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Laboratory - Frequently Asked Questions (FAQs)

Listed below are frequently asked wastewater laboratory technical questions. If you have another question for this list, please email the IWEA Laboratory Committee at labcommittee@iweasite.org

  1. When did the USEPA Part 136 methods change and where can I find what tests were part of those changes?

  2. What is the hold time for setting up BOD’s taken from a composite sample?

  3. A set of Laboratory Standards have been established by the National Environmental Laboratory Accreditation Conference (NELAP).  There are several versions from different conferences.  What version of the standards is approved?

  4. What is the acceptable range for the Glucose-Glutamic Acid (GGA) standard for BOD analysis?

  5. Standard Methods for the Examination of Water and Wastewater requires duplicates to be run as part of a quality control program.  What is the frequency of duplicates?

  6. Does the Illinois EPA require laboratories to be certified under their Environmental Laboratory Accreditation Program?

  7. What is the procedure to follow after a failed PT result?

  8. What do you do when your instrument doesn't go low enough to meet your permit limits?

  9. Is there any benefit derived from matrix matching standards & samples for ICP-OES or ICP-MS analysis?

  10. In a recent audit, we had a deficiency finding because our samples were not in the required temperature range of 20 +/- 3 degree C (Standard Methods 20 ed 5210B.4.e.5). Why do samples need to be in this range?

  11. Why are the bottles air incubated and thermostatically controlled at 20 +/- degree C for the BOD test?

  12. Why do you need to use different positions for your LCS in a hot block for metals analysis?

  13. What is the new low level mercury digestion procedure required by the IEPA for method 1631E?

  14. What guidelines are used to determine reporting limits (RL), method detection limits (MDL), and limit of quantitation (LOQ)?

  15. How do you keep glassware clean?

  16. How do I obtain copies of analytical methods?

 

When did the USEPA Part 136 methods change and where can I find what tests were part of those changes?
The  last changes to 40CFR part 136  Guidelines Establishing Test Procedures for the Analysis of Pollutants ,was finalized in March of 2007.    The final rule was published in the Federal Register , volume 72, Number  47, Monday March 12, 2007 under Rules and Regulations.  Methods from the 18th, 19th, and 20th editions of Standard Methods were approved for many analytes. Part 136 Table 1B deleted some of the EPA Methods in wet chemistry and AA metals analysis.  Please read the footnotes at the end of the table for additional clarification.

 What is the hold time for setting up BOD’s taken from a composite sample?
 Table II of 40CFR136 Required Containers, Preservation Techniques, and Holding times, states the maximum holding time is 48 hours.  Please remember that the hold time starts at the end of the composite period.  Footnote number 4 states that “For a composite sample collected with an automatic compositor (e.g., using a 24-hour composite sampler), the holding time begins at the time of the end of collection of the composite sample”.

A set of Laboratory Standards have been established by the National Environmental Laboratory Accreditation Conference (NELAC).  There are several versions from different conferences.  What version of the standards is approved?
The current approved standards were effective July 5, 2003 .   It is listed as EPA/600/R-04/003.  The website is nelac-institute.org and contains the standards in PDF format. These current standards are used by NELAC institute accreditation bodies for the accreditation of environmental laboratories.

What is the acceptable range for the Glucose-Glutamic Acid (GGA) standard for BOD analysis?
According to Standard Methods 18th Edition Method 5210B the mean should be 198 mg/L plus or minus 30.5 mg/L.   The quality Control limit range then would be 167.5mg/l to 228.5 mg/L.  Also remember that sample dilutions must meet the criteria of a residual DO of at least 1.0 mg/L and a DO depletion of at least 2.0 mg/L. 

Standard Methods for the Examination of Water and Wastewater requires duplicates to be run as part of a quality control program.  What is the frequency of duplicates?
In general, the frequency of a duplicate sample should be at a minimum of one duplicate sample per batch or on a 5% basis, whichever is more frequent. It is important to note that duplicate frequency requirements may vary depending on the type of method being used. If more specific precision guidance is provided within the method or the associated QC section for that class of methods then those requirements should take precedence and be followed. An example of this would be for the Part 2000 methods - Physical and Aggregate Properties. For this class of methods a duplicate sample is required for at least 10% of samples.

