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Table Value Standazd (TVS) calculations require the input of hazdness data for <br />the receiving water in the vicinity of the point of compliance. Discharge <br />standards were evaluated for a point of compliance at RS-2 under a condition of <br />zero flow (worst case scenario) under pre-mining conditions. Hardness data <br />collected from 1987 through 1989, when the mine opened, were used in the <br />calculations to reflect pre-mine conditions in the Rito Seco downgradient of the <br />mine deposit. The average hardness value calculated was 63.2 mg/L with a <br />standard deviation of 9.5 mg/L. This results in a 95'~ percent confidence interval <br />range of 57 to 69.4 mg/L. Hardness data were also evaluated at RS-3A, where <br />both low flow and analytical data were available. The hardness calculated using <br />the water quality data collected at RS-3A was 64 mg/L, which falls within the <br />confidence interval range for the more statistically defensible set of data available <br />from surface water station RS-2. This value was then selected as the hardness <br />value for use in the TVS-based calculations. Therefore, on this basis, BMRI <br />believes that the hazdness value of 64 mg/L as CaC03 is an appropriate value that <br />reasonably represents the natural influences on water quality along the reach of <br />the Rito Seco potentially affected by the flows associated wish water treatment <br />activities in the West Pit. <br />Comment: <br />III-Iron and Manganese: <br />Response: <br />The implementation of the TR-26 water management plan has resulted in the <br />reversal of the hydraulic gradient in the West Pit and groundwater flow from the <br />West Pit into the adjacent alluvial aquifer no longer occurs. The reversal of the <br />hydraulic gradient between the West Pit and the adjacent Rito Seco alluvial <br />aquifer is the fundamental best management practice (BMP) upon which all other <br />considerations associated with the West Pit are based. The condition is based on <br />physical parameters, which provides for a readily measured compliance <br />parameter, that is groundwater level. Through the implementation of this BMP <br />Bartle Mountain Resources, lnc. NS! GeoTrans <br />4 r„ryzl, aooo <br />