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~. <br />Mr. Mike Ludlow <br />Getty Coal Company <br />Page 2 <br />The quality control data for our reagent blank indicates that samples with <br />Silver values near our detection of 0.1 ug/1 have a 95 percent confidence <br />level of being within a range of ± 0.2 ug/1. This range is based on the <br />analyses of laboratory pure water, not real-world water samples which vary <br />greatly with respect to chemical matricies. The range for real-world samples <br />at this low level would be greater than the ± 0.2 ug/1. <br />An example of how the ranges work would be if we analyzed a water sample and <br />obtained a Silver value of 0.2 ug/l, the true Silver value for that sample <br />has a 95 percent probability of being between 0.0 ug/1 and 0.4 ug/1. This <br />water sample may or may not exceed the Colorado Department of Health stream <br />standard of 0.1 ug/1 Silver. To ascertain if a water sample exceeds an <br />established limit for some parameter, the analytical method for that <br />parameter should have a detection limit at least five (5) times lower than <br />• the established limit. Presently, there are no EPA approved analytical <br />methods for Silver with a detection limit low enough to determine if water <br />samples meet or exceed the 0.1 ug/1 Silver stream standards. <br />If you have any further questions or need any additional information, please <br />do not hesitate to contact me. <br />Sincerely, <br />ACZ INC. <br />/~~ / ~~ <br />Ralph V. Paulsen <br />Laboratory Director <br />RVP:ju <br />Enclosure <br /> <br />