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control systems. The hydrologic inputs to the modeling, the information used from existing permits <br />and the modeling results are presented below. <br />3.2.1 Hydrologic Inputs <br />Rainfall <br />The SCS Type II, 24 hour precipitation events (NOAA, 1973) and PMP (NOAA, 1984) storm events <br />used in the modeling are listed in Table 5. <br />Soils <br />Soils information was obtained from the National Resource Conservation Service (NRCS) Web Soil <br />Survey (NRCS, 2009). The primary soils within the drainage area for the RPE East are Type D soils. <br />Land Use <br />The following assumptions for land use were used in the SEDCAD modeling based on curve number <br />(CN) recommendations found in NRCS Technical Release 55 (NRCS, 1986): <br />• Undisturbed Slope Areas- CN= 63 for oak -aspen mountain brush mixture in fair condition <br />(30 -70% ground cover) for Type D soils <br />• Reclaimed Refuse Pile- CN =85 for herbaceous mixture of grass, weeds, and brush cover in <br />good condition ( >70 %) for Type D soils <br />3.2.2 Modeling Results <br />The results of the SEDCAD modeling are provided in Appendix F. Modeling demonstrates that the <br />existing sediment pond is adequate to control and treat runoff from the RPE and the RPE East for the <br />10 -year, 24 -hour storm as described in Section 3.2. <br />3.3 Ponds, Impoundments, Other Treatment Facilities and <br />Diversions (Rule 2.05.3(4) & 4.05.6) <br />The sedimentation basin serving the existing RPE provides adequate capacity to store the runoff from <br />the l 0 -year, 24 -hour storm event for the RPE and RPE East areas. Sediment and clear water <br />diversion ditches have been designed to provide capacity for runoff from the 100 -year, 24 -hour storm <br />to meet requirements of the Rules. Additional information regarding these facilities is provided in <br />the following sections. <br />3.3.1 Design Inputs and Assumptions <br />The three main design components for surface water runoff control for the RPE East include: <br />P \Mpls\06 CO \26 \06261003 RPE E Permit Mod Support \WorkFiles \Permit ApplicatwnlText \Exhibit 82 RPEE design 2011-07-21 TR 127 doe 15 <br />