2009-08-13_PERMIT FILE - C1981019A (4)

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RULE 2 PERMITS M Based upon analyses performed by Williams and Clark (1994) at the Seneca II Mine, the dominant anion would most likely be sulfate and that the oxidation of the pyrite would be the main source of TDS in the spoil pit water. Oxidation of minor pyrite in the spoil could produce soluble sulfate at the South Taylor pit, which will be the dominant ion causing the increased TDS. The duration of the elevated TDS can be predicted based upon the oxidation of pyrite in the reclaimed spoils pit aquifer. Saturation indices (SI) were calculated for the average constituent concentrations in well 84-0-OB (Williams Fork Formation well) and the Streeter Well. The SI is used to determine if a mineral will dissolve into or precipitate from solution. A negative SI indicates that the water is undersaturated with respect to the mineral and, if present, the mineral should dissolve. If the SI is positive, the water is supersaturated with respect to the mineral, and the mineral should precipitate from solution. An SI neaz zero indicates a condition neaz equilibrium. Table 2.05.6-3 presents the SI for the wells at Colowyo Mine. The SIs presented in this table aze very similar to those determined by Williams and Clazk (1994). Calcite and dolomite have positive saturations indices in the sampled wells; therefore, the water is saturated with respect to these minerals and it is not anticipated that an increase in TDS would occur. Sulfate minerals (gypsum and epsomite) have negative SIs; therefore, the water is not saturated with respect to these minerals and increases in TDS would occur if sulfate minerals were present in the spoil. This is consistent with the increase in sulfate in the Streeter Well (1,960 mg/L) as compazed to Good Spring Creek (average of 600 mg/L). The average pyritic sulfur concentration in the spoils is 0.09 percent in borehole 97-15, the only borehole in South Taylor with every interval analyzed for pyritic sulfur. The pyritic sulfur concentrations in • boreholes 83-D3-07, -10, -12, and -14 were measured at only selected intervals biased towazds high pyrite; the arithmetic mean of these samples is 0.45% pyritic sulfur. Based upon the exhaustion time for 0.20 percent pyrite of 300 years (Williams and Clazk 1994), the time of the elevated TDS dischazge would be between 150 and 600 years. The actual dumtion would be reduced in direct proportion to the amount of "piping" that occurs as a result of channel formation within the spoils. This type of flow is documented at other mines, and has reduced the amount of pyrite oxidized in the spoil. Prediction of the amount of piping that will occur is not possible, but assuming that 25 percent of the spoil pile would be bypassed by piping, then the duration of elevated TDS concentrations would be reduced by 25 percent to 110 to 450 yeazs. South TaylodLower Wilson -Rule 2, Page 120 Revision Date: 3/30/07 Revision No.: PR-02