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numbers are typically determined from soil survey hydrologic soils group classifications and <br /> vegetation cover and condition. NRCS classifies soil types into four hydrologic soil group (HSG) <br /> ratings: A, B, C or D, with A-type soils having very high infiltration rates and D-type soils having <br /> very low infiltration rates. The area, curve number (CN), and the time of concentration were <br /> determined for each of the subwatersheds and entered into the SEDCAD model. <br /> A soil survey map for El Paso County, Colorado, published by the Natural Resources <br /> Conservation Service was used to approximate the type of soil around the Pikeview Quarry Site <br /> (USDA, 2018). The hydrologic soil groups are D for the forested areas west of the quarry and B <br /> for the shrub-grass mixture on the lower slopes. The soil reports are included in Attachment G- <br /> 1. <br /> Nearly the entire area west of the mine boundary was burned in the Waldo Canyon Fire in 2012. <br /> This area is naturally restoring itself and contains a mixture of grasses and shrubs. A curve <br /> number of 63 was selected for this area, and this value is for semiarid rangelands with oak, <br /> aspen, mountain mahogany, and other shrubs with fair conditions and D group soils. <br /> A curve number of 70, described as "pinyon-juniper, pinyon, juniper, or both; grass understory", <br /> was used for native areas north and south of the quarry, based on Figure S-3 in Peak Flows in <br /> Colorado (SCS 1977). These areas have a B group soil, and a cover density of 25% was used. <br /> For the portions of the stockpiles and slopes that have been reclaimed as grassland, a CN of <br /> 74 was selected based on a grassland with light or occasional grazing with C-type soils. Curve <br /> numbers are summarized in Table G-2. A weighted curve number was calculated for <br /> subwatersheds that were comprised of a mix of these cover conditions. <br /> Table G-2 <br /> Curve Number Summary <br /> Cover Curve Curve Number Reasoning <br /> Number <br /> Reclaimed stockpile and slopes 74 Grassland with light or occasional <br /> grazing with C type soil <br /> Forested area 63 Oak-aspen-mtn brush with D type <br /> soil and fair conditions <br /> Pinyon-Juniper 70 Juniper-grass with B type soil and <br /> 25/o cover <br /> c. Sediment Control Structures <br /> Pikeview Quarry Amendment 4 <br /> 2019 <br /> G-5 <br />