EPA Pre-Publication Federal Register with Final PFAS MCLs

On April 10, 2024, EPA released a pre-publication version of the Federal Register with final Maximum Contaminant Levels (MCLs) for PFAS.  Once published in the Federal Register, the rule will be in effect within 60 days.

Link to website with pre-publication version of the Federal Register and supporting documents and Fact Sheets.


Here are some highlights from the pre-publication version of the Federal Register with the final PFAS MCLs:

  1. MCLs for PFOA and PFOS are set at 4.0 ng/L.  These are the same as proposed in March 2023.
  2. The Hazard Index (HI) MCL is 1.0 and is calculated using results for the following four PFAS: PFBS, PFHxS, PFNA, and HFPO-DA.  This is the same as proposed in March 2023, however, EPA has included a requirement that compliance with the HI must be based on at least two of the four PFAS being detected.
  3. EPA has set MCLs at 10 ng/L for three of the four PFAS included in the HI calculation (PFHxS, PFNA and HFPO-DA).  These are new MCLs, not included in the March 2023 proposal.
  4. EPA is not setting an MCL for PFBS.
  5. The final rule makes a distinction between the “initial monitoring period” and the “compliance monitoring period.”
  6. The initial monitoring must be completed within 3 years of publication of the rule in the Federal Register (i.e., 2027).
  7. Initial monitoring is four quarterly samples for all surface water systems and for groundwater systems serving a population over 10,000.  Initial monitoring for groundwater systems serving less than 10,000 is two samples, collected five to seven months apart.  Samples are collected at point of entry to the distribution system.
  8. Results collected after January 1, 2019, can be used to meet the initial monitoring requirements.
  9. Monitoring and reporting violations can be assessed three years after publication in the Federal Register.
  10. Compliance monitoring begins three years after publication in the Federal Register.
  11. Compliance is based on a running annual average of quarterly samples.
  12. MCL violations requiring public notification will not be assessed until five years after publication in the Federal Register (i.e. 2029). EPA has extended the deadline by two years to comply with the MCLs, In the March 2023 proposal, water systems needed to be in compliance with the MCLs three years after publication in the Federal Register. In the Federal Register preamble, EPA encourages State primacy agencies to require public notification, if appropriate, if a water system exceeds an MCL prior to the 2029 compliance deadline.
  13. EPA has increased the “trigger levels” to one-half of the MCLs.  In the March 2023 proposal, the trigger levels were set at one-third of the MCLs.  If a system is on reduced monitoring, exceeding a trigger level will require increase frequency of sample collection to quarterly.


EPA will hold three one-hour briefings on the final rule.  EPA’s description of each webinar, dates, times, and links to register are presented below.


  1. General Public Overview.  April 16, 2024, 2:00 to 3:00 pm (EDT)


  1. Water Sector Professional Technical Over.  April 30, 2024, 2:00 to 3:00 pm (EDT)


  1. Small systems Webinar, 2:00 to 3:00 pm (EDT)