The Safe Drinking Water Act (SDWA) Section 1412 provides the legal framework under which the U.S. Environmental Protection Agency establishes Maximum Contaminant Levels (MCLs) for substances in public water systems. As PFAS contamination has emerged as a nationwide concern, this statutory mechanism has become central to the regulatory response—culminating in EPA’s historic April 2024 final rule setting enforceable MCLs for six PFAS compounds.
The MCL-Setting Process Under Section 1412
Under Section 1412, EPA must first designate a contaminant as a candidate for regulation if it poses a health risk, occurs in public water systems, and if regulation presents a meaningful opportunity to reduce health risk. Once designated, EPA proposes a Maximum Contaminant Level Goal (MCLG)—a non-enforceable health target set at a level with no known or anticipated adverse health effects. For PFOA and PFOS, EPA set MCLGs at zero, reflecting their carcinogenic classification.
The enforceable MCL is then set as close to the MCLG as is technically and economically feasible. EPA must weigh analytical detection limits, available treatment technologies, and costs against benefits. For PFOA and PFOS, the final MCLs were set at 4 parts per trillion (ppt)—near the limit of accurate laboratory measurement. For PFNA, PFHxS, and HFPO-DA (GenX), MCLs were set at 10 ppt each, while a hazard index approach governs mixtures.
Implementation Timeline and Compliance Obligations
Public water systems must monitor for all six regulated PFAS within two years of the rule’s effective date—by 2026. Systems exceeding MCLs have five years to come into compliance through treatment installation or alternative water sourcing. EPA estimates roughly 6–10% of the approximately 66,000 regulated public water systems will need to take action, serving an estimated 100 million people.
The rule also triggers Unregulated Contaminant Monitoring Rule (UCMR) obligations for a broader list of PFAS compounds not yet regulated, building the occurrence data needed for future rulemaking. Utilities face significant capital expenditure—EPA estimates $772 million to $1.2 billion annually in compliance costs, offset by estimated health benefits of $1.1–1.6 billion per year from avoided illness and mortality.
Section 1412’s cost-feasibility standard distinguishes it from risk-only approaches. Critics argue it allows contaminants to remain above health-protective levels when treatment is costly, while proponents maintain that balancing economic feasibility with risk reduction is essential for practical implementation across thousands of water utilities of varying size and resources.