On March 14, 2023, the United States Environmental Protection Agency (EPA) announced the proposed National Primary Drinking Water Regulation (NPDWR) for six PFAS.  The public comment period will be open for sixty (60) days following publication in the Federal Register.  EPA anticipates finalizing the regulation by the end of 2023.

If finalized, the NPDWR will establish “Maximum Contaminant Level Goals” (MCLGs) and legally enforceable “Maximum Contaminant Levels” for the following PFAS compounds:

CompoundProposed MCLGProposed MCL
Perfluorooctanoic acid (PFOA)04.0 ng/L (ppt)
Perfluorooctane sulfonic acid (PFOS)04.0 ng/L
Perfluorononanoic acid (PFNA)
Hexafluoropropylene oxide dimer acid (HFPO-DA)
Perfluorohexane sulfonic acid (PFHxS)
Perfluorobutane sulfonic acid (PFBS)

1.0 (unitless)
Hazard Index

1.0 (unitless)
Hazard Index

Per EPA, a Hazard Index (HI) is a risk management approach for mixtures of chemicals.  For this approach, a “hazard quotient” (HQ) is calculated for each of the four PFAS by dividing the measured level of each PFAS in drinking water by a proposed “health reference value” for that particular PFAS.  In this instance, EPA’s “health reference values” are “Health Based Water Concentrations” (HBWCs), which EPA proposes to define under 40 CFR § 141.2 as “levels protective of health effects over a lifetime of exposure, including sensitive populations and stages.”  

As detailed in EPA’s Pre-Publication Notice, those “health reference values” are:

CompoundHealth Reference Value
PFHxS9.0 parts per trillion (ppt)
HFPO-DA10.0 ppt
PFNA10.0 ppt
PFBS2000 ppt

The individual PFAS HQs are then added together to yield an aggregate HI.  If the result of the sum exceeds 1.0, then the proposed MCL of 1.0 HI for those compounds will be exceeded.     

More information on EPA’s proposed regulations can be found at the following links:

  1. EPA rule proposal announcement
  2. Pre-Publication Federal Register Notice
  3. EPA Fact Sheet: Proposal to Limit PFAS in Drinking Water
  4. EPA FAQs: Proposed PFAS National Primary Drinking Water Regulation
  5. EPA Fact Sheet: Understanding the PFAS National Primary Drinking Water Hazard Index