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3. The geological and mineralogical presentations show that average NNP of the Cresson pit is <br />somewhat strongly positive (acid neutralizing) while the average NNP for the proposed <br />North Cresson, East Cresson, and the Main Cresson lateral extension are somewhat negative <br />(acid generating). While the overall NNP of the diatreme as a whole appear to be strongly <br />positive, for the system to contain a substantial increase in metal concentrations waste rock <br />from the positive NNP areas would need to be amended with alkali or blended or <br />interstratified with waste rock from the negative NNP areas to neutralize acid generation at <br />its source, or the waste would need to be capped to minimize infiltration of surface water. <br />Provided acid produced from the upper mining zone is neutralized at or very near its source <br />this could minimize dissolution ofinetal-bearing minerals. <br />The mine-diatreme-groundwater system may have a limited capacity to precipitate and <br />adsorb zinc (and other potentially problem metals) during non-upset conditions. Although <br />modeling predictions show that the Carlton discharge is saturated with respect to <br />hemimorphite - Zn(SizO~)(OH)Z•HZO) - none has yet been observed in the system. Absent <br />confirming mineralogy it is presumed that zinc adsorption by carbonates precipitated in the <br />diatreme and outside the Carlton is the dominant control over dissolved zinc. It appears <br />important to maintain zinc contributions to the groundwater at steady state levels and this <br />may mean not increasing the zinc load to the subsurface without increasing the volume of <br />carbonate precipitates. <br />cc: <br />The operator should demonstrate that the waste handling plan will assure either acid <br />neutralization in the Arequa Gulch and Squaw Guldt overburden storage areas, or <br />minimize surface xater infiltration to AGOSA and SGOSA, or submit an alternative plan. <br />Jim Dillie <br />Bruce Humphries <br />Jim Pendleton <br />Jim Stevens <br />