Program Manager message:
Colorado’s Safe Drinking Water Program is not the only such program in the United States with a newsletter. Over the years, I have subscribed to a few of these newsletters, and sometimes we have reprinted or used articles from them with permission. In this case, I recently read an excellent article in the Arkansas Drinking Water Update newsletter regarding EPA’s proposed perchlorate rule. I reached out to my counterpart in Arkansas, Lance Jones, who authored the article and gained his permission to reprint it here. We are also adding a Colorado perspective regarding likely perchlorate rule impacts on Colorado’s public water systems.
➽ Ron Falco, P.E., Safe Drinking Water Program Manager
EPA Proposes Perchlorate Rule
On January 2, 2026, the Environmental Protection Agency (EPA) issued a proposed Rule under the Safe Drinking Water Act to regulate perchlorate (ClO4-) in drinking water as part of the National Primary Drinking Water Standards.
The proposed Rule includes a Maximum Contaminant Level Goal (MCLG) of 20 micrograms per liter (ug/L). EPA is also co-proposing enforceable Maximum Contaminant Levels (MCLs) of 20 ug/L, 40 ug/L, or 80 ug/L for perchlorate and will apply to community and non-transient public water systems.
Initial monitoring consists of quarterly monitoring or semi-annual for small ground water systems, for a 12-month period, with routine monitoring determined by those results. Systems with a running annual average above the MCL require quarterly monitoring, systems less than the MCL but greater than or equal to 4 ug/L require annual monitoring (surface water) or triennial (ground water) monitoring, and every 9 years for systems less than 4 ug/L.
Perchlorate has had a back-and-forth regulatory history for the past 25+ years. Starting with including perchlorate levels in drinking water systems under the 1999 Unregulated Contaminant Monitoring Rule (UCMR). The results led to a 2011 decision by EPA to regulate perchlorate in drinking water. EPA proposed a Rule to regulate perchlorate in drinking water in 2019. In July 2020, EPA withdrew the determination to regulate perchlorate. A legal challenge of the decision to withdraw was filed and led to a 2023 court decision to vacate the withdrawal. EPA entered into a consent decree to sign and issue a final Rule to regulate perchlorate in drinking water by May 21, 2027.
Perchlorate is commonly used in solid rocket propellants, munitions, fireworks, matches, signal flares, and vehicle airbag initiators. It has also been associated with some imported fertilizers and trace amounts can result from improper handling and degradation of hypochlorite solutions.
Perchlorate can potentially interfere with the thyroid gland hormone production. Changes in thyroid hormone production in pregnant women are associated with adverse neurodevelopmental effects in their children. Thyroid hormone level changes at other life stages can lead to hyperthyroidism, developmental outcomes, and cardiovascular system impacts.
EPA’s data show that perchlorate is not widespread in drinking water systems and EPA expects less than 1,300 of the over 135,000 regulated water systems nationwide to find perchlorate levels above the proposed limits. For systems that do find elevated levels of perchlorate, treatment options include ion exchange, biological reduction, reverse osmosis, and blending with another source.
The sampling of several Arkansas water systems in 2001 and 2002 found no detects of perchlorate. ASD will add sampling of perchlorate to the current compliance monitoring efforts upon EPA promulgating a final Rule.
More information about perchlorate in drinking water can be found on the EPA website at:
https://www.epa.gov/sdwa/perchlorate-drinking-water#proposed-perchlorate
➽ Lance Jones, P.E. Health Program Administrator, Arkansas DPHP Environmental Health Engineering
