On May 23, 2019, the U.S. Environmental Protection Agency Administrator (EPA) signed a proposed rulemaking for the regulation of perchlorate in drinking water to establish a perchlorate Maximum Contaminant Level Goal (MCLG) at 0.056 mg/L as well as a Maximum Contaminant Level (MCL) at the same level under the Safe Drinking Water Act (SDWA). In the notice, EPA is requesting comment on the following three alternative regulatory options:


  • An MCL and MCLG for perchlorate set at 0.018 mg/L.
  • An MCL and MCLG for perchlorate set at 0.090 mg/L.
  • Withdrawal of the Agency’s 2011 determination to regulate perchlorate in drinking water.


The Agency is also requesting public input on all parts of the proposal but is particularly interested in feedback on the monitoring and reporting requirements. Persons wishing to comment on the proposal have 60 days from publication in the Federal Register and should reference Docket ID No. EPA-HQ-OW-2018-0780. A copy of the pre-publication rule version, can be found HERE. Public comments can be submitted at HERE.  Additional background information about perchlorate regulation can be found on EPA’s website HERE.


In October of 2008, EPA published a proposal to set an MCL for perchlorate at 0.015 mg/L. At that time, EPA determined that the risk posed by perchlorate in drinking water systems was low given occurrence data collected under the Unregulated Contaminant Monitoring Rule (UCMR). Specifically, EPA collected data showing that less than one percent of systems serving approximately 1 million people had perchlorate at levels above 0.015 mg/L.


Perchlorate is commonly used in solid rocket propellants, munitions, fireworks, airbag initiators for vehicles, matches, and signal flares. Perchlorate may occur naturally, particularly in arid regions such as the southwestern United States and is found as an impurity in hypochlorite solutions used for drinking water treatment and nitrate salts used to produce nitrate fertilizers, explosives, and other products. Some states have already established their own standards, including Massachusetts (0.002 mg/L) and California (0.006 mg/L).