February 6, 2014

Mr. Lemuel Walker U.S. Environmental Protection Agency Clean Water Act ATP Coordinator Engineering and Analysis Division Office of Science and Technology Office of Water [4303T] 1200 Pennsylvania Avenue, N.W. Washington, D.C. 20460 Regarding: Recommendations regarding the proposed update to the 40 CFR Part 136 method detection limit procedure Dear Mr. Walker, The Environmental Laboratory Advisory Board (ELAB or Board) is a standing Federal Advisory Committee Act board that advises the U.S. Environmental Protection Agency (EPA or Agency). The Board’s Charter states that it is to provide consensus advice, inform ation and recommendations on issues related to EPA measurement programs and facilitate operation and expansion of a national environmental laboratory accreditation program. ELAB has reviewed the proposed update to the method detection limit (MDL) drafted by The NELAC Institute (TNI) Chemistry Expert Committee. In ELAB’s opinion, the proposed update is a considerable improvement to the current MDL procedure, and therefore the Board recommends that EPA adopt the proposed changes as soon as reasonably possible. The Board recommends a few minor changes to the current draft procedure that ELAB believes improve clarity or strengthen the procedure. However, these changes do not alter the overall intent, and ELAB would recommend adoption even without incorporation of the suggested changes. Thank you for your consideration of the Board’s comments regarding TNI’s proposed revisions to the MDL procedure. Respectfully,

Patsy Root Chair, Environmental Laboratory Advisory Board

cc: ELAB Board TNI Chemistry Expert CommitteePage 2 of 4 ELAB Comments on the Revised Method Detection Limit (MDL) Procedure Background The detection limit of an analytical procedure is a critical property and vital to understanding the capability of the method and the range of data quality objectives that can be supported. The MDL serves the purpose of determining the single laboratory detection limit for methods approved under 40 CFR 136, and the importance of accurate estimates can hardly be overstated because inco rrect compliance decisions are likely to result from an inaccurate estimate. Unfortunately, the current MDL procedure is widely recognized to have serious flaws that can and do result in incorrect detection limit estimates. There have been previous efforts to update or replace the MDL procedure. In 2003, EPA issued a proposed update that was withdrawn after receiving consider able negative comment in the public review period.Subsequently, a federal advisory committee developed a replacement for the MDL that was generally considered technically sound, but implementation difficu lties were such that it was never implemented. In the Board’s opinion, the TNI procedure strikes a good balance between technical validity and ease of implementation. Detailed comments are provided below, and suggestions for language changes are included marked as revisions in the attached copy of the procedure.

Definition: ELAB supports the change in definition to reference method blanks rather than zero. For the purposes of determining compliance, it is important to identify the lowest level that can be reliably distinguished from a blank rather than zero. Section 2.a Selection of spiking level: Changing the initial spiking level from 1 to 5 times the estimated MDL to 2 to 10 times is beneficial. Spiking at only 1x the MDL is likely to result in many results below the MDL (i.e., the spiking level would be too low). It may be helpful to point out that spiking levels 10x the anticipated MDL should only be needed if the specific analyte is a poor performer in terms of recovery.

Section 2.b Blanks: The Board strongly supports including an assessment of blanks in the MDL procedure. As the objective is to identify the lowest level that can be distinguished from a blank, using actual blank data makes sense. Section 2.b.i Multiple instruments: The guidance for multiple instruments is valuable. This is a very common situation and lack of previous guidance has resulted in a wide and confusing range of different approaches. Section 2.c.iii Computation of the MDL based on blanks: ELAB supports calculation of the MDL based on blanks as mean plus Student’s t times the standard deviation. Incorporation of the mean is very important.

