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The EPA currently is doing extensive monitoring of ground water sources (as stated earlier, The Big Five <br />Tunnel drainage is monitored, collected, and pumped to the Argo Tunnel Treatment Facility located in Idaho <br />Springs). <br />As a part of normal mill operations, mill process water will be continuously monitored. A pH monitor and data <br />recorder will be installed at the tailings pump location within the mill. Should the pH reach a state outside of <br />the 7.5-9 range that is necessary to precipitate the heavy metals, alarm notification will be activated for the <br />operations personnel. The submittal notes on this Serfilco Model 432 monitor/recorder can be found in <br />Appendix N. <br />If the pH falls outside of the 7.5-9 range, the operators are instructed to shut down the tailings pump that <br />delivers waste to the impoundment. Once the source of the problem is corrected upstream in the process, waste <br />can then be discharged to the impoundment. <br />It is physically impossible for heavy metals to be in solution under these operating conditions (pH range of 7.5- <br />9) as shown in Appendix E. No explosive gases are present in the waste stream. <br />3.2.5.A Liner design components <br />The impoundment (a Class III Impoundment) is to be constructed on crystalline metamorphic and igneous rocks <br />with essentially zero hydraulic conductivity. A concrete barrier will be installed upon the up gradient face of <br />the first earth-fill terrace to minimize leachate through the structure (see Drawing T7 & T8). The natural slope, <br />upon which the fill will reside, is slightly less then 1:3. The clay contained in the waste stream (approximately <br />30% by weight) is sufficient to seal any joints or fractures in the impervious bedrock. Leachate and solid waste <br />qualities are given in Appendix F. Both leachate and solids meet or exceed all water quality standards. <br />Leachate quality exceeds existing groundwater quality by a minimum of 2-3 orders of magnitude. Metallurgical <br />and corrosion controls require that the pH of the process water be in the range of 7.5-9. It is physically <br />impossible for heavy metals to be in solution under these operating conditions as shown in Appendix E. <br />• A monitoring well will be installed 20-30 feet below the leachate collection structure which is approximately 60 <br />feet down gradient from the fill. After closure, within one year there should be no leachate produced. Net <br />precipitation for the site is in the range of minus 15" to 20" per year. There is no groundwater surfacing at the <br />site, the groundwater level is approximately 900' below the surface, and with the permanent stormwater <br />diversion structures no meteoric water should penetrate the fill. <br />There are no known domestic well or springs downgradient of the site (reference Appendix 1). Groundwater <br />flow beneath the site is controlled by mine openings as discussed above in section 3.2.2.D. <br />There is no potential for chemical reactivity from the waste with the barrier. Waste characterization testing has <br />shown that the proposed waste stream meets or exceeds all RCRA waste standards as shown by Appendix F. <br />Due to the chemical composition and type of waste to be deposited at the site, groundwater quality will not be <br />adversely affected. <br />3.2.5.C Barrier layer type <br />Natural lithology without re-compaction. Fractures and joints will be sealed with hydraulically deposited clay, <br />which is a constituent of the waste stream. <br />3.2.5.D Leachate collection and removal systems <br />A system consisting of a concrete barrier constructed and grouted to bed-rock down gradient of the <br />impoundment, including a process water return pump, will be used to collect and recycle leachate (see <br />Appendix C, Drawing T8). Additionally it is worth note that the leachate water quality exceeds that of the <br />groundwater as demonstrated in 3.2.2.G Hydrologic Data. <br />3.2.6 Surface water control systems <br />Please refer to Appendix C and D for our proposed Stormwater and Best Management Practices Plan and <br />• Tailings Impoundment Design Drawings detailing the diversions and control measures that will be implemented <br />20