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i, r <br /> <br />support the "leap" involved in extrapolating specific aquatic life Class 1 criteria of the <br />Segment 21 standards to a tributary to Segment 22. <br />Most importantly, when ambient concentrations of water-quality parameters in Arequa Gulch <br />aze compared with Table Value Standazds (whether computed on the basis of 220, 400, or <br />642 mg/1 total hardness), the in-stream concentrations of many pazameters would exceed the <br />proposed limitations due to natural conditions, as Dr. Posey has observed. CC&V cannot <br />agree to meet a set of water-quality criteria that aze going to be exceeded by natural <br />conditions. <br />Complimenting the ambient standards authority delegated to the Water Quality Control <br />Division is section 25-8-501(3) of the Colorado Water Quality Control Act which states <br />"that, in appropriate circumstances, the effluent limitations contained in a permit shall be <br />adjusted to account for the pollutants contained in the dischazger's intake water." This <br />provision is incorporated into decisions of the Commission via subsection 6.9.2 (4)(a) of the <br />Commission's Rules. CC&V believes there is unequivocal basis for finding this situation <br />"appropriate" given the background data for Arequa Gulch. <br />The ambient water-quality data for stations AG-1 and AG-1.5 aze summarized in the <br />following Table 3. Averages are based on normal statistical procedures with less than <br />numbers expressed as essentially the less-than value rather than zero as the Water Quality <br />Control Commission's and Water Quality Control Division's procedures espouses. Eighty- <br />fifth percentile values are developed from a statistical routine that groups and ranks the data <br />rather than an individual listing of each data point. Thus the 85th percentile values could <br />vary slightly if they were selected from a detailed ascending list of each measurement. <br />8 <br />