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acid. The Ruby Trust mined materials contain very little acid-bearing <br />materials (refer to Attachment C.1). The materials are net neutral and <br />have buffering capacity. This buffering capacity will control constituent <br />solubility and keep elements from significantly migrating into the <br />groundwater. To re-emphasize the key point to this item, there will be <br />very little residual water left in place as compared to the significant <br />amount of water that is pumped from the mine and managed as part of <br />the CDPS permit. Therefore it is unlikely that this residual amount could <br />impact the groundwater pool within the area. <br />4) As determined by CDPHE review as part of the CDPS permit process, the <br />primary water quality characteristics of concern would be total <br />dissolved and total suspended solids (which thus resulted in the <br />installation of the sedimentation basin as part of the permit <br />requirements). These characteristics are further 'controlled' at the <br />surface by the sedimentation basin which effectively eliminates TDS/TSS <br />release to Sneffel's Creek, but these characteristics would also be <br />controlled in the groundwater system due to gravimetric settling. <br />TDS/TSS are not highly mobile and 'settle' rapidly. TDS and TSS are not <br />toxic characteristics and are easily managed. The possibility of area <br />groundwater being adversely affected by the mine-groundwater would <br />be insignificant. <br />Milling: The proposed milling activities encompassed within this amendment <br />could possibly affect groundwater quality by; 1) introducing materials into the <br />re-circulated groundwater used within the mill circuit and 2) creating a source of <br />constituents of concern with the underground subgrade repository. The primary <br />concern related to milling in regards to groundwater impacts is associated with <br />the potential for the subgrade materials to contact groundwater and provide a <br />source of solubilized constituents that could affect the water quality. <br />The proposed milling process will rely on recirculated water. Since the milling <br />process is strictly gravimetric, it will not introduce any 'chemicals' into the <br />system. The water can be affected by TSS/TDS created as a result of the milling <br />process. However, the water is eventually decanted from the subgrade <br />repository (actively) and constantly recirculated into the system. This active <br />recirculation will contain the life-cycle of the water and the suspended <br />materials. As previously described (Item 4 above) TSS/TDS are not toxic <br />characteristics and are effectively controlled by gravity settling. <br />The proposed milling process will produce economic ore and subgrade <br />(uneconomic) ore. The economic ore will be removed for off-site processing. <br />5