As previously reported, the U.S. Environmental Protection Agency (EPA) published its most recent list of unregulated constituents to be monitored by public water systems (PWSs)—the fifth Unregulated Contaminant Monitoring Rule (“UCMR 5”)—on December 27, 2021. Requiring sampling for 30 chemical constituents between 2023 and 2025, UCMR 5 included 29 per- and polyfluoroalkyl substances (PFAS) capable of being analyzed within the scope of EPA analytical methods 533 and 537.1.

Last month, EPA unveiled its UCMR 5 data summary for the first round of monitoring. The initial data reveals, among other things, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) exceeded EPA’s interim Health Advisory levels in 7.8% and 8.5% of PWSs, respectively. EPA’s UCMR 5 website contains questions and answers about the initial UCMR 5 sampling dataset.

EPA’s latest data only represents about 7% of the data that EPA expects to receive over the next three years. Consequently, the preliminary sampling data provide a limited view of PFAS presence in the country’s PWSs. EPA intends to supplement its UCMR 5 sampling data in EPA’s National Contaminant Occurrence Database every three months until the 2026 reporting period’s end. After analytical labs, PWSs, states, and the EPA itself examine the data, data may be added, modified, or even removed.

Offering fresh insights, continued UCMR 5 data will enhance EPA’s understanding of how often these constituents appear in the country’s PWSs and the concentrations at which they are present.

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