Client alert for public water suppliers: USEPA finalizes PFAS National Primary Drinking Water Regulations

Both enforceable MCLs and non-enforceable maximum contaminant level goals (MCLGs) are included in the NPDWR. An MCL is the maximum level allowed for a contaminant (or a mixture of contaminants) in water delivered to any user of a public water system (PWS). USEPA defines an MCLG as the maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on the health of persons would occur, allowing for an adequate margin of safety.

USEPA’s finalized PFAS NPDWR includes perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) as individual contaminants, with MCLs of 4 parts per trillion (ppt, or nanograms per liter (ng/L)) and MCLGs of zero for each. Perfluorohexane sulfonic acid (PFHxS), perfluorononanoic acid (PFNA), and hexafluoropropylene oxide dimer acid (HFPO-DA) and its ammonium salt, commonly known as GenX chemicals, were incorporated in the final rule version as individual contaminants with MCLs and MCLGs of 10 ppt each.

The final rule also includes an MCL and an MCLG expressed as a Hazard Index (HI) of 1.0 for mixtures of two or more of the following four PFAS:

• PFNA
• HFPO-DA (GenX)
• PFHxS
• Perfluorobutane sulfonic acid (PFBS)

The HI is unitless and is the approach used in the final rule to evaluate whether the combined levels of these four PFAS pose a potential risk to health. The HI calculation is described under Compliance calculations below.

Monitoring frequency and compliance for PWSs will be based on running annual averages (RAAs), system size, population served, and exceedances of trigger levels. Initial monitoring must be completed within three years of the publication of the rule (2027), followed by compliance monitoring.

Capital improvements and other mitigation actions, if needed for compliance with the MCLs, must be accomplished within five years (2029) of the NPDWR being published in the FR, which occurred on April 26, 2024. The final rule has provisions whereby exemptions may be granted by USEPA or the states to extend the compliance date by up to an additional three years for large water systems and up to an additional six years for small water systems (≤3,300 population).

The NPDWR sets enforceable regulations for six PFAS, requiring those PWSs with RAAs in drinking water that exceed the standards to either a) implement methods (e.g., blending) to reduce PFAS concentrations, b) install or improve advanced treatment technologies, or c) develop a new water source. States that have been granted primacy under the Safe Drinking Water Act (SDWA) retain their authority to issue regulations relating to PFAS provided they are at least as stringent as the finalized NPDWR.

USEPA estimates that compliance with this rule will cost approximately $1.5 billion annually. However, a study completed last year by the Policy Navigation Group on behalf of the Association of Metropolitan Water Agencies (AMWA) estimated that the NPDWR would cost significantly more: as much as $6.4 billion each year.³

Ramboll advises clients to be aware of the following complexities in working toward compliance with this new rule:

• Initial and routine compliance monitoring and the associated compliance considerations
• Sampling requirements and compliance calculations
• Public notifications of violations
• Challenges complying with the regulations

PWSs have three years to complete their initial (year-long) sampling, which will determine their compliance with the MCLs. Compliance is based on the RAA for each regulated PFAS per entry point to the distribution system (EPTDS). This can be satisfied with previously collected data such as Unregulated Contaminant Monitoring Rule (UCMR5) or from other regulatory monitoring requirements performed after January 2023. In certain cases, older data may be allowable.

At a minimum, quarterly samples will be required from most PWSs to calculate the RAAs, unless reduced monitoring (annually or triennially) is approved based on the initial monitoring data and non-exceedance of trigger levels. The trigger levels are set at half of the MCLs (i.e., 2 ppt for either PFOA or PFOS, 5 ppt for PFHxS, PFNA, and HFPO-DA, and an HI of 0.5 for the mixture of two or more PFAS as listed previously). USEPA adopted a three-tiered approach under which the states can allow for reduced monitoring. PWSs with results below trigger levels during the initial monitoring or ongoing compliance may be allowed to sample triennially; systems with results at or above trigger levels but consistently below MCLs may be allowed to sample annually.

Key compliance status considerations include:

• A PWS is deemed out of compliance if the RAA at any sampling point (EPTDS) exceeds any MCL
• While a single detection above the MCL will not necessarily bring the PWS out of compliance, a single sample may bring a RAA above the MCL if detections are high enough
• PWSs may collect extra samples per quarter to calculate their RAAs for each sample point

Samples must be analyzed using USEPA-approved methods 533 or 537.1 for PFAS in drinking water by certified laboratories (including previous data permitted for initial monitoring). Composite samples (a mixture of various EPTDS in a single container) will not be allowed.

