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• will become less pronounced in each drainage (Dry and Sage Creeks) as flow progresses <br /> downstream; 3) a water rights augmentation plan has been developed and approved, and will <br />be administered by Peabody during the life-of-mine. <br />Effects of Sediment Ponds Discharges, Diversions, and Culverts at Road Crossings on <br />Surface Water Oua lity. As mentioned in the previous section, the impacts of discharges <br />from the sediment ponds (005, 006, and 009) will be long-term, but of minimal <br />significance. Sediment ponds are designed to contain the 10-year, 24-hour runoff volume <br />plus sediment, and the proposed permanent impoundments will be designed to safely pass the <br />100-year, 24-hour runoff volume in addition to storage of the corresponding sediment load. <br />Peabody's current NPDES Permit CO-0000221 (see~•Tab 15) includes Pond 006 as an active <br />ou tfall, and will be modified upon completion ofPonds 005 and 009 to include the outfalls <br />of both ponds. During mining, Peabody will comply with all terms and conditions of this <br />permit. After mining, discharges from both permanent impoundments (005 and 006) will have <br />long-term impacts on downstream water quality in Dry and Sage Creeks, but these impacts <br />will be of minimal significance, as the impacts will lessen as flow proceeds downstream, <br />and the impacts will not prevent existing and potential uses from occurring. <br />C J <br />During the life of mining operations at the Seneca II-W Mine, diversions and culverts will <br />be employed to control surface runoff within and around disturbed areas. Four temporary <br />diversions will be constructed to prevent additional surface water runoff from entering <br />disturbed areas and to convey runoff to sediment ponds (see Tab 13, Facilities). All <br />diversions are designed to handle the runoff from a 10-year, 24-hour runoff event. Peak <br />discharge rates for each diversion were determined using SEDIMOT II, and channel <br />velocities were found to be well under design limit velocities. <br />Culverts will also be designed to pass the 10-year, 24-hour and in some cases, the <br />25-year, 24-hour runoff event. Headwater diameter ratios will be kept below 1.5 to ensure <br />adequate freeboard. Culvert outlets on the .sediment ponds will be riprapped where <br />necessary to reduce the potential for erosion and additional contributions of sediment to <br />st reamflow below the outfalls. In addition, periodic inspection will be conducted at <br />other culvert sites to ensure that any accelerated erosion at the culvert outfalls does <br />not go unchecked. <br />• The effects of diversions and culverts on surface water quality will last through bond <br />release (when temporary diversions and cul vert s`•will be removed and reclaimed), and will <br />61 <br />