2016-10-28_PERMIT FILE - C2010089A (9)

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Appendix 2.05.3(4) -6 Pond NHN -001 As -Built Emergency Spillway The following four SEDCAD runs, including 10yr -24hr event with 2 - 6" weep holes wide open and weep holes closed, and 25yr -24hr event with 2 - 6" weep holes wide open and weep holes closed 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 these four SEDCAD runs occurs during the 25yr -24hr weep 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 ft. of freeboard. The emergency spillway is a combination of a rip - rapped trapezoidal channel 10ft. wide with 2h: 1v or flatter side slopes which flows into a 72" concrete drop inlet. This drop inlet feeds a 24" barrel CMP which then flows to outlet as shown on drawing 2.05.3(4) -6. SEDCAD runs have been revised to reflect this condition. Embankment Foundation preparation of the embankment of Pond NHN -001 included removal of vegetative and organic materials, and scarification of the ground. The embankment fill material was constructed free of sod, roots, vegetative matter and frozen soil. The engineering design for construction of Pond NHN -001 specified at least 90% Modified Proctor Density, ASTM D -1557, routine compaction standard for embankment construction. Actual constructed lifts were calculated to be an average of 10.7 inches in thickness. The faces and slopes of the embankment are being planted during the first growing season to establish vegetation. The freeboard of the pond during the sudden increase in volume as a result of a 25yr -24hr event is 2.88 ft. This freeboard is sufficient to prevent overtopping by waves. Revised April 2013 Appendix 2.05.3(4) -6 /Vv,q- 0z %1"r'-O/ .*prowl d3 A101 X013