2009-02-20_REPORT - C1980001 (4)

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in concentration from the 2007 sampling season and an overall decreasing trend since the 1996 sampling season in agreement with the TDS trend. The lowest calcium concentration in ' 2008 was recorded at monitoring site TR-A in October with a value of 21.5 mg/L and the high was recorded at monitoring site TR-D in April with a value of 63.9 mg/L. The lowest magnesium concentration in 2008 was recorded at monitoring site TR-A in August and October with a value of 8.0 mg/L and the high was recorded at monitoring site TR-D in April with a value of 41.2 mg/L. The lowest sodium concentration in 2008 was recorded at ' monitoring site TR-A in August with a value of 3.1 mg/L and the high was recorded at monitoring site TR-D in April with a value of 11.6 mg/L. 3.3.7 Surface Water Bicarbonate and Sulfate Charts 10, 11 and 12 show bicarbonate and sulfate concentrations and the sulfate/bicarbonate ratio for monitoring sites TR-A, TR-B, TR-C and TR-D for the period of record. As noted in previous annual hydrology reports, upstream of the mine on Trout Creek, bicarbonate is the major anion with sulfate concentrations increasing rapidly along the mine area to become predominating downstream. The sulfate level increase is most markedly noticed prior to the peak flow period of Trout Creek and adjacent to where mining activity took place, as are TDS levels in general. This increase is probably caused by early runoff at the mine site leaching pyritic and organic sulfur as flow passes over and through the spoils. Since the flow of Trout Creek is low at that time, the amount of sulfur is sufficient to cause an ionic shift from a bicarbonate type water to a sulfate type. During periods of higher flow and late in the season when runoff from the mine is small relative to total Trout Creek flow, the sulfate component is less able to shift the anion balance to a sulfate type with concentrations of bicarbonate and sulfate being approximately equal downstream. The 2008 data is similar to previous monitoring data indicating a trend that shows a topological change occurring generally at TR-B. This is believed to be the result of the spoil spring, which has developed at the base of the West Ridge mining area. As reclamation of West Ridge matures, the high levels of sulfur exhibited in the spring are anticipated to decrease. The recent trend showing peak sulfate levels at TR-C and TR-D are expected to continue for some time as spoil springs in the Moffat area have developed after the completion of mining in that area. Like the West Ridge area the sulfate sources within the Moffat area are anticipated to diminish as vegetation establishes and matures. An overall trend indicates a decrease in sulfate since the 1996 sampling season. While peak levels of individual constituents may be shifting as flow proceeds past the mine, they do not seem to be increasing overall. It is believed that an equalization in the sulfate- bicarbonate balance or a reversal (similar to the balance at TR-A) occurs downstream as the source of available sulfate (mining areas) is unavailable and dilution by runoff from undisturbed areas is introduced. The lowest bicarbonate concentration in 2008 was recorded at monitoring site TR-A in October with a value of 67 mg/L and the high was recorded at monitoring site TR-D in April with a value of 115 mg/L. The lowest sulfate concentration in 2008 was recorded at monitoring site TR-A in August and October with a value of 6 mg/L and the high was recorded at monitoring sites TR-C and TR-D in April with a value of 200 mg/L. 6