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• 2.05.3(4)(a)(ii) <br />Temporary terrace ditches are shown on drawing 2.05.3(4)-2a. These <br />ditches are sized in accordance with the information in Table <br />2.05.3(4)(d)-6 and on the drawing. It is anticipated that these <br />ditches will be maintained functional for two or three years until <br />the vegetation on the site is well established at which time the <br />ditches will be allowed to fill with sediment and gradually cease <br />functioning as terrace ditches. Since these ditches are temporary, <br />no rip rap will be placed in them. Straw bales may be used to slow <br />water velocities in obvious problem areas. <br />Information contained on the proceeding pages demonstrates that the <br />untreated drainage from the reclaimed mine site does not contribute <br />additional suspended solids above natural conditions. Therefore, <br />the temporary terrace ditches will no longer be maintained. <br />The upper diversion ditch for the refuse pile was designed using <br />the program SEDCAD+ Version 3. The area that contributes drainage <br />to the upper diversion ditch is 4.8 acres of unaffected Area 7 as <br />shown on drawing 2.05.3(4)-2a. A curve number of 74 was assigned <br />to this drainage area to remain consistent with the remainder of <br />the run-off calculations contained in the permit. The diversion <br />ditch is approximately 1075-feet long. <br />• The flow design was performed based on a 48 ditch grade. Since the <br />grade of the ditch will vary somewhat, the calculations at the <br />bottom of Table 2.05.3(4)(d)-12 were included to show the required <br />depth for ditch grades that range from 18 to 48. This table <br />indicates that a trapezoidal channel with a bottom channel width of <br />24-inches, 1.SH:1V side slopes, a minimum slope of 18 and a peak <br />discharge of 4.18 cfs must be at least 10-inches deep. At greater <br />slopes the required ditch depth is less. Therefore, the upper <br />diversion ditch for the refuse pile will be designed as a <br />trapezoidal channel with a bottom channel width of 24-inches, <br />1.SH:1V side slopes and 10-inches deep. <br />The refuse pile upper diversion ditch was constructed during the <br />first week of October 1994, The ditch was constructed to avoid the <br />cedar trees along the ditch alignment. In order to avoid the cedar <br />trees and follow the natural terrain, the grade of the ditch <br />exceeded 48 in a few areas. The Division inspected the ditch in <br />February 1995 and issued a notice of violation for failure to <br />construct the refuse pile upper diversion ditch in accordance with <br />the approved design. <br />In order to satisfy the Division's concerns, the Operator will <br />install an erosion control matting in the areas in the ditch where <br />the grade exceeds 4~. Based upon a preliminary survey, the 48 <br />grade is exceeded in three locations as follows: Stations 0+75 to <br />1+25, 6+75 to 7+25 and 8+50 to the end of the ditch. Stations are <br />. measured from the upstream end of the ditch. <br />-100- Rev. March 25, 1995 <br />