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Clarifying Which PFAS Compounds Have Federal MCLs as of 2024

PFOA, PFOS, PFHxS, PFNA, HFPO-DA Standards

The 2024 federal maximum contaminant levels (MCLs) apply to PFOA and PFOS at 4.0 nanograms per liter (ng/L or parts per trillion), and to PFHxS, PFNA, and HFPO-DA at 10 ng/L. These limits set enforceable thresholds intended for public water systems. Monitoring in the Central ASG system over 2023–2024 shows these compounds consistently below the reporting levels, far under their respective MCLs.

PFBS Detection and Lack of MCL

Of the other fluorinated compounds tested, PFBS was detected twice above the reporting level of 0.003 µg/L (3 ng/L) with a highest measurement of 3.2 ng/L. However, PFBS does not yet have a federal MCL, so its presence is noted without a regulatory limit.

Evaluating the Hazard Index for Mixtures of Newer PFAS Compounds

What the Data Does Not Confirm

While multiple PFAS compounds occur together, the data does not provide a hazard index value for these mixtures. This absence means no official risk score or health claim can be derived from the sample results alone.

Considerations for Homeowners Managing Mixtures

Understanding how individual PFAS compounds might interact or accumulate requires further scientific analysis beyond EPA occurrence data and is not established by current federal standards.

Sample Size and Scope: What 83 Results Represent

Comprehensive Sampling of the Central ASG System

The 83 sample tests represent a thorough federal occurrence monitoring effort for this public water system. This number indicates consistent surveillance across sources rather than isolated or sporadic checks.

Limitations of Small-Scale Sampling

Despite the volume of samples, these figures represent the system overall rather than any individual household’s water, which can vary. A homeowner’s own water quality requires specific testing to confirm local conditions.

Distinguishing PFAS Presence from Other Water Quality Issues

PFAS Are Not to Be Confused with Aesthetic or Secondary Standards

Unlike substances governed by aesthetic secondary standards—such as taste or staining—PFAS are fluorinated compounds monitored under health-based regulations. This distinction is crucial for understanding treatment priorities.

PFAS Differ from Other Contaminants Like Heavy Metals or Bacteria

PFAS chemical structures and behaviors do not correspond with metals, pathogens, or other common water concerns. Recognizing their unique nature helps identify appropriate filtration needs.

Understanding Measurement Ranges Versus Federal Limits

The Meaning of Non-Detects and Low-Level Detections

Zero detections above reporting levels for major PFAS compounds mean measured values were below analytical thresholds. Small detections, such as those for PFBS, fall well below any federal MCL and should not be equated with violations or unsafe conditions.

Why Detection Does Not Equal Exceedance or Contamination

EPA occurrence monitoring is not a compliance test but a survey. Detected concentrations are measurements to inform future regulation, not evidence of noncompliance or immediate health risk.

How Aesthetic Secondary Standards Differ from Health-Based Limits for PFAS

Aesthetic Standards Address Taste, Appearance, and Corrosivity

Secondary standards manage factors like taste and staining; they do not apply to PFAS, which are regulated under separate health-based criteria.

PFAS Federal MCLs Are Health-Based, Not Aesthetic

All current federal MCLs for PFAS focus on health considerations originating from toxicity studies, unlike aesthetic secondary guidelines.

Recommended Test to Confirm Your Household Water Quality

To determine the PFAS levels in your own tap water and assess whether your existing treatment equipment meets your household’s needs, order a comprehensive water test specifically measuring per- and polyfluoroalkyl substances. This direct analysis will identify individual compound concentrations, settling questions about treatment adequacy.

For ongoing management, consider water treatment options documented to reduce PFAS effectively, such as the Pentair PFAS Forever Chemicals Filter, which ships ready to configure for home use.

Where this information comes from

Source: EPA SDWIS public water system record. Sampled 2024-12-18. These figures describe the public water system's record, not the plumbing inside any individual building.

On record: EPA UCMR5 monitoring (2023-2025) for Central ASG (AS9711948), AS: 830 results across 10 listed contaminants, 2 detections above the reporting level; compared with the applicable federal MCL, none above