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Water: CWA Methods

Recent Regulatory Questions and Answers

On March 12, 2007 (72 FR 11200), we amended the analytical methods regulations at 40 CFR Part 136 for wastewater. The following information responds to questions you may have about these regulatory changes. In general where there is ambiguity in the regulations or analytical methods, try working mutual solutions with your accreditation or regulatory authority.


Reporting Requirements: What is the intent of the amendments to the text preceding Tables IA to IG at 136.3(a), and Table II at 136.3(e) that "reporting requirements of Parts 122 or 125 may take precedence over the otherwise applicable reporting or preservation requirements of a particular analytical method?"

This amendment is explained on page 72 FR 11206 in the preamble to the March 2007 rule. Some compliance methods require rejection of data that fail QC criteria. However, to do so when there is not opportunity for reanalysis, resampling or corrective action may cause a violation of Part 122 or 125 reporting requirements. These amendments remove this potential conflict by clarifying that the regulatory authority decides whether to request or accept data that have failed QC specifications in the method, or when problems have occurred during sample collection.

What is the impact and intent of the new 40 CFR Part 136.6 regulation that specifies the flexibility to modify approved Part 136 chemical methods without EPA oversight?

We provided 40 CFR 136.6 to help users of modified Part 136 methods satisfy clients, accreditors, and regulatory authorities who prefer the clarity and authority of a CWA regulation. This regulation describes modifications that do not require EPA review. Allowed modifications include changing purge volumes, and automating manual methods (e.g. discrete analyzers methods). We encourage you to read 136.6 carefully before using a modified Part 136 method (in particular, 72 FR 11239-41). Part 136.6 also is discussed on page 11203 of the preamble to this rulemaking.

The intent of this regulation is to codify a longstanding performance-based philosophy in the CWA program. It builds on the flexibility specified in section 9.2 of EPA's 1600-series chemical methods. We want users to be able to timely modify methods to overcome matrix problems, automate methods, or otherwise improve the efficiency or accuracy of a compliance analysis without unnecessary delay. Of course these modifications only are acceptable for compliance use, if the modification works, i.e., the performance should be comparable to the performance of the unmodified method on your sample.

What modifications are not within the allowable flexibility described in 40 CFR Part 136.6?

You should carefully read 40 CFR 136.6 before using a modified method or submitting your modification of a CWA method to our ATP program. In general, changes to the determinative step (e.g., the detector), the quality control, or significant chemistry of the method, are outside the scope of 40 CFR Part 136.6. Also outside the scope are some, but not all, changes to methods that measure a method-defined parameter, such as oil or grease. And 136.6 does not apply to methods for biological or microbiological pollutants.

Are some modifications to method-defined parameters, such as total suspended solids or oil and grease, within the allowable flexibility described in 40 CFR Part 136.6?

Yes. Although, method-defined methods do not fall within the scope flexibility of 40 CFR 136.6, this limitation does not imply that all modifications to these types of methods require approval. For example, interchange of the type of vessels, such as graduated cylinder and pipettes that transfer sample, are allowed. Oil and Grease, Method 1664 is a performance-based method applicable to aqueous matrices that requires the use of n-hexane as the extraction solvent and gravimetry as the determinative technique. For example, alternative extraction and concentration techniques are allowed, provided that all performance specifications are met.

Will 40 CFR Part 136.6 change the CWA ATP program?

Yes, an immediate impact is that developers who submit a CWA method modification to our ATP program now must clearly explain why their modification falls outside the scope of 136.6. We will not review ATP submittals that omit this explanation, or review methods that fall within the scope of 136.6. This requirement benefits the analytical community in two ways. First, it frees our chemists to focus on new or modified methods that clearly fall outside the scope of 136.6, and therefore justify review under ATP guidelines. Second, developers may use modified Part 136 methods without the delay of ATP review or rulemaking.

Our chemists and quality assurance personnel have informed our EPA regional, state and local colleagues of this authority to modify 40 CFR Part 136 methods by following the requirements of 40 CFR Part 136.6. We are encouraging them to understand and use this authority to allow more rapid introduction of better compliance methods.

Does the allowable flexibility described in 40 CFR Part 136.6 apply to drinking water methods?

No. The drinking water program has published the Final Rule for expedited approval of ATPs for use in drinking water which allows for more flexibility in their methods, and has different authorities under SDWA than we do under the CWA. See 73 FR 31616 (June 3, 2008).

