2009-08-10_GENERAL DOCUMENTS - M1977300 (3)

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Environmental Protection Plan, Schwartzwalder Mine 11-54 • Table 11-9. Uranium Concentrations in Ralston Creek, 1990 - Jan 2009 (Part 4) SW-AWD Date U m SW-A001 Date U m SW-DIS001 Date U (-gjL) SW-BPL Date U m SW-FBRG Date U m /L SW-ARH Date U m SW-LLHG Date U m /L 9/30/08 0.72 12/30/08 0.386 10/28/08 0.277 1/20/09 0.307 11/19/08 0.29 12/30/08 0.387 1/20/09 0.307 (iii) Summary of Water Quality Impacts to Ralston Creek Interaction with groundwater in the alluvium and fill has affected the water quality in Ralston Creek since the sumps were shut down in June, 2002 (Section I l(c)(ii). The four collector trenches and pumpback sumps were installed in the alluvium and fill during 1990 and 1991, and operated until June, 2002. Much of the fill has been in place since the 1960s, when Ralston Creek was re-routed to the north side of the canyon and mine facilities were constructed on the artificial fill. Areas of contamination in and above the fill have been excavated and removed, in accordance with the Mine Reclamation Plan (Cotter, 1983). The remaining fill material is not slated for removal. Based on the existing conditions, water quality in Ralston Creek is expected to continue to show distinct seasonal variation in uranium concentrations. High creek flows in the spring will result in low uranium concentrations, well below the water supply intake standard (40 pCi/L, 0.059 mg/L) and the acute (4.12 mg/L) and chronic (2.57 mg/L) aquatic toxicity standards (calculated in Section 11(a)(ii)). Low creek flows in the winter and late summer will result in increased uranium concentrations, which may sometimes exceed the water supply intake 20 standard but are unlikely to ever exceed the aquatic toxicity standards. The source of the increased uranium and TDS in Ralston Creek is believed to be from diffuse sources in the • fill material. Geochemical modeling of water under oxidizing conditions has not indicated a limiting control for uranium solubility. Rather, uranium concentrations are controlled by reaction kinetics, the velocity of groundwater flow within the alluvium and fill, and seasonal fluctuations in water levels. Seasonal fluctuations in water levels expose uraniferous fill to oxidizing conditions during low water periods. Infiltrating water which contacts these reactive surfaces solubilizes the stored uranium salts and transports uranium into the groundwater system. Groundwater in the alluvium and fill interacts with surface water in Ralston Creek, resulting in elevated uranium concentrations in the creek during certain times of the year. Uranium concentrations in Ralston Creek peaked within the first six months of turning off the sumps in 2002 (and turning off the Sump 1 recirculation in 2008). In 2002-2003, the reactive surfaces had been exposed for over a decade while the sumps were in operation. The "first flush" of uranium removed from the sump drains, fill, and alluvium was the "worst case" condition. Concentrations spiked, then came down in sampling events. A similar spike occurred in 2008, several months after the cessation of Sump 1 recirculation, after which concentrations began to trend downward. However, uranium concentrations during low flow period are not expected to fall below about 0.2 mg/L, the observed concentrations during low flow (Fall 2003) after the initial flush. The waste rocks dumps have had no discernable effect on water quality in Ralston Creek. Water quality at stations upgradient and downgradient of the reclaimed waste rock dumps shows negligible increases in uranium, and slight decreases in TDS. 20 The nearest water supply intake (Moffat Water Treatment Plant) receives combined flows from Ralston Creek and South Boulder Reservoir (Section 8(a)(i).2). These waters mix in Ralston Reservoir, with significantly more flow from South Boulder •. Reservoir than from Ralston Creek. Therefore, although the comparison is made between water quality in Ralston Creek and intake standards, water in the creek does not feed directly into any water supply intake without mixing. 4109C.090807