The D.C. Circuit Overrules EPA On Regulating Perchlorate

The U.S. Court of Appeals for the District of Columbia Circuit has the latest word in the long-running saga concerning regulation of the contaminant perchlorate in its decision dated May 9, 2023, when it ruled the U.S. Environmental Protection Agency (EPA) must issue drinking water regulations setting a Maximum Contaminant Level (MCL) for perchlorate. This has been a long road since Massachusetts was one of the first states to regulate perchlorate in drinking water in 2006, as described by Holland & Knight in "Massachusetts Proposes First-in-the-Nation Drinking Water and Cleanup Standards of 2 ppb for the Chemical Perchlorate."

Background

Beginning with the EPA's Unregulated Contaminant Monitoring Rule (UCMR) promulgated Sept. 17, 1999, EPA began collecting data from public drinking water suppliers on perchlorate, which is a highly soluble compound commonly used in solid rocket propellants, munitions, fireworks, signal flares and blasting materials. EPA and