EPA Proposes PFAS MCLs and PFAS Hazard Index MCL

March 14, 2023. The Environmental Protection Agency (EPA) has released a pre-publication Federal Register notice of the proposed Maximum Contaminant Levels (MCLs) for PFOA and PFOS. The proposed MCLs are 4 parts per trillion (ppt) for each compound. A copy of the pre-publication version of the Federal Register notice is here (Pre-Publication Federal Register Notice_PFAS NPDWR_NPRM_Final_3.13.23 ). A copy of an EPA Fact Sheet is here ( Fact Sheet_PFAS_NPWDR_Final_3.14.23) Once the proposed MCLs are published in the Federal Register there will be a 60-day public comment period. EPA is also proposing a “Hazard Index” for four PFAS (described below).

EPA will hold two webinars on the proposal on March 16, 2023 (2:00 to 3:00 pm, ET), and March 29, 2023 (2:00 to 3:00 pm, ET). EPA describes the March 16th webinar as a general overview of the proposal and the March 29th webinar as a technical overview of the proposal.

EPA will hold a public hearing on May 4, 2023 (11:00 am to 7:00 pm, ET).

Registration for March 16th webinar:

Registration for March 29th webinar:

Registration for May 4th public hearing:

Link to EPA Press Release

EPA Proposing Hazard Index for Four Other PFAS
In the enclosed pre-publication version, EPA is also proposing “….to use a Hazard Index (HI) approach to protecting public health from mixtures of PFHxS, HFPO-DA and its ammonium salt, PFNA, and PFBS because of their known and additive toxic effects and occurrence and likely co-occurrence in drinking water.”

Proposed Definition of Hazard Index
“Hazard index (HI) is the sum of component hazard quotients (HQs), which are calculated by dividing the measured regulated PFAS component contaminant concentration in water (e.g., expressed as ppt) by the associated Health-Based Water Concentration (e.g., HBWC expressed as ppt). For PFAS, a mixture HI greater than 1.0 is an exceedance of the MCL.” [emphasis added]

How To Calculate the Hazard Index
Steps to calculate the HI: “….a ratio called a hazard quotient (HQ) is calculated for each of the four PFAS (PFHxS, HFPO-DA and its ammonium salt (also known as GenX chemicals), PFNA, and PFBS) by dividing….the measured level of each of the four PFAS in drinking water, by a health reference value for that particular PFAS. For health reference values, in this proposal, EPA is using Health Based Water Concentration (HBWCs) as follows: 9.0 ppt for PFHxS, 10.0 ppt for HFPO-DA; 10.0 ppt for PFNA; and 2000 ppt for PFBS. The individual PFAS ratios (HQs) are then summed….to yield the HI. If the resulting HI is greater than one (1.0), then the exposure metric is greater than the health metric and potential risk is indicated.”