On April 10, 2024, the US Environmental Protection Agency (EPA) finalized its highly anticipated new rule aimed at reducing the level of certain per- and polyfluoroalkyl substances (PFAS) in drinking water. The final rule is not only the first enforceable federal drinking water regulation for PFAS, but also the first National Proposed Drinking Water Regulation under the Safe Drinking Water Act in decades.

Consistent with the proposed rule published in 2023, the final rule includes numeric maximum contaminant levels (MCLs) for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic (PFOS).

In the proposed rule, perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), and hexafluoropropylene oxide dimer acid and its ammonium salt (HFPO-DA) (more commonly known as GenX chemicals), along with perfluorobutane sulfonic acid (PFBS), were to be regulated solely using the agency’s novel Hazard Index (HI) MCL calculation. The final rule, however, sets newly introduced numerical MCLs for PFNA, PFHxS, and GenX chemicals while retaining the controversial use of an HI calculation to limit levels of PFNA, PFHxS, HFPO-DA, and PFBS as a mixture.

The EPA states that the HI provides an indication of overall potential risk of a mixture as well as individual PFAS that are potential drivers of a risk. An HI of 1.0 is the level at which there are no known or anticipated adverse health effects.

The final maximum contaminant level goals (MCLGs) and MCLs for each of the six regulated PFAS under the final rule are summarized below:

The final rule will take effect 60 days after its publication in the Federal Register.

MCL AND MCLG

In addition to the enforceable MCLs set by the final rule, the rule sets nonenforceable health-based MCLGs for the six regulated PFAS. MCLGs are levels at which there is no known or expected risk to public health and are not enforceable standards. MCLs are the highest level of contaminants allowed in drinking water and are set as close as possible to the MCLGs while also taking into account technical feasibility and cost. Exceedances of the MCLs can be enforced once the compliance period takes effect.

The EPA’s MCL of 4 ppt for PFOA and PFOS is equivalent to the practical quantification level, which is “the lowest level that can reasonably be reliably achieved within specified limits of precision and accuracy.” The EPA’s final individual MCLGs and MCLs for PFNA, PFHxS, and GenX chemicals are equivalent to their respective Health-Based Water Concentrations (HBWCs) set out in the final rule. Of note, the HBWC for PFHxS was increased from 9 ppt in the draft rule to 10 ppt in the final rule.

IMPLEMENTATION

The rule requires public water systems to continuously monitor for each of these PFAS. Those systems have three years (by 2027) to complete initial monitoring, followed by ongoing compliance monitoring and public reporting of the PFAS levels in drinking water starting in 2027. Public water systems have five years (until 2029) to implement solutions that reduce PFAS if their monitoring shows that the levels of chemicals in drinking water exceed the aforementioned MCLs.

Public water systems subject to the rule generally must monitor quarterly, and the monitoring requirements are triggered by levels set at one-half of the MCL for each regulated PFAS chemical (a slight increase from the one-third MCL level proposed in the draft rule) based on a running annual average. In other words, a system is not necessarily in violation of the rule until the annual average exceeds the applicable MCL.

Starting in 2029, public water systems that contain PFAS in drinking water and violate one or more of the MCLs must provide notification to the public and take immediate action to reduce the level of PFAS. This five-year compliance period is a change from the three-year compliance period found in the proposed rule.

FUNDING

The EPA concludes in its final rule that the costs and benefits are “nearly at parity,” with estimated quantifiable benefits of $1,549.40 million annually and quantifiable costs of $1,548.64 million annually (at a 2% discount rate). The Biden administration has emphasized the availability of funding available to public water systems to help implement PFAS treatment measures. The EPA announced roughly $1 billion in funding through President Biden’s Investing in America agenda to assist 56 states and territories to allow for PFAS testing and treatment at both public water systems and privately owned homes and wells.

The rule also points to the Bipartisan Infrastructure Law as another source of funding over a five-year period through appropriations of more than $11.7 billion to the Drinking Water State Revolving Fund (DWSRF) General Supplemental, $4 billion to the DWSRF for Emerging Contaminants, and $5 billion in grants to the Emerging Contaminants in Small or Disadvantaged Communities program.

IMPACT AND NEXT STEPS

While the final rule largely tracks the 2023 proposed rule, there are a number of changes, with the most notable departures being (1) the promulgation of separate numeric MCLGs and MCLs for PFNA, PFHxS, and HFPO-DA and (2) the extension of the compliance period from three to five years.

The final rule directly applies only to public water systems classified as community water systems and non-transient non-community water systems (excluding fuel/gas stations and shopping centers). While there is no immediate public reporting, regulated entities must take appropriate steps in the near term to ensure their ability to comply with the reporting requirement in 2027. Further, public water systems should begin developing solutions, if needed, to address levels of PFAS that exceed the amount enumerated in the new rule.

The new rule’s reach will also extend beyond the directly regulated entities. For example, once the rule takes effect, the new MCLs will become applicable, relevant, and appropriate requirements (ARARs) at Superfund sites. This will likely result in increased cleanup costs and possible expansion of existing Superfund sites to include new contaminants and potentially responsible parties. These impacts will be felt immediately upon the MCLs becoming effective (and possibly even sooner, as TBC (to be considered) requirements). These impacts will not be limited to Superfund sites, but can be expected generally for all contaminated site response actions where MCLs are typically used as groundwater cleanup criteria.

Further, notwithstanding the availability of federal funding, parties may see an increase in litigation brought by water districts as those entities seek to defray the costs of compliance with the new regulations. Similarly, the plaintiffs’ bar will likely point to the MCLs and MCLGs in toxic tort suits.

The establishment of federal MCLs for the six PFAS covered by this rule will help address the current patchwork of state-issued MCLs. Once the rule takes effect, it will preempt any state-issued regulations, meaning no state can have an MCL for a covered PFAS that is less stringent than the federal MCL. It also would require any state with primary enforcement responsibilities that does not have a drinking water standard to implement regulations that are at least as strict as the federal MCL. In short, states will have to act to align their existing MCLs with the new federal standard.

Following the EPA’s announcement of the proposed rule in 2023, the agency received more than 120,000 comments during its public comment period. Of these comments, many questioned the science behind the EPA’s calculation of these new levels and to what extent the standards would be enforced. Others challenged the EPA’s estimated implementation costs as being far too low.

While the EPA endeavored to respond to those comments in the final rulemaking, it is expected that the final rule may be subject to challenge by various groups. As required by the Safe Drinking Water Act, 42 USC § 300j-7, any legal challenges must be filed in the DC Circuit within 45 days of the rule’s publication in the Federal Register.

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