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• i <br />Table 1. Stunmary of Acid and Metals Production Potential Tests. <br />Unit <br />Santa Fe <br />Pink Gneiss <br />Acid Base Accounting <br />Very high acid <br />neutralization potential. <br />Very high acid <br />neutralization potential in <br />some samples (S1tK, <br />1994; 2 samples), but <br />very high acid generating <br />potential in others (Jones, <br />1994, 10 samples). <br />Metals Leachability <br />Potential for Se in <br />leachate exceeding <br />drinking water and <br />agriculture standards. <br />Potential for Se leachate <br />exceeding drinking <br />water and agriculture <br />standards. <br />Comments <br />Local groundwater <br />has elevated Mn and <br />Se. <br />Altered Biotite <br />Gneiss <br />2 samples; <br />one with equal abundance <br />of acid and base has no <br />margin of safety. <br />Another is a net acid <br />generator. <br />Must assume the <br />rock fi:is an overall <br />net acid production <br />potential. <br />Potential for Mn Local groundwater <br />exceeding drinking has elevated Mn and <br />water and agriculture Se. <br />standards. <br />Cu elevated in one <br />sample, but leachates <br />pass drinking water <br />standards. Se detection <br />levels too low to <br />evaluate. One sample <br />exceeds secondary <br />drinking water stds for <br />Fe and Mn. <br />May want to re-test <br />Se. <br />Humidity cell test <br />indicates no significant <br />acid generating <br />potential. <br />DISCUSSION <br />Of the two geologic units that will be placed in the West Pit in significant quantities, only the <br />Pink Gneiss has a net acid production potential. A net acid production potential of the Pink Gneiss <br />unit occurs in about 1/3 of the tested samples; another 1/3 (approximately) of the samples have similar <br />acid generating and acid neutralizing potential, and the residual 1/3 have a net neutralizing potential. <br />Overall, the Pink Gneiss should be considered a net acid generator. <br />8 <br />