Laserfiche WebLink
ITASCK <br /> Denver, Inc. <br /> components of a material. An NPR value of less than 1.0 indicates that the sample is PAG. BLM <br /> guidelines indicate that a sample is non-PAG if its NPR is greater than 3.0. Samples with NPR <br /> values greater than or equal to 1.0 and less than 3.0 are considered uncertain under BLM <br /> guidelines (BLM 2013). Samples with ANP/AGP ratios that are greater than 3.0 are considered <br /> non-PAG. <br /> 3.1.2 Limitations of ABA Testing <br /> Though ABA is a widely accepted method of predicting the potential for rock to generate acidic <br /> leachate,there are some uncertainties associated with the methodology. Four of the factors that <br /> contribute to uncertainty in ABA testing are the following: <br /> 1. ABA does not address rates of reaction, <br /> 2. ABA does not address the geochemical reaction environment, <br /> 3. ABA assumes that all sulfur minerals (or only sulfide minerals in some cases) contribute <br /> acidity in a manner similar to pyrite, and <br /> 4. ABA assumes that all ANP will be available to neutralize the AGP of the sample at an <br /> environmentally acceptable pH value. <br /> Each of these factors is discussed in more detail in the following paragraphs. Regarding the first <br /> factor contributing to ABA uncertainty, ABA is a static test, meaning that it does not examine the <br /> rate of acid generation or neutralization. Acid-base accounting evaluates the balance between <br /> the ultimate potential of rock to release acidity and its ultimate potential to neutralize acidity. In <br /> practice, the generation rate of acidity and the neutralization rate may differ, and some acidity <br /> or neutralization may not be available or readily reactive due to processes like encapsulation by <br /> silica or armoring by reaction products. The relative rates of acid neutralization and acid <br /> generation are examined more closely using the HCT results. <br /> Regarding the second factor contributing to ABA uncertainty, ABA does not address the <br /> geochemical reaction environment. Acid generation through sulfide oxidation occurs only under <br /> 14 <br />