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• 2.4 Sediment Control Demonstration <br />According to CDMG regulation 3.03.1(3)(b), Phase II bond release liability cannot be granted until the <br />applicant demonstrates that existing conditions will result in equivalent or lesser sediment <br />contributions to surtace runoff when compared wtth premining levels as determined by baseline data. <br />To demonstrate that runoff from each block will result in equivalent or less sediment contribution when <br />compared to baseline data, TemaMatrix Engineering 8 Environmental Services developed for Trapper <br />a stte drainage and sedimentology model to determine the peak settable solid concentrations for the <br />runoff from each block. The results were then compared to the effluent levels set by the state based <br />on baseline information. The block drainage and sedimentology motlels were developed utilizing <br />SEDCAD+. SEDCAD+ is a computer software program developed to assist in the evaluation of <br />stormwater runoff, erosion, and sediment control management techniques. <br />To develop an accurate model representing existing conditions for each block, the vegetation survey <br />outlined in section 2.2 and soil information from the existing permit docurient were input into the <br />SEDCAD+ program. Given the iregular shapes of the blocks in relation to the topography and the <br />• fact that portions of individual blocks may fall within adjacent sub-watersheds, it is difficult to develop <br />an accurate model for the entire block. In order to develop a representative model, typical twenty-acre <br />square sections of each block were modeled using the average slope and slope length for the entire <br />block. A summary of the inputs and results are shown on Table 2.4-1. The SEDCAD+ computer <br />printouts and input calculations sheets can be found in Appendix 2.4. <br />As shown in Table 2.4-1, the peak settleable solid concentration for the 10-year, 24-hour event ranges <br />from 0.23 mg/I to 0.48 mg/I, which is below the State standard of 0.50 mg/I. <br />• <br />2-18 <br />