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1 <br />r~ <br />!.IA11 1)1 (: ()1 ~flf A1111 II II I1A 1111 I1,~. ~...v ~.r•~~~i III IIIIII III IIII III <br />DEPARTMENT OF NATURAL RESOURCES <br />D. Monte Pascoe, Executive Drr ector <br />1V11NEU LANU RECLAMA'T'ION <br />423 Centennial Building, 1313ShermanStreet <br />Denver, Colorado 80203 Tel. (303) 839-3567 <br />David C. Shelton <br />December 3G, 1980 Director <br />Mr. Darrel itespe <br />Dorchester Colomine Coal Company <br />2795 Skyline Court <br />Grand Junction, Colorado 81501 <br />RE: Dorchester - Fruita Mines Refuse Pile <br />Our File No. 79-60 <br />Dear Darrel: <br />As I discussed with yoTt in a phone conversation on December 22, 1980, <br />the only outstanding issue to be resolved is the amount of topsoil to <br />be replaced on the refuse pile. The 3081 cubic yards of topsoil <br />which you plan to stockpile should be enough to replace 6 inches <br />rather than the two inches specified. Upon receipt of a statement <br />to this effect, the staff will be ready to approve this Technical <br />Revision. <br />Enclosed are comments from Jim Pendleton on the durable rock fill <br />and coal processing waste embankment stability analyses. Since i <br />have received a statement from you that the waste disposal pile <br />will be inspected and certified by a professional engineer, there <br />are no outstanding issues on the embankment stability. <br />I have reviewed the analyses of the coal refuse material and have <br />found no apparent deficiencies in the requested material. With <br />four feet of non-toxic non-combustible cover over the refuse and <br />the designed underdrain system, no environmental problems should <br />be encountered. <br />After reviewing the sediment control system for the refuse pile <br />site, 1 find that it is adequate. However, i noted several mistakes <br />which I feel should be brought to your attention. First, the <br />10-year 24-hour isopluvial for your mine is 1..6 inches not the 1.8 <br />inches you used. Second, the CN value as calculated by the Geo <br />Testing Labs had a mathcmrttical error C.or Pond No. 1. The CN should <br />have been 90 instead of 84. However, after discussion with other <br />staff members, we came to the conclusion that the CN value of 90 <br />was higher than needed. Combining your categories of bedrock and <br />open waste and soil stockpiles into one category of a 10°s sage- <br />grass cover on a "D" type soil, and using the SCS Peak Flows <br />nomogram on page 23, we came up with a CN value ofd {Veighting <br />this CN value with your values for structures and dirt roads, we <br />