9 Things To Know About The EPA's Regulations For PFAS In Drinking Water

By Naomi Senehi and Sudhakar Viswanathan

In April 2024, the U.S. EPA introduced new regulations¹ establishing maximum contaminant levels (MCLs) for six specific per- and polyfluoroalkyl substances (PFAS) in drinking water, highlighting the urgency to address their presence due to environmental and health risks. The regulations mandate MCLs for individual PFAS and utilize a hazard index for mixtures to ensure safe levels are maintained. Additionally, the EPA proposed the best available technologies for PFAS treatment and disposal methods for residuals, emphasizing the need for effective and sustainable water treatment solutions. The recent EPA regulations on PFAS in drinking water show the importance of addressing contamination, the need for substantial investment in infrastructure, and the importance of environmental justice and innovation, making these issues critical for the upcoming November elections.

Here are nine important things to know about the EPA’s PFAS regulations:

1. The EPA has determined MCLs and a hazard index (HI, for mixtures) for six PFAS in finished drinking water.

PFAS are a class of nearly 15,000 chemicals that have gained significant attention since their incidental production in the 1930s and subsequent manufacture and commercialization starting in the 1950s. Since the 1990s, the EPA has examined the impacts of PFAS and has now established enforceable individual MCLs for five PFAS (PFOS, PFOA, PFNA, PFHxS, and HFPO-DA) in finished drinking water. In addition, a sixth PFAS, PFBS, is also considered under an HI when it is present with PFNA, PFHxS, and/or HFPO-DA in excess of their limits.

These six PFAS were regulated based on their occurrence in drinking water and their corresponding health effects at low concentration levels. Occurrence data was mainly informed by results from the Unregulated Contaminant Monitoring Rule (UCMR 3) program, which required public water systems (PWSs) to monitor for these six PFAS in finished drinking water from 2013-2015.

2. The EPA mandated individual MCLs for five of these PFAS, which ranged from 4 to 10 parts per trillion (ppt).

The MCLs for the five individually regulated PFAS are 4 ppt for PFOS, 4 ppt for PFOA, 10 ppt for PFNA, 10 ppt for PFHxS, and 10 ppt for HFPO-DA. From the EPA’s occurrence analysis, median levels of these five PFAS at non-targeted sites (i.e., no suspected major PFAS contamination) ranged from 0.35 ppt (below limit) to 29.6 ppt (above limit), with maximum levels as high as 856 ppt. Compared to their health risk limits (HRLs) of 10 ppt, it is evident that levels of PFAS in finished drinking water must be addressed to protect public health. There is no individual limit for PFBS.

3. A calculated HI > 1 for any combination of PFHxS, PFNA, HFPO-DA, or PFBS indicates the need for action.

In certain instances, individual PFAS levels may be below their individual MCL, but the total PFAS concentration in finished drinking water may exceed maximum levels of safe exposure. In this case, an HI is calculated to ascertain the need for action and applies to any mixture of two or more of PFBS, PFNA, PFHxS, and/or HFPO-DA. Note that PFBS is regulated within the HI but not individually, as more data is needed to assess its occurrence.

4. The EPA’s proposed best available technologies for the treatment of PFAS in drinking water include the use of GAC, AIX, NF, and RO, which concentrate (vs. destroy) PFAS.

The EPA assesses the best available technologies (BATs) for drinking water treatment based on seven criteria. To qualify as a BAT, the technology must: (1) have a high removal efficiency, (2) have been demonstrated at full-scale, (3) be geographically applicable, (4) be economically feasible for large water systems, (5) have a reasonable service life, (6) be compatible with existing water treatment processes, and (7) be able to treat water to compliant levels. The EPA proposed granular activated carbon (GAC), anion exchange (AIX), nanofiltration (NF), and reverse osmosis (RO) as BATs for medium to large PWSs. Only GAC and AIX were suggested as BATs for small water systems (serving less than 3,300 people). GAC, AIX, NF, and RO are all designed to concentrate PFAS onto a particular media. Once spent, these residuals require regeneration and eventual disposal. Additionally, reject streams are generated, requiring further treatment or disposal.

5. The EPA’s proposed disposal methods for spent residuals and reject streams are reactivation (of GAC), incineration (of AIX), and treatment and discharge (of RO or NF reject streams).

