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Response to DRMS Comments <br />Environmental Protection Plan, <br />Denison Sunday Mines Group <br />time. The stockpile areas themselves are on the unlined surface of the <br />development rock of the staging area. Pursuant to Hard Rock/Metals Rule <br />64.20(7) it is appropriate that the ore stockpile areas be considered EPFs. <br />Denison must demonstrate that the existing ore stockpile areas provide adequate <br />containment of runoff and leachate of the toxic forming materials, or perform the <br />construction tasks necessary for the ore pad to provide such containment. Please <br />see the attached "General Ore Pad Construction Criteria. " Please provide a <br />statement as to whether the ore pads have been properly constructed and tested <br />to meet those requirements, or propose a construction and certification plan, <br />with a timeframe. <br />Response Please see Response to Comment 2. Denison will design and construct <br />ore storage pads with PVC geomembrane liners. Production and storage <br />of ore is not currently being conducted at the Sunday Mines Group. Prior <br />to resuming these operations, Denison will construct ore pads that are <br />compliant with DRMS' "General Ore Pad Construction Criteria." <br />Comment 4 Unsaturated (UNSAT-H) model and percolation estimation. Denison has <br />provided information showing the limited mobility and reduced threat from <br />various minerals in the mined and unmined rock material, based on the geologic <br />characteristics as well as the and climate at the mine. The wettest months are <br />August through October, which suggests that precipitation during those months <br />is delivered via thunderstorms - potentially high intensity events. It is known that <br />plumes can form beneath waste rock facilities in and climates in response to <br />seasonal patterns of such high intensity events. Please address the following: <br />Does the model account for high-intensity, short-duration precipitation events <br />such as thunderstorms? If not, what effect would these have on percolation <br />estimates? <br />Response Additional assessments using the UNSAT-H model have been completed <br />to address this comment. An addendum to the Environmental <br />Geochemistry Investigation of Rock and Soil Material Sunday Group <br />Mines (Attachment B of the EPP) has been developed; see attached <br />addendum for review. <br />Comment 5 Permanent stormwater structures. The Division has questions regarding control <br />of stormwater runoff originating from the affected areas (pad surfaces and <br />slopes, stockpile surfaces, and roads). Such runoff and its control during the <br />mining phase (including periods of temporary cessation, if any) are considered <br />by this office to be adequately addressed. However, the EPP states that certain <br />stormwater control structures will be permanent, and remain on the site after <br />final reclamation. The Stormwater Management Plan (SWMP) prepared for <br />CDPHE-WQCD, and included in this EPP within Attachment F, reiterates the <br />statement that certain Swales and Diversion Ditches will be permanent and <br />remain onsite, though which specific structures are not identified. It is the <br />Division's concern that there may be some such structures onsite that are <br />planned to remain after reclamation (understood to be after monitoring and <br />maintenance by the operator have ceased) that may not be able to continue <br />functioning adequately to control, convey or divert their designed working <br />Final RTC Sunday Mines EPP.doc 4