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2. Certain disturbances associated with the coal mine waste disposal pile will be <br />located within 100 feet of an ephemeral stream with a drainage area greater than <br />one square mile (Munger Creek). Pursuant to Rule 4.05.18(1), the Division <br />specifically authorizes disturbances within 100 feet of the Munger Creek channel <br />in accordance with specific plans outlined in Section 2.2.5 and 2.2-6 of the <br />application. Based on drainage and sediment control designs and documentation <br />included in the application, the Division finds that surface coal mining operations <br />will not cause or contribute to the violation of applicable water quality standazds <br />[4.05.18(1}(a}]. The Division fmds that during and after mining, the water <br />quantity and quality of the stream will not be adversely affected [4.05.18(1)(b)]. <br />Water quantity will not be adversely affected, because the total drainage azea of <br />the disturbance to be temporarily diverted into a sediment pond is less than one <br />half of one percent of the total drainage area of Munger Creek. There would be <br />no measurable impact on the quantity of water in Munger Creek, which flows only <br />a few times each yeaz in response to storm runoff and briefly in spring due to <br />snowmelt. Water quality of the stream will not be adversely impacted due to the <br />requirement that drainage and sediment control diversions and a sediment pond as <br />specified in the application will be constructed prior to initiation of site <br />development and will remain in place until reclamation has been completed and <br />the site adequately stabilized. Investigations conducted by the applicant have <br />demonstrated that the proposed disturbances aze outside of the 100 yeaz flood <br />plain of Munger Creek. <br />Based on monitoring data from an alluvial well at the site, the stream is not <br />rechazged by an alluvial water table in the project vicinity, precluding the <br />possibility of contamination of the stream via the alluvium. The Munger Creek <br />stream channel will not be temporarily or permanently diverted [4.05.18(1)(c)]. <br />B. Diversions and Conveyance of Overland Flow <br />The collection ditches, diversions, and culverts conveying runoff from the disturbed areas <br />at the mine bench and along the Munger Canyon access and haul road will adequately <br />carry the flow resulting from the 10-yeaz, 24-hour event. Ditches diverting undisturbed <br />flow, and conveying disturbed drainage from the coal waste disposal pile will adequately <br />carry the flow resulting from the 100-year, 24-hour event. <br />C. Sedimentation Ponds <br />A sediment pond has been approved and constructed to treat disturbed runoff from the <br />coal mine waste disposal area (also referred to as the waste rock disposal site). A plan <br />view of the pond and associated drainage structures is depicted on Figure 2.2-6, cross- <br />section and specifications are depicted on Figure 2.2-7. The pond is an incised <br />impoundment with a design capacity of 0.75 acre feet. The design includes a 6" valved <br />primary spillway pipe installed at the maximum sediment storage level, and a riprapped <br />open channel emergency spillway at an elevation four feet higher than the primary <br />22 <br />