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• Section 780.21(b) Continued. <br />The location of all sedimentation ponds is shown on Map 16a, Kerr <br />Mine Area Surface Water Hydrology and Map 11a, Kerr Tipple Area <br />Hydrology. These maps also show the locations of watershed <br />boundaries for which the design criteria were established. <br />Generally, ponds and spillways were sized and designed according to <br />required sediment storage volume, rate of flow and volume of flow for <br />the appropriate storm event. All ponds have been designed to handle <br />the 10-year, 24-hour precipitation event. <br />Pond embankments, slopes, spillways, have been designed and <br />construction methods have been planned in accordance with the <br />following criteria: structural integrity and stability; slope and <br />surface stability; adequacy in height, size, and shape to provide <br />sufficient volume for sediment and detained water; and selection of <br />proper spillways and outlet devices to provide for non-clogging <br />• operation, passing of design storm events, and proper outflow rates. <br />All ponds have been designed by one or more registered professional <br />engineers in accordance with the plan set forth under Section 780.25 <br />and in accordance with 30 CFR 816.46 and 816.49. <br />The purpose of the sedimentation ponds is not only to provide a final <br />measure to prevent additional contributions of sediment outside the <br />permit area, but also to provide a means of compliance with all <br />applicable effluent limitations, especially with respect to TSS. The <br />effluent quality which must be attained is controlled by the NPDES <br />Permits issued by the State of Colorado Department of Health under <br />the National Pollutant Discharge Elimination System. Of all rules <br />and regulations applicable to Kerr coal the NPDES permits set the <br />most stringent standards. A copy of the permits are contained in <br />Exhibit 33, NPDES Permits. <br />780-98R Revised - January, 1991 <br />