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Table 6. SEDCAD Variables and Basis for Selection <br /> Premining <br /> Parameter Trapper's Trapper's basis for selection Division's Comment <br /> Selection <br /> Produces the minimum 0.5 inch A greater than 100-year event is necessary <br /> Design 2.75 inches of runoff necessary to in modeling as SCS TR55 questions the <br /> Event in 24 hours maintaining program accuracy accuracy of the Curve Number method <br /> (SL24 application Sec 1.4.2). when runoff depth is less than 0.5 inch. <br /> 48 SedCad 4 Trapper's selected cover, soil Reasonable as per selections of cover, soil <br /> CN 68.2 group,hydrologic conditions, group,hydrologic conditions, and C <br /> B,W,H* and CP factor(see below). factor. <br /> Oak/Aspen— Sage/Grass Permit application,Appendix Q Reasonable as per pre-mining conditions. <br /> Section XII <br /> "Fair" hydrologic condition Permit application,Appendix Q Reasonable as per description of"Fair" in <br /> Section XII SCS TR55 <br /> Hydrologic soil group Permit application,Appendix Q Reasonable, as per soil types on bond <br /> classification "B' Section XII release blocks delineated on map M29 & <br /> consistent with soil group B. <br /> CP Factor: 0.025 Tables 2.3 &4.4-2 of permit Selection accounts for total cover and <br /> application C 1981010 canopy cover of premining vegetation. <br /> Time of Concentration Slope data on Summary pages Slope lengths and land use description <br /> in SEDCAD runs inputs accurately matched field data. <br /> Produces the minimum 0.5 inch <br /> Design 2.75 inches of runoff necessary to <br /> Event in 24 hours maintaining program accuracy Same event as used in preming model. <br /> (SL24 application Sec 1.4.2). <br /> 61 SedCad Trappers selected cover, soil Reasonable as per selections of cover, soil <br /> CN 78.8 B W H* group,hydrologic conditions, group,hydrologic conditions, and C <br /> and CP factor(see below). factor. <br /> Pasture, Grassland & Postmining land use Reasonable as per postmining land use. <br /> Rangeland <br /> "Good" hydrologic None Reasonable as per"Good" in SCS TR55 <br /> condition for other lands corresponding to. <br /> Hydrologic soil group Permit application,Appendix Q Reasonable, as per soil types on bond <br /> classification "B" Section XII release blocks delineated on map M29 & <br /> consistent with soil group B. <br /> SeDCad 4 table for permanent Cover values and treatment practices <br /> CP Factor: 0.022 pasture &rangeland indicate reasonable selection of this <br /> variable. <br /> * B, W, H: Barfield, Warner, Hann <br /> Based on Trapper's SEDCAD 4 modeling using baseline data, the Division finds that the lands <br /> proposed for Phase 11 bond release are not contributing suspended solids to streamflow or runoff <br /> Permit Number C1981010 <br /> SL24 Page 15 of 16 <br />