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Applicant's Response to Sewnd Adequacy Letter <br />Grand River Park Project, DRMS File M-2006-046 <br />January 2, 2007 <br />Page 21 <br />rip rapped spillways may require a filter fabric or sub-grade (please <br />address). <br />The applicant characterized flood hazards and mitigation strategies in response <br />to the Division's initial adequacy Comment 24. Regarding the Division's concern <br />that there might be "a significant flood event capturing the pit and causing off-site <br />damage," it should again be noted that the River was specifically engineered with <br />a floodway levee in this vicinity, such that topographic analysis demonstrates that <br />100-year flood waters would first enter the subject property at a considerable <br />distance from the main channel of the Colorado River. This existing topographic <br />constraint is very significant, as it will cause flood encroachment into pit areas to <br />be limited to flows typical of the flood fringe, relatively low in energy and <br />dispersed. For these and other previously stated reasons, pit capture by the <br />Colorado River is not deemed a significant risk. <br />Mitigation measures for flood and erosion control are discussed in greater detail <br />in the attached engineering response by R. Mike McDermid, P.E. Note also that <br />the applicant's revised approach to water quality no longer requires a large <br />surface clarification basin with gravity outlet to the Colorado River; the elimination <br />of a channel connection to the River (e.g., discharge water will now be lifted over <br />the levee by pumps to best protect the levee's integrity) is part of a general <br />strategy that minimizes the erosive potential of flood fringe waters. <br />The Division should also note that the applicant submitted materials to Garfield <br />County for review of a floodplain development permit. Generally, counties have <br />plenary authority to approve development in the flood fringe and require <br />appropriate mitigation for flood control. The County's review is currently pending. <br />25. Wetland/Riparian Impacts -Please identify the location and extent (acreage) <br />of any wetland resources and/or woody vegetation resources such as <br />cottonwoods or willows that occur between the proposed pit and the main <br />channel of the Colorado River. (This information may be provided on a revised <br />Mining Plan Map). If such features do exist, the Division requests that the <br />applicant identify the surface owner(s) of each feature, quantify the extent <br />(acreage) of each feature, quantify the expected drop in water table beneath <br />each feature as a result of de-watering activities, the expected length of time of <br />water table impact due to pit de-watering operations, specific mitigation <br />measure(s) that will be implemented to maintain the hydrologic conditions <br />supporting each feature, and proposed monitoring measures the applicant will <br />implement to verify that anticipated hydrologic impacts have been minimized. <br />Please address. <br />Initially, in the Division's first adequacy review, Comment 25 noted the presence <br />of cottonwoods and wetlands on the subject site and requested that the applicant <br />