WOTUS and PM NAAQS and PFAS, Oh My! Environmental Highlights in First Quarter 2023

Instead of the Land of Oz, we are in the land of acronyms. WOTUS, PM, NAAQS, PFAS —and more—are common acronyms used in environmental law. And during the first quarter of 2023, the United States Environmental Protection Agency (USEPA) adopted, revised, reconsidered, or proposed changes to the statutes, regulations, or standards connected to each of these.

But before starting down the path to highlight these changes, here’s a quick “translation” guide to help you navigate the acronyms you’ll encounter on your journey:

  • CAA – Clean Air Act
  • CWA – Clean Water Act
  • USEPA – United States Environmental Protection Agency
  • NAAQS – National Ambient Air Quality Standards
  • NPDWR - National Primary Drinking Water Regulation
  • PFAS – per- and polyfluorinated substances, including
    • HFPO-DA - hexafluoropropylene oxide dimer acid (commonly known as GenX chemicals)
    • PFBS - perfluorobutane sulfonic acid
    • PFHxS - perfluorohexane sulfonic acid
    • PFNA - perfluorononanoic acid
    • PFOA - perfluorooctanoic acid
    • PFOS - perfluorooctane sulfonic acid
  • PM5 – particulate matter less than 2.5 microns
  • WOTUS – Waters of the United States

The Takeaway

  1. The proposed NAAQS for PM setting a lower and more stringent standard, if adopted, will mean that several areas in Illinois will be designated as nonattainment.
  2. The proposed NPDWR for PFAS will affect public drinking water industries by requiring more reduction, testing, and notice of PFAS.
  3. The definition of WOTUS reverting back to the pre-2020 WOTUS rule would have provided more assurance in the usage of the term in future instances (though the long-awaited WOTUS decision in Sackett II was issued in the second quarter of 2023).

Revised Definition of “Waters of the United States”

In January 2023, USEPA published a final rule revising the definition of what waters are included in the term WOTUS. The rule became effective March 20, 2023.


In 1972, Congress enacted the Clean Water Act (CWA) “to restore and maintain the chemical, physical, and biological integrity of the Nation’s waters.” 33 U.S.C. 1251(a). Central to the framework and protections provided by the CWA is the term “navigable waters,” which is defined in the Act as “the waters of the United States, including the territorial seas.” 33 U.S.C. 1262(7).

Under the CWA, USEPA and, in certain instances, the Army Corps of Engineers, must define the precise geographic scope of which waters are included in the regulations. United States v. Riverside Bayview Homes, 474 U.S. 121, 134 (1985). In developing this latest revised definition, the agencies considered a number of sources, including the text of the relevant provisions of the CWA, the statute as a whole, the scientific record, relevant Supreme Court case law, and the agencies’ experience and technical expertise developed over more than 45 years of implementing the longstanding pre-2015 regulations that defined WOTUS.

It should be noted that in 2020, the Navigable Waters Protection Rule (2020 NWPR) substantially departed from prior rules in relation to WOTUS. Then through an executive order in 2021, President Biden directed all executive departments and agencies to review and address Federal actions taken that conflict with national policies of science-based decision making.

Revised Definition

The revised rule, consistent with the general framework of the pre-2020 NWPR, interprets “Waters of the United States” to include:

  • traditional navigable waters, the territorial seas, and interstate waters (“paragraph (a)(1) waters”);
  • impoundments of waters of the United States (Water impoundments refer to the process of raising the water level of a body of water above its natural level using a dam or other structure) (“paragraph (a)(2) impoundments”)
  • tributaries to traditional navigable waters, the territorial seas, interstate waters, or paragraph (a)(2) impoundments when the tributaries meet either the relatively permanent standard or the significant nexus standard (“jurisdictional tributaries”)
  • wetlands adjacent to paragraph (a)(1) waters, wetlands adjacent to and with a continuous surface connection to relatively permanent paragraph (a)(2) impoundments, wetlands adjacent to tributaries that meet the relatively permanent standard, and wetlands adjacent to paragraph (a)(2) impoundments or jurisdictional tributaries when the wetlands meet the significant nexus standard (“jurisdictional adjacent wetlands”)
  • intrastate lakes and ponds, streams, or wetlands not identified in paragraphs (a)(1) through (4) that meet either the relatively permanent standard or the significant nexus standard (“paragraph (a)(5) waters”).

Further, the rule provides clarification on the “relatively permanent standard” and the “significant nexus standard,” defines “significantly affect” in relation to significant nexus standard, and clarifies the determination of “adjacent wetlands.” The rule also codifies several exclusions from the definition of “Waters of the United States.”

