Laserfiche WebLink
<br /> <br />7. On page 3 of Exhibit 8 of the permit application, the rainfall <br />amount for the 25 year - 24 hour storm event is listed as 2.1 <br />inches. In Volume V, Appendix B, a rainfall amount of 2.0 <br />inches is used for the 25 year - 24 hour storm event. However, <br />an examination of the NOAA Atlas 2, 1973, seems to indicate <br />that the rainfall amount is closer to 2.2 inches. Please <br />reconcile the use of both 2.0 and 2.1 inches of rainfall for <br />the 25 year - 24 hour storm event, as opposed to using 2.2 <br />inches. <br />8. The Division has two concerns with the curve number <br />calculation for the burned out area, listed on page 3 of <br />Exhibit 8. First, Table 2-2c, Runoff curve numbers for other <br />agricultural lands, is used in the permit application <br />calculation of the curve number. However, the vegetation <br />description for this area, found on page 21 of Exhibit 5, does <br />not mention this area as being agricultural. It would seem <br />that Table 2-2d, Runoff curve numbers for arid and semiarid <br />rangelands would be more appropriate. Please justify the use <br />of Table 2-2c for the burned out area. <br />Second, a curve number of 65 is used for the burned out area. <br />Referring to Table 2-2c, a curve number of 70 is listed for a <br />cover type of Brush - brush-weed-grass mixture, a hydrologic <br />condition of fair and a C soil type (Absarokee). If you can <br />justify the use of Table 2-2c, rather than Table 2-2d, please <br />justify the use of a curve number of 65 for this particular <br />area. <br />9. On page 4 of Exhibit 8, a curve number of 63 is assigned to <br />the sagebrush rangeland area. On the next page, in the runoff <br />volume table for pond B, a curve number of 63 is listed for <br />sagebrush but a runoff of 0.00 inches of direct runoff is <br />presented. For 1.8 inches of rain for the 10 year - 24 hour <br />event, a curve number of 63 should result in a direct runoff <br />of .06 inches of water. Please determine which factor may need <br />to be changed, the curve number or the direct runoff amount. <br />10. The runoff from the material storage area that is located <br />below drainage area E and pond C does not go through a <br />treatment facility, such as a pond. Nor has the operator <br />requested a small area exemption status for this area. Whether <br />or not this is an old area of disturbance, the Bowie No. 2 <br />Mine will be using the area and is responsible for sediment <br />control of this area. Please submit either a design that <br />routes this runoff to a sediment pond or a design that shows <br />that a small area exemption status is appropriate. <br />11. On pages 6 and 9 of Exhibit 8, values are given for ~ canopy <br />and ~ cover. These values do not seem to correlate with the <br />vegetation values presented on pages 2, 3, and 4 of Exhibit 8. <br />3 <br />