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III IIIIIIIIIIIII III 999 STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Department of Natural Resources 1313 Sherman Sl., Room 215 Dem~er, CO BO?ol Phone. Doll 866 3567 FAX:(303)A32-8106 August 13, 1993 Mr. Ron Thompson Senior Mine Engineer Basin Resources, Inc. 14300 Highway 12 rJeston, CO 81091 RE: Golden Eagle Mine, Permit No. C-81-013, Basin Resources, Inc., TR-23, Adequacy Review Dear Mr. Thompson: In addition to the adequacy questions presented in the Division's letter of June 18, 1993, following are additional questions or comments: pF COQ „~`"/ 9 ~ ~ O ~.~ R re+r,®' . Roy Romer Governor Michael B. Long Dnivon Direc mr 1. The Sedcad runs use a 10 year - 24 hour event of 2.7 inches of precipitation: The NOAA atlas shows that 2.9 inches of precipitation is more appropriate. Please rerun the Sedcad runs using 2.9 inches of precipitation for the 10 year - 24 hour event. 2. If the operator chooses to remove the ditches and sump at the third north intake shaft, then the topsoil stockpile near the intake shaft will need demonstrations, since the topsoil pile would not report to a sediment pond. 3. Does the SAE demonstration for the third north intake shaft area include the gravel drop area as well? How will the gravel drop facility function while still maintaining the area as an SAE? 4. A CP value of .035 was used for the third north intake shaft area and for the NW-1 exhaust shaft area. According to the Sedcad manual, Table 5.5c, CP Factors for Permanent Pasture, Rangeland, Idle Land and Grazed Woodland, this CP value corresponds to a 65 percent vegetative cover and litter that contacts the ground, with no appreciable canopy and a cover of grass. My recollection of these 2 shaft areas makes me believe that this CP value is too low. At the NW-1 exhaust shaft area, my recollection is that about half of the area is bare soil, CP=1, and that about one-fifth of the vegetated area is a little sparse. At the third north intake, most of the vegetated areas were sparsely covered. Please justify the CP value used.