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Intr. Alan D, Cox • • <br />Corporate Manager -Environmental Affairs <br />September 22, 1997 <br />Page 2 <br />about the water:rock ratio used in the attenuation tests. The final issue raised by Dr. Posey is <br />related to whether tailings samples were rinsed prior to paste pH testing. The following <br />discusses each of these items. <br />Passe pH Testing. The samples were not rinsed prior to the paste pH tests. Test holes were <br />drilled using hollow stem augers and samples were collected by augeting 2.5-foot nominal length <br />core runs with a steel split-barrel liner. The samples were immediately analyzed for paste pH by <br />mixing approximately equal volumes of tailings and distilled water. <br />Oxygen Consumption. SMI concludes that oxygen profile and consumption data show that the <br />oxygen flux through the surfaces of the tailings impoundments due to sulfde oxidation is <br />immeasurable. Dr. Posey points out that because the oxygen content between shallow and <br />deeper parts of the tailings profile is relatively constant, the tailings aze fully open to the <br />atmosphere and are constantly being replenished with oxygen. <br />We did not mean to imply that the tailings are not connected to the atmosphere. Indeed, we agree <br />that the upper unsaturated tailings are in direct communication with atmospheric oxygen; <br />however, oxygen profiling was only one of two tests at Bulldog. An equally important <br />measurement was the oxygen flux. This measurement was taken by driving a capped, 20-cm <br />diameter, thin-walled cylinder into the tailings, leaving a small, air-filled head space above the <br />tailings surface. An oxygen sensor was installed in the sealed head space, and the decay in <br />oxygen concentration was recorded to determine the oxygen flux into the tailings over periods of <br />17 hours to several days. This information was used to show that there is no significant flux of <br />oxygen into the tailings. <br />Investigations by Blowes and Jambor (1990) show that the oxygen concentration in pore gases <br />beneath the surface of tailings impoundments decrease with depth where oxygen is being <br />consumed by active sulfide oxidation. The oxygen concentration decrease in the Blowes and <br />Jambor investigation was measured in the upper foot of materials, even though the impoundment <br />was open to the atmosphere. At Bulldog, oxygen profile and flux measurements did not indicate <br />any significant consumption of atmospheric oxygen within the impoundments. These results led <br />SMl to the conclusion that oxygen consumption (flux) due to sulfide oxidation within the <br />impoundments was immeasurable. The attached articles by Blowes and Jambor (1990) and <br />Nicholson et al. (1995) are provided as evidence of observed incidences of oxygen consumption <br />neaz the surface of tailings impoundments that contain actively oxidizing sulfide minerals. <br />Petrographic Analysts. Dr. Posey is concerned that the examination of petrographic sections <br />used by SMI is open to permissive interpretations, and he does not accept the absence of iron <br />oxide rinding as evidence that the tails are not being oxidized. Secondary mineral assemblages, <br />p \I]-) I~Vm~ep doc <br />