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Please refer to our most recent annual report for a full description of our quality control program and an evaluation of the most recent data.
Our quality control program includes, among other aspects, repeated sampling at one station during each sampling event. Original and sequential duplicate samples are collected about 15 minutes apart. The charts below depict the result of this sequential duplicate sample minus the original station result plotted against the date of sample collection. Station results with quality codes>4 (indicating some known problem) are not included. The yellow and red lines are +/-2 and +/-3 standard deviations, respectively.
Sources of error (variability) in these charts include analytical procedures, field processing, and short-term in-stream changes. These are not laboratory control charts which track only analytical error. Analytical error is typically about half the total error represented in these charts (see our most recent annual report). For some constituents, like suspended sediment, lab error may be even less. These charts are used to track changes in total precision. They cannot be used to assess bias.
Last updated April 2, 2004 (Charts may have been updated more recently). Questions or comments may be sent to Dave Hallock
Copyright © Washington State Department of Ecology. See http://www.ecy.wa.gov/copyright.html.
