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inputs and results for both the pre-mining and post-mining land conditions are shown on Tables 1.4-1 and <br /> 1.4-2, respectively. The SEDCAD 4 computer printouts and input calculation sheets can be found in <br /> Appendix 3. Input parameter references are also provided in Appendix 3. <br /> The SEDCAD 4 models serve to demonstrate that for the selected design event, less sediment is <br /> produced from the reclaimed lands than from the undisturbed lands. Given the nature of the vegetation <br /> characteristics, and consequently of the runoff characteristics occurring under both pre-mining and post- <br /> mining conditions, it is necessary to select an atypical design storm input in order to produce the requisite <br /> 0.5 inches of runoff necessary to maintain program accuracy. For the purposes of this demonstration, an <br /> input design event of 2.75 inches per 24 hours was utilized. This design storm input produces the desired <br /> minimum 0.5 inches of runoff from the pre-mining blocks and serves as the basis of comparison for the <br /> pre-mining and post-mining conditions. <br /> Curve Numbers (CN) representative of the vegetation at Trapper for both the pre-mining and post-mining <br /> conditions were selected from tables available within the SEDCAD 4 program. For the pre-mining areas, <br /> a CN of 48 was selected from the CN table for Arid & Semi-arid Rangelands using the oak-aspen — <br /> mountain brush mix cover type in "Fair" hydrologic condition with a hydrologic soil group classification <br /> (HSG) of B. For the post-mining areas, a CN of 61 was selected from the CN table for Other Agricultural <br /> Lands using the pasture, grassland, or range — continuous forage for grazing cover type in "Good" <br /> hydrologic condition with an HSG classification of B. The different CN values serve to model the differing <br /> runoff responses of the described cover types. More pronounced initial precipitation abstractions are <br /> accounted for in the lower CN selected for the pre-mining areas. After the initial abstractions are <br /> considered, erosion and sediment yield are evaluated considering vegetative cover conditions at ground <br /> level below the mountain brush vegetative type canopy. The documented cover percentage values of the <br /> vegetation occurring on the pre-mined and reclaimed lands were considered in selecting the CN model <br /> input values and are reflected primarily in the hydrologic condition classifications chosen. The CN values <br /> representative of the vegetation at Trapper for both the pre-mining and post-mining conditions were <br /> modified to reflect Antecedent Moisture Condition III (AMC lll) for the purposes of this demonstration in <br /> order to produce comparable model outputs which show runoff and sediment transport occurring. <br /> Further distinctions between the reclaimed lands and pre-mining conditions are characterized using the <br /> Control Practice (CP) factor model input variable. The C factors used in the models were obtained from <br /> the SEDCAD 4 table for Permanent Pasture, Rangeland, Idle Land, and Grazed Woodland utilizing cover <br /> and canopy data as appropriate. For pre-mining conditions, a canopy providing 50% cover and consisting <br /> of appreciable brush or bushes (fall height of approximately 2 meters) was used in conjunction with a <br /> range site area-weighted herbaceous cover measurement in accordance with the pre-mining cover data <br /> presented on Table 4.4-2 of Permit No. C-1981-010. For post-mining conditions, no appreciable canopy <br /> was utilized along with the actual herbaceous cover values existing on the reclamation as determined by <br /> direct transect measurements. These tabular C values were subsequently adjusted to reflect the more <br /> 14 <br />