the Rockcastle use of 0.24 is based on the Routt County SCS <br />revision of their soil erodability values. The Division needs <br />to have published verification of these values if the <br />consultant intends to use <br />them with any frequency. <br />