2019-03-18_PERMIT FILE - M2018016 (9)

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35. On Page E-1, Table E-I Reclamation Areas indicates 13.6 acres of undisturbed land. Please revise the Exhibit F-I map to indicate the undisturbed lands. See the revised Map F-1. Exhibit F -Reclamation Plan Map 36. The Exhibit F-I map indicates a purple line with two dashes approximately 300 offset from the proposed permit boundary. The line type is not identified on the map legend. Please explain this discrepancy and update the map and/or map legend accordingly. Please see the revised Map F-1. Exhibit G- Water Information On Page G-1, the Applicant states the proposed mine site is within the 100 year flood plain of the West Fork of Clear Creek. In the event of a significant flood event(100 year flood) it is likely the proposed mine site would be captured by the West Fork of Clear Creek. Where mining will occur within 400 feet of the river channel, a flood analysis and flood control plan must be evaluated and submitted for Division review and acceptance. The flood analysis should quantify the velocity and volume offlows expected on site from a 100 year flood event, as well as the elevation of the 100 year base flood event and its relation to the elevation of any proposed spillways and embankments. The flood control plan should address mitigation measures including pit side armoring, river side armoring, inflow and outflow channels, or other appropriate measures. The Applicant shall provide the flood elevations to be expected under a "worst case" flooding scenario and specific mitigation measures to be implemented to minimize the potential for any offsite impacts. Riverside berms are proposed in the Douglas Mountain Mine application amendment, which may be prone to erosion during a flood event. The potential for "berms"around gravel pits to be damaged during flooding is discussed in detail in the 1987 Urban Drainage and Flood Control District (UDFCD) Publication "Technical Review Guidelines for Gravel Mining Activities within or Adjacent to 100 year Floodplains."Strips of native ground or constructed fill between the stream and the gravel pit, and generally aligned with the flow direction of the river are referred to in the UDFCD document as riverside berms. Engineered inflow and outflow structures are intended to mitigate possible slope failure during flood events for these berms. The Douglas Mountain Mine is outside of the jurisdictional boundaries of the UDFCD, however the technical floodplain factors which led to the formation of the UDFCD guidance publication still apply and will be used to review the adequacy of the flood mitigation structures proposed for the site. Please provide a flood analysis and flood control plan satisfying the requirements of the UDFCD for the expected 100 year flood event during the life of the operation and after final reclamation for the Douglas Mountain Mine. A flood analysis is attached. Db1R aline AM-01 8 (.ng LVw Wk,am)1ssocul",PI l 1