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decrease in concentration from the 2006 sampling season and an overall decreasing trend <br />since the 1996 sampling season in agreement with the TDS trend. The lowest calcium <br />concentration in 2007 was recorded at monitoring site TR-A in October with a value of 19 <br />mg/L and the high was recorded at monitoring site TR-D in April with a value of 104 mg/L. <br />The lowest magnesium concentration in 2007 was recorded at monitoring site TR-A in <br />October with a value of 7 mg/L and the high was recorded at monitoring site TR-D in April <br />with a value of 77 mg/L. The lowest sodium concentration in 2007 was recorded at <br />monitoring site TR-A in October with a value of 3 mg/L and the high was recorded at <br />monitoring site TR-D in April with a value of 16 mg/L. <br /> <br /> <br /> <br /> <br /> <br />3.3.7 Surface Water Bicarbonate and Sulfate <br />Charts 10, 11 and 12 show bicarbonate and sulfate concentrations and the <br />sulfate/bicarbonate ratio for monitoring sites TR-A, TR-B, TR-C and TR-D for the period of <br />record. As noted in previous annual hydrology reports, upstream of the mine on Trout Creek, <br />bicarbonate is the major anion with sulfate concentrations increasing rapidly along the mine <br />area to become predominating downstream. The sulfate level increase is most markedly <br />noticed prior to the peak flow period of Trout Creek and adjacent to where mining activity <br />took place, as are TDS levels in general. This increase is probably caused by early runoff at <br />the mine site leaching pyritic and organic sulfur as flow passes over and through the spoils. <br />Since the flow of Trout Creek is low at that time, the amount of sulfur is sufficient to cause an <br />ionic shift from a bicarbonate type water to a sulfate type. During periods of higher flow and <br />late in the season when runoff from the mine is small relative to total Trout Creek flow, the <br />sulfate component is less able to shift the anion balance to a sulfate type with concentrations <br />of bicarbonate and sulfate being approximately equal downstream. <br />The 2007 data is similar to previous monitoring data indicating a trend that shows a <br />topological change occurring generally at TR-B. This is believed to be the result of the spoil <br />spring, which has developed at the base of the West Ridge mining area. As reclamation of <br />West Ridge matures, the high levels of sulfur exhibited in the spring are anticipated to <br />decrease. The recent trend showing peak sulfate levels at TR-C and TR-D are expected to <br />continue for some time as spoil springs in the Moffat area have developed after the <br />completion of mining in that area. Like the West Ridge area the sulfate sources within the <br />Moffat area are anticipated to diminish as vegetation establishes and matures. An overall <br />trend indicates a decrease in sulfate since the 1996 sampling season. <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. The lowest bicarbonate concentration in 2007 was recorded <br />at monitoring site TR-A in October with a value of 96 mg/L and the high was recorded at <br />monitoring site TR-D in July with a value of 178 mg/L. The lowest sulfate concentration in <br />2007 was recorded at monitoring site TR-A numerous times with a value of <10 mg/L and the <br />high was recorded at monitoring site TR-C and TR-D in April with a value of 450 mg/L. The <br />6 <br />