In September 2021, the U.S. Environmental Protection Agency (EPA), in collaboration with the U.S. Department of Defense (DoD), published a draft of Method 1633, the first EPA-validated laboratory analytical method to test for per- and polyfluoroalkyl substances (PFAS) in eight different environmental media. PFAS are a group of so-called forever chemicals used in firefighting foam, nonstick pans, food packaging, and other products whose effects on human health and the environment are under increasing scrutiny. Method 1633 can be used for National Pollutant Discharge Elimination System (NPDES) permits and other applications. In this interview, Robert Wood, the director of the Engineering and Analysis Division of the Office of Science and Technology in the EPA’s Office of Water, helps clarify how Method 1633 was developed, its uses, and the next steps for PFAS testing. 


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Municipal Water Leader: Please introduce the EPA’s role in validating laboratory analytical methods for water contaminants. 

Robert Wood: Clean Water Act (CWA) methods are validated and approved for nationwide use through rulemaking, primarily in support of National Pollution and Discharge Elimination System (NPDES) permits that regulate and monitor point source discharges to Waters of the United States. Dischargers are required by the Code of Federal Regulations (CFR) to use these approved methods when their permit requires analyses of pollutants for which there are approved methods that can measure to the level the permit requires. When there is not an approved method for a contaminant, as is currently the case for PFAS, it is up to the permitting authority to specify the analytical method that will be used to measure that pollutant parameter. 

CWA methods are also often used in surface water, biosolids, and other CWA applications. Other EPA method programs exist to support the Safe Drinking Water Act, the Clean Air Act, and the Resource Conservation and Recovery Act. Some EPA regions and the Office of Research and Development may use other methods for specific projects or sites. Those other EPA method programs have different requirements for validating methods but contain many of the same steps. 

Municipal Water Leader: Please tell us about the importance of testing for PFAS. What sort of requirements for PFAS testing currently exist? 

Robert Wood: Without PFAS testing methods, it is impossible to determine the presence and extent of environmental contamination of PFAS or to gauge their potential effects on human health and the environment. EPA analytical methods provide consistency to stakeholders, including industry, allowing for comparability of laboratory data from multiple sources. 

Currently, there are no PFAS methods from any source that have been approved by the EPA for nationwide CWA applications, so NPDES permitting authorities must determine what methods are most appropriate. Different states have taken different approaches to filling that methods gap. The EPA’s Office of Water recommends Method 1633 for CWA applications, since it has undergone single-laboratory validation in a wide variety of environmental matrices and will likely be proposed for approval through a public comment and rulemaking process in the future. 

Municipal Water Leader: How was Method 1633 developed? 

Robert Wood: Method 1633 is still a draft method, so it is more appropriate to ask, “How is Method 1633 being developed?” 

The entire method development process contains the following steps: 

  1. The identification of a promising technique or procedure based on internal (EPA) or external development efforts (e.g., literature review, lab standard operating procedures, or voluntary consensus standard body procedures). 
  2. Formal study planning documentation. 
  3. Single-laboratory validation, targeting a variety of different water and wastewater matrices. 
  4. The refinement of any issues identified in the single-laboratory validation study. 
  5. The drafting of an actual method in EPA format. 
  6. Multilaboratory validation testing of a variety of wastewater matrices at several laboratories. 
  7. The development of quality control acceptance criteria that reflect the real-world performance of the method in the multilaboratory validation study. 
  8. The publication of a final method. 
  9. The inclusion of the method and all the supporting documentation in a rulemaking docket, typically for proposal at 40 CFR part 136. 
  10. Following the proposal, the EPA reviews and responds to all public comments received and makes any needed revisions to the method based on the comments. 
  11. The method gains approval through a final rule that promulgates the method for nationwide use in CWA NPDES compliance monitoring. 

Method 1633 is currently undergoing the sixth step above. The EPA is collaborating with the DoD to carry out the multilaboratory validation of the method. 

No method is formally adopted for nationwide use in NPDES until step 11 of the rulemaking process is complete, but methods that have not yet been promulgated may still be useful to the EPA and other organizations. And importantly, permitting authorities can specify draft methods in permits if no approved method exists for that contaminant.

Municipal Water Leader: How frequently does the EPA cooperate with the DoD and other federal agencies in developing testing methods and other scientific advances? 

