Summary of the Final Rule: April 2024
On April 10, 2024, the U.S. Environmental Protection Agency published the final National Primary Drinking Water Regulation for PFAS, establishing Maximum Contaminant Levels (MCLs) for six PFAS compounds and a Hazard Index (HI) for a mixture of four. This rulemaking — the first EPA MCL rule for PFAS compounds — represents the most significant development in drinking water regulation in the United States since the 1996 Safe Drinking Water Act amendments. The rule was finalized under the Biden administration and carries the regulatory force of a federal standard, binding on all public water systems (PWS) serving at least 15 connections or 25 people.
The final MCLs are: PFOA at 4 ppt (ng/L), PFOS at 4 ppt, PFNA at 10 ppt, PFHxS at 10 ppt, HFPO-DA (GenX) at 10 ppt, and PFBS contributing to a Hazard Index along with PFHxS, PFNA, and HFPO-DA with a maximum HI of 1.0. Notably, the MCLs for PFOA and PFOS at 4 ppt are set at the practical quantitation limit (PQL) for current analytical methods — meaning EPA is effectively requiring measurement at the lowest reliably detectable level, not just a health-based threshold above that level. This signal-to-compliance convergence is unprecedented in federal MCL history and reflects the agency’s determination that no safe level of PFOA or PFOS exposure can be defined.
Compliance Timeline and Monitoring Requirements
Public water systems must complete initial monitoring for the six regulated PFAS compounds within three years of the rule’s publication (by approximately April 2027). Systems finding concentrations above the MCLs must initiate treatment to achieve compliance within five years of publication (approximately April 2029). This phased timeline provides utilities with a window for infrastructure planning, but the 2027 monitoring deadline effectively requires that analytical capacity, sampling protocols, and laboratory contracts be in place within three years.
For utilities that have not previously monitored for PFAS beyond UCMR5 obligations, the monitoring requirement represents a significant operational change. Sampling for PFAS at the 4 ppt detection level requires EPA Method 533 or Method 537.1, both of which demand rigorous field sampling protocols (including use of PFAS-free sampling equipment and containers), specialized laboratory handling, and validated detection limits below the MCL. Utilities in states with existing PFAS monitoring programs will have a head start; those in states with minimal prior PFAS regulatory activity will face a more compressed preparation timeline.
Treatment Technology Implications for Utilities
The 2024 MCLs are significantly more stringent than the 2016 health advisory (70 ppt for PFOA+PFOS), and treatment systems designed for the older standard will require evaluation for the new one. Granular activated carbon (GAC) is the most widely deployed PFAS treatment technology at utility scale, but GAC’s effectiveness at achieving sub-10 ppt effluent concentrations depends on carbon type, empty bed contact time (EBCT), influent PFAS concentration and mixture composition, and carbon replacement frequency. Systems with PFAS concentrations in the range of 100–500 ppt may achieve 4 ppt effluent with optimized GAC; systems with higher influent concentrations or shorter contact times may require additional treatment stages.
Ion exchange (IX) resins, particularly single-use anion exchange resins, have demonstrated more consistent performance for achieving very low PFAS effluent concentrations compared to GAC, at the cost of higher capital expenditure and spent resin disposal requirements. Reverse osmosis is highly effective for PFAS removal and is increasingly considered for utilities where brine disposal logistics are manageable. The EPA’s final rule does not specify treatment technology, leaving utilities to select the approach best suited to their influent water quality and operational context, but the stringency of the 4 ppt MCL may effectively force utilities that previously relied on GAC alone to consider supplemental or alternative technologies.
Procurement Implications: Rewriting Filter RFPs
For utilities issuing requests for proposals (RFPs) for PFAS treatment equipment under the new MCL framework, several specification changes are consequential. First, performance guarantees must reference the six regulated compounds individually and the Hazard Index collectively, not just PFOA and PFOS. Vendors that historically marketed systems as “PFOA/PFOS certified” without data on PFHxS, PFNA, PFBS, and GenX removal will face new documentation requirements. Second, performance guarantees must be expressed against the actual MCL values (4 ppt for PFOA/PFOS, 10 ppt for others), not against the 2016 advisory thresholds that many existing contracts reference.
Third, the 4 ppt MCL for PFOA and PFOS — essentially at the analytical detection limit — creates challenges for performance warranty language, since effluent concentration verification at that level requires careful quality assurance in sampling and analysis. Utilities and their legal counsel should consider how performance is verified, what analytical methods are specified, and what tolerances are acceptable when drafting procurement language. The transition from a health advisory to a legally enforceable MCL also changes the liability context for utilities: non-compliance now carries enforceable penalties and public notification requirements, elevating the stakes for procurement decisions.