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J.E. Stover 6 Associates -15- May 31, 1996 Bowie No. 2 Mine listed for a cover type of Brush - brush-weed-grass mixture, a hydrologic condition of fair and a C soil type (Absarokee). If you can justify the use of Table 2-2c, rather than Table 2-2d, please justify the use of a curve number of 65 for this particular area. 32. On page 4 of Exhibit 8, a curve number of 63 is assigned to the sagebrush rangeland area. On the next page, in the runoff volume table for pond B, a curve number of 63 is listed for sagebrush but a runoff of 0.00 inches of direct runoff is presented. For 1.8 inches of rain for the 10 year - 24 hour event, a curve number of 63 should result in a direct runoff of .06 inches of water. Please determine which factor may need to be changed, the curve number or the direct runoff amount. 33. The runoff from the material storage area that is located below drainage area E and pond C does not go through a treatment facility, such as a pond. Nor has the operator requested a small area exemption status for this area. Whether or not this is an old area of disturbance, the Bowie No. 2 Mine will be using the area and is responsible for sediment control of this area. Please submit either a design that routes this runoff to a sediment pond or a design that shows that a small area exemption status is appropriate. 34. On pages 6 and 9 of Exhibit 8, values are given for ~ canopy and $ cover. These values do not seem to correlate with the vegetation values presented on pages 2, 3, and 4 of Exhibit e. Please refer to the permit application pages where these data come from. 35. On pages 6 and 9 of Exhibit 8, an erosion control practice factor, "P", of .75 is used. Please describe the specific practices that will be employed at the mine site that would reduce this "P" factor from 1.0 to .75. 36. On pages 7 and 10 of Exhibit S, it is stated that riprap will not be needed for the top of the emergency spillways for ponds B and C, respectively. However, it is also stated that the velocity of the discharge from the 25 year - 24 hour storm event will be 5.25 feet per second. The Division would like to comment that this velocity may be erosive, depending upon the material used in the emergency spillways. The Division recommends that some type of erosion control material be used along the top of the emergency spillway. The material can be an erosion control fabric, riprap of the size already calculated on pages 7 and l0 of Exhibit 8 or some other material.