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Cotter Corporation (N.S.L.)'s Response to December 14, 2010 Adequacy Review, Comments 10, 11C Page 5, Item 10 — Charge Balance on Mine Water Samples from Upper Workings Provide comment on the significance of the reported charge imbalance of - 46.77% for the speciation calculation for the average water quality of the upper mine workings reported in Section 14(b)(iii),I.I. Does it indicate a deficiency in the cation analysis, and if so which cation(s), or is it more an artifact of the averaging? RESPONSE: The charge imbalance could indicate a missing cation or laboratory errors in the original analysis. The original laboratory results for sample ILLRS, which were summarized in Table 14 -5 of the EPP, indicate that the laboratory reported TDS concentrations (11,000 mg/L) were inconsistent with the reported electrical conductivity (7,190 uS /cm). This difference alone accounts for the reported charge imbalance. Therefore it is believed that the charge imbalance is likely due to analytical error for sulfate. As noted by Hem (1985): Water having dissolved - solids concentrations much greater than 1,000 mg/L tends to have large concentrations of a few constituents. In such water, the test of anion - cation balance does not adequately evaluate the accuracy of the values of the lesser constituents. Hem, John D., 1985. Study and Interpretation of the Chemical Characteristics of Natural Water, Third Edition, U.S. Geological Survey Water Supply Paper 2254. 263 pp. Page 6, Item 11(C) — Geochemical Studies on sorption /precipitation in Ralston Creek 1 Section 15(a) (iv), page 15 -3. The EPP states that "sorption and precipitation processes remove uranium from solution." Have any geochemical studies been conducted to verify that those processes are indeed occurring in the stream and are removing uranium? RESPONSE: May 4, 2011 Recent studies have not been performed to verify that sorption and precipitation processes remove uranium from solution in Ralston Creek. Therefore, while the referenced figure (11 -6) shows a decline in uranium concentrations along the 1.6 -mile flow path downstream of the mine, the processes contributing to this decline could include dilution as well as (or instead of) sorption and precipitation. A study of stream waters in the Denver West Quadrangle conducted by the USGS (Zielinski, 2007) indicated that sorption was more likely affecting uranium concentrations than precipitation: