Understanding Final MCL’s for PFAS and How to Navigate

The Environmental Protection Agency (EPA) sets Maximum Contaminant Levels (MCLs) for drinking water quality. These MCLs are legally enforceable standards that limit the levels of contaminants in public water systems under the Safe Drinking Water Act (SDWA).

Let’s take a closer look at some of these MCLs for PFAS.

On April 10, 2024, the EPA established maximum contaminant levels (MCLs)
for per- and polyfluoroalkyl substances (PFAS) in drinking water.
The final MCLs are as follows:

PFOA 0 4 ppt
PFOS 0 4 ppt
PFNA 10 ppt 10 ppt
PFHxS 10 ppt 10 ppt
HFPO-DA (Gen X) 10 ppt 10 ppt
Two or more PFHxS, PFNA,
HFPO-DA & PFBS 1.0 Unitless Hazard Index (HI) 1.0 Unitless Hazard Index (HI)
* Federal enforcable level

Understanding the Hazard Index Maximum Contaminant Level

Decades of research show mixtures of different chemicals can have additive health effects, even if the individual chemicals are each present at lower levels. This means that low levels of multiple PFAS that individually would not likely result in adverse health effects may pose health concerns when combined in a mixture. The Hazard Index is a long-established approach that EPA regularly uses, for example in the Superfund program, to determine the health concerns associated with exposure to chemical mixtures. EPA’s Hazard Index Maximum Contaminant Level (MCL) is set at 1 and applies to any mixture containing two or more of PFNA, PFHxS, PFBS, and HFPO-DA (known as “GenX chemicals). These PFAS can often be found together in different mixtures and research shows that exposure to mixtures of these chemicals may have additive health impacts.

How do I calculate the Hazard Index?

The Hazard Index is made up of a sum of fractions. Each fraction compares the level of each PFAS measured in the water to the highest level below which there is no risk of health effects. EPA is currently developing an online calculator to assist water systems in determining their Hazard Index result. 
The online calculator will perform the calculation explained here.



MYCELX® P-Fluormer-N blended media (a.k.a GAC 2.0) is a PATENT PENDING cutting-edge solution designed to remove per- and polyfluoroalkyl substances (PFAS) from water streams more efficiently than traditional granular activated carbon (GAC) media. ANSI/NSF-61 certified and produced in the U.S., P-Fluormer-N media continues MYCELX®’s reputation for providing superior solutions for water purification. Benefits over conventional GAC include:

Lower EBCT

Smaller Footprint

Increased Bed Volumes

No Backwash

Lower Headloss

Safe, Sustainable Disposal (non-hazardous)

Ability to remove PFOA, PFOS, PFBS, PFNA, PFHxS and HFPO-DA (GenX) to non-detect levels

MYCELX® P-Fluormer-N blended media is typically deployed in a series of adsorber vessels, (lead-lag configuration) to maximize PFAS treatment efficiency.

Standard system designs are available treating flows as low as 10gpm up to 2,100gpm.

Download the P-Fluormer-N Media Data Sheet


Find out how our revolutionary approach to water

and air filtration can help your system.

Contact Us