EPA Proposes to Regulate Six PFAS in Drinking Water
On March 14, 2023, the U.S. Environmental Protection Agency (EPA) announced its proposal for a National Primary Drinking Water Regulation (NPDWR) for six PFAS, including the following:
- Perfluorooctanoic acid (PFOA)
- Perfluorooctane sulfonic acid (PFOS)
- Perfluorononanoic acid (PFNA)
- Perfluorohexane sulfonic acid (PFHxS)
- Perfluorobutane sulfonic acid (PFBS)
- Hexafluoropropylene oxide dimer acid (HFPO-DA, or GenX chemicals)
Proposed MCLGs and MCLs
The EPA is proposing Maximum Contaminant Level Goals (MCLGs) and Maximum Contaminant Levels (MCLs) for the six PFAS. MCLGs are not enforceable and are the level of a contaminant in drinking water below which there is no known or expected risk to health. MCLs are enforceable drinking water standards and are set as close to MCLGs as feasible using the best available treatment technology and taking cost into consideration. For PFOA and PFOS, the proposed MCLGs are zero and the proposed MCLs are 4 parts per trillion (ppt). For PFNA, PFHxS, PFBS, and HFPO-DA, the EPA is proposing a combined hazard index of 1 for both the MCLG and MCL.
Analytical Methods and PQLs
The six PFAS proposed for regulation can be measured by EPA Method 533 and EPA Method 537.1, and both methods would meet the monitoring requirements of the proposed regulations. The EPA established practical quantitation levels (PQLs) for PFOA and PFOS of 4 ppt, equivalent to the proposed MCLs. The PQL is the lowest level a constituent can be reliably quantified within specific limits of precision and accuracy during routine laboratory operating conditions. The EPA has also established PQLs of 4 ppt for PFNA, 3 ppt for PFHxS, 3 ppt for PFBS, and 5 ppt for HFPO-DA. The EPA believes there will be sufficient laboratory capacity to handle the imposed drinking water monitoring requirements but is requesting public comment on this assumption.
Hazard Index
EPA’s proposed hazard index approach uses individual measurements of PFNA, PFHxS, PFBS, and HFPO-DA in a drinking water sample to evaluate their combined risk. Each of the four individual PFAS measurements are divided by their respective health-based water concentration – the level at which no health effects are expected for that PFAS. The health-based water concentrations are 10 ppt for PFNA, 9 ppt for PFHxS, 2,000 ppt for PFBS, and 10 ppt for HFPO-DA. The four values are then summed and compared to the proposed hazard index MCL of 1. While the hazard index is a long-established tool that EPA regularly uses to understand health risk from chemical mixtures, it has not previously been used as an MCL for chemical contaminants. The EPA has developed a fact sheet describing the process of calculating the hazard index PFAS MCL in more detail.
Proposed Values Relative to Drinking Water Health Advisories
On June 15, 2022, the EPA released interim health advisories of 0.004 ppt for PFOA and 0.02 ppt for PFOS. The interim health advisories are higher than the proposed MCLGs of zero but orders of magnitude lower than the proposed MCLs of 4 ppt. Final health advisories of 2,000 ppt for PFBS and 10 ppt for HFPO-DA were also released, which are equivalent to their proposed healthbased water concentrations used to calculate the hazard index MCL. Health advisories for PFNA and PFHxS have not been established. Health advisories identify the concentration of a contaminant in drinking water at which neither adverse health effects nor aesthetic effects are anticipated to occur over specific exposure durations. The PFAS health advisories assume a lifetime of exposure to these PFAS in drinking water and account for potential sources of exposure to these PFAS beyond drinking water (e.g., food, air, and consumer products). Drinking water health advisories, health-based water concentrations, and proposed MCLs and MCLGs are summarized in the table below:
Guidance and Proposed Regulatory Values for PFAS Drinking Water
Background PFAS Concentrations
Numerous studies have shown that PFAS are widely detected in the environment, often in areas without identifiable local sources. The terms "PFAS background," "anthropogenic background," and "ambient background" are often used to describe these ubiquitous PFAS levels that are not attributable to a specific local source and are the result of an amalgamation of diffuse sources.
Researchers are still actively studying how to quantify the extent and expected range of PFAS background concentrations across different environmental media. Recent peer-reviewed studies have shown that PFAS are routinely detected in soil, precipitation, and groundwater in areas with no known local sources and often at concentrations exceeding regulatory standards and guidance. For example, Johnson et al. reported mean concentrations of 13 ppt for PFOA and 46 ppt for PFOS in groundwater samples collected from locations with no identified local PFAS sources, which exceed the EPA’s proposed MCLs for PFOS and PFOA.
In the EPA’s Economic Analysis for the Proposed PFAS National Primary Drinking Water Regulation, the EPA used Third Unregulated Contaminant Monitoring Rule (UCMR 3) data and state PFAS monitoring data to estimate the public water systems and population exposed to PFAS above the proposed MCLs. Based on the EPA’s analysis, an estimated 7% of public water systems and an estimated 24% of the US population are exposed to at least one PFAS that exceeds the proposed MCLs. Large public water systems are disproportionately impacted, with an estimated 24% of large systems (>10,000 people) having at least one PFAS exceedance, compared to an estimated 5% of small systems (≤10,000 people) with at least one PFAS exceedance.
Implications for Drinking Water Utilities
The EPA is proposing to amend 40 CFR part 141 by adding a new subpart to incorporate the PFAS proposed for regulation. Under this new subpart, public water systems would be required to sample entry points to their distribution system using a monitoring regime based on EPA’s standardized monitoring framework (SMF) for synthetic organic chemicals (SOCs). Under the SMF for SOCs, the monitoring frequency for a public water system is dependent on previous monitoring results, among other factors.
Conventional drinking water treatment technologies do not effectively treat PFAS. If the proposed NPDWR is promulgated, drinking water utilities may need to upgrade their treatment facilities with advanced treatment processes. The EPA identified four best available technologies for treatment of the six PFAS proposed for regulation, including ion exchange, granular activated carbon, nanofiltration, and reverse osmosis. A best available technology is selected based on several criteria, including treatment efficacy, cost, service life, geographic applicability, and compatibility with other water treatment processes. More information on best available technologies will be included in a forthcoming document from the EPA titled Technical Support Document - Best Available Technologies and Small System Compliance Technologies for PFAS in Drinking Water.
Next Steps for the EPA
The EPA is holding two information webinars on the proposed NPDWR. A webinar on March 16, 2023, will provide a general overview of the proposed rule and a webinar on March 29, 2023, will provide a technical overview of the proposed rule. Additionally, the EPA is holding a public hearing on May 4, 2023, on the proposed NPDWR. To join the public hearing, registration must be completed by April 28, 2023.
Once the proposed rule is published in the Federal Register, public comments will be accepted for 60 days and can be submitted online. The EPA anticipates the rule will be finalized by the end of 2023.
Additional Information
If you have questions or would like to discuss how these proposed regulations could impact your business, please reach out to one of Geosyntec’s nationally recognized PFAS subject matter experts. PFAS practitioner biographies can be found at https://www.geosyntec.com/pfas.
