Maximum Contaminant Level (MCL)

Definition

The Maximum Contaminant Level (MCL) is a legally enforceable standard that identifies the highest permissible concentration of a particular contaminant in public drinking water systems. The MCL is set by the United States Environmental Protection Agency (EPA) under the Safe Drinking Water Act (SDWA). These levels are designed to protect public health by ensuring that drinking water is safe from contaminants that can pose health risks.

Examples

Lead: The MCL for lead in drinking water is 0.015 mg/L (15 parts per billion). Exceeding this level requires water systems to take action.
Benzene: The MCL for benzene in drinking water is 0.005 mg/L (5 parts per billion). Compliance with this MCL ensures that benzene levels are minimized to prevent adverse health effects.
Nitrate: The MCL for nitrate, typically found in agricultural runoff, is 10 mg/L. Exceeding this threshold necessitates immediate remediation actions to mitigate risks associated with excessive nitrate levels, such as methemoglobinemia (blue baby syndrome).

Frequently Asked Questions (FAQs)

1. What is the purpose of setting an MCL?

MCLs are established to protect public health by ensuring that drinking water contains contaminants at levels that are considered safe for human consumption over a lifetime of exposure.

2. How is an MCL determined?

The EPA sets MCLs based on the best available science, considering both health risks and technological feasibility. Risk assessments, toxicological studies, and cost-benefit analyses contribute to the determination of an MCL.

3. Are MCLs the same for all contaminants?

No, MCLs vary by contaminant. Each contaminant has a distinct MCL based on its specific health effects and the environmental processes that govern its occurrence and movement in water.

4. What happens if a water system exceeds an MCL?

If a water system exceeds an MCL, it must inform the public and take corrective actions to reduce the contaminant levels. This could involve treatment processes, alternative water sources, or infrastructure improvements.

5. Can individual states set their own MCLs?

While the EPA sets federal MCLs, individual states can establish their own MCLs as long as they are at least as strict as the federal standards.

Contaminant: Any physical, chemical, biological, or radiological substance or matter in water.
Safe Drinking Water Act (SDWA): A federal law that protects public drinking water supplies in the U.S., setting national health-based standards to control pollutants.
Primary Drinking Water Standards: Legally enforceable standards that apply to public water systems, protecting public health by limiting the levels of contaminants.
Maximum Contaminant Level Goal (MCLG): The level of a contaminant in drinking water at which no known or anticipated adverse effect on health would occur, providing a margin of safety.
Treatment Technique: A required process intended to reduce the level of a contaminant in drinking water, used when it’s not economically or technologically feasible to establish an MCL.

Online Resources

References

United States Environmental Protection Agency. “Drinking Water Contaminants – Standards and Regulations.”
Safe Drinking Water Act. Public Law No. 93-523, 88 Stat. 1660.
National Primary Drinking Water Regulations, Code of Federal Regulations, Title 40 (40 CFR Part 141).

Suggested Books for Further Studies

“The Drinking Water Handbook” by Frank R. Spellman
“Safe Drinking Water Act: Amendments, Regulations and Standards” by Thomas B. Curtis
“Introduction to the US Public Water Systems: Regulations and Contaminants” by Joseph Cotruvo

Real Estate Basics: Maximum Contaminant Level (MCL) Fundamentals Quiz

### What is the purpose of setting an MCL for drinking water? - [x] To ensure contaminants in drinking water are at safe levels to protect public health. - [ ] To reduce the taste and odor issues in drinking water. - [ ] To decrease the cost of water treatment processes. - [ ] To increase the mineral content for taste and health. > **Explanation:** MCLs are established to ensure contaminants in drinking water are at safe levels to protect public health over a lifetime of exposure. ### Who sets the MCLs for drinking water in the United States? - [ ] State health departments - [x] Environmental Protection Agency (EPA) - [ ] Food and Drug Administration (FDA) - [ ] Department of Agriculture > **Explanation:** The Environmental Protection Agency (EPA) sets the Maximum Contaminant Levels (MCLs) for drinking water in the United States. ### What action must be taken if a water system's contaminant level exceeds the MCL? - [ ] Nothing, as long as the levels decline eventually. - [x] Inform the public and take corrective action to reduce contaminant levels. - [ ] Increase water usage to dilute the contaminant. - [ ] File an exemption with the EPA for higher levels. > **Explanation:** If a water system's contaminant level exceeds the MCL, it must inform the public and take corrective measures to reduce the contaminant levels. ### What is a key consideration in setting an MCL other than health risks? - [ ] Mineral content of water - [ ] Water's aesthetic attributes - [ ] Feasibility of treatment technology - [x] Technological feasibility > **Explanation:** The EPA considers both health risks and technological feasibility when setting an MCL for a contaminant. ### Can states have different MCLs than those set by the EPA? - [x] Yes, but state MCLs must be at least as strict as federal MCLs. - [ ] No, states must adhere strictly to EPA's MCLs without deviation. - [ ] States can set any MCLs regardless of federal regulations. - [ ] Only in the event of a public health emergency. > **Explanation:** States can set their own MCLs as long as they are at least as strict as the federal standards set by the EPA. ### What is the MCL for lead in drinking water? - [ ] 0.1 mg/L - [ ] 0.01 mg/L - [x] 0.015 mg/L - [ ] 0.02 mg/L > **Explanation:** The MCL for lead in drinking water is set at 0.015 mg/L to safeguard public health. ### What is an MCLG, in relation to MCL? - [x] Maximum Contaminant Level Goal – a non-enforceable health-based goal. - [ ] Maximum Cost of Level Going-up – a financial threshold for water systems. - [ ] Minimal Contaminant Level Guidance – a recommendation for low contaminant levels. - [ ] Major Contaminant Level Guard – a preventive measure for major pollutants. > **Explanation:** An MCLG, or Maximum Contaminant Level Goal, is a non-enforceable health-based goal where no known or anticipated adverse effects on health occur. ### What is an example of a contaminant with an established MCL? - [ ] Hydrogen - [ ] Silver - [x] Benzene - [ ] Oxygen > **Explanation:** Benzene is one example of a contaminant with an established MCL, set by the EPA. ### Why might treatment techniques be employed instead of setting an MCL? - [ ] When water quality goals are unclear. - [x] When it's not economically or technologically feasible to establish an MCL. - [ ] To enhance the aesthetic qualities of water. - [ ] To avoid legal responsibilities. > **Explanation:** Treatment techniques are used when it's not economically or technologically feasible to set an MCL for a particular contaminant. ### What U.S. law governs the setting of MCLs? - [ ] Clean Air Act - [x] Safe Drinking Water Act (SDWA) - [ ] National Environmental Policy Act - [ ] Water Pollution Control Act > **Explanation:** The Safe Drinking Water Act (SDWA) governs the setting of Maximum Contaminant Levels (MCLs) for public drinking water systems in the United States.