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<br /> <br />-a- <br />4.. On page 4.05-10 the applicant requested a variance from <br />stream buffs[ zones to accomodate the main ent[ies of the <br />mine. The Division will issue it's decision on the request <br />after a finding on the impacts of subsidence have been made, <br />the effects of mining on the surface and ground water systems <br />have been determined and findings on alluvial valley floors are <br />made. At this point, it does not appear this will be a ma]or <br />trouble spot. <br />5. Several concerns were noted with the revised design <br />calculations contained in Exhibit 6, Table A. In using the SC5 <br />TR-55 watershed model, the applicant failed to ad]uat peak <br />runoff rates for varying slope and basin shapes. The applicant <br />should refer to Appendix E of SCS TR-55, Peak Flows in <br />Colorado, 1977 and make the appropriate ad]uatmenta. <br />6. Problems were identified with Table B, Exhibit 6 with <br />regards to culvert sizing. The Manning open channel equation <br />is only applicable to a depth of flow of 94~ of capacity, after <br />which closed conduit hydraulics apply. Culvert designs should <br />be rechecked using an appropriate closed conduit design <br />procedure. <br />7. Page 4.05-19 of Volume 1 and page 3, Exhibit 6 of Volume <br />2 state thac the Division approved a sediment storage criteron <br />of 0.02 ac-ft/ac of disturbance on January 29, 1902 for the <br />CYCC mines. This statement is incorrect and should be deleted <br />from the application. When this criteria was proposed in the <br />winter of 1901-02, the Division responded with a letter of <br />concerns that needed to be addressed p[ior to out approval of <br />the criteria. That letter was dated December 10. 1981 from <br />Sandy Emrich of MLRD to Kent Watson of CYCC. Instead of taking <br />trie time to respond to this lette[ CYCC instead chose to pursue <br />a quick solution to the issue by developing a sediment yield <br />criteria for a specific subwaterahed. The response was <br />contained in a letter dated December 11, 1901 from Michael <br />McCarthy to Sandy Emrich (hand delivered). The Division <br />reviewed this criteria and found it to be acceptable for the <br />particular watershed. However, approval was never granted to <br />allow its use over the entire basin. Topographic (LS) factors <br />vary too much to allow such a site specific criteria over a <br />wide region. <br />It should be noted that the Division reviewed the sediment <br />ponds considering the old sediment storage criteria (O.l <br /> <br />