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June 25, 2010 2 of 15 <br />Since loading to Ralston Creek is recognized to occur from groundwater in the alluvium and fill, the <br />corrective action should focus on this source. If the mine pool were to contribute uranium and other <br />constituents, then that loading would occur through the alluvium and fill as groundwater from the mine <br />pool slowly seeped into the alluvium. Mixing calculations provided in the Environmental Protection Plan <br />(EPP) indicated that the flow from the mine pool to the alluvium would represent, at most, 0.8% to 8% of <br />the flow in the alluvium. If this were occurring, then the logical and most effective place to circumvent it is <br />by capturing and treating groundwater in the alluvium and fill, thus preventing it from reaching Ralston <br />Creek. <br />Studies have shown that the mine pool is not affecting Ralston Creek via the Schwartz Trend. <br />The Schwartz Trend is a thin band of garnet-biotite gneiss (GBG) and quartzite rock, which was the host <br />rock for uranium ore in the vicinity of the mine. The Schwartz Trend rocks are oriented nearly vertically <br />and are about 100 ft thick (Norquist, 2001). Packer tests conducted in 1999 indicated that the permeability <br />(or hydraulic conductivity) of the Schwartz Trend (GBG) rocks ranged from <1.Ox10-7 cm/sec to 6x10-6 <br />cm/sec. <br />The Schwartz Trend extends several miles beyond the ore deposit to the northwest and southeast. DRMS <br />has postulated that the southeast extension of the Schwartz Trend may be a conduit for water in the mine <br />pool to reach Ralston Creek. In response to DRMS concerns, Cotter and its consultants conducted water <br />quality monitoring and gamma surveys in and along Ralston Creek where the creek flows over the <br />Schwartz Trend (about 1,900 feet downstream from the mine site) in 2008 and 2009. The electrical <br />conductivity (E.C.) survey conducted in November 2008 showed an increase of 21 µs/cm (4%) as the creek <br />flowed over the Schwartz Trend rocks (Figure 1). It is should be noted that the Schwartz trend may have <br />caused the 4% increase in E.C. simply due to the difference in rock type from the surrounding rocks. The <br />electrical conductivity in the creek increased 26% as the creek flowed past the mine site, which is due to <br />loading from the alluvium and fill. There was no increase as Ralston Creek flowed past the waste rock <br />piles (Figure 1), which are capped with an engineered cover and isolated from groundwater. The E.C. <br />increase in the vicinity of the mine is associated with measurable increases in uranium concentrations in <br />Ralston Creek, and mitigation efforts should clearly be focused on this area.