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The proposed site configuration - within the floodway, parallel to the existing river, <br /> and with open cells on both sides of the river, has a high likelihood of stream capture <br /> during a flood event. In the past, DRMS has approved various methods to attempt <br /> mitigate the potential impacts from flood events such as: setback restrictions (no <br /> mining within 400'of the riverbank); seasonal restrictions on mining activity near the <br /> river, such as prohibiting slopes steeper than 5:1 within 200'of the river between <br /> April 1 and October i, or requiring that flood control structures be installed <br /> immediately following excavation of a cell. How does the permittee intend to <br /> minimize the impacts to the hydrologic balance and prevent stream capture <br /> during/food events? <br /> The permittee has chosen to install flood control structures immediately <br /> following the excavation of a cell. The design and engineering of the <br /> structures is given in the revised 6.4.7 Exhibit G -Water Information. An <br /> additional study has been conducted by Ayres & Associates titled No Rise <br /> Certification Report Amen Pit. This report was generated in support of the <br /> Weld County Floodp/ain Hazard Permit and demonstrates that the mining and <br /> reclamation operations will not create a significant rise in the 100 year flood <br /> water surface elevations in the vicinity of the site. <br /> EXHIBIT E - Reclamation Plan (Rule 6.4,51 <br /> This site is located almost entirely within the floodway of the Big Thompson River. <br /> The permittee will need to provide flood protection for the water storage cells and <br /> clay liners to ensure long-term stability (such as armored inlet/outlet structures, or <br /> other). Design and construction details for flood control structures for each cell will <br /> need to be provided, and the installation costs will need to be included in the <br /> reclamation cost estimate. <br /> As described above, the design and engineering of flood control structures is <br /> given in the revised 6.4.7 Exhibit G -Water Information. Plan and profile <br /> drawings of the flood control structures are given in 6.4.6 Exhibit F Sheets 4- <br /> 11. 6.4.12 Exhibit L— Reclamation Costs has also been revised to include the <br /> costs associated with the <br /> DRMS will also require additional details for the removal/reclamation of the low <br /> water crossing. These costs will also need to be included in the reclamation cost <br /> estimate. <br /> The low water crossing will not be constructed. Instead an overland conveyor <br /> will be constructed to span the river. The costs for removal of the concrete <br /> supporting piers has been added to 6.4.12 Exhibit L— Reclamation Costs. <br /> �l <br /> W Weiland. Inc.---- - ---- -------- <br /> Environmental£ Engineering <br />