On January 6, the EPA issued a proposal to establish a National Primary Drinking Water Regulation (NPDWR) for perchlorate – a chemical linked to thyroid disruption. This was the result of a 2023 DC Circuit Court Ruling that ordered the EPA to begin regulating perchlorate by January 2026, after the Agency, in 2020, reversed its 2011 determination that perchlorate occurs at levels of public health concern in US drinking water and should be regulated.
The DC Circuit Court was correct in ruling that the Safe Drinking Water Act does not give EPA the discretion to reverse its decision that perchlorate warranted regulation. The statute is unambiguous once EPA makes its regulatory determination, a two-step mandatory process must be followed: setting a Maximum Contaminant Level Goal (MCLG), an unenforceable aspirational level, and an enforceable Maximum Contaminant Level (MCL), that must be set “as close to the maximum contaminant level goal as feasible.”
The EPA followed the court ruling, if somewhat reluctantly. It was clear they did not believe in the value of the regulation, stating, “The Administrator has determined that the benefits of this regulation would not justify the costs; however, the EPA is required to issue [a response].” The EPA failed to acknowledge the auxiliary benefit of this regulation in terms of cleaning up military sites and neighboring communities, an ongoing issue in this country.
Let’s examine the practical implications of this regulation.
Understanding Perchlorate
Perchlorate is a chemical ion that does not exist on its own; it must be bound to other chemicals, such as ammonia, magnesium, and potassium. It can form naturally in the air and is found at low levels in rain and snow. It is also manufactured primarily as an oxidizer for use in solid fuels to power rockets, missiles, and fireworks, and as airbag initiators for vehicles, matches, and signal flares.
Perchlorate has been found at low levels in drinking water supplies across the US, but the major concern is its contamination of military bases and facilities where it was used extensively.
Perchlorate health concerns result from its inhibition of iodide uptake, which can interfere with a person’s thyroid gland. Thyroid hormones are critical for growth and development, and changes in thyroid levels during pregnancy can be associated with adverse developmental effects in offspring.
This is not a new issue. In fact, as I wrote about in my 2019 article, it goes back to the 1990s when perchlorate was first discovered in drinking water wells across the US, with the EPA first evaluating its health effects and calling for perchlorate monitoring in select public water systems in 1999. Twenty-seven years later, after countless back-and-forth decisions between different Administrations, the EPA may have finally reached the end of the road and is forced to act on perchlorate.
The Proposed Regulation
On January 6, the EPA proposed both an MCLG at 20 micrograms per liter and alternative MCLs at 20, 40, or 80 micrograms per liter. These were intended to protect against thyroid hormone disruption in a sensitive population, i.e., pregnant women. MCLs are enforceable drinking water regulations, and the EPA requires that drinking water systems monitor for perchlorate and reduce it to the MCL when detected.
The official comment period is open until March, with the EPA to review the comments and draft a final rule by the May 2027 deadline. Although the EPA proposed three alternative MCLs, the final MCL is likely to be set at 20 micrograms per liter, since the Safe Drinking Water Act mandates that the MCL be set as close to the MCLG as feasible, and there is no “feasible” reason to set the level above 20 micrograms per liter. The date by which a water system must take action to reduce its perchlorate levels below the MCL is three years after publication of the final rule, i.e., May 2030.
EPA says this regulation will not have a meaningful positive effect on public health because, although perchlorate may have an adverse impact on health at high levels, the levels found in drinking water are sufficiently low not to affect human health. There are no known instances of adverse effects from low-level perchlorate exposure; it is only harmful to people who are exposed to very high levels and have very low thyroid hormone levels. The EPA set the perchlorate regulation to protect the fetuses of iodine-deficient women with low thyroid hormone levels in the first trimester of pregnancy, a very limited subset of the population.
The EPA estimated that the annual cost of the proposed MCL (20 micrograms per liter) is $16 million with an annual benefit of $8 million.
Implications of the Regulation
Even without a federal drinking water regulation, levels of perchlorate have decreased in public drinking water supplies over the years, as states and municipalities have acted on their own. Although only two States, Massachusetts and California, have enforceable standards for perchlorate in drinking water, eight other states have non-regulatory action levels or advisories [1].
However, there is an important benefit from federal regulation, adding momentum to the cleanup of military sites contaminated with perchlorate.
A 2005 GAO Report said that perchlorate had been found at almost 400 sites across 35 states, estimating that 65% of the sites were defense-related industries, including propellant manufacturing, rocket motor testing, and explosive testing and disposal. There is no central list to track how many of these sites have been cleaned up.
The GAO further discussed the problems with perchlorate cleanup in its 2007 report on emerging contaminants, stating that since no drinking water standard exists for perchlorate, the Department of War’s (DOW) responsibilities are less clear than with other regulated contaminants. The DOW has used a patchwork of statutes, regulations, and general oversight authorities to address perchlorate contamination. Without a federal drinking water regulation, the DOW set a “level of concern” at 24 micrograms per liter for perchlorate cleanup, almost identical to the EPA’s proposed MCL of 20 micrograms per liter.
Among the bases undergoing perchlorate cleanup:
- Otis Air National Guard Base (Massachusetts)
- El Toro Marine Corps Air Station (California)
- Edwards Air Force Base (California)
- Kirkland Air Force Base (New Mexico)
- Letterkenny Army Depot (Pennsylvania)
There are hundreds of smaller military sites undergoing cleanup across the country. This is a problem not just at the sites themselves, but in the neighboring communities.
The EPA’s proposed perchlorate regulation underscores a persistent tension in environmental policy—between legal mandates, scientific judgment, and cost-benefit realities. By the Agency’s own assessment, perchlorate at levels found in US drinking water poses little to no measurable public health risk for the general population, and even the projected benefits of regulation fall short of the estimated costs. This makes the regulation notable less for its direct health impact than for the precedent it enforces. Once the EPA determines a contaminant warrants regulation, the Safe Drinking Water Act leaves no room for reversal or delay.
Still, the regulation may achieve an outcome that decades of fragmented oversight could not. A clear, enforceable federal standard removes ambiguity for the DOW and accelerates long-overdue cleanup of perchlorate-contaminated military installations and neighboring communities. If that is the regulation’s lasting contribution, it will serve as a reminder that regulatory action, even when scientifically marginal, can have practical and overdue consequences. What remains troubling is not the standard itself, but the nearly 30 years it took to arrive at it.
[1] New York, Nevada, Arizona, Maryland, New Mexico, Texas, Oregon, and New Hampshire
