PFAS MCLs Header
EPA Issues Final PFAS MCLs: Get Ready for Compliance

They are finally here, the highly anticipated Maximum Contaminant Levels (MCLs) for six per- and polyfluoroalkyl substances (PFAS) were published in Final Register on April 26, 2024, making the rule effective on June 25, 2024. This major Safe Drinking Water Act (SDWA) development concerns the National Primary Drinking Water Regulation (NPDWR) for perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid (HFPO-DA; and its ammonium salt), perfluorohexane sulfonic acid (PFHxS), and perfluorobutane sulfonic acid (PFBS). The final rule aims to place further controls on PFAS as outlined EPA’s Action Plan and Roadmap, which together aim to better prevent and manage human health and environmental impacts.


Tell Me More About NPDWR

The National Primary Drinking Water Regulations (NPDWR), include legally enforceable MCLs and non-enforceable Maximum Contaminant Level Goals (MCLGs) under the Safe Drinking Water Act (SDWA). 

MCLs set the maximum allowable concentration of a contaminant in public drinking water systems, while MCLGs represent the level at which there is no known or expected risk to human health. MCLGs are generally set to lower, more stringent levels since the MCLs also consider the types and costs of treatment technologies available to public drinking water systems. EPA relies on an independent body of experts called the Science Advisory Board (SAB) to review the scientific basis and implementation feasibility for proposed MCLs and MCLGs through a process involving risk assessment and public comment. The latter included over 120,000 comments received, indicating the importance of this issue to many entities. 

Promulgated MCLs require public drinking water systems to put processes in place to prevent relevant contaminants from occurring in drinking water at levels higher than the MCLs. Systems that fail to comply with MCLs are subject to EPA enforcement actions. 


A Long Road for Final PFAS MCLs

This announcement constitutes an important regulatory milestone of a process that originated two decades ago. In the early 2000s, EPA began reexamining the manufacture and use of certain PFAS and some industries followed suit. In 2009, EPA established non-enforceable health advisories (HAs) for PFOS and PFOA, with subsequent revisions in 2016 and again in 2022. In 2021, EPA reached final determination to regulate PFOA and PFOS under the SDWA, thus paving the way for publishing draft MCLs/MCLGs in March 2023 and final MCLs/MCLGs on April 10, 2024. Details on the new limits and how they changed from the March 2023 draft version can be accessed on EPA’s NDPWR page.


Figure 1: MCL/MCLG Timeline

MCL Timeline


Table 1: EPA PFAS Drinking Water Limits Evolution 2009-2024

Table 1: EPA PFAS Drinking Water Limits Evolution 2009-2024


  • NA – Not available
  • *Interim
  • **Assumes dose additivity of co-occurring PFAS
  • ppt-parts per trillion (or nanograms per liter [ng/L])
  • HI – Cumulative PFAS Hazard Index cannot exceed 1 to ensure compliance


Explaining EPA’s Final PFAS Numbers

As shown in Table 1, in addition to standard MCL values for direct comparison, the MCLs include a Hazard Index (HI) approach to regulate cumulative exposures. The HI approach requires that the detected concentrations of one or more of the co-occurring PFAS (i.e., PFNA, PFHxS, PFBS, and HFPO-DA) are divided by the corresponding toxicity reference values to calculate a Hazard Quotient (HQ) for each analyte; the HI is then calculated as the sum of HQs for each of the four constituents. Should the cumulative HI equal or exceed 1, MCL compliance conditions are violated and corrective actions required.

How PFAS MCLs Impact the Regulated Community? 

Public water systems will be subject to the new MCLs via a staggered schedule:

  1. Monitoring – complete initial monitoring for the six PFAS with MCLs by 2027 and continue regular monitoring/reporting thereafter. 
  2. Public Notification - water systems have to report results and notify the public if any results exceed PFAS MCLs beginning in 2027.
  3. Treatment – if MCLs are exceeded, public water systems will be required to reduce PFAS concentrations to meet MCLs by 2029.

Albeit expensive, PFAS monitoring is relatively commonplace, and approved analytical methods/attested laboratories are available. Furthermore, existing water treatment technologies such as activated carbon, ion exchange, and membrane filtration are generally capable of treating drinking water to the required levels. Please see the updated EPA guidance on PFAS destruction methodologies for more information. However, implementing water treatment technologies and alternate water sources may be challenging, especially for the smaller drinking water systems. EPA estimates that approximately 7,000 public drinking water systems may need to address PFAS levels in excess of the new MCLs. All public water systems have 3 years to complete their initial monitoring for these chemicals. To alleviate resource challenges, EPA states that a billion dollars in funding will be available to help public water systems and private well owners to comply with the new MCLs. Moreover, exemptions for up to 9 years from MCL implementation may be available for small water systems.  


Speaking of Analytical Methods, What Method is EPA Specifying for MCLs?

The MCLs are to be analyzed via EPA 537.1 Version 2.0, which measures 18 PFAS compounds and/or EPA 533, which measures 25 PFAS compounds. These methods are also specified by the EPA under the ongoing Fifth Unregulated Contaminant Monitoring Rule (UCMR5) program. UCMR5 monitoring is being conducted from 2023 through 2025, involves sampling from all mid- and large-scale water treatment systems across the U.S, and includes the six PFAS with MCLs.  


Figure 2: Key Implications of the Draft MCLs/MCLGs

PFAS MCL Implication


What’s Next?

The rule is set to become effective on June 10, 2024; background information is filed under Docket ID: EPA-HQ-OW-2022-0114.


Curious About How the Latest PFAS News Impacts You? We Can Help.

We will continue to monitor this important development and keep you updated throughout. Please be on the lookout for additional articles on this topic. Meanwhile, if you have PFAS-related questions, concerns, or challenges, drop your information into our contact form and we’ll schedule time to discuss how you can prepare for and manage PFAS-related regulations. 

Contact Us

Andrew Pawlisz Headshot
Andrew Pawlisz, D.A.B.T.
Regulatory Toxicologist, Owasso, Oklahoma

Andrew is a board-certified toxicologist with over 21 years of experience in risk assessment and evaluation; hazard assessment; and regulatory compliance, including the legacy and reformed Toxic Substances Control Act (TSCA). Andrew specializes in finding practical solutions to regulatory and human health/environmental issues related to toxicants.

Did you find this information useful? Click the icons below to share on your social channels.

facebook twitter linkedin
Other News


Receive the latest technical and regulatory updates in your inbox.