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USEPA Announced Today That It Will Propose PFAS Drinking Water Limits with a 4 Parts Per Trillion Maximum for PFOS and PFOA

By Brooke Zentmeyer

Kristin Watt contributed to this post.

On Tuesday, March 14, 2023, USEPA announced that it will propose a PFAS National Primary Drinking Water Regulation that would set legally enforceable limits for six PFAS in drinking water, including 4 parts per trillion (ppt) limits for PFOS and PFOA.  If finalized, Public Water Systems (“PWSs”) will have three years to comply with the limits in the proposed rule.

The proposed rule, if finalized, would establish:

  1. Maximum Contaminant Levels (“MCLs”) and Maximum Contaminant Goal Levels (“MCGLs”) for PFOS and PFOA;
  2. A Hazard Index for PFHxS, GenX Chemicals, PFNA, and PFBS;
  3. Monitoring requirements for PWSs; and
  4. Reporting requirements for PWSs that are community water systems.

MCLs and MCGLs for PFOS and PFOA

MCGLs are non-enforceable and health-based.  MCLs, on the other hand, are legally enforceable drinking water limits that take into consideration a PWS’s ability to measure, treat, and remove a contaminant as well as the associated costs.  

The proposed MCGLs for PFOS and PFOA are zero.  The MCLs for PFOS and PFOA are 4 ppt. This is significant because 4 ppt is the lowest concentration at which a laboratory can reliably measure PFOA and PFOS, indicating that USEPA has determined that there is no “safe” level for either chemical in drinking water.  

If a PWS detects an MCL violation, the proposed rule would require the PWS to provide public notification within 30 days, and take action to bring the PWS into compliance, such as installing treatment systems to remove PFAS. However, a one-time exceedance will not necessarily result in an MCL violation under the proposed rule—compliance would be calculated using a running annual average approach. For example, if a PWS has a quarterly monitoring obligation, and the PWS had a sample result of PFOA at 5.0 ppt and the remaining quarter sample results were all 2.0 ppt each, the PWS would not in be violation as the quarterly average would be less than 4 ppt.

Hazard Index for PFHxS, GenX Chemicals, PFNA, and PFBS

USEPA is proposing a Hazard Index for PFHxS, GenX Chemicals, PFNA, and PFBS to account for the increased risk posed by mixtures of PFAS in drinking water. The proposed rule also sets an enforceable Hazard Index MCL, and a non-enforceable Hazard Index MCGL. 

The proposed rule would require PWSs to monitor for all four PFAS and input the sampling results into a USEPA-provided calculation. The Hazard Index MCL is 1.0 (unitless), so the PFAS mixture would exceed the proposed rule’s Hazard Index MCL if the result of the Hazard Index calculation exceeds 1.0. The Hazard Index MCGL is also 1.0 (unitless).  

Although the Hazard Index is intended to account for PFAS mixtures, the Index would apply to any combination of the four PFAS and could be exceeded even when just one of the four PFAS is present. Like the PFOS and PFOA MCLs, however, compliance with the Hazard Index MCL would be calculated using a running annual average approach under the proposed rule.

PWS Monitoring Requirements

Initial Monitoring
The proposed rule would require all PWSs to conduct initial monitoring within three years after the rule is finalized. Monitoring frequency would be either biannually or quarterly based on the size of the PWS.

PWSs that have previously collected monitoring date using approved EPA Methods 533 or 537.1 would be able to satisfy the initial monitoring requirements with this previous data. 

Compliance Monitoring 
The proposed rule would also require all PWSs to conduct quarterly compliance monitoring. PWSs would be eligible for reductions in compliance monitoring frequency if their monitoring results are below “trigger levels.” The proposed rule sets the trigger level at 1.3 ppt for PFOA and PFOS, and a 0.33 Hazard Index (unitless) for mixtures of PFHxS, GenX Chemicals, PFNA, and PFBS. As noted above, PFOA and PFOS cannot be reliably detected below 4 ppt—USEPA, however, states in the proposed rule that these less definitive measurements are appropriate for establishing monitoring frequency. 

The proposed rule would not allow for PWSs to use composite samples to satisfy monitoring requirements. The proposed rule also would not allow state agencies to grant monitoring waivers to PWSs.  

Water Quality Reports
PWSs that are community water systems are required to provide annual Water Quality Reports (a.k.a. Consumer Confidence Reports) to their customers. Under the proposed rule, these community water systems would be required to report measured levels of PFOA, PFOS, PFHxS, GenX Chemicals, PFNA, and PFBS, and the Hazard Index for the mixtures of PFHxS, GenX Chemicals, PFNA, and PFBS.

The Role of States
The vast majority of states, including Ohio, have primary enforcement authority for their PWSs. In order to keep this authority, states will be required to develop state regulations that are no less strict than the proposed rule within two years of the rule being finalized. 

Comments on the proposed rule are due 60 days after it is formally published in the Federal Register. 

In the meantime…
USEPA had previously established interim drinking water Health Advisory Levels (HALs) for PFOA and PFOS and final HALs for PFBS and GenX chemicals—these HALs remain in effect. HALs are non-enforceable and non-regulatory, and are intended to reflect the levels below which adverse human health effects are not expected to occur. The PFAS HALs are as follows:
•    Interim HAL for PFOA = 0.004 ppt
•    Interim HAL for PFOS = 0.02 ppt
•    HAL for GenX chemicals = 10 ppt
•    HAL for PFBS = 2,000 ppt

If you have any questions about the proposed PFAS drinking water limits, reach out to Kristin Watt, Brooke Zentmeyer, or your Vorys attorney.

Tags: Environmental, Safe Drinking Water, PFAS, USEPA

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