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0 0 <br />MR: ROBERT J. SHUKLE <br />CDPS N0. CO-0027154 <br />OCTOBER 3, 1985 <br />PAGE 5 <br />consider ten silver analyses of water known to have a silver concentration of <br />0.0001 mg/l. Analytic uncertainty inherent in the BAT analysis would very <br />likely lead to some silver values greater than 0.0001 mg/1. An average of the <br />ten silver values using the .method prescribed for 30 day averages (less than <br />0.0001 is averaged as 0.0001) would have a very high probability of being <br />greater than the proposed 30 day average limitation of 0.0001 mg/l. Thus, <br />water, whose actual silver concentration meets the 30 day limitation, would <br />have a very high probability of a ea~ ring to exceed the standard. CYCC be- <br />lieves that an appropriate 30 day imitation for silver is 0.0003 mg/l, which <br />is the upper limit of the 95Y confidence region around the 0.0001 mg/1 limit <br />proposed by the Water Quality Control Division. <br />Consider water with a known silver concentration of 0.0001 mg/1. Ac- <br />cording to the information supplied by Bookcliffs, there is a 95`d probability <br />that an analysis of this water would yield a value between 0.0000 mg/1 and <br />0.0003 mg/1. Statistically, it is quite possible that water with a true con- <br />centration of 0.0001 mg/1 would exceed the proposed daily maximum limitation <br />of 0.0002 mg/1. Since Bookcliffs Laboratories recommends that an established <br />limit should be five times greater than tl~e detection limit (in this case <br />0.0001 using BAT), CYCC believes that a daily maximum limitation of 0.0005 <br />mg/1 is appropriate. <br />CYCC believes that a 30 day average limitation of 0.0003 mg/1 and a daily <br />maximum limitation of 0.0005 mg/1 will not have adverse environmental impacts. <br />These limitations are well below the drinking water standard of 0.05 mg/l. <br />The EPA quality criteria for water (1976) recommends a silver criterion of <br />0.01 of the 96-hour LC50 for sensitive resident species. LC50 data is not <br />available, but the 1972 EPA criteria for water suggests that concentrations of <br />silver equal to or exceeding 0.005 mg/1 constitute a hazard to the marine <br />environment, and levels less than 0.001 mg/1 present minimal risk of deleter- <br />ious effects. <br />This letter should provide an adequate response to your letter of August <br />29. Please contact me with any of your questions or concerns. <br />Sincerel , <br />~~` ~ C/ <br />Kent Crofts <br />Environmental Manager <br />KC:kmk <br />cc: M. Kondelis <br />T. Johnson <br />D. Arkell <br />J. Hendrickson <br />M. Ludlow <br />R. Tifft <br />M. Day <br />K. Gormley <br />