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Complete Article from Edition 49 APG eNewsletter
Article by Jamie Hoban , QC Supervisor at APG
The Federal Register dated January 4, 2006 details the Final Rule of 40CFR Parts 9, 141 and 142 the “National Primary Drinking Water Regulations: Stage 2 Disinfectants and Disinfection Byproducts Rule”. (Click to View Entire Rule) The rule was effective on March 6, 2006 and was promulgated as of January 4, 2006. This update will change, among other things, the manner in which proficiency testing (PT) samples are evaluated.
The changes could potentially make passing a PT study more difficult for the affected parameters. The acceptance range calculation used by PT providers will be changing from using interlaboratory statistics to fixed percent limits. The individual trihalomethane (THM) compounds will be evaluated by an acceptance range of the true value ± 20 percent.
The Total Trihalomethane (TTHM) acceptance criteria will still be based on meeting all four individual THM compounds acceptance limits successfully. The individual Haloacetic Acid (HAA) compounds will be evaluated using an acceptance range calculated using the true value ± 40 percent. Chlorite and Bromate acceptance ranges will be calculated using the true value ± 30 percent. Table IV.0-1 on page 52 in the link listed above (use the pdf view) provides a consolidated list of the PT (a.k.a. PE) acceptance criteria.
There are some important dates within the final rule document, page 480 (CFR page number)
the laboratory must:
(ii) Until March 31, 2007, in these analyses of PE samples, the laboratory must achieve quantitative results within the acceptance limit on a minimum of 80% of the analytes included in each PE sample. The acceptance limit is defined as the 95% confidence interval calculated around the mean of the PE study between a maximum and minimum acceptance limit of +/- 50% and +/- 15% of the study mean. Beginning April 1, 2007, the laboratory must achieve quantitative results on the PE sample analyses that are within the following acceptance limit: (referring to the table on page CFR page 480)
APG’s study schedule is such that the fixed percent limit acceptance criteria will be used beginning in the March 2007 WS study.
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