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invert elevations for all of the structures and bottom elevations for each of the ponds, as well as <br />the expected pond embankment and water surface elevations. Relevant hand and <br />computer-based calculations performed for the hydraulic analysis are included in Appendix E. <br />The three upper ponds will be equipped with a gated culvert a minimum of 12 inches in <br />diameter that will connect each pond to the pond below it. The recommended material for the <br />culverts is PVC pipe; however, other plastic or corrugated metal materials would function. The <br />headgates should lie a Waterman Model P-30 Pressure Gate or similar that will resist a 10 feet or <br />greater unseating head. The culvert and headgate will require a concrete headwall on the inlet <br />end with the top elevation constructed at least one foot above the maximum water surface <br />elevation. A total of three gated culverts will be required. The invert elevations of the culverts <br />and the intake elevation of the pump have been calculated such that the entire system can be <br />drained except for enough water in Pond 4 to maintain the minimum open water requirement for <br />the 404 permit. <br />The elevation differential between Pond 4 and the Poudre River will not allow for gravity <br />release of water te~ the river channel directly adjacent to the property. In light of this fact it was <br />determined that the most cost effective means to transport water from Pond 4 to the River would-; <br />be to construct a pump station on the east side of Pond 4. The pump station should consist of a <br />foundation and platform to support two 465 GPM electric pumps. The output from the pump <br />station will be piped a short distance and released into an outlet ditch constructed directly east of <br />the pump station 1;hat will carry the water to the river. The ditch should be roughly three feet <br />wide and at least one foot deep. In order to measure the outflow from the ponds, a Parshall <br />Flume with anine-inch throat width will be placed within the outlet ditch. In order to control <br />flow into and out of the flume, appropriate entrance and exit transition sections will need to be <br />provided. <br />The last structure included as part of the proposed layout is the grade control structure <br />shown on northern border of the Timnath Pit in Figure 3.1. The inclusion of this .structure in the <br />layout is based upon the Ayres Associates report dated May 1, 1998. This report dealt with the <br />potential for channel cut-off by the Poudre River during a 100-year flood. The report concluded <br />that during such an event it would be likely that the river would re-channel itself through the <br />fully excavated T'imnath Pit if no provisions were made to prevent this occurrence. The <br />suggested methods of mitigation were to either leave 440 feet of undisturbed embankment <br />between that edge of the pit and the river; or to construct a 50 foot wide concrete rubble grade <br />control structure t~o bedrock extending the width of the mined area. We chose to include the <br />latter method in the final layout in order to maximize the water storage volume and the mining <br />area of the pit. The 340 feet wide portion of the 440 feet setback that could be mined contains an <br />estimated $4.4 million in gross material, based on average net sales of asphalt, concrete, sand <br />and gravel in Colorado. The cost of constructing the grade control structure, as shown in <br />T:IOPEMCodkcOllcodkc0/finnlreporLdoc 11 ANdER50N CONSU~TINCI ENCIINEERS, ANC. <br />