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PART I <br /> Page 3- of 13 <br /> PERMIT NO; CO-0000396 <br /> 2. Containment Requirements and Storm Exemption* <br /> Structures shall be designed, constructed , and maintained to contain or <br /> treat the volume of runoff from active mining areas, preparation plants, <br /> and associated areas resulting from a 10-year, 24-hour precipitation event <br /> (i .e. rainfall or equivalent snowmelt) . Any untreated overflow (from facilities <br /> with ten year containment) caused by a hydrologic event shall not be <br /> subject to the limitations on page 2 (Amended) of this permit . The term <br /> "10-year, 24-hour precipitation event" shall mean the maximum 24-hour <br /> precipitation event with a probable reoccurrence interval of once in 10 <br /> years. The 10-year, 24-hour precipitation event for this facility shall be <br /> 1 .8 inches as found in "Precipitation-Frequency Maps for Colorado" <br /> published by the U.S. Department of Commerce. The rain gage of record shall <br /> be Aspen, Index No. 0370. The permittee has the option to maintain and <br /> operate a rain gage at the facility. <br /> The permittee shall submit to the Colorado Water Quality Control Division <br /> by December 31 , 1980, design criteria, as-built drawings, or other data <br /> which verify containment or treatment structures have been designed and <br /> constructed for the 10-year, 24-hoer precipitation event. <br /> Federal Register, December 28, 1979, Coal Mining <br /> Point Source Category <br /> . Amended <br /> 9 <br />