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<br />Memo - Steve Renner <br />-4- <br /> <br />December 22, 1989 <br />23. The spillway design calculations are provided in Appendix L. A <br />velocity of 10.5 fps results in the channel below the concrete <br />control section for the PMF flow event. A smaller channel for the <br />100-year, 24-hour event is also proposed and shown on Figure F-3. <br />The 100-year channel is proposed to be riprapped while the PMF <br />channel is proposed to be revegetated. No stability calculations or <br />construction specifications were provided. Please provide the <br />following: <br />a. A cross-section of the final spillway channel, <br />b. Riprap size based on stability calculations, <br />c. Riprap and bedding specifications, <br />d. Velocity in the revegetated section of channel, <br />e. Revegetation specifications if different from general <br />specifications. <br />24. The collection pond is proposed to be filled with riprap to act as an <br />energy dissipation structure for the engineered spillway upon <br />reclamation. What size riprap and thickness of riprap will be used? <br />What depth of overburden, if any, will be placed over tF~e folded-in <br />liner? What size and thickness of riprap bedding material is <br />proposed? <br />25. Has consideration been given to grouted riprap versus the concrete <br />proposed for the spillway entrance and control section? This may <br />alter the hydraulics somewhat but may improve the post-mine <br />appearance upon reclamation. <br />Exhibit G, Water Resources <br />26. The water balance identifies the three (3) sources of water to be <br />obtained from: (1) offsite, (2) recycled tailings slurry, and (3) <br />pit dewatering. The offsite supply is dependent upon a water court <br />decision on change of use yet to be finalized. A <br />plan-for-augmentation is also a part of this ruling. A second court <br />case is pending to adjudicate non tributary water. At this time, <br />please discuss the following for clarification purposes; <br />a. As the tailings disposal area is to be lined and designed to <br />recycle incident precipitation from a 205 acre area, is this <br />amount of water considered in the plan-for-augmentation or <br />temporary substitute supply plan? <br />b. How is the amount of moisture retained in the tail~,ngs <br />considered from a water rights perspective? <br />/ern <br />2354E <br />