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0 Section 3 <br />Assessment of Potential Acid-Forming Rock <br />The section presents an assessment of the potential for development rock at the Van 4 <br />mine to be acid- forming as defined by the HRMMR. The HRMMR §1.1(2) defines <br />acid mine drainage as: <br />"Acid Mine Drainage" means contamination of water by low pH or heavy <br />metals that occurs from mined or disturbed materials as a result of the <br />chemical and biological oxidation of reactive sulfide minerals when exposed to <br />air and water. The possibility of generating "Acid Mine Drainage" exists <br />where the pH of any exposed or potentially exposed overburden, waste rock, <br />mill tailings, waste water treatment sludge, or other mined, placed, disposed <br />or stockpiled material has the potential to develop a pH of 5.8 or less..." <br />Evaluation of the potential for acid mine drainage is based on evaluation of ABA data, <br />observational data regarding mineralogy of the mine rock, and effluent pH data from <br />MWMP column tests. <br />ABA data for development rock samples are shown in Table 3-1. These data show an <br />overall low sulfur content and excess of neutralization potential over acid potential in <br />all samples. ABA data are compared to the empirical thresholds described in Section 2 <br />to evaluate the potential for the rock to generate acid in the future. <br />The first threshold is based on the NNP. The NNP of development rock samples <br />collected at the Van 4 Mine range from 42.1 to 90.1 t/kt CaCO3 eq. These NNP values <br />are greater than the 20 t/kt CaCO3 eq. threshold, which indicates that the <br />development rock has a low potential to generate acid. ABA data are compared to the <br />second empirical threshold in Figures 3-1 and 3-2. This threshold is based on the <br />NP:AP ratio. All samples exceed the NP:AP ratio threshold of 4, which indicates that <br />the samples are unlikely to generate acid. <br />The ABA data support field observations that visible sulfide minerals are not present <br />and that ubiquitous calcite is present in the development rock. Trace concentrations of <br />nitric acid soluble sulfur are present in several samples. These trace concentrations <br />may be a result of trace barite (BaSO4) within the samples rather than sulfide minerals. <br />The effluent pH values from the MWMP analyses provide additional data to evaluate <br />the potential for the rock to be acid forming. These data range from 8.03 standard <br />units (su) to 8.26 su. These development rock and ore sample data indicate pH values <br />well above the pH criteria of 5.8 su set forth in HRMMR §1.1(2) and support that the <br />Van 4 Mine development rock is unlikely to generate acid rock drainage and is not <br />considered acid-forming material. <br /> <br />3-1 <br />7:64986-Denison Mines\Te