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Ponds shall be designed, constructed, and maintained to treat the volume from a 10 -year, 24 -hour <br />precipitation event. Discharges from ponds will be monitored to detect exceedances of <br />limitations listed in the CDPS permit. <br />2. The Division has approved several small areas of disturbance to be exempt from the use of <br />sediment ponds to treat runoff. Typical of these small areas are topsoil stockpiles, electric power <br />substation installations, [Rule 4.05.2(3)]. Colowyo demonstrated that treatment facilities were <br />not necessary for the drainage to meet the effluent limitations of Rule 4.05.2 and applicable State <br />and Federal water quality standards for receiving streams. There will be no mixing of surface <br />drainage with a discharge from underground workings areas at the exempted areas. These areas <br />are described in the PR -3 application (Exhibit 7, Item 23, Part H). <br />The Division considered the proposed small area exemptions (SAEs) proposed for surface water <br />treatment of the Collom facilities area to require re- evaluation due to the size of the proposed <br />drainage area. As a result the Division is imposing Stipulation No. 14 to the permit. <br />STIPULATION 14 <br />PRIOR TO DISTURBANCE OF THE COLLOM FACILITIES AREA, COLOWYO MUST <br />REEVALUATE SEDIMENT CONTROL STRUCTURES IN ACCORDANCE WITH <br />RULES 4.05.2, 4.05.5, AND 4.05.6. IN PARTICULAR, TWO AREAS IN COLLOM THAT <br />WERE PLANNED FOR SAE STATUS, NAMELY THE 9.8 -ACRE CORNER OF THE SHOP <br />AREA AND THE 7.2 -ACRE AREA OUTSIDE DEER DRAW, REQUIRE AN ALTERNATIVE <br />PLAN. THESE AREAS MUST BE REMOVED FROM THE DISTURBED AREA OR <br />RUNOFF FROM THESE AREAS MUST BE ROUTED TO SEDIMENT PONDS. THIS WILL <br />REQUIRE RE- SUBMITTAL OF THE ASSOCIATED FIGURES, TEXT, AND EXHIBITS FOR <br />SEDCAD RUNS. <br />B. Diversions and Conveyance of Overland Flow - Rule 4.05.3 <br />The Division approves the use of riprap channel lining for permanent diversions constructed on <br />the reclaimed area. Channel protection is warranted due to steep slopes and large watershed <br />areas that exist and that are planned on the post- mining topography. Pre - mining bedrock control <br />is removed by the mining operation and channel protection is necessary to provide long -term <br />stability on the reclaimed area, especially until vegetation is established. These permanent <br />diversions are shown on Map 41, Watershed Boundaries for Hydrologic Modeling for the <br />original Colowyo mining area and on Map 4 1 A for the South Taylor area. The riprap lining will <br />provide stability in order to protect fills and property and to avoid danger to public health and <br />safety (4.05.3(3)). <br />For the Collom expansion area, the Division approves the use of permanent and temporary <br />diversion ditches to carry flow from undisturbed areas around disturbed areas. Channel <br />protection shall be used as necessary in channel reaches with steep slopes and large watershed <br />Colowyo Coal Mine C1981 -019 PR -03 42 April 10, 2013 <br />