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Section 4 <br />Rofentia/forRock to be Toxic Forming <br />¦ Screening using BLM RMCs a <br />present at concentrations that <br />separately below) <br />¦ A site-specific RMC for arses <br />measured arsenic bioavailat <br />suggest toxic-forming poten <br />USEPA RSLs indicates that no constituents are <br />,gest toxic-forming potential (arsenic is addressed <br />using site-specific exposure considerations and <br />?, indicate that arsenic concentrations also do not <br />Overall, available data for development rock present at the Van-4 Mine does not <br />suggest significant toxic-forming potential. No restrictions to currently assumed land <br />use appear necessary for protecti n of' human health for future range workers or other <br />future site visitors to the site. <br />It should be noted that risks to miners were not evaluated as part of this assessment <br />because mine safety, including exposure to mine rock and minerals, is regulated by <br />MSHA in accordance with the federal Mine Safety and Health Act of 1977 as <br />amended, and other federal laws and regulations. Denison s mining operations <br />comply, with these regulations. <br />4.2 Potential Leachate <br />The potential for development i <br />on several factors including the <br />¦ The propensity for the rock to <br />evaluate this factor, MWMP <br />ore samples. The MWMP an, <br />level evaluation to assess if t <br />containing metals concentral <br />forming material; <br />¦ The volume of percolation thr <br />two methods: 1) a water-bala <br />evaporation, and available w <br />using a software program ca. <br />evaluation through simulatic: <br />evaporation and percolation, <br />rock piles addresses uncertai <br />MWMP tests as compared to <br />¦ The propensity for naturally o, <br />potentially toxic constituents <br />Soils underlying the facilities <br />that could be present on leacl <br />capacity may slow movemen <br />process that is referred to as i <br />[igration Risk <br />to form Leachate containing metals is dependent <br />lease metals to infiltrating water (leaching). To <br />alyses were conducted on development rock and <br />sis provides data that can be used for a screening- <br />rock piles have the potential to generate leachate <br />is such that the rock could be considered a toxic- <br />ugh the rock piles. Percolation was estimated using <br />ce approach that considers precipitation, <br />ter holding capacity; and 2) computer modeling <br />ed UNSAT-H, which provides a more rigorous <br />i of the processes of precipitation, infiltration, <br />Estimation of the volume of percolation through the <br />ties associated with the rock to soil ratio used in the <br />field conditions; and <br />-urring soils underlying the rock piles to attenuate <br />hat could leach from development rock and ore. <br />nay have significant attenuation capacity for metals <br />rte from the rock storage facilities. The attenuation <br />of contaminants in the subsurface significantly, a <br />• <br />r? <br />U <br />0 <br />4-8