Section 2.d Set the MDL: The Board believes that EPA should consider favoring the blank-calculated MDL over the spike-calculated MDL, assuming that there is more blank data than spike data. Section 3. Ongoing data collection: ELAB believes that spreading data collection over time is important, and the requirement for a minimum of two spikes per quarter is a reasonable compromise between collecting sufficient data and having a pr ocedure that is not too onerous. EPA may want to consider providing clearer guidance regarding what is meant by “per quarter.” Section 4. Ongoing annual verification: Although an annual recalculation of the MDL is not in the current procedure, the Board believes that this recalculation (annual verification) is a sound practice for maintaining MDLs that reflect the current capability of the laboratory; therefore, ELAB believes that it is a good addition toPage 3 of 4 the procedure. EPA may wish to consider clarifying the annual requirement. For example, “recalculation of the MDL must be performed within 13 months of the previous MDL determination or recalculation.” Section 4.f. Adjustment of the MDL: No justification is provided for the factor of three used as a limit for determining whether the current MDL needs to be adjusted. Some degree of justification would be useful and ELAB notes that the upper 99% confidence interval for a population standard deviation based on 6 degrees of freedom is 2.98. Addressing Previous Objections to the MDL ELAB has reviewed objections to the 2003 MDL update that were received in the public comments, with a view to determining whether they have been addressed in the new draft. Many comments were received on each of the following general issues. Variability: Long-Term Variability— The new draft does a good job of incorporating longer term variability. Interlaboratory Variability— There is no additional material covering interlaboratory variability; however, the procedure is intended as a single laboratory detection limit determination. Recently, EPA has set MDLs based on the highest MDL from participating laboratories, after removal of outliers, and the same approach could be used with the new draft. Another option for estimating the interlaboratory variability would be to calculate a pooled MDL from a large population of laboratories. ELAB would be able to assist EPA in gathering this data once the revised MDL has been in use for a year or more. Analyte Concentration, Calibration and Analytical Range— Determining the spiking concentration is similar in the current and new drafts, but the new draft has the benefit that there are steps to verify the MDL determined.

Definitions: Many concerns were raised regarding the definition of the MDL. ELAB believes that adjusting the definition to refer to blanks, and clarifying that the MDL is based on results rather than true concentrations, will be beneficial in removing some of the current confusion. The MDL does not purport to be equivalent to the IUPAC limit of detection, but is more similar to the critical level because it only controls false positives.

Precision and bias: Concerns were raised especially concerning bias, and the new draft addresses these well by incorporating the mean of the blanks into the MDL b calculation. Error types: The current MDL does nothing to control false negatives. The revised draft addresses false negatives to some extent through the requirement that the ongoing spikes return positive results. The Board would encourage EPA to consider further control of fa lse negatives through a subsequent effort to provide better definition of a single laboratory quantitation limit, which could be used to replace the minimum level. Iterative procedure: There were many complaints regarding the proposed iterative procedure in the 2003 proposed update. This iterative procedure has fortunately been removed from the current draft and replaced with ongoing evaluations of the MDL. Outlier testing: There were various comments both in favor and opposed to outlier testing. The new draft does not include an outlier test, but the nonparametric option for method blanks could be considered a useful alternative.Page 4 of 4 Spike levels: The new draft includes options and requirements for adjusting spike levels if needed based on the ongoing data collection.

Use of blanks: Many comments concerned the lack of considerati on of blanks in the 2003 draft; these are fully addressed in the new draft. Number of replicates: Some comments noted that more replicates would be desirable. The new draft still allows starting with seven replicates (a reasonable compromise), but in most cases many more replicates would soon be available through the ongoing data collection.

Tolerance vs. confidence intervals: Some comments stated that tolerance intervals should be used for the MDL. This is a point of contention between statisticians, and ELAB does not take a position on which is preferable. However, retaining Student’s t will certainly make implementation of the new draft easier, and in many cases, the increased number of replicates will reduce the difference between the confidence and tolerance intervals. Also, the use of nonparametric statistical tools when possible eliminates this contentious issue. Sensitivity check: Comments in favor of a sensitivity check are addressed by the requirement for ongoing data collection and the requirement that the spikes return positive detections

.