EPA Again Extends Deadline To Propose Enforceable National Drinking Water Standards For Perchlorate

The U.S. Environmental Protection Agency (EPA) has again extended its deadline from November 21, 2025, to January 2, 2026, to issue a proposed rule setting a Maximum Contaminant Level Goal (MCLG) and Nationwide Primary Drinking Water regulations for the chemical perchlorate. The November 21 deadline was established in a 2016 consent decree between the Natural Resources Defense Council (NRDC) and EPA. EPA informed the court on November 21 that it had reached an agreement with NRDC to extend the rulemaking deadline to January 2, 2026, in light of the recent federal government shutdown that lasted from October 1 until November 12.

According to EPA, 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 in nitrate salts used to produce nitrate fertilizers, explosives, and other products."

EPA has been considering nationwide drinking water standards for perchlorate since 2011, when the agency determined it had the authority to regulate the chemical under the federal Safe Drinking Water Act. This determination was based on EPA's finding that perchlorate may have an adverse effect on human health (specifically its interference with the thyroid hormone synthesis); that perchlorate occurs and/or has a substantial likelihood of occurring in public water systems with frequency and at levels of concern for public health; and that based on then-best available peer reviewed science EPA could meaningfully reduce public health risks from perchlorate in public water systems.

In June 2019, EPA proposed a regulation setting the enforceable Maximum Contaminant Level (MCL) and the health-based MCLG at 56 µg/L [note that µg/L are frequently referred to as "parts per billion"]. EPA did not finalize those proposed perchlorate standards and instead in July 2020 proposed to rescind the 2011 regulatory authority determination. In 2023, the U.S. Court of Appeals for the District of Columbia Circuit held that EPA lacked authority to rescind the 2011 regulatory authority determination, forcing the agency to proceed with a national drinking water rulemaking proposal as required by consent decree in the separate SDNY litigation (D.C. Circuit No. 20-1335).

At present, it is unclear what levels (both enforceable and not) EPA will ultimately propose for perchlorate in the forthcoming rulemaking. In EPA's 2019 proposal, although the agency ultimately proposed enforceable standards at 56 µg/L, it also took comment on proposals to regulate perchlorate in drinking water at alternative levels of 18 µg/L and 90 µg/L.

In the absence of nationwide drinking water standards set by EPA, some states have already established their own enforceable drinking water standards for perchlorate. Massachusetts set a first-in-the-nation enforceable MCL of 2 µg/L and California has set an enforceable MCL of 6 µg/L (and it is currently reviewing whether to propose a lower MCL in the state). Other states have set action levels, health-based guidance, and non-enforceable goals for perchlorate in drinking water.

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