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Section 13 <br />Geochemical Data and Analysis <br />• A site-specific RMC for arsenic, using site-specific exposure considerations <br />and measured arsenic bioavailability, indicate that arsenic concentrations also <br />do not suggest toxic-forming potential. <br />Overall, available data for development rock present at the Sunday Mines Group does <br />not suggest significant toxic-forming potential. No restrictions to currently assumed <br />land use appear necessary for protection of human health for future range workers or <br />other 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 />the Mine Safety and Health Administration (MSHA) in accordance with the federal <br />Mine Safety and Health Act of 1977 as amended, and other federal laws and <br />regulations. Denison 's mining operations comply with these regulations. <br />Potential Leachate Migration Risk <br />The potential for development rock or ore to form leachate containing metals is <br />dependent on several factors including the following: <br />¦ The propensity for the rock to release metals to infiltrating water (leaching). To <br />evaluate this factor, meteoric water mobility procedure (MWMP) analyses were <br />conducted on development rock and ore samples. The MWMP analysis provides <br />data that can be used for a screening-level evaluation to assess if the rock piles <br />have the potential to generate leachate containing metals concentrations such that <br />the rock could be considered a toxic-forming material; and <br />¦ The volume of percolation through the rock piles. Percolation was estimated using <br />two methods: 1) a water-balance approach that considers precipitation, <br />evaporation, and available water holding capacity; and 2) computer modeling <br />using a software program called UNSAT-H, which provides a more rigorous <br />evaluation through simulation of the processes of precipitation, infiltration, <br />evaporation and percolation. Estimation of the volume of percolation through the <br />rock piles addresses uncertainties associated with the rock to soil ratio used in the <br />MWMP tests as compared to actual field conditions; and <br />A comparison of MWMP leachate data to the Colorado groundwater standards <br />indicates that a number of constituents were detected at concentrations that are <br />greater than the Colorado groundwater standards. Below is a list of constituents <br />detected in MWMP leachate that were detected at concentrations greater than the <br />screening criteria for each of the development rock and ore stockpiles: <br />¦ Topaz Mine Development Rock: arsenic, chloride, molybdenum, nitrate, nitrite, pH, <br />selenium, sulfate, uranium, vanadium. <br />¦ Sunday Mine Development Rock: antimony, arsenic, molybdenum, nitrate, nitrite, <br />selenium, sulfate, and vanadium. <br />13-4 <br />TA64988-Denison Mines\Task Order 4; EPP Sunday Mines GrouptFINAL EPPWINAL - Environmental Protection Plan Sunday Mines.doc