Does the Illinois EPA require laboratories to be certified under their Environmental Laboratory Accreditation Program?
Participation in IL ELAP (Environmental Laboratory Accreditation Program) is voluntary except for any laboratory submitting community water supply compliance data to Illinois EPA, Bureau of Water, Compliance Assurance Section. Any laboratory submitting community water supply water compliance data must be accredited for those particular analytes.

More information on ILAP is available at http://www.epa.state.il.us/labs/

What is the procedure to follow after a failed PT result?
Any lab that receives a “not acceptable” PT result must conduct an investigation to determine the cause for the failure and take appropriate corrective where assignable error is found. The investigation and corrective action must be documented and reported to the primary accrediting authority (IL ELAP). To remain in good standing, the lab must successfully analyze two of the most recent three PT studies for an analyte.

What do you do when your instrument doesn’t go low enough to meet your permit limits?
You have a few options. You can reevaluate your MDL which may be lower than your previous evaluation, concentrate the sample if applicable depending on the analysis, try a new method or outsource the analysis to a lab that can achieve the desired reporting limits.

Is there any benefit derived from matrix matching standards & samples for ICP-OES or ICP-MS analysis?
Matrix interferences occur when the physical characteristics (viscosity, surface tension, etc.) of the sample and standard solutions differ considerably. Matrix matching samples and standards is a very beneficial technique that aids in correcting interferences and increasing the likeness of introduction. For best results, the standards should have a similar matrix to the unknowns. If samples and standards are not matrix-matched, the accuracy of results may be compromised.

In a recent audit, we had a deficiency finding because our samples were not in the required temperature range of 20 +/- 3 degree C (Standard Methods 20 ed 5210B.4.e.5). Why do samples need to be in this range?
Laboratory glassware is calibrated to contain or deliver volumes of liquid at specific temperature ranges, typically at 20 degrees C. In order for the glassware to deliver the correct amount of volume, you need to make sure your sample temperatures are within the specified calibration range. In your case, the sample temperature range was 20 +/- 1 degree C for your referenced method. The 21st edition of SM gives a little relief by allowing the sample temperature range to be 20 +/- 3 degrees C.

Why are the bottles air incubated and thermostatically controlled at 20 +/- degree C for the BOD test?
This allows for the uniformity of temperature for the duration of the analysis. Any fluctuations in temperature can compromise the accuracy of your results.

Why do you need to use different positions for your LCS in a hot block for metals analysis?
There can be variability in temperature in different well positions on the hot block. The LCS should be treated like a regular sample and should not be placed in a designated well position.

What is the new low level mercury digestion procedure required by the IEPA for method 1631E?
Method 1631E  is a performance based analytical test method used to determine low level mercury in water by oxidation, purge and trap, and cold vapor atomic fluorescence spectrometry. There are three methods that are approved for use in NPDES monitoring of mercury; methods 245.1, 245.2 and 1631E. Method 1631E is 400 times more sensitive than methods 245.1 and 245.2 yielding a quantitation level of 0.5 ppt. Water quality criteria by the EPA tend to be in the 1-50 ppt range for most states thus making method 1631E the only one of the three methods that can detect and quantify mercury at the regulated ranges.

What guidelines are used to determine reporting limits (RL), method detection limits(MDL), and limit of quantitation(LOQ)?
Specific guidelines to generate the MDL can be found in 40 CFR Part 136, Appendix B. It is common to use a multiplier of the MDL to arrive at an LOQ, usually 3 to 5 times. The LOQ is usually set as the low standard in a calibration curve.

How do you keep glassware clean?
Allow laboratory glassware to air dry upside-down in a drain rack after it has been cleaned. Proper storage is the best way to keep your glassware clean. Replace corks, caps, stoppers and other covers onto the glassware before storing. Store clean laboratory glassware in a closed cabinet or drawer to prevent the items from getting dusty.

How do I obtain copies of analytical methods?
Searchable index of public and private methods:  www.nemi.gov
EPA Clean Water Act (CWA) methods:  www.epa.gov/waterscience/methods
EPA SW846 methods:  www.epa.gov/epaoswer/hazwaste/test/sw846.htm
EPA Pesticide methods:  www.epa.gov/pesticides/methods/index.htm
Standard Methods:  www.standardmethods.org
ASTM methods: http://www.astm.org/Standard/index.shtml
HACH Methods:  www.hach.com/download-resources