2010-08-02_REVISION - M1977300 (36)

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Environmental Protection Plan, Schwartzwalder Mine 15-1 • 15. MITIGATION OPTIONS AND CONSTRUCTION SCHEDULE Rule 6.4.20(15) requires that the EPP provide a detailed construction schedule for (1) all facilities designed to contain or transport toxic materials, acid-forming materials, or designated chemicals used in the extractive metallurgical process and (2) all facilities proposed to contain, hold, or for disposal of, material that has the potential to cause acid mine drainage. The Schwartzwalder Mine has been reclaimed, and no new facilities are planned for mining activities, mine operations, or extractive metallurgical processes. However, facilities will be constructed for the mitigation of groundwater in the alluvium and fill. Mitigation strategies for the alluvium and fill were proposed by DRMS in a letter dated October 21, 2009. These options and others have been considered in a preliminary screening of mitigation alternatives. The mitigation options considered include the following: (a) Convey, transport or divert surface water around or away from toxic-forming material; (b) Capture and/or retain surface water run-off, (c) Remove the alluvium/fill and replace with inert fill; (d) Pump and treat the pore water in the alluvium/fill; (e) Isolate the creek from the alluvium/fill; (f) Capture and treat the pore water in the alluvium/fill using a funnel-and-gate style permeable reactive barrier (PRB) system; (g) Capture and treat the pore water in the alluvium/fill using an engineered wetland; • (h) Set up institutional controls to limit human activities (and exposure) at the site. These potential strategies have been evaluated in light of the following criteria: (a) Overall protection of human health and the environment, (b) Compliance with applicable or relevant and appropriate requirements, (c) Long-term effectiveness and permanence, (d) Reduction of toxicity, mobility or volume through treatment, (e) Short-term effectiveness, (f) Implementability, (g) Cost, (h) State acceptance, and, (i) Community acceptance. Sustainability and effectiveness are particularly important criteria, based on the remoteness of the site, closure and reclamation status, longevity of constituents, and the potential post-closure uses of the property for recreation, wildlife, and open space. The most highly ranked mitigation options have been selected and prioritized as follows: (1) targeted source removal (2) a permeable reactive barrier (funnel and gate) system, (3) grout curtain or sheet piling for localized isolation of Ralston Creek from groundwater in the alluvium and fill, and (4) an engineered • wetland. The approach to targeted source removal is described in Section 15(b)(iii). Preliminary details for an engineered wetland and a permeable reactive barrier (funnel and gate) system were described in the April 19, 2010 version of the EPP, and have been updated in Sections 15(b)(v) and 15(b)(iv). The location 4109C.100731 Whetstone Associates