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CO-0000906 <br />New Elk Mine Water Quality Assessment <br />• BWQ Concentrations Based on the BWQ Equation <br />BWQ concentrations calculated using the BWQ equation requires the determination of the upstream <br />existing ambient water quality during the antidegradation period. This is further discussed in the <br />paragraphs that follow. <br />Currently, it is the Division's approach to evaluate five years of ambient water quality data, if <br />available, for the five years prior to September 30, 2000, when determining the ambient water quality <br />during the antidegradation review period (M„ is). The period of record for the ambient water quality <br />data evaluated as part of the antidegradation review differ from the ambient water quality data <br />previously set forth in Section II. Ambient water quality data used for the antidegradation review <br />were gathered at the same location as the other data, but were evaluated for a period of record from <br />October 1995 through September 2000, where available. For Boron, historical data were used <br />consistent with the ambient water quality data discussion in Section II of this WQA. These data are <br />summarized in Table A-8. Note that existing quality was again determined as the 50th percentile for <br />total recoverable metals and the 85 percentile for dissolved metals. <br />Table A-8 <br />Ambient Water Quality for Middle Fork of the Purgatoire River <br />C <br />• <br /> f or the Ant ide radat ion xevIe <br />Y w <br /> <br />Chronic <br /> <br /> <br />Parameter umber <br />N <br />of <br />Samples <br />I Sth `? . <br />percentile 510th <br /> <br />Percentile 85th <br /> <br />Percentile Mean <br /> <br /> <br />0 Stream <br /> <br /> <br />Standard <br />100 Notes <br /> <br /> <br />2 <br />1 <br />As, TR (µg/1) <br />4 <br />0 <br />0 <br />0 <br />071 <br />55 <br />0 <br />, <br />2 <br />1 <br />/1) <br />Di <br />( <br />d 46 0 0 0.14 0. . , <br />s <br />µg <br />C <br />, NA 3 <br />/1) <br />T 0 0 <br />0 <br />p <br />p <br />ot (µg <br />Cr, 1 12 2 <br />1 <br />/1) <br />( <br />Di <br />C 44 0 1.6 3.7 2. , <br />s <br />µg <br />u, 0 1000 2 <br />1 <br />/1) <br />TR ( <br />F 46 0 146 340 21 , <br />µg <br />e, 12 70 <br />3 2 <br />1 <br />/1) <br />Dis ( <br />Pb 46 0 0 0 0. . , <br />µg <br />, 29 1854 1 <br />2 <br />/1) <br />Di <br />( <br />M <br />46 <br />12 <br />24 <br />45 <br />, <br />s <br />µg <br />n, 01 <br />0 3 <br />Hg, Tot (µg/1) <br />/1) <br />Dis ( <br />Ni 0 <br />0 0 <br />0 0 <br />0 0 <br />0 0 <br />p . <br />70 3 <br />µg <br />, 55 4 <br />6 1 <br />2 <br />/1) <br />Dis ( <br />S 4 0 0 1.2 0. . , <br />µg <br />e, 0 14 <br />0 3 <br />Ag, Dis (4g/1) <br />Zn, Dis (µg/1) <br />B, Tot (mg/1) <br />g/1) <br />TR ( <br />A 1 0 <br />46 <br />9 <br />4 0 <br />0 <br />0 <br />67 0 <br />0 <br />0 <br />l03 0 <br />16 <br />0.028 <br />156 7.7 <br />0.010 <br />111 . <br />168 <br />0.75 <br />NA 1,2 <br /> <br />1 <br />µ <br />, <br />As, Dis (µg/1) 4 0 0 0 0 NA 1,2 <br />Note 1: In the absence of total recoverable and dissolved data for metals, available metals data in the total form were used. <br />Note 2: When sample results were below detection levels, the value of zero was used in accordance with the Division's standard <br />approach for swnmarization and averaging purposes. <br />Note 3: Based on the previous discussion for chromitun, nickel, mercury and silver in Section iV of this assessment, the <br />- ,,. e,, n„ h-, been :.?. ned to be zero. <br />ambient water quaury c;onccui, auuun - <br />Appendix A (WQA Version 5-4(FABt.)) Page 24 of 29 <br />Last Revised August 26, 2008