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Discharges from the Collom area will be subject to the requirements of the CDPS. These <br />requirements include standards, effluent limitations, and a monitoring schedule. To meet these <br />requirements, the Collom area will drain through sediment ponds and other treatment methods. <br />Ponds shall be designed, constructed, and maintained to contain or treat the volume from a 10 - <br />year, 24-hour precipitation event. The Collom area ponds include the large ponds shown on Map <br />23B (Section 25, Section 26, Section 36, Middle, and Sidehill) as well as the stockponds below <br />the topsoil stockpiles. Discharges from the downgradient larger ponds (Section 25 Pond and <br />Section 26 Pond) will be monitored in accordance with the CDPS permit. <br />For the Collom area, the Division proposes to grant SAEs from use of sediment ponds due to the <br />fact that ponds and treatment facilities are not necessary for the drainage to meet the effluent <br />limitations of Rule 4.05.2 and applicable State and Federal water quality standards for receiving <br />streams. Exhibit 7, Item 23, Part G presents an analysis of three specific SAEs using the <br />SEDCAD grass filter routine, and Part H provides an additional analysis for unspecified areas <br />that may become an issue in the future. The results of the analysis show that settleable solids <br />concentrations in the discharge from these areas will be in compliance (less than 0.5 ml/1) with <br />applicable water quality standards. <br />Note that SAEs are only acceptable to the Division where mixing of surface drainage with a <br />discharge from underground workings will not occur. <br />B. Diversions and Conveyance of Overland Flow - Rule 4.05.3 <br />For the Collom permit expansion area, the Division approves the use of four temporary clean <br />water diversion ditches to carry surface runoff from undisturbed areas around disturbed areas. <br />Exhibit 7, Item 23, Part A in the PAP provides design specifications, maps, and SEDCAD <br />analyses for these four ditches (CWD-1, CWD-2, CWD-3, and CWD-4), which shall be <br />triangular in shape and vegetation lined. CCC designed these ditches to carry the 100 -year, 24- <br />hour precipitation event. This was done to reduce inflow to the pit and the need for pumping. <br />Per Rule 4.05, temporary ditches do not need to be built for the 100 -year event. They can be <br />built for a smaller event, depending on the size of their drainage area. <br />The Division approves CCC's plan to permanently restore drainage channels that will be <br />temporarily removed by mining. Locations of these channels are shown on Map 4113, and <br />channel profiles are on Map 33, Sheets 1 through 3. Details of the analysis and design for these <br />channels are in Exhibit 7, Items 23 and 25. Most of the channels (all but Little Collom) have <br />drainage areas less than one square mile, and thus design of them is governed by Rule 4.05.3, <br />which requires that they convey the 10 -year, 24-hour precipitation event. <br />PR -04, Colowyo Coal Mine C1981-019 36 August 2016 <br />