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these structures prior to the completion of mining would lead to mining through them during the last <br /> days of the operation. <br /> ii) Within the detail on F-1, the term "highwater thalweg"is used. The Division <br /> understands that a thalweg is the lowest point of the bed of a river or stream, and <br /> finds this terminology confusing. Please explain or improve the terminology on <br /> the detail of F-1. <br /> Highwater thalweg has been removed from Map F-1, as it is not crucial to the design. <br /> iii) Regarding the reference to the Mile High Drainage District document, is the <br /> referenced document a Wright Water Engineers report from January 2013 or an <br /> alternate version? <br /> The referenced document is the Wright Water Engineers report from January 13. <br /> • Please give more details on the design process for the inflow/outflow structure in <br /> Exhibit G. Refer to particular figures, text, and equations in the Mile High Drainage <br /> District document. <br /> See the revised Map F-1 Details 1 and 2 for the MHDD references. <br /> The river adjacent slopes are less than 1300' and the area of the pond divided by 12,000 is 44.2. <br /> Therefore, the minimum spillway bottom width is 100', according to the MHDD methodology. <br /> • In Exhibit G, as applicable, please describe how water elevations during flooding of <br /> the Gunnison River were used in the analysis and list any sources of information. <br /> Only base flood elevations (100-YR event) are available along the Gunnison River in this area. <br /> Given the MHDD methodology only uses the 2-YR event elevation, and that is not readily available, <br /> the annual high-water mark is used in its place (see Map F-1). The annual high-water mark is lower <br /> than the 2-YR flood elevation, typically, and therefore makes the design more conservative. <br /> 14) To ensure that the Delta Paving Gravel Pit does not impact the hydrologic balance of the <br /> Gunnison River, the application needs to include a water quality monitoring plan, specifically for <br /> the alluvium. The groundwater monitoring plan should be developed in accordance with Rule <br /> 3.1.7(7)(b) and should include a Quality Assurance Project Plan (QAPP) for the collection of <br /> groundwater samples. The plan should provide mitigation steps if there is an exceedance at a <br /> groundwater or surface water monitoring location. Potential impacts to quality and/or quantity <br /> the nearby domestic wells should also be addressed. A copy of the Division's Groundwater <br /> Monitoring and Protection Technical Bulletin has been included as an enclosure to this letter for <br /> your reference. <br /> • DRMS is reviewing the monitoring plan, and our comments will be forthcoming. <br /> Please see the revised Appendix G-2 that addresses the November 8, 2022 memo from Leigh <br /> Simmons. <br /> 6.5 Geotechnical Stability Exhibit <br /> DRMS is reviewing the geotechnical analysis and our comments will be forthcoming. <br /> Delta Paving <br /> September 2022 2 Lewicki&Associates <br />