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eme CONTINENTAL MATERIALS CORPORATION <br /> characteristics. SEDCAD utilities were used to determine surface areas, storage capacities, <br /> routing parameters, and storm runoff for the proposed ditches and sediment basins. <br /> a. Site Climate <br /> Precipitation data for the Colorado Springs area are available from NOAA Atlas 14, point <br /> precipitation values for site area (NOAA 2013). Table G-1 shows the 24-hour storm event data. <br /> Table G-1 <br /> Storm Event Estimates <br /> Return 24-hour Rainfall <br /> Period (in) <br /> 2 Years 2.06 <br /> 10 Years 3.19 <br /> 100 Years 5.64 <br /> A Natural Resource Conservation Service (NRCS, formerly the Soil Conservation Service) Type <br /> II rainfall distribution was applied to the 24-hour storm. The Type II distribution applies to mid- <br /> continent locations where there are intense localized storms. <br /> The 100-year, 24-hour storm event was used to model runoff and design the ditches for the final, <br /> reclaimed condition. The SEDCAD result model reports are included in Appendix G-1 for <br /> reference. <br /> b. Site Curve Numbers <br /> The modeled runoff volume is a function of the curve number (CN), watershed area, and storm <br /> size, with the soil curve numbers used to define the runoff from soils in the model. Runoff curve <br /> 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 /> Pikeview Quarry Amendment 4 <br /> G-4 <br />