WEF Discussion Forums
Laboratory Management and Technical Issues
New 0.20 mg/l blank REQUIREMENT for BOD in the MUR
The MUR update approves only the 21st edition of the BOD method (2001 online method.) This method seems to say that you must reject data if the blank results exceed 0.20 mg/l. Currently, it's not an absolute requirement ("should" not "must".) Will this requirement affect the quantity of data that you can report for compliance purposes (say on a DMR)? We plan to comment on this point and would like to hear from others. How often are your blanks outside the range of 0 - 0.20 mg/L range?
None of the prior methods make this a requirement. We don't see that EPA has provided a basis for this new stricter requirement.
The deadline for comments is December 22. If you want to comment, you can do so online at
http://www.regulations.gov/search/Regs/home.html#docketDetail?R=EPA-HQ-OW-2010-0192 . The rule was published Sept 23 in the federal register. There's a copy in the docket folder.
There are generally two categories of blank failures. One is where you have an "out of the blue" exceedance. This can be, and often is, the result of one bottle being contaminated. Since the problem is with only the one bottle, and other bottles are most likely not affected. IMHO, such is no reason to disqualify or even flag data for other samples in the batch. The Standard Methods BOD committee obviously doesn't agree with my opinion.
The second category is where the blank averages higher than 0.2 mg/L (i.e., is an exceedance most of the time). In this case, the cause is NOT contamination of just one bottle and it can be caused by any of several factors. In such a situation, all other data is questionable. Such would require that the majority of BOD data be invalidated or flagged. That would be very embarassing to say the least. Instead, the cause of the problem should be found and eliminated on a priority basis. Until the cause is found/eliminated, data should be invalidated or flagged. This is obviously not acceptable, whether the test is being run in a WWTP lab or a commercial lab. Finding the cause of consistently high blanks can be easier said than done, but a systematic trial and error process can usually do it.
These would make excellent comments on the proposed rule. I hope you will share these thoughts. It would be a shame if all blank occurrences above 0.20 mg/l required that the data be rejected.
I can do that, Kay. But first I would like to ask for clarification on where the requirement is found. I checked the docket you referenced and the only reference to BOD I could find involved the LDO probe method which was originally proposed by Hach as an alternate test procedure.
If that is the method we are addressing here, I will comment not only on the blank issue, but also on other QC requirements, many of which are overkill in my opinion. Hach originally peddled their LDO method as being significantly easier than membrane probe, and under their initial method, it was. But the current edition of the method makes it grossly more complicated than membrane probe (unless DO measurement using a membrane probe was also made more complicated in the on-line version, which this retired guy can't afford!).
So if you can let me know which method(s) we are addressing, I will submit a comment.
The rule was published in the September 23, 2010 Federal Register, but you have to go to Standard Methods (21st edition) to see the change in the membrane BOD method—it’s not really discussed in the preamble to the rule. They just change the approval to the new method with the different blank requirements without discussion in the preamble. Josh Kathrinus from our lab posted comments in the docket in case you want to take a look.
I have read the 21st ed. Std. Methods and interpreted it to say if the dilution water blank exceeds 0.20 mg/L you must discard all data or clearly identify all samples in data records. I do not think this is a change from previous approved methods.
CA did a training session last May on the topic of the 12 essential QA/QC elements. Spent a whole day just going over them for the common tests. Note that EPA insists on discussion of the 12 but provides no resources, references, or requirements. So a lab could choose a + 25% RPD for precision while another lab could choose + 50%.
Will make assessing labs fun.
In This Before Dirt (aka Bill Ray)