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• Roadside North Portal <br />Ditches Across Reclaimed Area <br />Calculation Rational and Results Summary <br />Rational: <br />Calculated using SEDCADT"' 4 for Windows <br />Areas, slopes and flow paths obtained from electronic media. <br />Ditches have been designed across the reclaimed North Portal to accommodate <br />storm runoff from the primary drainage chutes originating on the steep slopes <br />above the reclaimed area. This runoff is currently diverted around the site by the <br />east and west diversion ditches as shown on Exhibit 86. After the vegetation on <br />site is established and a demonstration is made that shows runoff from the <br />reclaimed area does not contribute suspended solids to streamflow or runoff <br />outside the permit area in excess of premining levels, the diversion ditches will <br />be regraded to AOC and the ditches across the reclaimed area will be <br />constructed. <br />Curve Numbers based on Table 2-2d, Runoff curve numbers for arid and <br />semiarid rangelands, with Herbaceous cover. The reclaimed area is considered <br />• to have good cover because the ditches will not be constructed until the <br />vegetation is adequate to control erosion. <br />Upland Area <br />93 - D soil group, Poor Cover <br />Reclaimed Area <br />62 - B soil group, Good Cover <br />10 year 24 hour storm event of 1.4" used for all run-off calculations <br />The ditch layout and sizing for the ditches across the North Portal are presented <br />on the following pages and on Exhibit SC. <br />ENGINEER'S CERTIFICATION <br />The SEDCAD calculation ration presented on pages 14-6-118 through 14-6- <br />140 were prepared by~g~c~~nth of April 2003, and the information <br />presented is true and~~it~t to tf~b~f my knowledge and belief. <br />~c~ . C T; a <br />~Aa,James E. Stowe P.E. bate <br />R~~Stered Professto'nal Engineer <br />• Siaf~~fp~Alti~a Rio' IVo. 19230 <br />•.~o.• <br />14-6-118 (New 4/03) <br />