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Christy Woodward <br />July 31, 2008 <br />Page 9 <br />Neutralization potential is estimated by adding a known quantity of hydrochloric acid to the <br />sample followed by titration of the solution back to a pH of 8.3. The quantity of remaining <br />acid is estimated based on the amount of sodium hydroxide necessary to raise the pH back to <br />a value of 8.3. The quantity of acid consumed by the sample is the neutralization potential, <br />which is estimated by difference and expressed in units of tons per kiloton calcium carbonate <br />equivalent (t/kt CaC03 eq). <br />In interpretation of ABA analyses, acidity produced by one mole of pyrite is assumed to be <br />neutralized by 2 moles of calcite, which results in a stoichiometric conversion factor of 31.25 <br />t/kt CaC03 eq. per percent pyritic sulfur. This allows both the acid potential and <br />neutralization potential of a rock to be expressed in equal units of t/kt CaC03 eq. However, <br />the acid generation and neutralization reactions used in the ABA interpretation are not <br />unique. Therefore, interpretation of ABA analyses is commonly based on empirically derived <br />thresholds. These thresholds are based on the difference between the acid potential and <br />neutralization potential, referred to as net neutralization potential (NNP), and/or the ratio <br />between the neutralization potential and the neutralization potential (NP:AP ratio). <br />Commonly applied thresholds for interpretation of ABA data include the following: <br />¦ NNP values relative to the potential to generate acid in the future: <br />¦ <0 t/kt CaC03 eq. indicates a high potential. <br />¦ 0 to 20 t/kt CaC03 eq. indicates an uncertain potential. <br />¦ >20 t/kt CaC03 eq. indicates an unlikely potential. <br />¦ NP:AP relative to the potential to generate acid in the future: <br />¦ <1 indicates a high potential. <br />¦ 1 to 2 indicates a moderate potential. <br />¦ 2 to 4 indicates a low potential. <br />¦ >4 indicates unlikely potential. <br />These thresholds are used along with evaluation of mineralogical data in order to classify the <br />potential for the source material to generate acid in the future. <br />Potential for Constituents to be Mobilized from Development Rock <br />The potential for development rock to be toxic-forming is a critical concern. Some mine rocks <br />have the propensity to cause problematic mine drainage, which contains elevated <br />concentrations of problematic constituents but is not acidic. Examples of constituents that <br />0:\64986 - Denison\Task Order 3 - DMO Sampling and Analysis Plan\Task 3.1 - Soil Ore Rock Data Collection PlanTinal Denison Sunday Mines Group Soil Ore Rock Data <br />Collection Work Plan.doc