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Whetstone <br />Associates, <br />Technical Memorandum <br />such as minor fluctuations in ground water level, pH or redox conditions. Some type of management <br />of this feature is warranted. <br />Bedrock monitoring wells - Cotter has identified a preferred location for bedrock monitoring wells, <br />and proposes to install paired wells (shallow and deep) to better determine hydraulic heads and flow <br />directions in bedrock (to the extent that water flows in the low-permeability bedrock). The proposed <br />locations and completion depths for bedrock monitoring wells are included in plan view and cross <br />section in the revised EPP. <br />Management of alluvial water quality <br />focus on the potential pathways for <br />communication with Ralston Creek. <br />groundwater in the alluvium and fill. <br />studies are performed, will provide <br />releases to the environment. <br />- Cotter agrees that the mitigation strategies in the EPP should <br />exposure. The alluvial groundwater is in direct hydraulic <br />The revised EPP contains potential mitigation strategies for <br />Implementation of these strategies, after suitable engineering <br />management of alluvial groundwater and minimization of <br />6) With respect to the alluvium, the Operator must comply with Rule 6. 4.20(6) pertaining to <br />designated chemicals and materials handling. The Operator must describe the procedures for the <br />disposal, decommissioning, detoxification or stabilization for the toxic forming materials in the <br />alluvium. Specifically describe measures to be taken to prevent any unauthorized release of <br />pollutants to the environment. Options for management might include one or more of the following: <br />(a) convey, transport or divert surface water around or away from toxic forming material, (b) <br />capture and/or retain surface water run-off, (c) remove the alluvium and replace with inert fill, (d) <br />pump and treat the pore water in the alluvium, or (e) isolate the creek from the alluvium. <br />As discussed in the March 19 meeting, Cotter and their consultants evaluated numerous mitigation <br />strategies for the alluvium and fill, including the strategies listed above. The mitigation options were <br />evaluated with consideration for EPA's nine criteria: <br />a. Overall protection of human health and the environment, <br />b. Compliance with applicable or relevant and appropriate requirements, <br />c. Long-term effectiveness and permanence, <br />d. Reduction of toxicity, mobility or volume through treatment, <br />e. Short-term effectiveness, <br />f. Implementability, <br />g. Cost, <br />h. State acceptance, and <br />L Community acceptance. <br />The revised EPP describes the two mitigation options that will be carried forward to engineering <br />studies, feasibility, and design. Preliminary details for an engineered wetland and a permeable <br />reactive barrier (funnel and gate) system are described in the revised EPP, along with an <br />approximate timeline for engineering studies, evaluation, DRMS review, and construction. <br />7) Because the alluvium contains toxic forming materials, DRMS contends that the alluvium should <br />also be designated as an Environmental Protection Facility and therefore subject to the provisions <br />4109C.100416 5