The EPA provided guidance on managing the solid residuals (spent GAC, spent resin, or spent membranes) and reject streams (from NF or RO) from their proposed BATs. For solid residuals, EPA suggested reactivation of spent GAC and incineration of spent AIX resin. Guidance was not provided for disposal of spent GAC after the number of reactivation cycles is surpassed. Notably, while acceptable, these management methods have not been shown to mineralize PFAS fully, and improved test methods for quantifying PFAS emissions from processes such as incineration are still in development. No guidance was provided for the disposal of solid wastes from RO or NF (i.e., spent membranes). The suggested management for the reject streams was general: Reject streams should be treated and discharged to surface water or the sewerage system in compliance with NPDES permits. In some cases, groundwater injection is recommended.

6. The EPA does not expect the designation of PFOA and PFOS as hazardous substances under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) to jeopardize these disposal methods.

According to some public comments, these management methods are simply “media shifting” rather than the terminal elimination of PFAS, as these methods have poor destruction efficiency. In combination with the recent designation of PFOA and PFOS as CERCLA hazardous substances, disposal of these residuals and retentates must be carefully evaluated. The EPA’s response to these concerns is that PWSs will likely not generate enough PFAS-laden waste to require reporting under CERCLA. These systems would have to report if ≥ one pound of PFAS is released in a 24-hour period. Municipal water, wastewater, and landfills are not expected to be heavily impacted by this CERCLA designation, which instead affects agencies such as industrial dischargers.

7. Treatment options are not limited to the EPA’s proposed BATs, leaving the gate open for technologies such as supercritical water oxidation.

While the EPA proposed BATs for medium to large PWSs (GAC, AIX, NF, or RO) and small PWSs (GAC, AIX), PWSs are not required to use the suggested BATs. Alternatively, PWSs can elect treatment processes that evade or minimize the generation of difficult-to-handle solid and liquid wastes. For example, a PWS could combine a concentration process such as foam fractionation or precipitation (with a commercial polymer) with destruction technologies such as supercritical water oxidation (SCWO). This ability can also help PWSs make informed investments in technologies that would be suitable not only for treating PFAS, but other currently or soon-to-be regulated contaminants.

8. SCWO technology has a demonstrated ability to destroy treatment residuals (spent GAC, spent AIX, and spent membranes) contaminated with PFAS.

When water is heated and pressurized above 374° C and 221 bar, organic wastes, such as PFAS, break down into their elemental components (e.g., C, F, etc.). 374Water’s AirSCWO system is unique because this process is further aided by the introduction of ambient air (containing oxygen) into the waste stream to initiate oxidation reactions that destroy the organics (i.e., PFAS) within seconds. Notably, the system has the unique capability to destroy a wide range of organic compounds, including pharmaceuticals, microplastics, and over 40 different types of PFAS and their precursors.

AirSCWO can destroy up to 99.99% of total PFAS (⅀40 PFAS) from (1) spent GAC (after processing PFAS-laden groundwater), (2) spent AIX (after processing PFAS-laden groundwater), and (3) spent AIX (after processing wastewater). Full destruction results can be found in the peer-reviewed study in the Journal of Hazardous Materials.²

9. Additional upcoming changes to look out for include the potential additional listing of nine PFAS as hazardous constituents under the Resource Conservation and Recovery Act (RCRA).

In addition to regulating PFAS in drinking water and designating certain PFAS as hazardous substances under CERCLA, the EPA is proposing to regulate nine additional PFAS under RCRA due to their negative health effects to humans and other life forms. These PFAS include PFOA, PFOS, PFBS, HFPO–DA, PFNA, PFHxS, PFDA, PFHxA, and PFBA. Future management of solid drinking water treatment residuals contaminated with PFAS may be altered depending on what the RCRA definition entails. PWSs may need to keep this in mind to avoid the accumulation of PFAS-laden wastes on site prior to any new RCRA requirements.

References:

1. https://www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas
2. https://pubmed.ncbi.nlm.nih.gov/37633016/

About The Authors

Naomi Lynn Senehi, the municipal technical solutions lead and global access manager at 374Water, holds a bachelor’s and master’s in environmental engineering. With five years of R&D experience, she specializes in applying SCWO technology to diverse waste streams.

Sudhakar (Sunny) Viswanathan is vice president at 374Water. He has a bachelor’s and a master’s degree in environmental engineering from Syracuse University. He has nearly 25 years of industry experience, including leadership positions at Suez and Veolia, and has authored over 35 technical papers. He currently spearheads the commercialization and business development of SCWO technology.