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24 ;Cresson, East Cresson, and the Mairs Cresson lateral extension are somewhat negative (acid • :generating). While the overall NNP of the diatreme as a whole appear ro be strongly positive, • :for the system to contain a substantial increase in metal concentrations waste rock from the negative NNP areas would need to be amended with alkali or blended or interstratiJed with '~wasre rock from the positive NNP areas to neutralize acid generation ar its source, or the waste .would need to be capped to minimize irlfiltration of surface water. Provided acid produced from the upper mining zone i.r neutralized at ar very near tts source th/s could mintmize. itissolurion ofineral-bearing minerals. Response: Ultimately, even if the neutralizing capacity of the high NNP material in the overburden piles is exhausted, the seepage, if any, from the piles would have to travel through the entire diatreme, snd the great excess cazhanate at depth within the diatreme is sufficient to neutralize this theoretical load of acid for tens of thousands of yeazs. The mine-diatreme-groundwater system may have a limited capacity to precipitate and adsorb ='zina (and ocher potentially problem metals) during non-upset wndtdons. Although modeling predictions show that the Carlton discharge is saturated with respect to hemimorphite- '7~t(SiaOr)(OH)a•Xa0) - ,none has yet been observed in the system. Absent cot~irneing %inineralogy it is presumed that zinc adsorption by carbonates precipitated in the diatreme and .outside the Carlton is the dominant control over dissolved zinc. It appears important to .maintain zinc contrihurions ro the groundwater at steady state levels and this may mean not • ~ ~inereasing the zinc load to the subsurface without increasing the volume of carbonate precipitates. The operator should demonstrate that the waste handling plan will assure either acid neutralization in the Aregua Gulch and Sguaw Gulch overburden storage areas, or minimize surface water infeltratton to AGOSA and SGOSA, or submit an alternative plan. Response: The ~geochemical modeling has been extended and the zinc precipitation ptncesses have been further addressed in a separate memorandum (see Attachment 11 to this adequacy response document). This additional modeling shows that precipitation of zino-bearing calcite is effective at maintaining low ambient concentrations of zinc in the Carlton Tunnel water. The great excess of carbonate buffeting at depth (mainly by dolomite) can be expected to remove and maintain ambient zinc coacetttrations at the current levels for tens of thousands of years. ,~ I7i;. 6.4.9 tEXffiBTT I -SOU Ifatotmagop A. Al! available growth material na maner how small, has to be salvaged. The Division will allow teinporti'ry placement of these stockpiles in close proximity prior to placement in a permanent area. Response: As previously mentioned the criteria for topsoil removal was taken dueexly from the approved Amendtitent No. 7 language (see Amendment No. 7 pages 4-30 and 5-34 of the accompanying text in Volume I). The depth of recovery is a function of the nature of the soil, weathered bedrock, and slope angle, as well as the capabilities of the dozers and other tttechaaized soil salvage equipment, In addition; as correctly painted out by the OMLR io Section V.B.1 of theso continents, CC&V is projecting an excess of about 388,900 cubic yards of growth medium which indicates that an adequate gitahtity~will be available for reclamation. As a result, CC&V believes that the criteria employed for growth medium salvage is the most appropriate for the equipment being used end the nature of the soils is the area. CC&V appreciates the ability to develop temporary soil stockpiles during operations. Grow4ttnedium that can be easily and efficiently removed with available training equipment wiU be salvaged