2011-11-14_REVISION - M1986015 (8)

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• • • prevent potentially large runoff volumes from entering the Phase 7 excavation, a drainage channel will be built to divert this flow around the east side of the excavation. The channel is designed to Pueblo County standards. See Exhibit C for the location and cross section and Appendix B (Section U) for the engineering design. In the first year of the operation, a levee will be built along River to prevent high water events from entering the Phase 7 excavation. The levee will be nine feet tall and be constructed of compacted overburden. The material will come from the above mentioned drainage channel excavation and overburden stripping. This levee will be located in the northern portion of the setback from the River and be approximately 100 feet from the River bank. The levee will be seeded with the same mixture as used on the topsoil and overburden stockpiles. See Exhibit C for the location and cross section. The topsoil and overburden from the first year's excavation will be stored along the northern setback areas. As the mining of the sand and gravel commences, this material is first run through a screen plant at the mine face to separate out fine sand and clay. As much as 50 percent of the sand and gravel resources will be screened out at the mine face. The recovered sand and gravel is transferred to the field conveyor, while the reject sand and clay is moved to the rear of the excavation area and placed as backfill. There will be enough reject material to backfill the first 11 to 13 feet of the hole. During the first one to 1 1/2 acres of mining, there will be no open area to place the reject sand. This reject sand will be stored in a stockpile along the northern setback to be used in the backfilling of the last mining area in Year 3. In the second year of operation, the stripped overburden and topsoil from the second 20 acres will be placed on the reject material of the first year mining. The backfill material will be compacted by the continuous movement of the scrapers and dozers over the site. In the third and last year of mining, the stripped overburden and topsoil from the last 14 acres will be placed on the reject material of the second year. The reject material from the third year mining will be placed as backfill in this pit area. When the third year mining is done and the hole partially backfilled, the overburden and topsoil from the first year mining, stored along the northern setback area, will be moved on top to the reject material. (c) Water Diversions and Impoundments As described in the previous section, the drainage channel will carry off site runoff around the Phase 7 excavation. The dewater trench will collect groundwater from the Phase 7 excavation area to allow dry mining by a front loader. The settling basin will allow the precipitation of turbidity from the groundwater before it is released to the River.