2005-07-20_REVISION - M1977403HR

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Bill Lyle, /darado Mining Company June 16, 1005 Page 2 Acid-base accounting (ABA) tests were performed to characterize the net neutralization potential (NNP), acid generation potential (AGP), and acid neutralizing potential (ANP) of the material contained in the repository. The results of the ABA tests are summarized in this Technical Memorandum. Sample Collection and Analysis Twenty soil samples were collected at various representative locations along the repository on September 21, 2004 by MFG, Inc. The samples were collected at regularly spaced horizontal and vertical intervals to characterize the soil contained within the repository. The repository was constructed by end-dumping of the mixed soiUmine and mill-related materials from trucks along a central haul ramp that progressed in elevation as the repository was constructed. Given the mixing of the soils and mine and mill-related materials that occurred during excavation and repository construction, the materials are believed to be uniformly distributed throughout the repository and the bulk of the materials contained within the repository are represented by the samples collected at the horizontally and vertically spaced intervals. The sampling of the repository surface was conducted to examine the materials final placement within the repository and not to prejudice the geochemical nature of the stockpile construction due to the manner in which the materials were mixed during excavation and placement. Therefore, the stockpile sampling was completed to examine the materials geochemical nature in final placement rather independent material characterizations (i.e., tailing, native soils, and waste rock) from the excavated surface. The locations of the samples collected within the repository are shown on Figure 1. Samples were collected on a grid along north-south trending lines spaced 30, 110, 190, and 240 feet east of the southwestem corner of the repository, and along east-west trending lines located 30, 60, 90, and 120 feet from the southwestern comer of the repository. Four additional samples were collected on the eastern slope face of the repository. Samples were collected between 10 and 65 feet above the base of the repository (Figure 1). Samples were collected from zero to six inches in depth. Since removal activities had not been completed at the Gold Run Mill at the time of sampling, four additional samples were collected from areas being excavated at the Gold Run Mill on September 22, 2004. The samples were collected [o a depth of six inches at the locations shown on Figure 2. The soil samples were submitted to SVL Analytical, Inc. for ABA analysis. The ABA analysis was preformed in accordance with the Modified Sobek Method using EPA Method 600. The sulfur forms (non-extractable sulfur, pyritic sulfur, sulfate-sulfur, and total sulfur) were analyzed using a Leco SC-132 Automatic Sulfur Determinator. The AGP is calculated based on only the total pyritic sulfur content. ABA Test Results The ABA test results for the 24 samples are provided in Table 1. The NNP is detertnined by subtracting the AGP from the ANP. A negative NNP value (or an ANP/AGP ratio less than 1) indicates that a potential exists for the soil to form acid. On the other hand, samples with a positive NNP value are considered alkaline in nature and predicted to have a reduced potential to produce acid. Geochemically, it is believed NNP values greater than 20 (or ANP/AGP ratios greater than 3) are considered unlikely to generate acid. As shown in Table 1, the sample materials demonstrated relatively low acid generation potential (AGP range of 0.9 to 20.0, a mean concentration of 5.9, and a median concentration of 5.3 tons CaC03/1000 tons) and considerable neutralization potential (ANP range of 9.9 to 71.3, a mean concentration of 30.5, and a median concentration of 29.5 tons CaC03/1000 tons). All samples had a positive NNP value except for one sample. The NNP sample values range from -8.1 to 65.1 tons CaCO}/1000 tons with ANP/AGP ratios ranging from 0.6 to 22.4. The average NNP value for all 24 samples is 24.6 tons CaC03/1000 tons P:000]I SNliiiga~bn\ABA t wing-Final.doc