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Transit Mix Concrete Co. <br /> detention. The basins will require periodic maintenance when sediment reaches this sediment <br /> level. The calculated runoff volumes and recommended capacities are included in Table G-6. <br /> The basins will typically be between 10 to 20 feet deep, but the depths will vary depending on <br /> the necessary capacities and area available for the basin. It is not anticipated that the height of <br /> the embankments will require permits for the Colorado Office of the State Engineer. If conditions <br /> will require a higher height of embankment, the proper permits from the State Engineer will be <br /> obtained. The sediment detention basins are planned to be excavated into the pit floor at <br /> locations that are away from the mine infrastructure. Inside the pit areas, where the detention <br /> basins will be constructed into bedrock, the sediment detention basins walls will be sloped at <br /> 0.5H:1 V. The design includes an access ramp sloped at 10%to provide access for maintenance <br /> equipment. Sediment detention basins located in unconsolidated materials will be excavated <br /> with walls sloped at 3H:1V. The County requires installing a forebay to collect large sediment, <br /> and the forebays will have capacities of approximately 10% of the storm runoff volume. Outlet <br /> works that drain the sediment detention basins but retain solids are required by the County and <br /> will be installed at each sediment detention basin. The outlet works will cause basin water levels <br /> to be drawn down following storm events and will discharge to nearby drainages. The outlet pipe <br /> will be controlled by an orifice plate at the pipe inlet and will be sized to drain the 100-year <br /> storage volume in less than 120 hours, as required by Colorado Department of Water Resources <br /> guidelines. A typical sediment detention basin is shown on Figure G-15. <br /> Detention Basin P-DET-1 is the only clean water detention basin. All other basins are sediment <br /> basins which have shifting drainage areas throughout the mine life. The drainage areas shown <br /> are for the worst-case phases with the greatest drainage area. Detention Basin P-TEMP <br /> represents a low area in the pit that will act as a temporary basin during the Phase 2 to Phase <br /> 3 transition that will act as an overflow for basin P-SP-1. Runoff from P-TEMP will be pumped <br /> back to P-Plant as the runoff drains. <br /> Hitch Rack Ranch Quarry Permit Application <br /> October 3,2017 G-23 <br />