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RULE 4 PERFORMANCE STANDARDS <br /> impounded will be riprapped or otherwise stabilized,where necessary.Areas in which revegetation <br /> is not successful or, where rills and gullies develop, will be repaired and revegetated. <br /> Sedimentation ponds that are subsequently approved as part of the post-mining land use will <br /> remain in place after the termination of mining activities. <br /> Colowyo will inspect the condition of each pond and submit a quarterly report. None of Colowyo's <br /> ponds meet the size criteria of 30 CFR 77.216(a)(1989). <br /> A small area exemption for sediment control will be utilized for sediment control for the remaining <br /> reclamation area in the Gulch A watershed that has not achieved Phase II or Phase III bond release. <br /> This small area exemption allows for a grass filter to be utilized for sediment control for the small <br /> area exemption.Please see Volume 2C, Item 18 for the small area exemption demonstration(grass <br /> filter) for the Gulch A watershed. <br /> 4.05.7 Discharge Structures <br /> The sedimentation ponds at Colowyo are designed to treat the 10-year, 24-hour storm event in <br /> accordance with Rule 4.05.6(3)(a). As such, the general operation of the ponds will be a passive <br /> discharge system where water is allowed to discharge automatically as necessary. Colowyo will <br /> sample discharges as appropriate to remain in compliance with applicable CDPS Permit <br /> requirements. Pond dewatering through a manual headgate may be performed as necessary to <br /> lower the water level depending on operational requirements. Manual dewatering of ponds will <br /> meet applicable CDPS Permit standards. Discharge from sedimentation ponds will be controlled <br /> by energy dissipaters and flow check devices where necessary. All embankment ponds utilize <br /> separate principal and emergency spillways with the emergency spillway located at a minimum of <br /> 1 foot above the elevation of the maximum water surface during the discharge of the 10-year, 24- <br /> hour storm event through the principal spillway. The principal spillways are designed for the 10- <br /> year, 24-hour storm event and the emergency spillways are designed to pass the 25-year, 24-hour <br /> storm event in accordance with Rule 4.05.9(2)(c)(i). The design requirements for existing ponds <br /> can be found on each of the pond as-built drawings or in Exhibit 7, Item 15 of the existing permit <br /> document. All embankment sedimentation ponds will provide a non-clogging dewatering device <br /> or conduit spillway to remove water storage from inflow. Design requirements for all sediment <br /> ponds associate with the Collom Pit be found in Exhibit 7, Item 23. For compliance purposes, in <br /> systems that incorporate ponds in a series, CDPS effluent quality parameters will only apply to the <br /> last pond in the series that directly discharges into the receiving stream or drainage. Out of pit <br /> designed ponds internal to the last pond in the series will be inspected and maintained in the same <br /> manner as the "compliance"pond to ensure proper sediment control and design performance. <br /> The sumps along Haul Road A are required to have flow measurement devices at the outflow of <br /> each sump. Each sump therefore will have a flume installed at the outflow to measure any flow <br /> discharged from each sump. <br /> Rule 4 Performance Standards 4-12 Revision Date: 12/20/19 <br /> Revision No.: TR-135 <br />