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I • Section 816.46(c) Continued. <br />(ii) The pond effluent is shown to achieve and maintain applicable <br />effluent limitations. <br />(2) The regulatory authority may approve a theoretical detention time <br />of not less than 10 hours when the person who conducts the surface <br />mining activities demonstrates that the size distribution or the speci- <br />fic gravity of the suspended matter is such that applicable effluent <br />limitations are achieved and maintained. <br />(3) The regulatory authority may approve a theoretical detention time <br />of less than 24 hours to any level of detention time, when the person <br />who conducts the surface mining activities demonstrates to the regula- <br />tory authority that the chemical .treatment process to be used-- <br />(i) Will achieve and maintain the effluent limitations; and <br />• (ii) Is harmless to fish, wildlife, and related environmental values. <br />(4) The calculated theoretical detention time and all supporting docu- <br />mentation and drawings used to establish the required detention times <br />under subparagraphs (c)(1)-(3) of this Section shall be included in the <br />permit application. <br />All sedimentation ponds have been designed to store aflood-routed <br />volume equal to the runoff resulting from a 10-year, 24-hour pre- <br />cipitation event (design event). Precipitation data were obtained <br />from NOAA Atlas 2, Volume III for Colorado. Sail types were ob- <br />tained from Map 25, Kerr Mine Area Soils. The method described in <br />SCS Technical Release No. 55, Procedures for Determining Peak Flows <br />in Colorado, was used for computing runoff volumes and rates. Al- <br />though mining activities within each watershed of the Mine Plan <br />• Area will create changing hydrologic conditions, the designs are <br />based on the worst case condition that topsoil has been removed <br />816-50 <br />