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g) Illustration 44 contains a table and associated sketch that break each of the RP-2/3/4 <br />perimeter ditches into 8 segments, with specified slope and velocity control (either <br />riprap or rock check dam with design spacing) for each segment. -Check dam spacing <br />varies from 1 check dam every 17.2 feet to 1 check dam every 64.5 feet. These <br />specifications apply to permanent ditch designs, but the extent to which they apply to <br />"interim in-pit ditches" is not cleaz. Please amend text as necessary to clarify velocity <br />control measures and specifications that apply to interim in-pit ditches. Straw <br />bale checks and dug-out sediment traps referenced in the text have proven to be <br />ineffective. Their use should be discontinued, existing straw bale checks should be <br />broken up or removed, and text should be accordingly amended. <br />h) Subsequent pages provide SEDCAD channel designs for the various segments, with <br />some triangulaz (V) and some Trapezoidal (T) designs, and some segments with both <br />types of design, all with 2:1 side slopes. Based on permit text, specified channel <br />capacities aze applicable to the "interim in-pit ditches". Recent inspection reports <br />identified one location where sediment clean-out was warranted, and several locations <br />where stabilizafion is warranted. Please implement timely maintenance and <br />stabilization work in the following locations. <br />• West ditch seg.3 design (V) d=2.02', tw=8.07'. Inspection report indicated need <br />for maintenance in this segment to remove accumulated sediment. <br />• West ditch seg.6 design (T) d=.55', tw=8.2', D50=12". Ditch erosion was noted at <br />lower end of this segment. Installation of angular riprip, in accordance with <br />the permanent design specification, appears to be warranted. <br />West ditch seg.7 design (~ d=2.32', tw`9.26'; Ditch erosion was noted in the <br />inspection report dated March 5, 2002. Stabilization measures are warranted. <br />East Ditch seg. 3 design (V) d=0.95', tw=3.81', D50=18"; East Ditch seg. 3 design <br />(T) d=0.68', bw=6.0', tw=8.72', D50=6". Inspection report indicated <br />downcutting within upper portion of Segment 4 or lower portion of Segment 3. <br />Rock checks and river cobble previously placed in this section as temporary <br />stabilization measures apparently were not adequate. Angular riprap should <br />be installed in this section in accordance with permanent ditch design <br />specification. <br />i) Illustrations 5 and 6 contain refuse area pond and ditch designs that aze outdated, and <br />the illustrations should be removed from the application (with cover page notations <br />indicating that contents were replaced by information contained in Illustration 44). <br />Deserado Mine Apri130, 2002 <br />15 <br />