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• 7-4 Pond 003 The SEDCAD+ Version 3 demonstrations appropriate to Pond 003 are C:\SEDCAD3\CR7\PND3A23, Date 02-01-1996 Time 11:16:01 (10-year, 24-hour precipitation event) and Time 11:18:34 (25-year, 24-hour precipitation event). Contributing watersheds drain, via ditches 3Na, 3Nb, 3Nc, 3N1, 3N2, 3Sa, 3S6, 3Sc, and 3Sd to Pond 3. Watershed definition is based primarily on degree of slopes. The steep watersheds are characterized by repetitive terraces and benches. Pond 003 configuration is taken from the Sedimentation Pond As-Built, Pond 003, date 5-30-91. Rev. 1 and Kaiser Steel Resources Chimney Rock Mine Sedimentation Pond 003 Embankment Design Change Permit C-81-023 TR-23 ll-2b-90. The as-built configuration [baffle plate over the lower third of a 24-inch corrugated metal pipe (CMP) trickle tube] of the primary spillway is not compatible with SEDCAD+ documentation. To simulate the as-built configuration, a trickle tube of equal azea (10.4-inch CMP) was used, placing the top of both tubes at the same elevation to better match dischazge flow characteristics. Kaiser Steel Resources, Inc., proposes to maintain the water level of the pond below 6457.5 (Maintenance Water Level) by pumping. This operational procedure is simulated by a fixed siphon tube. Basin capacity information and curve (SEDCAD+ BASIN CAPACITY UTILITY Pond 3) were developed from the Stage Storage Data on the As-Built. With regard to a 10-yeaz, 24-hour precipitation event, the design sediment storage volume is 0.03 acre feet, between elevations 6456 and 6456.23. Peak Settleable Concentration of pond dischazge is demonstrated at 0.00 mUl (< 0.50 ml/1 criteria). Peak stage is 6461.09 (below the 6461.4 elevation of the emergency spillway). There would be no dischazge over the emergency spillway. The caution statement • (SEDCAD+ Pond InpuUOutput Table) is generated due to the proximity of the top of sediment storage and the simulated fixed siphon tube, and is not applicable to actual conditions. Cleaning of sediments from the pond is scheduled when 60% (0.018 acre feet) of the design sediment storage is occupied, a maintenance sediment elevation of 6456.14, interpolation between 6456.0 @ 0.0 and 6456.23 @ 0.03). Peak stage from a 25-yeaz, 24-hour precipitation event is 6461.62, providing 1.38 feet of emergency spillway freeboard to the top of the embankment. Peak dischazge over the emergency spillway is 4 cubic feet per second (cfs) (interpolation between 1.8 @ 6461.50 and 11.0 @ 6462.00). Riprap is required to protect the emergency spillway crest and exit channel. The SEDCAD+ RIPRAP CHANNEL DESIGNS demonstrate that the design depth would be (with 1 foot of freeboard) 1.20 feet across the crest (l.b provided) and 1.02 down the exit channel. Pond configuration is summazized in the figure titled Sedimentation Pond 003 Supplemental Information, 2/7/96. Designs of ditches 3Na, 3N6, 3Nc, 3N1, 3N2, 3Sa, 3Sb, 3Sc, and 3Sd are presented under Pazagraph 7-7. 7-5 Pond 004 The SEDCAD+ Version 3 demonstrations appropriate to Pond 004 are C:\SEDCAD3\CR7\PND4A7, Date 01-17-1996 Time 12:48:32 (10-year, 24-hour precipitation event) and Time 12:49:47 (25-year, 24-hour precipitation event). A narrow strip of ground west of a ridge near the western edge of the Barren Ridge Area (see Map 8) and an undisturbed azea above the disturbed azea drain, via ditches 4Na and 4Nb, to Pond 4. Slopes of an undisturbed ridge that make up the eastern side of Pond 4 also drain into the pond. Watershed definition is based on degree of slopes and vegetative cover. The steep watersheds with disturbed azeas aze . characterized by repetitive terraces and benches. Pond 004 configuration is taken from the Sedimentation Pond As-Built, Pond 004, date 7-7-91, Rev. 1. Additional as-built configuration detail concerning weep holes in the primary riser are indicated on Sedimentation Pond 004 Supplemental Information 1/96. Basin capacity information and curve (SEDCAD+ BASIN 7-7 8 May 1996