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As shown in a Table 5, the permeability of cover soils was assumed to be 1 x 10-6 cm/sec, or one <br />order of magnitude faster than the permeability used for colluvium in geotechnical modeling. A <br />faster permeability was used due to the anticipated impact of roots and the freeze -thaw cycle that will <br />tend to loosen cover soils. The cover soil permeability was increased to 1 x 10-5 cm/sec to conduct a <br />sensitivity evaluation. Under this assumption, the average drainage to the underdrain increased to <br />approximately 1.96 gallons per day for the entire facility, after completion of reclamation. The <br />actual average drainage rate is expected to be between 0 and 1.96 gpm for the entire facility. <br />3.2 Hydrologic and Hydraulic Modeling <br />The sediment and clear water diversion ditches and sedimentation ponds were modeled using <br />SEDCAD 4, a computer modeling program that evaluates surface water and erosion and sediment <br />control systems. The hydrologic inputs to the modeling, the information used from existing permits <br />and the modeling results are summarized 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 7. <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 RPEE 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 Waste rock Pile- CN=85 for herbaceous mixture of grass, weeds, and brush cover <br />in good condition (>70%) for Type D soils <br />17 <br />PAMpls\06 CO\26\06261003 MCC Refuse Pile Site Review & Permit\WorkFiles\Permit Application\2014 Revision\Exhibit 82 2014-05- <br />29.docx <br />