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Potential for rock to be toxic forming <br />Total Metals <br />Total metals concentrations were evaluated to consider whether the development rock or temporary ore <br />stockpiles have the potential to be toxic-forming as a result of incidental ingestion or inhalation. The first phase <br />of this evaluation compares total metals data to three screening criteria: <br />1) BLM soil screening criteria' <br />2) Environmental Protection Agency (EPA) soil screening criteria for Industrial Soi12, and <br />3) Estimated background soil concentrations calculated using guidance provided by the Colorado <br />Department of Public Health and Environment (CDPHE)3. <br />A comparison of total metals content to background soil concentrations indicate that some development rock <br />and stockpiled ore metal concentrations are above the background concentrations for the following constituents: <br />antimony, arsenic, cadmium, copper, iron, lead, manganese, magnesium, mercury, molybdenum, selenium, <br />sodium, thallium, titanium, uranium and vanadium. The background soil samples were collected from soils that <br />are derived from un-mineralized rock outcrops near the mines. This comparison shows that the development <br />rock and stockpiled ore is naturally enriched in numerous metals in addition to uranium and vanadium; <br />however, the observed concentration levels do not indicate that the development rock is toxic-forming. <br />As a preliminary screening for potential toxicity via the incidental ingestion/inhalation pathway, the total metals <br />data were compared to soil screening criteria. None of the samples were above the EPA industrial soil screening <br />criteria for any of the above constituents, except for arsenic. Samples were also above the BLM screening <br />criteria for arsenic, and no other constituents. The EPA screening levels are not a regulatory driver, but simply <br />suggest that we need to look at this constituent in more detail. <br />Although the arsenic levels in development rock are not extremely high, based on this information, arsenic <br />appears to be the only constituent of concern presented by the total metals analysis. Exceedance of the <br />screening criteria does not indicate that this rock is toxic-forming, but it suggests that additional work should be <br />completed to evaluate potential site-specific toxicity of the rock with regards to arsenic. Denison is in the <br />process of completing site-specific evaluations of potential arsenic toxicity via the incidental <br />ingestion/inhalation pathway. <br />Meteoric Water Mobility Procedure <br />The meteoric water mobility procedure is the first phase of an analysis to evaluate whether development rock or <br />temporary ore stockpiles are toxic-forming with regard to release of potential contaminants into the <br />environment as a result of percolation of precipitation through the piles and subsequent discharge. There are <br />several components to this evaluation: <br />1. Completion of MWMP tests and preliminary screening of the results by comparison to Colorado <br />Groundwater standards; <br />2. Evaluation of the potential flux of water through piles; <br />3. Evaluation of natural attenuation capacity of soils underlying the piles; and <br />' BLM Soil Screening Criteria were obtained from Risk Management Criteria for Metals at BLM Mining Sites, U.S. <br />Department of Interior, Bureau of Land Management, Technical Note 390 rev., October 2004, Table 2, Human Risk <br />Management Criteria. <br />2 EPA Industrial Screening Criteria were obtained from a combination of EPA Region 3 risk based concentrations (RBCs), <br />Region 6 Human Health Medium-Specific Screening Levels (HHMSSLs), and the Region 9 Preliminary Remediation <br />Goals (PRGs). <br />3 Estimated Soil Background values were calculated from site-specific background soil sample data in accordance with <br />Proposed Soil Remediation Objectives Policy Document, CDPHE, December 1997. <br />4 A1 <br />DENISON r, <br />MINES <br />2