RAAs are calculated considering detections below the practical quantitation levels (PQL) as zeros. PQLs were defined as 5 ppt for HFPO-DA/GenX, 4 ppt for each of PFOA, PFOS, and PFNA, and 3 ppt for PFBS and PFHxS. The HI is calculated by summing the ratios of each regulated PFAS concentration in the sample by its health-based water concentration (HBWC) according to the formula:

It is important to note that the presence of PFBS can only trigger an MCL violation if it is present as part of a mixture with at least one of the other three PFAS (PFHxS, PFNA, and HFPO-DA).

Consumer confidence reports (CCR) must be provided annually to customers and list detections of the six PFAS, even if below the PQLs. Public notification of MCL violations should be provided at the earliest opportunity, but must be provided no later than 30 days after a violation is detected.

There may be numerous challenges complying with the regulation. Due to the low quantification and regulatory levels established, any PFAS detections could be impactful to compliance. Therefore, sample collection and analysis may pose important analytical challenges such as:

• The limited data available on matrix effects of salinity or organic materials potentially affecting results
• Quality control, cross-contamination of samples, and risk of triggering non-compliance or monitoring due to inaccurate sample collection and processing (i.e., false positives)
• Limited availability of certified laboratories causing longer turnaround times, which could result in extended non-compliance durations
• Because compliance is determined by year-long RAAs, a year of data must be available within the three-year timeframe following the FR publication
• The cost of sample collection and analyses could be significant

In addition to analytical challenges, the best available technologies (BATs) that USEPA determined feasible for meeting the MCLs are granular activated carbon (GAC), anion exchange resins (AIX), nanofiltration (NF), and reverse osmosis (RO). These treatment systems can require considerable initial capital investment and have elevated maintenance costs and operational challenges. For example, there may be rapid exhaustion of GAC due to competition with other pollutants or organic matter; fouling or degradation of the AIX resins due to minerals; chlorine and other dissolved compounds; and membrane fouling and potential low recovery rates for NF and RO.

Furthermore, the BATs are removal technologies that all produce significant amounts of PFAS-concentrated waste requiring further treatment and/or disposal.

Finally, while identification of the source or sources of PFAS that contribute to detections is possible, such evaluations can be challenging.

While PWSs are immediately affected by the PFAS NPDWR, this federal regulation will also have far-reaching implications for municipalities, the public, and other stakeholders.

Apart from the direct impact to PWSs, MCLs defined under the SDWA might also be used in other environmental regulations and cleanups under the Clean Water Act (CWA), Resource Conservation and Recovery Act (RCRA), and Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, commonly referred to as Superfund). For instance, MCLs might be used during permitting under the CWA for discharges to surface water and therefore the new MCLs could impact publicly owned treatment works (POTW) and industrial direct and indirect dischargers.

Other evolving CWA programs involve POTW PFAS surveys (proposed March 26, 2024), aquatic life criteria for PFOA and PFOS (final expected soon), PFAS in biosolids risk assessments (public review draft expected by end of 2024), and industrial effluent limit guidelines (ELGs) that include PFAS (proposal expected this year).

Regarding RCRA, proposed revisions (February 8, 2024) list specific PFAS as RCRA hazardous constituents, and the recent updated PFAS disposal guidance was released (April 9, 2024 by USEPA). Regarding CERCLA, the MCLs (and MCLGs, unless set at zero) are typically considered to be applicable or relevant and appropriate requirements (ARARs) and may serve as cleanup objectives for groundwater.

Stay tuned for a separate, forthcoming publication from Ramboll that will address this topic further.

For more than two decades, Ramboll has developed PFAS management solutions for our clients including planning, permitting, and engineering for the design and construction of complete PFAS treatment systems for public water supplies. We understand the complex environmental, chemical, and toxicological characteristics of PFAS and the challenges that they present. Our multi-disciplinary expertise and experience have been instrumental in assisting clients in understanding and reducing PFAS discharges. For drinking water, stormwater, and wastewater management, we provide the following services for PFAS and other contaminants:

• Source identification and control
• Sampling and analysis
• Treatment technology evaluation and piloting
• Biosolids/residual management
• Process/detail engineering
• Turnkey installation and operational support

> Learn more about Ramboll's PFAS experience and capabilities

¹ Per- and Polyfluoroalkyl Substances (PFAS) [USEPA]

²PFAS National Primary Drinking Water Regulation [Federal Register]

³AMWA record statement on liability for PFAS cleanups under CERCLA [AMWA]

_{The information contained and opinions expressed herein: (i) are for discussion/informational purposes only, without representation or warranty; (ii) are general in nature, may not be applicable to your particular circumstances, and cover subject matters for which information and practices may change/develop quickly over time; and, therefore, (iii) should not be relied upon for any particular circumstances without consulting an environmental professional experienced in both PFAS and the specific issues related to your matter.}