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,Nr Mike Re/er-CAMAS Co., fnc. • • <br />September ?6. ?000-Atfequnn• Lv.-A1- `00005? <br />Page 2 <br />commit to mining no deeper than the highest ground water elevation at any time during the year. In this case, <br />if ground water is exposed, please commit to backfilling the exposed water to 2 fee[ above the water table and <br />notifying the OSE and DMG immediately. <br />Exhibit G -Water Information <br />Section 8.02 - Stvface Water System <br />I) This section states that the proposed mining operation lies within [he 100-year floodplain on the north <br />bank of the Cache La Poudre River. Also, in Exhibit C (Pre-mining Plan and Affected Lands). i[ is <br />stated [hat "In addition, 100-year floodplain information is depicted on the topography/ air photo <br />map...." However, the Division could not identify a 100-year floodplain on the referenced map, <br />Exhibit C (Pre-mining Plan Map). <br />Please provide a map that clearly defines [he boundaries of the 100-year floodplain for the Cache La Poudre <br />River relative to the proposed affected area and an engineering analysis that predicts any changes to the <br />current 100-year floodplain elevation, width boundaries of the current 100-year floodplain and flowpath of a <br />100-year Flood event both during mining and final reclamation, based on the proposed plans. <br />2) Other related floodplain concerns that will need to be addressed include the following: <br />a) All product, overburden and topsoil stockpiles should be located outside of the boundaries of <br />the 100-year floodway, if possible. The applicant should provide a map showing the location, <br />orientation and configuration of any stakpiles. <br />b) The applicant will need to provide a Flooding impact analysis characterizing the floodpath <br />and flow velocities for Flooding events expected during the life of the operation. The <br />applicant will need to assess how much of the pit or lakes will be flooded, how the <br />floodwaters will be safely routed back to the main channel of [he Cache La Poudre and how <br />the riverbank and pitside banks will be protected from excessive erosion. <br />Section 8.03 -Groundwater System <br />1) Since the applicant proposes to dry mine the upper 30 feet of the deposit and, in Section 8.06, states <br />that an application for a NPDES Permit will be submitted for "construction dewatering'", it appears <br />that pit dewatering will take place. <br />Please provide details of this process, including the location of any dewatering trenches, water routing, <br />settling ponds and how, when and where this water discharge will occur. <br />2) The applicant has proposed dry mining methods, which will, apparently, intercept the ground water <br />[able of the affected land. The applicant has also proposed open pit gravel lakes or lined water <br />storage reservoirs, which will expose water at reclamation. Based on these criteria, it appears that the <br />proposed operation may directly affect surface or ground water systems. Accordingly, [he Division <br />requests that the applicant provide adequate information to characterize the alluvial-ground water <br />aquifer that will be intercepted during ruining and reclamation. At a minimum, the applicant should <br />define the Following information for the affected land and surrounding area: average depth to ground <br />water, ground water gradient or Flow direction, depth of aquifer and aquifer transmissivity. <br />