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CO-0000906 <br />New Elk Mine Water Quality Assessment <br />• Table A-4 <br />Ambient Water Qualit for the Middle Fork of the Pur atoire River <br />Chromic. ; <br />Number 15th 50th 85th <br />Mean Stream Notes_ <br />Parameter of Percentile Percentile Percentile Standard <br />Samples <br />10 6.2 20 -- <br /> <br />• <br />Temp (°C) 50 1.4 6 <br />11 <br />DO (mg/1) 50 8.2 <br />8 9.4 <br />8.4 8.5 <br />pH (su) 45 <br />37 <br />0 <br />0 0 <br />As, TR (µg/1) 0 0 0 <br />Cd, Dis (µg/1) 44 0 1.8 <br />Cu, Dis (µg/1) 44 0 <br /> <br />42 <br /> <br />84 <br />166 <br />Fe, TR (µg/1) 44 <br />0 <br />0 0 <br />Pb, Dis (µg/1) 44 <br />0 <br />16 27 <br />Mn, Dis (µg/1) 44 0 2 <br />2 <br />Se, Dis (4911) 37 0 <br />0 . <br />0 <br />Zn, Dis (µg/1) 44 0 <br />0 0 0.028 <br />B, Tot (mg11) 9 <br />5 0 1.0 3.0 <br />.0 <br />Chloride, Tot (mg/1) 12 13 <br />Magnesium (mg/1) 12 8.2 46 52 <br />Calcium (mg11) 12 33 <br />0 2 2 <br />Se, Dis (Temp Std) (µg/1) 37 0 137 <br />Al, TR (µg/1) 37 21 49 <br />0 <br />As, Dis (4911) <br />37 <br />6 <br />0 <br />27 <br />0 <br />0 <br />0.30 <br />0.36 <br />Conductivity (dS/m) . 17 24 <br />Sodium (mg/1) 12 7.4 <br />113 <br />140 169 <br />50 <br />Hardness as CaCOa (mg/I) <br />Note 1: When sample results were below detection levels, <br />the value of zero was used in accoi <br />approach for summarization and averaging purposes. <br />the torn, of the standard, total data were used. <br />i <br />f d <br />n <br />ata <br />Note 2: In lieu o <br />9.5 <br />8.3 <br />0 <br />0.037 <br />0.71 <br />142 <br />0.12 <br />19 <br />0.62 <br />1.2 <br />0.010 <br />1.4 <br />43 <br />0.62 <br />95 <br />0.31 <br />28 <br />142 <br />e with the <br />7 <br />6.5-9 <br />100 <br />0.55 <br />12 <br />1000 <br />3.70 <br />1854 <br />4.6 <br />168 <br />0.75 <br />1,2 <br />1,2 <br />11,22 <br />11,22 <br />1,2 <br />11,22 <br />1,2 <br />1,2 <br />250 1 <br />NA <br />NA <br />11.2 1,2 <br />NA 1,2 <br />NA 1,2 <br />NA <br />NA <br />,isil n's standard <br />Ambient Water Quality for the Left Fork of Apache Canyon Creek <br />The Division evaluates ambient water quality based on a variety of statistical methods as prescribed <br />in Section 31.8(2)(a)(i) and 31.8(2)(b)(i)(B) of the Colorado Department of Public Health and <br />Environment Water Quality Control Commission Regulation No. 31. The ambient water quality was <br />not assessed for the Left Fork of Apache Canyon Creek because the background in-stream low flow <br />condition is zero, and because no ambient water quality data are available for the Left Fork of <br />Apache Canyon Creek upstream of the New Elk Mine Outfall 009 discharge. <br />111. Water Quantity <br />The Colorado Regulations specify the use of low flow and chronic conditions <br />low flows. The acute w flow, referred <br />based effluent limitations, specifically the acute <br />Page 9 of 29 Last Revised August 26, 2008 <br />Appendix A (WQA version 5-4(I=ABL))