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Bicarbonate/Sulfate <br />As noted in previous annual hydrology reports, upstream of the mine on Trout Creek, <br />bicarbonate (Figure 10) is the major anion with sulfate (Figure 11) concentrations increasing <br />rapidly along the mine area to become predominating downstream (Figure 12). The sulfate <br />levels increase is most markedly noticed prior to the peak flow period of Trout Creek and <br />adjacent to where mining activity took place, as are TDS levels in general. This increase is <br />probably caused by eazly runoff at the mine site leaching pyritic and organic sulfur as flow <br />passes over and through the spoils. Since the flow of Trout Creek is low at that time, the <br />amount of sulfur is sufficient to cause an ionic shift from a bicarbonate type water to a sulfate <br />type. During periods of higher flow and late in the season when runoff from the mine is small <br />relative to total Trout Creek flow, the sulfate component is less able to shift the anion balance <br />to a sulfate type with concentrations of bicarbonate and sulfate being approximately equal <br />downstream. <br />The 2004-2006 trend shows that the topological change generally still occurs at TR-B. <br />This is believed to be the result of the spoil spring, which has developed at the base of the <br />West Ridge mining area. As reclamation of West Ridge matures, the high levels of sulfur <br />exhibited in the spring aze anticipated to decrease. The 2004-2006 trend showing peak sulfate <br />levels at TR-C and TR-D are expected to continue for some time as spoil springs in the <br />Moffat azea have developed after the completion of mining in that azea Like the West Ridge <br />area the sulfate sources within the Moffat area are anticipated to diminish as vegetation <br />establishes and matures. <br />While peak levels of individual constituents may be shifting as flow proceeds past the <br />mine, they do not seem to be increasing overall. It is believed that an equalization in the <br />sulfate-bicarbonate balance or a reversal (similar to the balance at TR-A) occurs downstream <br />as the source of available sulfate (mining areas) is unavailable and dilution by runoff from <br />undisturbed areas is introduced. Bicarbonate and sulfate concentrations are provided in tabular <br />format in Appendix A. <br />17 <br />