2007-11-23_HYDROLOGY - M1977300 (9)

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Appendix G - Sump Shutdown Test Methods and Results 7 • • mine site and 2 cfs near Ralston Reservoirs. Well MW-9 was pumped at 15 gpm, which represents 14% of the average sump pumping rate for March and 8% of the average sump pumping rate for April. 'Water quality field parameters (temperature, pH, and conductivity) were measured around the clock at 11 stations in Ralston Creek, and samples were collected for laboratory analysis of uranium. The data are presented in Table 4. pH measurements declined slightly over the duration of the shutdown test (Figure 6). 'When plotted spatially (Figure 7), pH shows a slight increase with distance downstream. The stream standard for pH in this stream segment is 6.5 to 9.0, and the only samples that fell outside this range were collected near midnight on April 1, and are believed to be related to an instrument calibration error. Although conductivity values increased during the course of the shutdown test (Figure 8), the increases were the same at each station downstream of the D001 discharge point and were attributable to changes in 'the flow rate and concentration of the water treatment plant discharge (Figure 9) rather than input from the alluvium downstream. Conductivity did not increase with distance downstream (Figure 10), except 2 miles downstream at station SW-LLHG, which showed variable trends. Uranium concentrations increased slightly over the duration of the test (Figure 11) and with distance downstream (Figure 12). Uranium values increased from about 0.5 ppb (0.0005 mg/L) above the mine to approximately 1.4 ppb (0.0014 mg/L) downstream of the facility, at station SW-BPL. Uranium concentrations in the discharge water averaged 1.7 ppb (0.0017 mg/L) during this period, and the average flow from the water treatment plant was 200 gpm (0.44 cfs). A mixing calculation was performed using these concentrations and the flow rates from the water treatment plant and in Ralston Creek, according to the following formula: Cds - Cu -Fu + Cwt - Fwr Fu + Fwt Where: Cds = downstream concentration of uranium Cu = upstream concentration of uranium Cwt = concentration of uranium in water treatment plant discharge F„ = upstream flow rate (calculated as total flow minus Fw ) FWt = discharge flow rate from water treatment plant The mixing calculation results (Table 3) indicate that the loading from the water treatment plant would raise uranium concentrations by only 0.11 to 0.27 ppb (0.00011 to 0.00027 mg/L). Since the observed increase was on the order of 0.9 ppb (0.0009 mg/L), the remainder of the loading was likely derived from the alluvium. The loading from the alluvium appeared to increase toward teen o the pumping (and sump shut-down) test, when the sumps had been shut down for a total of 7 days. Uranium concentrations in Ralston Creek also increased beyond the property line, and averaged 2.7 ppb 0.0027 mg/L) at the ong ake Head Gate (station SW-LLHG). The increase in uranium below the property line is believed to be the result of natural uranium input after the water leaves the mine property, in part because the. Schwartz trend intersects Ralston Creek downstream of the Schwartzwalder Mine. • ° Ralston Creek flow near the mine site is based on staff gage readings for station SW-BPL. s Ralston Creek flow near Ralston Reservoir is based on Denver Water records. 4109B.071109 Whetstone Associates