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Flatirons, Inc. — Surveying & Engineering <br />2.0 DRAINAGE DESIGN CRITERIA <br />Reizulations <br />This report was prepared with criteria set forth in a letter from the Colorado, Division of <br />Reclamation, Mining and Safety (DRMS) to Nick Michael in a letter dated January 22, <br />2014. The letter had an attached memorandum from the DRMS. The memorandum <br />requested additional storm water related information from Mr. Michael. <br />The revisions to the original report were in response to DRMS review of the original <br />drainage report. The results of the DRMS review are set forth in a letter from Tim Cazier, <br />P.E. sent to Michael Cunningham, dated March 21, 2014. <br />Development Criteria Reference and Restraints <br />There is neither a project master plan, nor a regional or local drainage master plan for the <br />site. <br />Hydrological Criteria <br />This drainage report was prepared using the 10 -year event for the minor storm and the 100 - <br />year event for the major storm using the NRCS method. The NRCS method follows the <br />criteria set forth by Urban Hydrology for Small Watersheds, TR -55 by the United States <br />Department of Agriculture (USDA), Natural Resources Conservation Service (MRCS), <br />Conservation Engineering Division, dated June 1986. Copies of the runoff worksheets can <br />be found in Appendix A. <br />The design rainfall was obtained from National Oceanic and Atmospheric Administration <br />(NOAA) Precipitation Frequency Data Server website. The values are based on NOAA <br />Atlas 14, Volume 8, Version 2. The nearest station to the site is Leadville, which is located <br />about a mile to the southeast. The Leadville Station ID is 05 -4885 and is located at <br />39.22420 North latitude, 106.31640 West longitude, and at an elevation of 9938. The rain <br />data is can be found in Appendix A <br />The minor storm (10 -year) precipitation depth is 0.64 inches for the 1 -hour event, 0.89 <br />inches for the 6 -hour event, and 1.58 inches for the 24 -hour event. The major storm (100 - <br />year) precipitation depth is 1.03 inches for the 1 -hour event, 1.37 inches for the 6 -hour <br />event, and 2.48 inches for the 24 -hour event. <br />The NRCS Web Soil Survey shows the soil covering the onsite and offsite drainage basins <br />is the Leadville Sandy Loam, 3 to 35 percent slopes. The soils are well drained and consist <br />Union Mill 5 March 5, 2014 <br />