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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 III) 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 />