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NuvEMCO LAST CHANCE MINE <br />STORM WATER MANAGEMENT PLAN <br />i = rainfall intensity, inches/hour <br />A = Area, acres <br />C — Rational Method Runoff Coefficient <br />From the photographs, the areas have been cleared of almost all of the vegetation. Those <br />areas that have vegetation will eventually be cleared and covered with waste rock. The <br />area has been described as mostly rock with little, if any infiltration. The equipment will <br />also compact the area and reduce infiltration. Therefore the coefficient, C, will be high. <br />From different tables available to estimate the coefficient will be approximately 0.95. <br />i — Rainfall Intensity <br />The Nuvemco Monogram mine is located in Hydrologic Zone 2, San Juan, Upper Rio <br />Grand, Upper Colorado, and Gunnison River Basins, and Green River Basin below <br />confluence with the Yampa River in the State of Colorado. See Appendix B. <br />From the NOAA ATLAS 2, Volume III Figures 22 through 31 in Appendix C the <br />precipitation for various storms can be estimated in tenth inch. The estimates, based on <br />the site latitude and longitude, are as follows: <br />This information was entered into UD- RainZone v 1.01 a, Z -2 to calculate the Rainfall <br />Intensity - Duration- Frequency Table for Zone Two in the State of Colorado that is <br />attached. <br />SEDIMENT POND #1 <br />Time of Concentration <br />In order to use this information it is necessary to calculate the Time of Concentration, or <br />duration for the study area. The time of concentration used to determine the average <br />intensity of rainfall, is equivalent to the amount of time needed for runoff to travel from <br />the most remote point of the basin to the design point. <br />For the study area, this distance is only approximately 540' using the previously <br />described AutoCAD drawing, Figure 1. There are various methods available to compute <br />the time of concentration. Various publications recommend minimum times from 5 <br />March 2010 3 <br />DURATION <br />6-HR <br />24 -HR <br />FREQUENCY <br />(INCHES) <br />(INCHES) <br />2 -YR <br />0.9 <br />1.2 <br />5 -YR <br />1.2 <br />1.6 <br />10 -YR <br />1.35 <br />1.9 <br />25 -YR <br />1.6 <br />2.4 <br />50 -YR <br />1.8 <br />2.75 <br />100 -YR <br />2.0 <br />2.95 <br />This information was entered into UD- RainZone v 1.01 a, Z -2 to calculate the Rainfall <br />Intensity - Duration- Frequency Table for Zone Two in the State of Colorado that is <br />attached. <br />SEDIMENT POND #1 <br />Time of Concentration <br />In order to use this information it is necessary to calculate the Time of Concentration, or <br />duration for the study area. The time of concentration used to determine the average <br />intensity of rainfall, is equivalent to the amount of time needed for runoff to travel from <br />the most remote point of the basin to the design point. <br />For the study area, this distance is only approximately 540' using the previously <br />described AutoCAD drawing, Figure 1. There are various methods available to compute <br />the time of concentration. Various publications recommend minimum times from 5 <br />March 2010 3 <br />