Robert Wood: This is the first laboratory method collaboration between the DoD and the EPA’s CWA methods program. The CWA methods program has approved multiple methods from the U.S. Geological Survey and hundreds of methods from voluntary consensus standard bodies, such as ASTM International and Standard Methods. Additionally, many private vendors and other organizations have had their methods approved through the EPA’s alternate testing program (ATP). There must already be an approved method in order for the ATP route to be taken. Since there currently is no approved method for PFAS analytes, this is not an option for PFAS. 

Because of the multiple federal and state players involved in PFAS investigation and remediation activities, DoD’s Strategic Environmental Research and Development Program sought a unified approach and approached the EPA’s Office of Water in 2019 to start a collaborative effort to develop, validate, and give formal EPA approval to a PFAS method that would be useful for the DoD and various EPA programs. 

The DoD and the EPA are working collaboratively to complete the full, multilaboratory validation of EPA Method 1633 for 40 specific PFAS analytes. The DoD is funding and managing the method validation study. The method is being validated in eight matrix types: wastewater, surface water, groundwater, leachate, soil, sediment, biosolids, and tissue. The EPA’s goal is to produce sufficient data to validate a CWA method and a solid waste (SW-846) method. 

Municipal Water Leader: Would you please describe Method 1633, particularly how it differs from other methods of PFAS testing? 

Robert Wood: Virtually all PFAS procedures for specific compounds employ high-pressure liquid chromatography (HPLC) to separate the target analytes and tandem mass spectrometry (MS/MS) to detect and quantify them. Method 1633 uses HPLC and MS/MS and is most similar to EPA Drinking Water Method 533. The primary difference is that the procedure is designed to accommodate the challenges of analyzing samples that contain high levels of organic, mineral, and solid materials, unlike drinking water. When the method is finalized, it will contain required quality control criteria that will be statistically generated from data obtained from numerous laboratories that have tested a wide variety of wastewaters. This will provide consistency to the laboratory analysis community, something regularly requested by many states and other laboratory organizations. 

Purchasers of laboratory services for CWA applications currently use a variety of other methods. Method 1633 is unique in having been tested in a wide variety of matrices (wastewater, surface water, groundwater, soil, biosolids, sediment, landfill leachate, and fish tissue). 

Municipal Water Leader: How does the validation of this method change the status quo? 

Robert Wood: The status quo has changed because now there is a single-lab-validated method for PFAS compounds in wastewater that the EPA is recommending for use in the NPDES program. The method is, of course, useful in the other matrices listed above as well, including biosolids, fish tissue, and soil. As stated on the EPA’s website, “The method will support NPDES implementation by providing a consistent PFAS method that has been tested in a wide variety of wastewaters and contains all the required quality control procedures for a CWA. While the method is not nationally required for CWA compliance monitoring until the EPA has promulgated it through rulemaking, it is recommended now for use in individual permits.” The DoD may also use this method at some of its sites. 

Municipal Water Leader: What are the next steps for research into PFAS detection and monitoring? 

Robert Wood: Aside from the completion of the method validation for Draft Method 1633 and its proposal and promulgation through rulemaking, the CWA methods program anticipates two other PFAS method efforts in 2022. First, the EPA’s Office of Water is pursuing a validation on adsorbable organic fluorine by combustion ion chromatography. Organic fluorine is very rare in nature, so this will be a good screening method for synthetic organic fluorine compounds, such as PFAS, fluorine-based pesticides, and some pharmaceuticals. The Office of Water thinks that this tool is needed for PFAS monitoring because it is logistically impossible to make a method that can identify the thousands of PFAS chemicals that have been manufactured and their degradation products. Second, the CWA Method Program is also in discussions with VCSBs about validating other PFAS methods. Other EPA offices are pursuing a wide variety of methods. 

The CWA Methods Program requires that analytical methods have well-documented performance data from multiple laboratories, testing a wide variety of wastewater types, before methods are considered for approval through rulemaking. Given all the method validation and approval steps, this is a multiyear process. 

Robert Wood is the director of the Engineering and Analysis Division of the Office of Science and Technology in the U.S. Environmental Protection Agency’s Office of Water. For more on the EPA, visit For more on PFAS methods, see the EPA’s frequent questions about PFAS methods for NPDES permits webpage at