On April 10, 2024, U.S. EPA announced finalization of drinking water standards, also known as Maximum Contaminant Levels (MCLs) for six per- and polyfluoroalkyl substances (PFAS) and a Hazard Index MCL for mixtures of specific PFAS.
| Analyte | Maximum Contaminant Level Goal | Maximum Contaminant Level |
| Perfluorooctanoic acid (PFOA) | 0 parts per trillion | 4 parts per trillion |
| Perfluorooctane sulfonic acid (PFOS) | 0 parts per trillion | 4 parts per trillion |
| Perfluorohexane sulfonic acid (PFHxS) | 10 parts per trillion | 10 parts per trillion |
| Perfluorononanoic acid (PFNA) | 10 parts per trillion | 10 parts per trillion |
| Hexafluoropropylene oxide dimer acid (HFPO-DA) (also known as GenX chemicals) | 10 parts per trillion | 10 parts per trillion |
| Mixtures of PFHxS, PFNA, HFPO, and perfluorobutane sulfonic acid (PFBS) | Hazard Index = 1 | Hazard Index = 1 |
MCLs and non-zero MCL Goals are enforceable standards for public drinking water systems. The new PFAS MCLs are expected to be effective in June 2024 (60 days after publication in the Federal Register). Public drinking water systems must sample for PFAS to determine compliance with MCLs by 2027 and PFAS treatment systems must be in place by 2029. Federal MCLs may trigger States to finalize their own standards and may prompt development of surface water criteria for water bodies used as drinking water — critical for facilities who have National Pollutant Discharge Elimination System permits or industrial wastewater discharge permits.
This regulatory action may have wide-reaching effects, even for clients which do not have drinking water systems onsite. MCLs provide the Federal government and States with enforceable criteria for both drinking water and resources considered to be potential drinking water sources (i.e., groundwater, surface water). Regulatory agencies may act to reassess drinking water wells and facilities that were previously tested using prior unenforceable criteria (e.g., Lifetime Health Advisories or other U.S. EPA guidance). Agencies may also elect to move forward with or expand investigations at new facilities now that enforceable criteria are in place. At existing remediation sites, remedial goals for the PFAS identified above may be established, requiring implementation of remediation systems or modification of existing systems. Remedial sites that have already achieved closure may be subject to reopening to assess and address PFAS, as applicable.
Issuance of PFAS MCLs is expected to change the PFAS investigation and compliance landscape for drinking water, surface water discharge, and other disposal needs (wastewater treatment plants, landfill leachate, biosolids). To help our clients navigate these uncertainties — whether associated with sampling, permitting, treatment, or compliance — EnSafe has an established PFAS Workgroup, with technical experts drawn from various disciplines, including investigation, engineering, compliance, chemistry, toxicology, and forensics/litigation support. If you would like to learn more about EnSafe’s PFAS expertise, you can refer to our PFAS Statement of Qualifications , our PFAS Assessment and Remediation Factsheet, or our PFAS Compliance and Pollution Prevention Factsheet. You can also contact Lori Goetz or Dave Warren for any questions you may have regarding the PFAS MCLs, their effects on your facility, or other PFAS regulatory matters.