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Station RS-1 should be used to provide representative data for the hazdness <br />evaluation. Station RS-1 is located upstream of all BMRI disturbances and has an <br />extensive monitoring record. We also recommend that the RS-1 hazdness <br />database be tested for seasonality to determine if the use of season hazdness <br />values is appropriate, rather the using the median value for all seasons. <br />Response <br />Hazdness is used to calculate Table Value Standazd (TVS) concentrations of <br />constituents that show variable levels of toxicity to aquatic wildlife as buffered by <br />the hazdness of the receiving water. The value of hazdness reported in the August <br />30, 1999 Technical Support Document (57.3 mg/L as CaCO3) was calculated <br />using the period of record for RS-2 beginning 1987 and ending 1989, which is <br />prior to any potential BMRI mining-related effect on water quality in the Rito <br />Seco. Hazdness values aze used to calculate the TVS for selected metal <br />constituents using the general form of a power function wherein the value of the <br />exponent depends, in part, on the natural logarithm of the hazdness value. Thus, <br />the difference in the natural logarithm of the hardness value referenced by the <br />reviewers (i.e., natural logarithm of 64) versus the natural logarithm of the <br />hardness value reported in the Technical Support Document (i.e., natural <br />logarithm of 57.3) results in a minimal difference in the final calculated TVS <br />value. <br />The reviewers call for the use of RS-1 in the calculation of the hazdness value for <br />use in establishing effluent standazds. There is no question that the location of <br />RS-1 is upstream from the historical mining activity in the vicinity of the West <br />Pit. However, the reviewers fail to note that the intent of the process to establish <br />effluent standards for CDPS permits is to base the resulting standazds on a set of <br />water quality data that reasonably reflect the combined hydrologic and <br />geochemical processes that contribute to the water quality of the Rito Seco prior <br />to the dischazge of water from a water treatment facility. The use of RS-1 to <br />determine the value of hardness is not appropriate because the hydrologic and <br />geochemical system contributing to the water quality observed at RS-1 is not <br />comparable to the hydrologic and geochemical processes affecting the quality of <br />Bar(le Moun(ain Resources, /nc. NS/GeoTrans <br />16 July 21, 2000 <br />