USEPA Finalizes National Primary Drinking Water Regulation for Six PFAS

April 15, 2024

On April 10, 2024, the United States Environmental Protection Agency (USEPA) finalized a National Primary Drinking Water Regulation (NPDWR), establishing legally enforceable maximum contaminant levels (MCLs) for six (6) per- and polyfluoroalkyl substances (PFAS) in drinking water. Five PFAS (perfluorooctanoic acid [PFOA], perfluorooctyl sulfonate [PFOS], perfluorohexanesulfonic acid [PFHxS], perfluorononanoic acid [PFNA], and hexafluoropropylene oxide dimer acid [HFPO-DA, or “GenX”]) have individual MCLs.

Additionally, the USEPA finalized an enforceable Hazard Index (HI) MCL of 1.0 when mixtures containing at least two (2) or more of the following four (4) PFAS:  PFHxS, PFNA, GenX and perfluorobutanesulfonic acid (PFBS) are present. The HI, which is unitless, is a sum of fractions. Each fraction is comprised of the level of each individual PFAS (PFHxS, PFNA, GenX, and/or PFBS) detected in drinking water divided by the health-based water concentration (HBWC), the level below which no health effects are known or expected for an individual PFAS. If the sum of all fractions is above 1.0, it is a violation of the new regulation.

PFAS ENFORCEABLE MCL (in parts per trillion, ppt)
PFHxS 10
GenX 10
(mixture of two or more)
HI= 1.0 (unitless)


Initial Monitoring (April 2024 to April 2027)

  • The USEPA requires community water systems and non-transient, non-community water systems to complete initial monitoring by April 2027 (three years following the date of the final rule promulgation).
    • Monitoring must be conducted at all entry points to the distribution system.
    • Surface water systems and groundwater systems serving populations greater than 10,000 must monitor quarterly within a 12-month period, and samples are required to be collected two to four months apart.
    • Groundwater systems serving populations of 10,000 or less must monitor twice within a 12-month period, with samples collected five to seven months apart.
    • Previously collected monitoring data may be used if sampling was conducted using EPA Methods 533 or 537.1, as part of the Fifth Unregulated Contaminant Monitoring Rule (UCMR 5) or other state-level monitoring programs.

Ongoing Compliance Monitoring (to begin in April 2027)

  • In April 2027, community water systems and non-transient, non-community water systems are required to begin quarterly compliance monitoring at all entry points and must issue public notification for any monitoring and testing procedure violations.
    • Monitoring may be reduced to annual sampling for systems with four consecutive quarterly sampling results below MCLs.
    • If the system can demonstrate three consecutive annual samples below the rule trigger levels (set at one-half of the MCLs for regulated PFAS and one-half of the HI MCL) for all regulated PFAS, monitoring may be reduced to once every three years.
  • Compliance monitoring may be reduced to once every three years if initial monitoring results are below rule trigger levels.
    • If a system monitors triennially and receives sampling results at or above the rule trigger level, the system will need to revert to quarterly monitoring.
  • Starting in April 2027, community water systems must include their monitoring results for regulated PFAS in their Consumer Confidence Reports (CCRs).

Community water systems and non-transient, non-community water systems with detections above MCLs must implement solutions to reduce PFAS and must comply with all regulated PFAS MCLs by April 2029. Additionally, public notification for MCL exceedances is required.