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The location of the two proposed detention basins is shown on Map 20, <br />Permanent Sediment Control Plan. Map 4A, Mine No. 3 Hydrology, shows the <br />tributary area associated with the detention basins and associated diversion <br />ditches. Generally, ponds and spillways were sized and located according to <br />such hydrologic factors as required sediment storage volume, rate of flow <br />and volume of flow for the appropriate storm event. All ponds have been <br />designed for the 10-year, 24-hour precipitation event, as documented in <br />Exhibit 3, Sediment Control Plan. <br />Embankments, berms, slopes, spillways, and construction methods have <br />been designed according to such engineering factors as structural integrity <br />and stability; slope and surface stability; adequacy in height, size, and <br />shape to provide sufficient volume for sediment and detained water; and <br />selection of proper spillways and outlet devices to provide for non-clogging <br />operation, passing of design storm events, and proper outflow rates. The <br />sediment control facilities have been certified by registered professional <br />engineers in accordance with Rule 4.05.6. <br />• The purpose of the detention basins is not only to provide a final <br />measure to prevent additional contributions of sediment outside the proposed <br />permit area, but also to provide compliance with all applicable effluent <br />limitations, especially with respect to TSS. The effluent quality is <br />regulated by Rule 2.05.2 and by NPDES Permit No's. CO-0027154 and COG-850013 <br />(formerly CO-0036021). The permits, issued by the Colorado <br />• PRen 2.05-147 Revised 06/14/90 <br />