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• 1.4 Sediment Control Demonstration <br />According to CDMG regulation 3.03.1(3)(b), Phase II bond release cannot be granted until the applicant <br />demonstrates that existing conditions will result in equivalent or lesser sediment contributions to surface <br />runoff when compared with pre-mining levels as determined by baseline data. <br />To demonstrate that runoff from each block will result in equivalent or lesser sediment contribution as <br />compared to baseline conditions Trapper is including two evaluations; Universal Soil Loss Equation <br />(USLE) calculations and a SEDCAD analysis. The USLE provides a basis for predicting the gross erosion <br />per acre from an area on an annual basis. SEDCAD modeling, on the other hand, addresses both runoff <br />and erosion estimates and provides results on the basis of single storm events. <br />1.4.1 Universal Soil Loss Equation - - <br />The Universal Soil Loss Equation (USLE) provides a mechanism to predict the gross annual erosion <br />occurring on a given area. The technique does not account for the deposition of eroded sediment within <br />the area being evaluated. Nonetheless, within the bounds of certain assurnptions, USLE provides a <br />reasonable basis for comparing sediment yield from undisturbed and reclraimed lands. The USLE <br />• calculations presented are based upon an approach applied by the Colorado Division of Minerals and <br />Geology (CDMG) to assess the Phase II sediment control criteria for reclaimed blocks submitted under <br />the SL-1 Bond Release Application. Previous calculations by the Division suggest the sediment yield from <br />reclaimed areas is approximately 10% higher than that occurring on undisturbed areas. However, this <br />assumption is not utilized in this assessment because the "undisturbed" lands in this instance consist of <br />cu11'rvaled croplands (wheal) while the reclaimed areas support alfalfalgrass hay vegetation stands that are <br />much less intensively cultivated. For the pre-mining block value, the USLE i:s calculated as follows for <br />lands formerly cultivated with winter wheat crops: <br />_ (30)(.34)(0.7)(0.20)(0.8) <br />= 0.86 tons per aae per year <br />• <br />R 30 SCS Map of R factors for Colorado <br />K 0.34 Trapper Permit C-81-010 Appendix C1, Section XIII, Table E-3 <br />LS 0.7 SCS LS table (TR51, 1977); 50' slope length, 8% avg slope <br />C 0.20 SCS C factor for Winter Wheat and fallow cropping sequence <br />with approximately 500 Ibs residue (Erosion Handbook Water <br />and Wind, SCS, June 1988) <br />P 0.6 Trapper Permit C-81-010 Appendix C], Section XIII, Table E-4 <br />7 <br />