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9.2 Impounded Water at the American Tunne! Level <br />Water that will be impounded behind the American Tunnel is conceptualized as ground <br />water from the fractured volcanic rocks that make up the country rock. Whole water <br />analyses of this water were collected from drill holes extending several hundreds of <br />feet back from the tunnel and are the best estimate of the bulk water chemistry. The <br />chemical analyses of these drill hole waters are shown in Table 9. <br />Integrating the data from these and other whole water analyses from the deeper <br />portions of the American Tunnel, metals-only analyses, Petrographic data (Appendix <br />D and Casadevall and Ohmotol and local and regional geology produced a modeled <br />reference water for the American Tunnel. This reference water is descriptive of both <br />the In•situ ground water of the country rock and of the water that will be impounded <br />behind the American Tunnel bulkhead. The composition of this water is shown in <br />Table 10. The reference water is a calcium sulfate water with significant bicarbonate <br />concentrations. Based on being in equilibrium with both calcite and pyrite the <br />modeled water is strongly reduced IpE _ -2.5) and is slightly basic of neutral (pH = <br />7.21. <br />MINTEQA2 shows the reference water to be at saturation or equilibrium with both the <br />rock-forming minerals of the country rock and with the principal ore and vein minerals <br />that would be associated with the migration paths to the surface. There should be <br />no significant reaction between the American Tunnel reference water and minerals <br />Fumy\wpln~cd225 P,Mr 199J. Wri 60 <br />H:1 SI(11011 HYDRO-SERRCH <br />