Skip to main content


On March 14, 2023, the United States Environmental Protection Agency (EPA) issued its proposed PFAS National Primary Drinking Water Regulation (NPDWR) under the Safe Drinking Water Act (SDWA) for six PFAS under the Proposed Rule: perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX), perfluorohexane sulfonic acid (PFHxS), and perfluorobutane sulfonic acid (PFBS) (the Proposed Rule). Although EPA and regulated entities disagree on the compliance costs imposed by the proposed rule, conservate estimates indicate that such costs are likely to exceed $700 million. If these six PFAS are also regulated as hazardous waste, early compliance costs for water providers alone could increase by $30 to $61 million a year.

This Proposed Rule stems from EPA’s March 2021 final regulatory determination to regulate PFOA and PFOS as contaminants under the SDWA, but it goes further than that determination by also regulating PFHxS, GenX, PFNA, and PFBS, as well as mixtures of these PFAS. The Proposed Rule is the first time EPA seeks to establish drinking water regulations for any PFAS. The Proposed Rule will, among other things, require public water systems to monitor for these PFAS, notify the public of the levels of these PFAS in drinking water, and ensure that PFAS levels in drinking water do not exceed the proposed Maximum Containment Levels (MCL):

The Proposed Rule was published in the Federal Register on March 29, 2023, triggering a 60-day comment period that ends on May 30, 2023. EPA is soliciting public comment on the proposed rule as well as the preliminary determinations to regulate PFHxS, GenX, PFNA, and PFBS, as well as mixtures of these PFAS.


As we have previously reported on, PFAS are a group of thousands of chemicals that have been in use by a variety of industries since the 1940s for their ability to resist heat, oil, stains, grease, and water. Also known as “forever chemicals” due to their persistence and mobility in the environment, PFAS exposure may lead to a number of adverse health effects, including cancer and issues with reproduction and human development.

PFOS and PFOA are two of the most commonly studied PFAS, and may be found in numerous consumer goods, construction supplies, emergency equipment, manufacturing processes, water treatment facilities, and landfills.


These four additional PFAS are alternatives for some older PFAS. Like PFOS and PFOA, these newer PFAS are used in a myriad of commercial applications due to their unique properties, including resistance to low and high temperatures, resistance to degradation, and nonstick characteristics. GenX and PFBS were developed to replaced PFOA and PFOS, respectively.

Like PFOS and PFOA, PFHxS, GenX, PFNA, and PFBS may lead to a number of adverse health effects, including cancer, suppressed vaccine response in children, liver complications, and thyroid issues.


Unlike EPA’s proposed rule designating PFOS and PFOA as Hazardous Substances under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) [see our previous article for more details], the Proposed Rule is likely to affect mostly public entities. More specifically, according to EPA, such entities may include the following non-exclusive list:


As noted previously, the Proposed Rule sets MCLs for PFOS and PFOA individually, while setting PFHxS, PFNA, PFBS, and GenX as a PFAS mixture. MCLs are generally set, as required by the SDWA, as close as feasible to the Maximum Contaminant Level Goal (MCLG). According to U.S. Code 42 U.S.C. §300g-1 National Drinking Water Regulations, MCLGs are the non-enforceable levels at which “no known or anticipated adverse effects on the health of persons occur and which allows an adequate margin of safety.” EPA set the MCLG for PFOS and PFOA at 0 ppt, meaning it believes that there is no safe level for these chemicals. For PFHxS, GenX, PFNA, and PFBS, the MCLG is set at 1 HI.

Based on the MCLGs, EPA set the PFOA and PFOS levels, expressed in parts per trillion (ppt, also expressed as ng/L), at 4 ppt. EPA set the limit at 4 ppt because that is the lowest concentration level for PFOS and PFOA that can be reliably quantified with accuracy.

Also based on the MCLGs, EPA set the standard for PFBS, PFNA, PFHxS, and GenX at 1 HI (the same number as the MCLGs). The HI is a tool used to evaluate potential health risks from exposure to chemical mixtures. The HI is calculated by adding the measured concentration of each PFAS divided by its health-based value. EPA developed the health-based values, also called Health Based Water Concentration (HBWC), based on prior toxicity assessments for each chemical. EPA set the HBCW for GenX at 10 ppt; PFBS at 2000 ppt; PFNA at 10 ppt; and PFHxS at 9 ppt. The HI is calculated as follows:


The Proposed Rule, if finalized as written, will require states that have their own PFAS drinking water standards, like Massachusetts, Pennsylvania, and Washington, to lower their standards to ensure compliance with the federal standard. Regulated entities will need 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 MCL. According to EPA, the best treatment options are granular activated carbon (GAC), anion exchange resins (AIX), reverse osmosis (RO), and nanofiltration (NF) systems.

In order to monitor and, if necessary, reduce PFAS levels, public water systems will need to secure funding for technological upgrades and lab testing. EPA has identified the Bipartisan Infrastructure Law as a possible source for the treatment systems necessary to meet its new PFAS standards.

The Proposed Rule may indirectly affect entities that manufacture, process, or use PFAS, as well as waste management and wastewater treatment facilities. For example, the Proposed Rule, (in line with other actions in EPA’s PFAS Strategic Roadmap) is likely to lead federal and state agencies to include monitoring requirements as a condition for acquiring or renewing industrial discharge permits.


Now that EPA has published the Proposed Rule in the Federal Register, EPA will accept public comments until May 30, 2023. After that, the EPA will review the comments, make any necessary revisions, and finalize the rule. Once final, the rule will be codified in the Code of Federal Regulations. According to EPA’s PFAS Strategic Roadmap, we should see a final rule in Fall 2023.

This article is provided for informational purposes only—it does not constitute legal advice and does not create an attorney-client relationship between the firm and the reader. Readers should consult legal counsel before taking action relating to the subject matter of this article.

  Edit this post