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CGRS — Report an Overtopping and Erosion Probability during the 100 year flood for the <br />Western Sugar Reclamation Site — July 20, 2011 <br />Page 4 of 6 <br />3. The CGRS report does not address the stability of the proposed 100 foot mining offset from <br />the Cache La Poudre River. Please provide specific details related to justification for the <br />proposed 100 foot offset, pit side armoring, river side armoring, inflow and outflow <br />channels and specific mitigation measures that will be implemented to minimize the <br />potential for any offsite impacts. <br />4. The report identifies an area of "High Risk Erosion Area" within the proposed offset area in <br />Tract D. The proposed 100 foot offset is not adequate to prevent potential offsite impacts. <br />Please commit to increasing the offset from Cache La Poudre River to at least the floodway <br />limits indicated on Plate 3 in Tracts D and C for the Western Sugar site. <br />5. On Page 4 in the Proposed Conditions section, the Operator states (flood) water would be <br />allowed to flood the pit to the level of the adjacent river. Please explain how the water <br />level will be controlled and how the flood water will be allowed to passively return to the <br />river channel from Tracts C and D after reclamation of the site. <br />6. The USACE model used by the Operator to evaluate the potential for overtopping and <br />erosion of Tracts C and D is flawed and should not be used to estimate the overtopping and <br />erosion potential. The model does not account for the drop structure in the Poudre River. <br />If the drop structure were included in the model, the resulting flood elevation upstream of <br />the drop structure would be increase substantially. Please re- evaluate the overtopping and <br />erosion potential for site with the affects of the drop structure included in the model. <br />7. On Page 6 in the Tract C section, the Operator states a weir will be constructed to train flow <br />through a suitably armored location. Please provide additional information pertaining to <br />the design and construction of the weir. At minimum, please include the following <br />information: <br />a. Justification for the weir location <br />b. Spillway invert elevations <br />c. Cross - section details (both lateral and longitudinal) <br />d. Design parameters <br />e. Definition for "suitably armored" <br />The design parameters should include the expected flood flow elevations and peak flows, <br />frequency of the expected flood flows, the expected water elevation in the lake and if the <br />spillways are designed to control the lake surface elevation. <br />8. The proposed Tract C weir location is not located within the approved permit boundary for <br />the Western Sugar site. The weir is considered affected land per Rule 1.1(3) and must be <br />included into the permitted acreage. Please commit to submitting an amendment, Per Rule <br />1.10, to increase the permitted acreage for the site. Additionally, the Operator must <br />4 <br />