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L sampling points, all show peak concentrations coinciding with spring runoff, as would be expected. As with TD S, all three cations show general increases in concentration as the water passes active mining areas. While trends in their subsequent dilution downstream have yet to form a consistent pattern, little or no dilution in the calcium and magnesium concentrations have occurred between sampling points TR-C and TR-D, except a calcium reading in mid-1988, since 1987, For 1990 and 1991, it is believed that this is due to the Moffat area mining activities. However, as this occurrence existed prior to these activities, the trend may also suggest that inflow from undisturbed areas downstream of TR-C contains approximately the same concentrations of these parameters as runoff from the mine. As the Moffat area mining activities initiated in 1990 are directly adjacent to TR-C, it. is expected this pattern will continue. Since 1989, sodium concentrations, unlike calcium and magnesium, have decreased from TA-C to TR-D. while cause is unknown, this current pattern appears to be seasonal, as dilution increases from spring to fall. As noted in previous annual hydrology reports, upstream of the mine on Trout Creek, bicarbonate (Figure 5) is the major anion with sulfate (Figure 5) concentrations increasing rapidly along the mine area to become predominating downstream. The sulfate levels increase is most markedly noticed prior to the peak flow period of Trout Creek and adjacent to mining activity, 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 the input of sulfate is generally insufficient to shift the anion component to a sulfate type with concentrations of bicarbonate and sulfate being approximately equal downstream. As mining activities have shifted from the West Ridge area to the Moffat area, the 1990-1991 trends showing peak sulfate levels at TR-C and TR-D are expected to continue. while peak levels may be shifting downstream, they do not seem to be increasing and it is believed that an equalization in the sulfate-bicarbonate balance occurs downstream as the source of the sulfate (mined areas) is unavailable and dilution by runoff from undisturbed areas is r introduced. I~