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Colowyo Coal Company <br /> <br /> <br />COG-0045161 <br /> <br />Parameter Number <br />of <br />Samples 15th <br />ercentile <br />p 50"' <br />ercentile <br />p 85th <br />ercentile <br />p <br />Mean Chronic <br />Stream <br />standard <br />Temp-°C 1 19 - <br />DO mg/1 I 6 5.0 <br />pH -s.u. 1 8.6 8.6 6.5 - 9 <br />Fecal coli #/100 tnl 0 325 <br />Un-ionized NH3-N mg/1 1 0.00 0.06 <br />Boron µg/1 0 750 <br />Arsenic (Trec)µg4 1 0 100 <br />Cadmium (dis) µg/1 1 0 6.2 <br />Copper (dis) µg/I 1 0 29.3 <br />Iron (Tree) µg/1 I 0 1000 <br />Iron (dis) µg/1 I 0 WS <br />Lead (dis) µg/1 1 0 10.9 <br />Manganese (dis) µg/I 1 0 2618/wS <br />Mercury (tot) µg/1 1 03 0.01 <br />Nickel (dis) µg/1 0 168 <br />Selenium (dis) µg/I I 4.0 4.6 <br />Silver (dis) µgJl 1 0 3.5 <br />Zinc (dis) µg/1 1 SS.O 379 <br />Hazdness as CaC03 mJl 1 590 <br />Da[a from WQCD wiIson Creek @ Cnty. Rd 51 (Station #11341). Period of Record August 23, 2000. <br />The calculated mean is the geometric mean. For summarization purposes, the value of one was used where there <br />was no detectable amount because the geometric mean of one is equal to zero. <br />All samples below detection limit. <br />Bold values represent statistical evaluation point against the stream standard. <br />III. Water Quantity <br />Permit limits are set based on the critical instream conditions. Standards must be protected at all <br />times including during low flow conditions. These conditions include the acute (one in three year <br />interval or lE3) and chronic (30 day harmonic mean flow in three year interval or 30E3) low flows. <br />Low Flow Analysis: <br />To best determine the low flows available at the Colowyo Coal Company outfalls, a flow gage <br />measurement immediately upstream of these outfalls should be used. Because there aze no flow <br />gages immediately upstream of the outfalls, the ]ow flows were determined based on the known <br />characteristics of the streams. The annua11E3 (acute) and 30E3 (chronic) low flows for all of outfall <br />locations was determined to be zero for both acute and chronic situations. It is felt that this zero low <br />flow value is the most accurate available low flow estimate for the Colowyo Coal Company outfalls, <br />. and is considered the best low flow data until additional informafion becomes available. <br />WQA 6 Revised 1/24/2005 <br />