USEPA releases first six months of PFAS sampling data collected under UCMR5

Under the Safe Drinking Water Act (SDWA), USEPA issues a UCMR every five years to collect data for contaminants to assess their occurrence in public drinking water supplies and consider possible regulation. All large public water systems (PWSs), those with more than 10,000 users, and 800 randomly selected small PWSs are required to sample and analyze up to 30 contaminants during each UCMR cycle.

The fifth and latest UCMR was published in March 2021 and includes 30 new contaminants that must be monitored in 2023-2025, all but one of which are PFAS. The 29 PFAS being analyzed during UCMR5 are those associated with two laboratory analytical methods for drinking water promulgated by USEPA, namely 533 and 537.1. All PWSs with more than 3,300 users (rather than the typical 10,000 users) and 800 randomly selected smaller PWSs must perform the UCMR5 sampling.

Many will recall that the results from UCMR3 caused quite a splash in 2016. The UCMR3 sampling was performed in 2013-2015 and included just six PFAS, including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). The reporting limits used for UCMR3 ranged from 10 parts per trillion (ppt) for perfluoroheptanoic acid (PFHpA) to 90 ppt for perfluorobutane sulfonic acid (PFBS); the reporting limits for PFOA and PFOS during UCMR3 were 20 and 40 ppt, respectively. At the time the full UCMR3 dataset became available, USEPA had a lifetime health advisory (LHA) of 70 ppt for PFOA and PFOS, individually and combined. USEPA reported that 0.9% of the more than 4,900 PWSs tested had PFOS above 70 ppt, and 0.3% had PFOA above 70 ppt.¹

The testing that is currently underway with UCMR5 is significantly different than what was performed in 2013-2015 under UCMR3:

• All of the 29 PFAS included in USEPA promulgated drinking water analytical methods 533 and 537.1 are being quantified during UCMR5. UCMR3 only included quantification of six of the 14 PFAS included in USEPA promulgated drinking water analytical method 537.
• The reporting limits being used for UCMR5 are much lower, generally in the 2-8 ppt range. The reporting limits used during UCMR3 were 10-90 ppt.
• During UCMR3, all PWSs with more than 10,000 users were tested along with 800 randomly selected smaller PWSs. In contrast, all PWSs with more than 3,300 users are being tested during UCMR5 plus 800 randomly selected smaller PWSs. In addition to capturing a much larger number of PWSs, this is significant because many of the more vulnerable groundwater-based supplies are smaller systems. For example, the Village of Hoosick Falls, New York, which had PFOA detections above 70 ppt in its supply wells, was not included in UCMR3 because the village’s water supply serves only about 3,600 users.

Fast forward to today … USEPA proposed a maximum contaminant level (MCL) of just 4 ppt for both PFOA and PFOS in March 2023, far lower than the reporting levels of 20 and 40 ppt used for these two compounds in UCMR3.² Although not enforceable, USEPA issued new Health Advisories (HALs) for PFOA and PFOS in June 2022 (0.004 and 0.020 ppt, respectively); these very low HALs are well below the reporting levels that are being used for the UCMR5 testing.

In August 2023, the results of the UCMR5 sampling performed in January-June 2023 were released by USEPA.³ This partial dataset includes approximately 4,600 samples from 2,000 PWSs. Although the dataset will grow significantly over the next 2½ years (the current dataset is reportedly ~7% of the ultimate dataset), the early results are already enlightening and reinforce just how ubiquitous some PFAS are in the environment.

Thirteen of the 29 PFAS analyzed were detected in the UCMR5 testing, including seven perfluoroalkyl carboxylic acids (PFCAs), four perfluoroalkyl sulfonic acids (PFSAs), one fluorotelomer sulfonic acid (FTS) and HFPO-DA (aka Gen X). As shown in the graph below, the percentage of the UCMR5 samples collected in January-June 2023 that had detections ranged up to 7.6% depending on the PFAS, while the percentage of the PWSs with detections ranged up to 10.3% depending on the PFAS. In both cases, perfluoropentanoic acid (PFPeA), the five-carbon PFCA, was the most frequently detected PFAS, but PFOA and PFOS were not far behind.

The figure below shows boxplots for the January-June 2023 data. The highest concentration of any PFAS detected in any sample was 235 ppt of PFOA. Excluding that maximum, the detected concentrations of PFOS were generally higher than the detected concentrations of PFOA. The highest concentration of PFOS detected in any sample was 95 ppt.

Although only detected in 23 samples (approximately 0.5%), 6:2 FTS was the PFAS reported at the highest mean and median detected concentrations (approximately 20.9 and 9.8 ppt, respectively); the maximum 6:2 FTS concentration was 168.3 ppt.

The dataset will grow significantly over the next 2½ years, but it's still worth noting that HFPO-DA (aka Gen X) was only detected in six samples, with a maximum concentration of 34 ppt. In addition, 4,8-dioxa-3H-perfluorononanoic acid (ADONA) was not detected in any of the approximately 4,600 samples.

Based on the percentage of PWSs with detections (results at or above the reporting limits), the 13 PFAS detected in the January-June 2023 UCMR5 data are, in declining order:

• Perfluoropentanoic acid (PFPeA) (10.3%, maximum 122.9 ppt)
• Perfluorobutanoic acid (PFBA) (9.9%, maximum 147.2 ppt)
• Perfluorohexanoic acid (PFHxA) (9.9%, maximum 65 ppt)
• Perfluorobutane sulfonic acid (PFBS) (9.6%, maximum 73 ppt)
• Perfluorooctane sulfonic acid (PFOS) (8.5%, maximum 95 ppt)
• Perfluorooctanoic acid (PFOA) (7.8%, maximum 235 ppt)
• Perfluorohexane sulfonic acid (PFHxS) (6.1%, maximum 51 ppt)
• Perfluoroheptanoic acid (PFHpA) (3.6%, maximum 43.1 ppt)
• 6:2 fluorotelomer sulfonic acid (6:2 FTS) (0.7%, maximum 168.3 ppt)
• Perfluorononanoic acid (PFNA) (0.4%, maximum 10.8 ppt)
• Hexafluoropropylene oxide dimer acid (HFPO-DA aka Gen X) (0.3%, maximum 34 ppt)
• Perfluoropentane sulfonic acid (PFPeS) (0.2%, maximum 7.0 ppt)
• Perfluorodecanoic acid (PFDA) (0.05%, maximum 3.5 ppt)

Note that the UCMR5 reporting limits for PFOA and PFOS are both 4 ppt, the same as the MCLs proposed by USEPA in March 2023. Thus, the percentages of PWSs with detections of PFOA and PFOS are the same as the percentages of PWSs that are equal to or above the proposed MCLs (7.8% for PFOA and 8.5% for PFOS).

1. The Third Unregulated Contaminant Monitoring Rule (UCMR 3): Data Summary, January 2017 (epa.gov)
2. USEPA also proposed an MCL for a group of four other PFAS (perfluorononanoic acid [PFNA], perfluorobutane sulfonic acid [PFBS], perfluorohexane sulfonic acid [PFHxS], and hexafluoropropylene oxide dimer acid [HFPO-DA, aka GenX]) using a hazard index (HI)-based procedure. PFNA, PFBS, and PFHxS were included in UCMR3, although the reporting limits were relatively high (20, 90, and 30 ppt, respectively); HFPO-DA is a modern replacement PFAS and was not included in UCMR3.
3. USEPA Releases Initial Nationwide Monitoring Data on 29 PFAS and Lithium | USEPA

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