---
title: "What Is MCL (maximum contaminant level)? Remediation Glossary"
description: "Maximum contaminant level, or MCL, is the highest level of a contaminant that federal law allows in public drinking water, and it is an enforceable standard."
url: https://aes.multisites.ai/glossary/mcl-maximum-contaminant-level
publisher: Advanced Environmental Services
phone: +1-314-865-2662
quote: https://aes.multisites.ai/contact
---

Regulation

# MCL (maximum contaminant level)

Maximum contaminant level, or MCL, is the highest level of a contaminant that federal law allows in public drinking water, and it is an enforceable standard.

An MCL is the legal ceiling for a contaminant in public drinking water. EPA defines it as the highest level of a contaminant that is allowed in drinking water, and says MCLs are enforceable standards.

EPA sets each MCL as close as feasible to a health goal called the MCLG, using the best available treatment technology and taking cost into consideration. The MCLG itself is only a non-enforceable goal.

For PFAS, EPA has set MCLs for [PFOA](https://aes.multisites.ai/glossary/pfoa) and [PFOS](https://aes.multisites.ai/glossary/pfos) at 4.0 parts per trillion, plus limits for other PFAS. These apply to public water systems. They do not set a legal limit for a private well or for soil.

Property owners still use them as a yardstick. A well result near the MCL is a reason to call a professional. Keep in mind that the compliance timeline is under proposed changes as of May 2026.

To read a lab report, learn [parts per trillion](https://aes.multisites.ai/glossary/parts-per-trillion-ppt) first. Then compare your result with the table on EPA's page.

## Related terms

-   [PFOA](https://aes.multisites.ai/glossary/pfoa)
-   [PFOS](https://aes.multisites.ai/glossary/pfos)
-   [Parts per trillion (ppt)](https://aes.multisites.ai/glossary/parts-per-trillion-ppt)
-   [PFAS](https://aes.multisites.ai/glossary/pfas)

## Sources

1.  [EPA: National Primary Drinking Water Regulations](https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations)

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