2010-08-02_REVISION - M1977300 (25)

Home Browse Search

Environmental Protection Plan, Schwartzwalder Mine 11-11 is 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. Because uranium had been removed, the treated water may have been a source of dilution for uranium concentrations in Ralston Creek during operations. (ii) Water Quality After Turning off the Sumps and WTP After the sumps were shut down and the water treatment plant stopped discharging, the major ion concentrations have fluctuated in the creek near the mine site (Figure 11-4). When the plant and sumps were first shut down, major ion and TDS concentrations increased for several months, then decreased to about half the long-term average concentrations. 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. Subsequent fluctuations in major ion and TDS concentrations result from seasonality, and shutting down the Sump 1 recirculation. 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 11-2). The low concentrations in Spring 2003, 2005, 2006, 2007, and 2009 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 followed the same trend as sulfate, bicarbonate, and TDS (Figure 11-5), indicating that the processes that generate TDS in the creek (initial sump flushing, seasonality, and the Sump 1 recirc shutdown) also control uranium. Uranium concentrations in 229 samples collected at Station SW-BPL from January 1990 to June 2010 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 over 20 years. The results are shown graphically in Figure 11-7 through Figure 11-9. The concentrations of uranium and other constituents in surface water from 1998 - 2010 were presented in Table 11-7. Table 11-9 presents uranium data from 1990 - 2010. The highest uranium values were observed (1) in January 2003, approximately six months after the sumps were initially shut down, when creek flows were at their lowest, (2) in September 2008, approximately five months after the Sumpl recirculation was shut down (again when creek flows were low), and (3) in September 2009 (again during low-flow). The source of uranium and TDS loading to the creek is derived from alluvium and fill, which may be both a primary source (from slightly mineralized waste rock used as fill material) and a secondary source (from historical pond leakage which impacted sediments and fill). Although the former storage pond and the ore sorter area have been remediated to specified cleanup levels and reclaimed, the historical releases from these facilities may have created a dispersed secondary source of loading to Ralston Creek. Partial source removal is planned for 2010, as part of the RML decommissioning (Section 15) and additional mitigation options are being considered for groundwater in the alluvium and fill, to ultimately protect water quality in Ralston Creek. • 4109C.100731 Whetstone Associates