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downgradient water quality monitoring stations RS-2 or RS-5, the latter of which <br />integrates the combined hydrologic and geochemical processes of the Rito Seco <br />upgradient of that location. <br />Comment: <br />5. Section III.B.1, page 3 <br />The use of the 85a' percentile data for RS-5 is inconsistent with the use of the 50`~ <br />percentile data for RS-1. The use of a lower percentile for the upstream loading <br />allows for a lazger loading from the dischazge point(s). The same percentile <br />loading must be considered for both the upstream and downstream points. <br />Stations RS-2 and RS-5 aze located approximately 3,000 feet and 9,000 feet <br />downstream of the West Pit, respectively. A comparison of loading from stations <br />RS-2 and RS-5 must be provided to demonstrate that station RS-5 is the <br />appropriate location to determine baseline loadings. We believe that geochemical <br />reactions and additional loadings in the more than one mile between Stations RS- <br />2 and RS-5 make RS-2 a more appropriate selection for this analysis. <br />As discussed in Comment 44, we also recommend that the metals data be tested <br />for seasonality to determine if the use of seasonal concentration values is <br />appropriate, rather than using the 50'~ or 85a' percentile values for all flow <br />regimes. <br />Response: <br />No comment. The statistical representation of the water quality data was a <br />determination by the WQCD staff. <br />BMRI and its technical experts believe that the range of influences as recorded in <br />water quality from RS-5 provides a better measure of the range of natural <br />hydrologic and geochemical processes influencing water quality in the reach of <br />the Rito Seco that would be the receiving water for the water treatment facility. <br />The CDPHE conducted the analysis referenced by the reviewers and reached the <br />correct conclusion. <br />The issue of seasonality is implicitly addressed by the structure of the loading <br />calculation. That is, the flows used to calculate loading correspond to the low- <br />flow period of the yeaz when the concentrations of constituents at the upstream <br />Bartle Mountain Resources lnc. HSI GeaTrans <br />18 July 1 /, 1000 <br />