Article written by
Wade DeLong, Lab Manager, Analytical Products Group
Recent Updates to the Stage 2 Disinfection
Byproduct Rule
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”.
http://www.epa.gov/fedrgstr/EPA-WATER/2006/January/Day-04/
The rule is effective on March 6, 2006 and is 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 successfully meeting all four individual THM
compounds acceptance limits.
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 438 (CFR page number)
“The new acceptance limits are effective 60 days after promulgation.
Laboratories that were certified under the Stage 1 DBPR PE
acceptance criteria will be subject to the new criteria when it is
time for them to analyze their annual DBP PE sample(s)” Then on page
480 …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. (iii)Beginning April 1, 2007 the
laboratory must achieve quantitative results on the PE sample
analyses that are within the following acceptance limits:” which
refers to a table detailing the fixed percent limits.
APG’s study schedule is such that the fixed
percent limit acceptance criteria will be used beginning in the March 2007 WS
study. In the WS studies beginning March 2006 through January 2007 we
will provide a sample evaluation using the fixed percent
limit acceptance criteria. We hope this will help our laboratories ease through this transition by
identifying any areas of concern before the change in acceptance criteria affects
certification requirements.
|
