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necessary for the drainage from these 21 sites to meet the <br /> effluent limitations of Rule 4.05.2 and applicable State and <br /> Federal water quality standards for receiving streams and also <br /> due to the fact that no mixing of surface drainage from these <br /> areas with a discharge from underground workings will occur. <br /> The small areas to be exempted are listed in Table 2 .05. 3 M of <br /> the permit application (4.05.2(3)(b)(i )) . <br /> 3. The Division proposes to grant an exemption from the use of <br /> sediment ponds for drainage from underground mine workings <br /> because sediments are settled out in underground sumps before <br /> being discharged into the Colorado River and additional ponds <br /> and treatment facilities are not necessary for the drainage to <br /> meet the effluent limitations of Rule 4.05.2 and applicable <br /> State and Federal water quality standards for receiving <br /> streams . These discharge points are located as follows <br /> (4.05.2(3)(b)( ii )) : <br /> Discharge Location NPDES Point <br /> Roadside Mine Portal 001 <br /> Northwest Intake Portal 002 <br /> Cameo Mine Portal 004 <br /> B. Diversions and Conveyance of Overland Flow <br /> 1 . All conveyance structures within the permit area are designed <br /> and constructed in accordance with Rule 4.05. 3. Permanent <br /> diversions above coal mine waste banks are designed and <br /> constructed in accordance with Rule 4.09.2(7) . Table 2 .05. 3 of <br /> the application lists all diversion and conveyance ditches <br /> along with references to the appropriate exhibits for designs <br /> and cross sections . Calculations used to design these <br /> structures are given in various appendixes to the permit <br /> application. <br /> C. Stream Channel Diversions <br /> Construction of Cameo Refuse Disposal Areas Nos . 2 and 3 will <br /> involve the installation of two permanent ephemeral stream channel <br /> diversions along segments of Coal Canyon. The diversions are <br /> necessary to provide sufficient area for the installation of <br /> sediment ponds situated below the toe of each refuse area. A total <br /> of approximately 1600 linear feet of the Coal Canyon drainage will <br /> be diverted, consisting of a 600-foot segment below refuse area <br /> No. 2 and a 1000-foot segment below refuse area No. 3. <br /> Both diversions will be designed to carry the runoff from a <br /> 100-year, 24-hour precipitation event. The velocities of runoff <br /> through diversions Nos . 2 and 3 were calculated to be 12 .6 feet per <br /> second (fps) and 15. 1 fps , respectively, during a 100-year runoff <br /> event. These velocities are erosive ; however, examination of the <br /> Coal Canyon drainage channel indicates that runoff through <br /> undisturbed portions of the stream channel during the 100-year <br /> -19- <br />