2013-03-11_REVISION - C2010089 - Laserfiche WebLink

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Doug White, Western Fuels C- 2010 -089 TR -01 PAR Mar. 11, 2013 Page 3 of 9 (1.96 cfs) of pit water pumping, with the initial pool elevation at 5671.5 ft., the gated valve elevation. SEDCAD calculated no discharge through the emergency spillway for all four cases. DBMS: Response accepted. 4. DBMS: The placement of the primary spillway in the as -built configuration of pond NHN -001 differs from the design. The spillway has been placed west of the approved location, closer to the inlet of Ditch NHN -001 West. This location may result in short- circuiting of the pond. Please indicate, in accordance with Rule 4.05.6(6), how WFC will ensure that the pond is not short - circuited with Ditch NHN -001 West inflows. WFC: The approved Pond NHN -001 principal spillway was located approximately 290 feet from the inlet of Ditch NHN -001 West. The as -built principal spillway was relocated to accommodate alignment with the existing county road culvert, and is approximately 215 feet from the inlet of Ditch NHN -001 West. This distance is closer than the approved design of Pond NHN -001, but exceeds the distance approved by DRMS in the design for Pod NHN -002, which shows the inlet of Ditch NHN -002 North located approximately 160 feet from the principal spillway, still a sufficient distance to prevent short circuiting. This assertion is reinforced in the approved permit in Appendix 2.05.3(4) as stated on page 6, "gated principal spillways, as designed for all three ponds, prevent short circuiting." DBMS: Response accepted. 5. DBMS: Please include design information for the emergency spillway channel to indicate the flow depth and demonstrate adequate embankment height to ensure I ' of freeboard, as required by Rule 4.05.9(7) (d). WFC: The four SEDCAD runs for the as -built pond show no discharge through the emergency spillway, therefore no emergency spillway flow is indicated for use in calculating freeboard. The minimum freeboard resulting from there four SEDCAD runs occurs during the 25yr -24hr seep holes closed case, where the peak pool stage elevation is 5,676.62 ft. This provides for 2.88 feet of freeboard to the top of the dam at 5,679.5 ft. The emergency spillway has been built to the elevation of 5,677.5, two feet lower than the top of the dam embankment. The approved Pond NHN -001 design done by Arcadis included a 25yr -24hr SEDCAD run assuming no flow through the primary spillway, resulting in a flow depth through the designed 10 ft. wide, 2:1 side slope emergency spillway of 0.18 ft. The resulting freeboard in such a scenario is 1.82 ft. In this worst case situation, where the primary spillway would become blocked, the emergency spillway as built would still have greater than the required 1.0 of freeboard. The emergency spillway channel as -built is a rip- rapped trapezoidal channel, 10 ft. wide with 2h:Iv or flatter side slopes.