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<br />-4- <br />3. The revised NPDES Permit No. CO-0036935 should be described in <br />Section 2.03.10 of the mining and reclamation permit <br />No. C-81-034. Appropriate page revisions should be submitted <br />to accurately describe this change of NPDES permit. <br />4. The additional information requested by the Division on <br />October 11, 1984 in reference to Stipulation No. 2, drainage <br />channel reconstruction, has not been submitted to date. This <br />information should be provided to complete the review by the <br />Division: <br />A) The Drainage System Map and Final Contour Map submitted do <br />not show the entire drainage contributing to the headwater <br />of the reconstructed channel. From the Drainage System <br />Map, the permittee states that areas 5 and 6 contribute to <br />the upper stream. Why are areas 4 and 7 excluded from <br />contributing to the headwaters? <br />B) A point midway down the channel was considered to receive <br />1/2 of the peak discharge of the lower reclaimed area. <br />From the configuration of the basin, it appears that this <br />point would receive greater than 1/2 of the drainage. <br />Intermediate points from the upper to lower reconstructions <br />should be evaluated to determine the minimum <br />cross-sectional area required to contain the flow. These <br />points should coincide with the intersection of major <br />sub-basins into the reconstructed stream channel. <br />C) Using equation: <br />N = 0.0395 d50 1/6 <br />a riprap d50 sizing of 4.85 inches does not coincide with <br />an n value of .04. The n value should be justified. <br />D) On page 128b, it is stated that the "riprap will be well <br />graded with the majority of the material over 4.85 inches <br />in diameter." The definition of d50 is "rock size for <br />which 50 percent of the riprap by weight is smaller." The <br />permittee's statement should be modified to reflect <br />accepted riprap sizing methods. <br />Following review by the Division, a revision of <br />Section 2.05.4(2)(c) which incorporates these responses into <br />the narrative discussion should be submitted as revised pages <br />for insertion into the permit document. <br />5. The reclamation plan timetable (page 126 of the application) <br />needs to be revised to update this section to include present <br />