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<br />EXHIBIT D -MINING PLAN (continued) <br />• <br />The resulting peak flow is 4.09 cfs, which is reasonable for a small watershed such as this. A <br />corrugated metal culvert of 18" diameter can handle 6.0 cfs at a HW/D ratio of .95, meaning that <br />there must be approximately 19" of compacted earth above the culvert. Therefore, the 18" culvert <br />will provide a 50% safety factor for the peak flow for the 100 year - 2d hour event. <br />Since the mining will reduce the area on both sides of the unnamed drainage by IS to 30 feet, the <br />site will then consist of two relatively flat depressions that will not drain. Ditches will be cut into <br />the unnamed drainage from both mine areas once final vegetation has received approval. The <br />design for these ditches is given in Exhibit E -Reclamation Plan. <br />Undisturbed Runoff Handling <br />• No undisturbed runoff can enter the pit area because it is bounded by the south berm on the south, <br />Spring Creek on the west, the north bern on the north and a small 2' high berm will be installed on <br />the east side of the permit boundary to ensure that runoff from the adjacent pasture does not enter <br />the pit area. <br />Groundwater Sprtng Handling <br />As described in Exhibit G -Water Information, there is a possibility that mining the gravel may <br />encounter shallow water during irrigation periods of the summer and fall. If any water of this type <br />is encountered, it will be channeled to the unnamed drainage to the point where the upper springs <br />are located. This will be done through ditches, pipes or other means so that the water will not <br />contact the disturbed areas of the pit. No system can be designed at this time since it is unknown if, <br />when, where and how much water will be encountered. <br />r~ <br />U <br />Carol Ann Permn CDMG Application 2 1 <br />