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John Hamrick and Randy Whicker Cotter Corporation (N.S.L) October 10, 2011 Page 3 pool, although the radium -226 activity in Sump No. 10 (0.60 pCi /L) is similar to radium -226 levels at several other downgradient locations (Sump No.4, Sump No.5, MW -6). Relative to mine pool water, the concentrations of molybdenum and radium -226 in Sump No. 10 and downgradient alluvial groundwater are much reduced compared to uranium (Figures 6 and 7). Mine pool water is reducing (low Eh) and contains elevated uranium, molybdenum, radium -226, iron, and manganese (Table 1). However, the chemistry of mine pool water can be modified as it migrates through faults and bedrock fractures and transitions into near - surface alluvium. Under pH- neutral conditions in the presence of carbonate, uranium is expected to remain largely mobile (Langmuir, 1997). Molybdenum and radium -226, however, can be attenuated to a much greater extent compared to uranium and major ions (e.g., magnesium, sulfate). Although the maximum potential for molybdenum adsorption is greatest under low pH (pH = 4 to 5), some adsorption does occur at higher pH values (Goldberg et al., 1996). In the presence of calcium, molybdenum can also precipitate as solid calcium molybdate (CaMoO (Lindsay, 1979). Radium concentrations in solution can be reduced through cation exchange onto clay minerals or coprecipitation with gypsum (Langmuir, 1979). If oxidizing conditions (high Eh) are encountered in the near - surface alluvium, iron and manganese will precipitate from solution as oxide minerals, providing additional adsorption sites for attenuation of radium -226 (Schott and Wiegand, 2003; Zwahlen, et al. 2007). 3.0 CONCLUSIONS ame0 Evaluation of the recent geochemical data supplied by Cotter for the Schwartzwalder Mine indicate that elevated uranium concentrations in Sump No. 10 result from a mixture of upgradient alluvial groundwater and geochemically- modified mine pool water. The major ion and uranium concentrations of water in Sump No. 10 are consistent with conservative mixing, while modification by geochemical attenuation has reduced the concentrations of molybdenum and radium -226 to a greater extent. This conclusion is based on: • The presence of elevated concentrations of major ions, TDS, and uranium in Sump No. 10 which are intermediate between those of mine pool water and both upgradient and downgradient alluvial groundwater; • Demonstration of conservative mixing between alluvial groundwater and mine pool water with distance downgradient across the site;