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Draft Environmental Protection Agency (EPA) Method 1633: A Data User's Perspective

Elizabeth Denly & Kristen Morin | March 15, 2022

TRC’s Elizabeth Denly and Kristen Morin recently published an article reviewing the United States Environmental Protection Agency (EPA) Method 1633.

EPA Method 1633, currently in draft form, is a developing standardized procedure for accurately measuring PFAS levels in nonpotable water matrices, such as wastewater, surface water, and groundwater. Unlike existing methods EPA 537.1 and EPA 533, which are strictly for drinking water samples, Method 1633 aims to address matrix interferences and provide reliable results for a broader range of environmental samples. This method is considered a critical advancement for the laboratory community in assessing PFAS contamination.


Currently, the availability of multilaboratory-validated analytical methods for per-and polyfluoroalkyl substances (PFAS) is limited. Two of the more commonly known testing methods are the finalized United States EPA methods for the analysis of select PFAS in drinking water samples, EPA 537.1, Determination of Selected Per- and Polyfluorinated Alkyl Substances in Drinking Water by Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS) (EPA 600-R-20-006) and EPA 533, Determination of Per- And Polyfluoroalkyl Substances in Drinking Water by Isotope Dilution Anion Exchange Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry (EPA 815-B-19-020). These two methods were developed specifically for drinking water samples, which generally do not have matrix interferences and are generally an easier matrix to analyze. EPA also finalized SW-846 Method 8327, Per- and Polyfluoroalkyl Substances (PFAS) by Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS), which covers the analysis of select PFAS in nonpotable water matrices.

However, one of the critical deficiencies in this method is the lack of the gold standard for quantitation, isotope dilution, which has become a critical necessity for the analysis of PFAS in nondrinking water matrices, to accommodate for potential matrix interferences. In addition, the United States Department of Defense (DoD) Environmental Data Quality Workgroup (EDQW) has stated that SW-846 Method 8327 should only be used as a screening method and should not be used for the collection of definitive data. The release of Draft EPA Method 1633, Analysis of Per-and Polyfluoroalkyl Substances (PFAS) in Aqueous, Solid, Biosolids, and Tissue Samples by LC-MS/MS (EPA 821-D-21-001), for nonpotable water matrices, is a first step toward providing the laboratory community with a standardized method that can provide accurate results for PFAS in nonpotable water matrices.

Elizabeth Denly

Elizabeth Denly serves as TRC’s Vice President, PFAS Initiative Leader. She is also the Quality Assurance & Chemistry Director, responsible for the creation and implementation of the Quality Management Plan and standard operating procedures (SOPs) for field sampling and documentation protocols. Ms. Denly also leads Quality Coordinator networks, which are responsible for the development and communication of quality initiatives within the organization. She is a chemist with 29 years of consulting experience encompassing field and laboratory analyses and audits, QA/QC, data validation, and consulting for regulatory agencies.

Ms. Denly is a leader in ITRC’s PFAS and TPH Risk Work Groups and in TRC’s Center of Research & Expertise (CORE) Emerging Contaminants Team and received the ITRC’s Industry Member of the Year Award in 2017. She is currently focusing on PFAS, specifically the nomenclature, chemistry, sampling procedures, QA/QC, and laboratory analytical methodologies, and has a significant role in educating clients, attorneys, and regulators about PFAS.

As a senior QA specialist at TRC, Ms. Denly is responsible for providing QA/QC oversight in support of a variety of environmental investigations and remediation programs including risk-based soil cleanups, ambient air monitoring, and human health and ecological risk assessments. In this role, she has directed the preparation of QAPPs, coordination with the laboratory, selection of the appropriate analytical methodologies to achieve the desired remedial standards, oversight and performance of the data validation process, and determination of the usability of the data and achievement of data objectives. Ms. Denly has provided this oversight under different regulatory programs.
Read more on Ms. Denly’s bio page. Please contact her at

Kristen Morin

Kristen is a QA Chemist based in TRC’s Lowell, Massachusetts office. She has over eight years of experience in environmental analytical chemistry and seven years of experience in providing QA/QC oversight related to laboratory analysis, data review, DV, and data usability in support of a variety of environmental investigations under various federal and state regulatory agencies.  In addition, Kristen has experience in laboratory audits and Quality Assurance Project Plans (QAPPs), including preparation of QAPPs in accordance with the Uniform Federal Policy (UFP) for QAPPs.

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