Do modified Part 136 methods that already have an ATP approval letter have more status than modified methods that will no longer receive these letters because the modification falls within the scope of 40 CFR Part 136.6?

No. These methods have equal status. For example, all discrete analyzer methods (or any other method modified pursuant to section 136.6) have the same status as any method for which an ATP determination letter had been issued in the past. Thus, both a "lettered discrete method" and a "non lettered discrete method" are authorized test procedures under Part 136 so long as the non-lettered method complies with the requirements of section 136.6.

Does this rule withdraw approval of any ATP program method that was originally compared to a now withdrawn EPA method?

No. Although the MUR withdrew 109 methods published by EPA in "Methods for the Chemical Analysis of Water and Wastes (MCAWW)", EPA did not propose to withdraw approval of any alternate test procedure (ATP) letter associated with a now withdrawn EPA method. The EPA methods were not withdrawn for performance reasons. The EPA methods were withdrawn because approved, Part 136 methods published by voluntary consensus standards bodies (VCSB), such as Standard Methods and ASTM, use the same measurement technologies, and have the same or similar performance characteristics as the withdrawn EPA methods. These equivalent VCSB methods have been updated more recently than MCAWW methods. Thus, there was no reason to withdraw an ATP method associated with a withdrawn method. You may choose to associate a VCSB (or other equivalent Part 136 method) with a corresponding acceptable version ATP method, and acceptable version letters issued by EPA with or without an ATP case number continue to be valid.

REVISED (September 15, 2008): If you choose to associate an acceptable version ATP method with a Part 136 method published by a VCSB, cite as My Method X that employs the same measurement technology as the approved VCSB method. See "Citing Clean Water Act Limited-Use ATP Methods as Modifications" (PDF) (1 pp., 50 K, April 14, 2008; About PDF)

Freon methods for Oil and Grease

This rule withdrew EPA method 413.1 for determinations of oil and grease because it uses a banned solvent, Freon. Information about use of the replacement method EPA 1664, which uses a hexane solvent.

Are Freon methods for Total Petroleum Hydrocarbons (TPH) also withdrawn?

Because TPH is not part of CWA monitoring there is no TPH method at Part 136 to withdraw. However, some entities require use of an EPA-published method for TPH determinations that uses a Freon solvent. We note that recent air regulations specifically disallow use of methods, such as the Freon-based TPH methods. You might consult with appropriate parties before continuing to use Freon-based analytical methods.

Where can I get a copy of EPA method 245.7?

Method 245.7 Mercury in Water by Cold Vapor Atomic Fluorescence Spectrometry (PDF) (33 pp, 195K, About PDF)

Where can I find background documents associated with the MUR?

In the water docket at www.regulations.gov, docket number is EPA-HQ-OW-2003-0070.

Is there a difference between Standard Methods On-line and Standard Methods 21st Edition?

No. For convenience between editions of their analytical methods book, the Standard Methods Committee electronically publishes versions of methods that will be in the next print edition. Because these methods are identical, users may use either the print or electronic version of the applicable Standard Method that was approved in the March 2007 rule.

In Table 1B, is distillation and titration required for Kjeldahl, Nitrogen - Total?

No, Footnote 20 to Table 1B notes that, when using this method with block digestion, distillation and titration are not required.

In addition, the published indents for the block digester method are formatted incorrectly. The correct formatting is:

  • "Block Digester, followed by:
    • Auto distillation and Titration, or
    • Nesslerization, or
    • Flow injection gas diffusion."

Thus, the block digester may be used with all three of the sample introduction techniques.

Chromium VI Preservation Information

Responses to questions concerning hexavalent Chromium ("Chromium 6") in the method update rule.

May one use collision cell technology with EPA Method 200.8 for CWA uses?

Yes, provided that you document that the method performance specifications relevant to ICP/MS measurements in the collision mode are met. To answer this question, we considered our experience with CWA methods and problems with matrix interferences, and information that use of a collision cell improved the accuracy of analyses in some wastewater samples. Thus, use of collision cells with EPA Method 200.8 for CWA purposes falls within the scope of the explicit flexibility described at 40 CFR Part 136.6. This regulation, which was promulgated on March 12, 2007, allows, without EPA review, many modifications that improve the performance of CWA (Part 136) methods.

What if I find an error or omission in this final rule?

Please contact us.


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