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PFOA, PFOS and Other PFASs

EPA Drinking Water Laboratory Method 537 Q&A

Must EPA Method 537 be used to analyze drinking water samples for PFAS?

EPA’s Unregulated Contaminant Monitoring Rule (UCMR 3) required that Method 537 be used to analyze UCMR 3 samples for PFOA, PFOS, and four other PFAS. UCMR 3 monitoring ended in 2016 and the last of the sample results have been reported to EPA.

Those who are now monitoring for PFAS in drinking water are doing so outside the scope of UCMR 3. EPA’s drinking water program does not have any requirements (including a method specification) for the post-UCMR monitoring since PFOA, PFOS, and the other UCMR target analytes are not regulated under the Safe Drinking Water Act.

Method 537 was developed with particular attention to accuracy and precision, has been through multi-lab validation, and was demonstrated during UCMR 3 to be a robust and reliable method. Other methods may be appropriate for the analysis of PFAS in drinking water but they have not been evaluated by EPA’s Office of Water. Those considering alternative methods should consider the degree to which method performance has been evaluated and documented, as well as the degree to which the method capabilities align with project-specific objectives that will be used to assess data quality.

Is EPA Method 537 appropriate for the analysis of PFAS in ground water samples?

Method 537 was developed and validated for the analysis of finished drinking water (i.e., potable water) from both surface water and groundwater sources. The method was successfully used to support analyses of more than 22,000 samples from approximately 2000 public water systems with groundwater sources during UCMR 3. The method is expected to be effective for ground water used as drinking water.

Conditions evaluated during method development include very high total dissolved solids (TDS)/hardness (up to 300 mg/L) and substantially elevated total organic carbon (TOC) [up to 5 mg/L]. The method performed effectively under those conditions and it is possible that performance would be effective under even more challenging conditions. The conditions evaluated do not necessarily represent an upper limit, though it is possible that measurement uncertainty will be greater for the analysis of samples with higher TDS or TOC and/or elevated suspended solids. 

What is “Modified Method 537” and can it be used effectively for analysis of drinking water samples?

EPA is aware of laboratories that are offering analysis for PFAS by techniques described as “Modified Method 537.” These modified methods have been offered for drinking water and other environmental media (e.g., soils, ambient water) and to address PFAS analytes not currently addressed by Method 537. EPA is not aware of a standardized description of the modified methods, nor is the Agency aware of studies that have validated the performance of these modified methods across multiple laboratories. Therefore, EPA cannot address the performance of “Modified Method 537 in a general manner. If you are considering using a modified method 537 to analyze a sample, EPA recommends that you evaluate its appropriateness relative to your goals for the data and data quality objectives.

What method(s) does EPA recommend for the analysis of Gen X in drinking water?

EPA is currently working to develop a new drinking water method to address multiple short-chain PFAS, including GenX. We anticipate that the new method will be completed in early 2019. EPA is also investigating whether GenX can be successfully integrated into Method 537. We anticipate that this investigation will be completed in 2018.

What method(s) does EPA recommend for the analysis of PFAS in source water, wastewater, non-potable groundwater, soils, sediments, and other media?

EPA has formed a cross-Agency method development and validation workgroup to provide sampling guidance and validated methods for sample types other than drinking water. Further details are available at  

Must testing laboratories be certified/accredited by EPA to analyze drinking water samples for PFAS? Are certified/accredited laboratories available?

EPA does not currently regulate PFAS under the Safe Drinking Water Act and therefore does not have any particular requirements for the monitoring that states or public water systems choose to undertake.

States generally certify/accredit laboratories that support drinking water compliance monitoring (i.e., for regulated contaminants). EPA is aware that some states also offer (and others plan to offer) programs for laboratories that wish to be certified/accredited to analyze drinking water samples using Method 537. EPA is also aware that ISO 17025 accreditation bodies (“ILAC signatories”) offer such service for laboratories conducting non-regulatory monitoring (such as PFAS monitoring). Lastly, EPA is aware that the Department of Defense (DOD) manages a PFAS laboratory accreditation program. EPA will continue its efforts to make the certification/accreditation community aware of the ongoing interest in PFAS analyses.

Does EPA have advice for those having difficulty finding a commercial laboratory that will perform PFAS analyses for drinking water samples?

Laboratory capacity has historically grown to meet demand, though there may be temporary challenges with laboratory availability as that capacity develops. EPA encourages interested parties to look broadly for laboratories that measure PFAS in drinking water, considering, for example, the network of laboratories across the country that supported UCMR 3 monitoring (see for the list of those laboratories). Some laboratories may no longer be performing Method 537, may be using a modified version of the method, or may not currently be accepting samples for PFAS analysis. Also, laboratories beyond those approved to support UCMR 3 are now performing PFAS analyses using various techniques. EPA encourages interested parties to be specific with prospective laboratories about the type of PFAS analysis they want performed for drinking water samples.

The American Council of Independent Laboratories has surveyed their membership about PFAS capability/capacity and concluded that significant laboratory capacity is currently available. EPA will continue its efforts to make the laboratory community aware of the ongoing interest in PFAS analyses.

When interpreting drinking water analytical data, what is EPA’s recommendation for handling “non-detect” values for PFAS analytes?

Because PFOA, PFOS, and the other PFAS are not regulated under the Safe Drinking Water Act, EPA looks to states and water systems to decide how to interpret PFAS drinking water monitoring data. However, EPA took the following approach when assessing the UCMR 3 PFOA/PFOS results relative to the 2016 Health Advisories:

  • EPA treated results below the UCMR minimum reporting levels (MRLs) [20 ppt PFOA; 40 ppt PFOS] as “zero”
  • EPA used MRL (not detection limit) as our reference point because we have greater confidence in the analytical accuracy for values at/above the MRL
  • EPA calculated the sum of the PFOA and PFOS results and then rounded to the nearest 10 ppt (e.g., 70 ppt versus 74 ppt; 80 ppt versus 76 ppt).

Does EPA recommend particular minimum reporting levels for drinking water PFAS analyses?

EPA used UCMR 3 MRLs in assessing the results from that program. EPA set the MRLs for UCMR 3 after looking at the performance of multiple laboratories that conducted “lowest concentration” MRL (“LCMRL”) studies to determine how low they could reliably measure, and EPA vetted those MRLs through the notice-and-comment UCMR 3 rulemaking. EPA set the UCMR 3 MRLs such that we would have high confidence that a capable analyst/laboratory could meet those levels. EPA is aware that some laboratories are able to reliably measure PFAS in drinking water at lower levels. States or others who may be leading the collection of PFAS data may wish to establish lower MRLs to meet any project-specific data quality objectives, provided the laboratories can demonstrate acceptable performance at the specified concentrations of interest. Method 537 includes a process for a laboratory to confirm that it is capable of meeting the established MRL (see section 9.2.5 MINIMUM REPORTING LEVEL (MRL) CONFIRMATION).