2014-11-24_REVISION - C1981010 (2)

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Pre - mining Parameter Selection Trapper's basis for selection Division's Comment 2.75- Produces the minimum 0.5 inch The greater than 100 -year event is necessary in Design inches in of runoff that is necessary to the model as SCS TR -55 questions the accuracy Event 24 hours maintain program accuracy (SL- of the Curve Number method when runoff depth is 16 app. Sec. 1.4.2) less than 0.5 inch. CN 48, AMC 11 68-69, Trapper permit Appendix Q, Reasonable based on selections of cover, soil AMC III Section XIII, Table E -3 group, hydrologic conditions, and C factor. Oak /aspen /mtn. brush Permit application., Appendix Q, Reasonable based on premining conditions mix Section XII "Fair' hydrologic None Reasonable based on description of "Fair" in SCS condition TR -55 Hydrologic soil group Permit application., Appendix Q, Reasonable based on the soil types on the bond classification "B" Section XII release blocks located on map M -29, consistent with group B CP Factor: 0.049 -0.050 Tables 2.3 -13 and 4.4 -2 in permit Selection accounted for total cover and canopy application C- 1981 -010 cover of premining vegetation Slope data from three locations Slope lengths and land use description inputs Time of concentration on Summary pages in the accurately matched field data SEDCAD runs Post - mining Parameter Trapper's Trapper's basis for Division's Comment Selection selection Produces the minimum 0.5 inch of Design 2.75- runoff that is Event inches in necessary to Same event used in the premining model 24 hours maintain program accuracy (SL -16 app. Sec. 1.4.2) Trapper's selected 61, AMC cover, soil group, Reasonable based on selections of cover, soil group, CN II 78.8, hydrologic hydrologic conditions, and C factor (see below) AMC III conditions and CP factor (see below) Pasture, Grassland None Reasonable based on postmining land use and Rangeland "Good" hydrologic Reasonable based on the term "good" in SCS TR -55 for other condition None ag lands corresponding to >75% ground cover, which is consistent with Trapper's SL -16 vegetation data. Hydrologic soil group "B" Permit application., Appendix Q, Reasonable based on the soil types on the bond release blocks classification Section XII located on map M -29, consistent with group B SEDCAD 4 table for Cover values and treatment practices indicate the reasonable CP Factor: 0.014 permanent pasture, selection of this variable rangeland