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BMRI -San Luis Pit Bac~• HCT Tests • <br />batch test analyses are a better simulation of weathering behavior at San Luis than are <br />the HCT experiments. <br />6.0 CONCLUSIONS <br />Even under the aggressive leaching environment of a humidity cell test, with rapidly <br />cycling redox conditions and a continuous supply of moisture, Pink Gneiss samples A, <br />B, and C do not generate aggressive solutions with high acidities, high sulfate and <br />metals in solution. Two of the three samples produce net alkalinity, and even the most <br />sulfur-rich sample produces only a mildly acidic effluent, and after only a few weeks of <br />simulated weathering, all three samples behaved nearly inertly. <br />Furthermore, in evaluating these data, the Division will recall that BMRI have <br />committed to the State that they will not place Pink Gneiss across the water-table <br />fluctuation zone in the backfilled pit. The water-table fluctuation zone is the <br />environment most analogous to the weathering environment of a humidity cell. <br />Instead, BMRI plan to place all of the gneiss below the permanent water table, an <br />environment shown by the saturated leach testing of Pink Gneiss (Memo of 18 October <br />1995) to prevent acid generation in the waste rock. Thus, even the very limited extent <br />of reactivity observed in these humidity cell tests is not expected to occur at San Luis. <br />The testing is reported and discussed to close BMRI's commitment to provide all <br />additional geochemical test data to the Division in a timely manner. <br /> <br />Geochimica, Inc. 6 95021/1-feb96 <br />