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Schwartzwalder Mine -Hydrologic Evaluation of Mine Closure and Reclamation 53 6.5.1 Water Quality During Operation of the Sumps and WTP While the sumps and water treatment plant were operating, the TDS in Ralston Creek increased to about 250 mg/L and the water changed to acalcium-magnesium-sodium-bicarbonate water as Ralston Creek passed the mine site (Figure 28). TDS concentrations varied seasonally (Figure 29), and were generally highest during the winter months and lowest during the spring months. Bicarbonate and sulfate were the dominant components of TDS in Ralston Creek adjacent to and below the mine site (Figure 29). Sulfate concentrations averaged 20 mg/L upstream of the mine and 68 mg/L downstream of the mine, and did not exceed the water quality standard of 250 mg/L in any of the samples analyzed. The shift from acalcium-bicarbonate type water to acalcium-magnesium-sodium-bicarbonate type water was evident in the Piper diagram of average water quality at 14 stations (13 stations in Ralston Creek plus the treatment plant discharge.) Stations SW-UP, SW-UC, SW-AWD, and SW-A001 plot in a single cluster in the cation field of the Piper diagram (Figure 30), while stations SW-BDIS, SW-OS, SW-BOS, SW-GS, and SW-LLHG plot in separate cluster. The discharge water (Station SW-DIS001) had lower calcium and higher sodium than the upstream and downstream waters (Table 24). Minor ions and trace metal concentrations remained essentially constant upstream and downstream of the mine, with the exception of uranium and molybdenum. Most trace metals were below detection at all sample stations. Uranium increased from about 0.003 mg/L upstream of the mine to about 0.006 mg/L near the downstream property boundary (Table 25), well below the drinking water intake standard of 0.059 mg/L (40 pCi/L) and the hardness-based aquatic toxicity standards. Molybdenum increased from below detection (<1 mg/L) above the mine to about 0.3 mg/L below the mine. No surface water standard has been established for molybdenum. While the sumps and water treatment plant were operating, the increases in TDS, sulfate, magnesium, sodium, uranium, and molybdenum as Ralston Creek passed the mine site were due to treated discharge, which entered the creek at flow rates of 200 - 350 gpm (0.45 - 0.78 cfs). The discharge water contained sulfate concentrations of about 500 mg/L, sodium concentrations of about 150 mg/L, and magnesium concentrations of about 50 mg/L. 6.5.2 Water Quality After Turning off the Sumps and WTP After the sumps were permanently shut down and the water treatment plant stopped discharging, the major ion concentrations in the creek near the mine site increased for several months, then decreased to about half the long-term average concentrations, then increased to about 50% above the long-term average (Figure 31) and again began to decline. Uranium concentrations followed the same trend as sulfate, bicarbonate, and TDS (Figure 32), indicating that the processes that generate TDS in the creek (initial sump flushing, seasonality, and possibly surface disturbance) also control uranium. The effect of seasonality on water quality in Ralston Creek became even more evident after the sumps and water treatment plant were shut down (Figure 29). The initial increase in uranium and major ions after the sumps were shut down was due to a "first flush" phenomenon, as water in the sumps and alluvium came into contact with Ralston Creek for essentially the first time. The low concentrations in Spring 2003, 2005, 2006, and 2007 are the result of seasonal flushing and dilution. The second (July 2003) and third (July 2005) increases in concentration also could have resulted from regular seasonal variation in creek water quality, which was previously masked by discharge from the water treatment plant into the Ralston Creek. Uranium concentrations in 201 samples collected at Station SW-BPL from January 1990 to September 2007 indicate distinct seasonality, with concentrations at their lowest in the spring and highest in the winter. Ralston Creek has been monitored for uranium at stations SW-AWD, SW-BPL, SW-ARH, and SW-LLHG regularly for nearly 18 years. The results are shown graphically in Figure 34 through Figure 36. The concentrations of uranium and other constituents in surface water from 1998 - 2007 were presented in 4109B.071116 Whetstone Associates