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Blue Mountain Energy 4 Illustration 61 <br />Discharge Pond <br />BME has historically included a small settling pond on similar dewatering facilities even though the <br />water is typically clean and free of sediment. The purpose of the pond is to allow reaction time and <br />settling in the unlikely event that sediment makes its way to the pump intake. Though small, the pond is <br />much larger than it needs to be and reduces the settleable solids concentration to effectively 0.0 ml/l. <br />The outlet of the discharge pond will be a simple broad crested weir with a width of three feet. Side <br />slopes of 3:1 will result in a slightly lower peak elevation than calculated by SEDCAD. Again, SEDCAD <br />does not have a way to include a base flow, so the pumped flow rate of 0.89 cfs must be added to the <br />100 -Year runoff rate of 3.36 cfs for a total of 4.25 cfs. Interpolating from the stage vs. discharge table <br />yields a peak pond elevation of 5532.58. SEDCAD Calculations for the discharge pond area can be found <br />in Appendix C. <br />Sedimentology <br />The particle size distribution used in the model is the same as has been used in our SEDCAD models for <br />more than 20 years. The author is not sure where it came from. A retired SEDCAD modeler was called, <br />and his recollection is that a soil sample was sent to the University of Kentucky for analysis and the <br />particle size distribution was a result of that analysis. <br />Sedimentology was modeled for the 10 Year storm. Both well pad sediment trap and the pond reduce <br />the settleable solids concentration well below the permitted level of 0.5 ml/L. <br />Additional Rip Rap Considerations <br />It is the author’s experience that SEDCAD calculates a rip rap size that is either too small or too large <br />depending on the method used when compared to other methods. Smaller is acceptable on long <br />stretches of perimeter ditches, but near outlets and dams, the author prefers to use other methods. <br />Calculations using other methods can be found in Appendix D. The SEDCAD channel calculations can be <br />found in Appendices B and C. <br />References <br />OSMRE. Guidelines for the Use of the Revised Universal Soil Loss Equation on Mined Lands, Construction <br />Sites, and Reclaimed Lands. Version 1.06. August 1998. <br />USDA NRCS Conservation Engineering Division. Technical Release 55 (TR-55). June 1986. <br />USDA NRCS. Web Soil Survey. https://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm <br />NOAA National Weather Service. Precipitation Frequency Data Server. <br />https://hdsc.nws.noaa.gov/hdsc/pfds/ <br />