Proposed Reconsideration of PM2.5 NAAQS

In January 2023, USEPA proposed reconsideration of the air quality criteria and the NAAQS for PM2.5.


The CAA governs the establishment and revisions of the NAAQS. The CAA directs the Administrator of the USEPA to list certain air pollutants that have emissions that “cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare.” The Administrator is also directed to issue air quality criteria on relevant air pollutants. In addition, the Administrator shall define primary and secondary NAAQS for pollutants for which air quality criteria are issued. 42 U.S.C. 7409(a). Primary standards are ones that the Administrator deems are needed to protect the public’s health. Secondary standards are ones the Administrator believes are needed to protect the public’s welfare and must include specific, measurable air quality levels. In implementing these standards, USEPA may not consider costs, attainability, nor technological feasibility. See generally Whitman v. American Trucking Associations, 531 U.S. 457, 465-472, 475-76 (2001); American Petroleum Institute v. Castle, 665 F.2d 1176, 1185 (D.C. Cir. 1981).

The CAA requires that every five years, existing air quality criteria be reviewed. That review should reflect advances in scientific knowledge on the effects of pollutants on the public’s health and welfare. When the last review of the PM NAAQS was completed in December 2020, no revisions were made to either the primary or secondary standards. However, in June 2021, the Agency decided to reconsider the 2020 PM NAAQS because the available scientific evidence and technical information indicated current standards might not adequately protect the public health and welfare as required by the CAA.

Revised Criteria

Upon USEPA’s reconsideration of the air quality criteria and the NAAQS for PM, the USEPA proposed to revise the PM2.5 standards as indicated in the following table:


Current Standard

Proposed Standard

Alternative Proposed Standard

Primary Annual PM2.5

12.0 µg/m3

9.0 to 10.0 µg/m3

As low as 8.0 µg/m3 and up to 11.0 µg/m3

Primary 24-hour PM2.5

35 µg/m3

Retain current standard

25 µg/m3

Primary 24-hour PM10

Retain current standard

Retain current standard

Retain current standard

Secondary Annual PM2.5

Retain current standard

Retain current standard

Retain current standard

Secondary 24-hour PM2.5

Retain current standard

Retain current standard

25 µg/m3

Secondary 24-hour PM10

Retain current standard

Retain current standard

Retain current standard

USEPA also proposed revisions to other key aspects related to the PM NAAQS, including revisions to the Air Quality Index (AQI) and monitoring requirements for the PM NAAQS. The deadline to submit public comment on the proposed rule was March 28, 2023.

Proposed PFAS National Primary Drinking Water Regulation

In mid-March, USEPA proposed establishing a NPDWR—which USEPA aims to finalize by the end of 2023— to establish legally enforceable Maximum Contaminant Levels (MCLs) for six PFAS in drinking water: PFOA, PFOS, PFNA, HFPO-DA (GenX), PFHxS, and PFBS. The proposal is being made under the authority of the Safe Drinking Water Act. The proposed MCLs address PFOA and PFOS as individual contaminants, but address PFHxS, PFNA, PFBS, and HFPO-DA as a PFAS mixture. USEPA is also proposing health-based, non-enforceable Maximum Contaminant Level Goals (MCLGs) for these six PFAS. The proposed rule would require public water systems to monitor for these PFAS, notify the public of the levels of these PFAS, and reduce the levels of these PFAS in drinking water if they exceed the proposed standards.

The table below summarizes the proposed values:


Proposed MCLG

Proposed MCL (enforceable levels)



4.0 parts per trillion (also expressed as ng/L)



4.0 parts per trillion


1.0 (unitless) Hazard Index

1.0 (unitless) Hazard Index



HFPO-DA (commonly referred to as GenX Chemicals)


In the First Quarter of 2023, the environmental law community, or the land of the acronyms, saw a revision of the definition of WOTUS, reconsideration of the NAAQS for PM, and a proposed PFAS NPDWR. We suggest you return for environmental law updates for the Second Quarter of 2023; they are just a “yellow brick road” away.

To stay up to date on how these and other highly complex environmental regulations affect your business, please contact our Environmental Law team.

  • Andrea M. Quade

    Andrea M. Quade specializes in environmental law practice. She assists clients with a variety of environmental issues, including:

    • counseling them on environmental compliance issues involving both federal and state statutes and ...
  • Melissa S. Brown

    Melissa S. Brown focuses her practice on environmental law, assisting clients on a wide variety of environmental issues. Her clients regularly benefit from her ability to:

    • counsel them on environmental compliance issues ...

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