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Perchlorate Rears Its Head Again
On January 6, 2026, the Environmental Protection Agency (EPA) published a proposed National Primary Drinking Water Regulation (NPDWR) for Perchlorate (91 FR 398).
EPA had previously made a regulatory determination to regulate perchlorate in drinking water (76 FR 7762, February 11, 2011) and subsequently withdrew the determination (85 FR 43990, July 21, 2020).
On May 9, 2023, the Natural Resources Defense Council (NRDC) sued the EPA over this latter action in D.C. District Court, claiming that EPA is required by the Safe Drinking Water Act to propose and finalize a NPDWR and Maximum Contaminant Level Goal (MCLG) for perchlorate once a final regulatory determination to regulate it had been issued. The District Court ruled in favor of the NRDC, vacating the regulatory determination withdrawal and requiring EPA to move forward with the rulemaking.
What the Proposed Rule Requires
The Proposed Perchlorate Rule proposes a Maximum Contaminant Level (MCL) and a Maximum Contaminant Level Goal (MCLG) of 0.02 mg/L, and will require monitoring, reporting, and public notice requirements. It also will require mitigation of perchlorate levels that exceed the final MCL by Community Water Systems (CWSs) and Non-Transient Non-Community Water Systems (NTNCWSs). The action also proposed alternative MCLs of 0.04 mg/L, 0.06 mg/L, and 0.08 mg/L for consideration.
Most of the regulatory burden will be the monitoring requirements, which all CWSs and NTNCWSs will have to conduct regardless of perchlorate levels. All PWSs will be required to conduct and complete initial monitoring by the compliance date of the rule (usually three years after publication of the final rule in the Federal Register). The initial monitoring results will be used to establish compliance monitoring frequencies, shown in the table below.
Monitoring Requirements
Monitoring Requirements in Proposed Perchlorate Rule (91 FR 398, January 6, 2026)
- To be completed by the compliance date.
- Starting after the compliance date.
Violations, Mitigation, and Public Notification
In the proposed rule, a violation of the MCL is calculated as an average of the result of a sample collected after the compliance date and the result of a repeat sample taken within a specified period of time (e.g., 24 hours) after the initial sample. An MCL violation is a trigger to initiate mitigation measures (e.g., blending, biological treatment, reverse osmosis) to reduce perchlorate below the MCL.
In the proposal, an MCL violation will require a Tier 1 public notification, which requires notifying the EPA, state primacy agency, and the public within 24 hours of receiving the analytical result. Monitoring and reporting violations are Tier 3, requiring public notice within one year of the violation (e.g., Annual Consumer Confidence Report). The public notifications should include the information required by the public notification regulations.
Timeline and Next Steps
final rule after the close of the public comment period (approximately September 9, 2027).
The proposed rule can be found here: Federal Register :: National Primary Drinking Water Regulation for Perchlorate.
In the proposal, an MCL violation will require a Tier 1 public notification, which requires notifying the EPA, state primacy agency, and the public within 24 hours of receiving the analytical result. Monitoring and reporting violations are Tier 3, requiring public notice within one year of the violation (e.g., Annual Consumer Confidence Report). The public notifications should include the information required by the public notification regulations.
SAMS Water will be ready to assist clients with required monitoring and reporting requirements upon final rule publication.
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About The Author
At NJBSoft, we’re proud to collaborate with experts like Robert Hollander, P.E., whose extensive experience in water quality and regulatory compliance allows us to design SAMS in order to meet industry needs. Bob’s leadership and deep industry knowledge supports utilities in staying organized, compliant, and focused on protecting public health every day.
Robert Hollander
- 45 years of experience in water quality, regulatory compliance, and utility management
- President of Hollander Consulting Services
- Held senior roles at the City of Peoria, City of Phoenix, and the Arizona Department of Environmental Quality
- Served as President of the AZ Water Association and the Western Coalition of Arid States
- Licensed Professional Engineer in Arizona with multiple Grade 3 operator certifications
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