Laserfiche WebLink
Energy Fuels believes that the current ditch designs for the permanent channels in the <br />permit area are more than adequate for the following reasons: <br />a The PMP would have a devastati ~ effect on the whole area, which could not be <br />avoided. <br />When considering the sizing of the permanent storm water diversion structures for the <br />Whirlwind Mine, it is helpful to calculate the flows for Lumsden Creek at 5/10' <br />Road near the mine if a Possible Maximum Precipitation (PMP) event were to occur <br />in that drainage basin. This calculation was done and is included in Attachment G. <br />The rainfall of 13 inches for a PMP event in the area of the Whirlwind Mine was <br />taken from the published report for the PMP in this area. Portions of this report are <br />reproduced in the same attachment. <br />The flow was calculated using the hydrology module of SurvCad. The drainage basin <br />boundary, average slope, and length of the drainage basin were estimated using the <br />USGS quad map for the area. The Curve Number for the basin was taken from <br />Appendix B -Mine Surface Water Hydrology Designs of the 112d Application. A <br />0% ponding was used because there are no ponds large enough to show on the USGS <br />map. Using this information and the Graphical Peak Discharge method on SurvCad, <br />the Peak Discharge is calculated to be approximately 7,385 cubic feet per second <br />(cfs). This flow would occur in a drainage that is dry 99.5% of the year. <br />The dimensions of Lumsden creek at 5/10' Road are approximately 3H:1 V side <br />slopes, a 2 ft bottom width and an 8.3% downstream grade. Using the calculated peak <br />discharge in the Manning's Equation for a trapezoidal channel, results in a calculated <br />velocity of 35.6 feet per second (fps) for the PMP flow. If a PMP event were to <br />happen in this basin, the streambed would erode at an extreme rate. This small arroyo <br />would become a small canyon in a mater of minutes as soil would be eroded down to <br />bedrock. The erosion would be so substantial that most of the area would be greatly <br />and permanently affected. Under these circumstances, it would be futile to design <br />diversions around the waste embankment for the PMP flows. <br />b The current designs utilize a conservative 100-year rainfall event. <br />The 100-year, 24-hour rainfall presented in Procedures for Determining Peak Flows <br />in Colorado (TR-55) is approximately 2.4 inches. See the chart from this report <br />included in Appendix G. <br />h,~'ter~n~ F~ u~1s 12esc~u~•c~ s C;o~r~or~ttic~rl =1~ 'C~~rior7 13c~tllr;~-.a~•d, ;~Sui1~e EiOt) 11 <br />1:,~~1:~r~~c~«cj. t'C) 8{)128 1'hE~~7e: 3t}3-x)74-2140 <br />