The laboratory analyst certification of the California-Nevada section of the American Water Works Association, aimed at drinking water compliance — maximum contaminant levels, state reporting deadlines, and accredited methods.
Start studying Grade 3Quality assurance: control charts · an original practice item written only from publicly available sources, not a real exam question
A laboratory control sample's historical mean recovery is 98% with a standard deviation of 3%. The lab sets warning limits at ±2 standard deviations and control limits at ±3. Today's recovery is 106%. What does it mean?
A. In control, but beyond the warning limit: flag it and watch for a trend
Warning limits are 98 ± 6 = 92 to 104%; control limits are 98 ± 9 = 89 to 107%. 106% sits between the warning and control limits, so the batch is still in control, but the point should be flagged and the next results watched for a trend. Calling it inside the warning limits forgets that 104% is the upper warning limit; calling it out of control uses the warning limits as if they were the control limits. The method detection limit governs low-level reporting, not recovery control.
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Topic coverage follows 2020 Certification Candidate Handbook — Water Quality Laboratory Analyst (California-Nevada American Water Works Association, issued 20 October 2020). Practice questions are written only from publicly available sources (that outline and the regulations and references it cites); they are not real exam questions, which are confidential. Check current application requirements, fees and exam dates on the certifying body's own page: official certification page.
Questions, flashcards, and explanations are AI-written from publicly available sources only: the exam content outlines and candidate materials each certifying body publishes without restriction, and the regulations and technical references they cite. No confidential material is used, including actual exam questions, recollections of any exam sat by the author, or any handbook or document released under a confidentiality agreement. Content is then put through repeated review — regulatory values checked against primary sources, every calculation recomputed, and errors corrected — plus spot checks by the author, who holds California water operator certifications and a California civil engineering licence. Those spot checks are sampling, not a professional review: nothing here is stamped, sealed, or offered as engineering advice, and not every item has been individually verified, so mistakes can still slip through.