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Section 4 <br />Potential for Rock to be 'toxic-Forming <br />Screening using:BLM RMCs and USEPA RSLs indicates that no constituents are present , <br />at concentrations that suggest toxic-forming potential (arsenic is addressed separately <br />below) <br />A site-specific RMC for arsenic, using site-specific exposure considerations and <br />measured arsenic bioavailability, indicate that arsenic concentrations also do not suggest <br />toxic-forming potential. <br />Overall, available data for development rock present at the Sunday Mines Group does not <br />suggest significant toxic-forming potential. No restrictions to currently assumed land use <br />appear necessary for protection of human health for future range workers or other future site <br />visitors to the site. <br />It should be noted that risks to miners were not evaluated as part of this assessment because <br />mine safety, including exposure to mine rock and minerals, is regulated by the Mine Safety and <br />Health Administration (MSHA) in accordance with the federal Maine Safety and Health Act of <br />1977 as amended, and other federal laws and regulations. Denisori's mining operations comply <br />with these regulations. <br />4.2 Potential Leachate Migration Risk <br />The potential for development rock or ore to form leachate containing metals is dependent on <br />several factors including the following: <br />¦ The propensity for the rock to release metals to infiltrating water (leaching). To evaluate this . <br />factor, MWMP analyses were conducted on development rock and ore samples. The <br />MWMP analysis provides data that can be used for a screening-level evaluation to assess if <br />the rock piles have the potential to generate leachate containing metals concentrations such <br />that the rock could be considered a toxic-forming material; <br />¦ The volume of percolation through the rock piles. Percolation was estimated using; two <br />methods: 1) a water-balance approach that considers precipitation, evaporation, and <br />available water holding capacity; and 2) computer modeling using a software program <br />called UNSAT-H, which provides a more rigorous evaluation through simulation of the <br />processes of precipitation, infiltration, evaporation and percolation. Estimation of the <br />volume of percolation through the rock piles addresses uncet'tainties associated with the <br />rock to soil ratio used in the MWMP tests as compared to actual field conditions; and <br />¦ The propensity for naturally occurring soils underlying the rock piles to attenuate potentially <br />toxic constituents that could leach from development rock and ore. Soils underlying the <br />facilities may have significant attenuation capacity for metals that could be present on <br />leachate from the rock storage facilities. The attenuation capacity may slow movement of <br />contaminants in the subsurface significantly, a process that is referred to as retardation <br />(Freeze and Cherry 1979). <br />These assessments are discussed below. <br />• <br />cm 4-8 <br />7:\64988-Denison Mines\Task Order 3 - DMO Sampling and Analysis Plan\Task 3.12 - Soil, Ore, Rock Data Assessment RepornSunday Rook lteponAnal report\ReportWinal Sunday Mines Group Soil Ore Rock <br />Data Assessment Report_051509.doc