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December 23, 2009 <br />Revised 7/21/2011 <br />112(d) Permit — May Day and <br />Wildcat Min oration <br />ine and Mill Application <br />Peak Flow (Type II Storm -Steep Slope >16% slope <br />(Wilkes and King, 1975 Figure D -2) <br />NRCS -Runoff Curve Number 58 <br />Annual Rainfall 19.9 inches <br />Snowfall 68.8 inches <br />Pan Evaporation 37.8 inches <br />Average Temp High 62.7 inches <br />Average Temp Low 29.9 inches <br />Rain fall low May <br />Rain fall high August <br />Return Period Rainfall Duration Rainfall Amount Runoff Drainage Area CFS/inch Runoff Peak flow (cfs) Flow Velocity <br />(acres) <br />2 24 1.25 0.10 2.07 5 0.5 <br />Reference <br />Table U -2 <br />May Day No 1 Drainage above portal includes permimeter ditch and channel inlet to Culvert <br />May Day Idaho Mine Complex <br />Durango, Colorado <br />10 24 2.7 0.89 2.07 5 4.5 <br />25 24 3.5 1.43 2.07 5 7.2 <br />100 24 3.78 1.67 2.07 5 8.4 <br />U.S. Department of Commerce, 1961, Technical Paper 40- Rainfall Frequency Atlas of the United States for Durations from 30 minutes to 24 hours <br />and Return Periods fromm 1 to 100 years. Washington , D.C. <br />Wilkes, S. Glade and Erke C. King, 1975, Procedures forDetermining Peak Flows in Colorado, Incorporateds and Supplements Technical Release No. 55 <br />Uraban Hydrology for Small Water <br />Soil Conservation Service, Soil Conservation Naltion Engineering Handbook, Section 4- Hydrology NEH-4. <br />* Handbook of Steel Drainage & Highway Conststruction Products, Second Addition, 1972 <br />18 inch culvert' <br />Culvert No. 3 <br />Table U -2 Culvert 113 May Day No.1.xlsx 1 <br />