On June 26, 2019, EPA published a Notice of Proposed Rulemaking requesting comment on a proposed Maximum Contaminant Level (MCL) for perchlorate under the Safe Drinking Water Act (SDWA). Perchlorate is both a man-made and naturally-occurring chemical, most commonly found in industrial operations associated with the use or manufacture of rocket fuel, missiles and fireworks. Perchlorate inhibits the uptake of iodide to the thyroid and has been detected in certain public water supply systems, primarily in the western United States. In its Notice, EPA proposes an MCL of 56 µg/L, but at the same time requests public comment on whether the MCL should be set at a higher or lower standard, or whether the agency should re-evaluate its decision to regulate perchlorate based on updated data. This rule, if finalized, could affect thousands of public water systems that would be required to comply with the new standard, as well as state and tribal agencies responsible for drinking water regulatory development and enforcement.

EPA first identified perchlorate for potential regulation under the SDWA in 1998, and in 2011 made a determination to regulate perchlorate through the National Primary Drinking Water Standards. Pursuant to its determination, EPA now proposes to set both a Maximum Contaminant Level Goal (MCLG) and an MCL at 56 µg/L, a level public water supply providers can achieve with the existing treatment technologies. EPA selected this level based on its 2011 findings and more recent 2017 peer-reviewed studies showing this level of exposure to be acceptable to even vulnerable populations. EPA also invites the public to comment on two potential alternative values – a lower level of 18 µg/L and a higher level of 90 µg/L, both of which it states are feasible with current treatment technologies. The proposed rulemaking also includes monitoring and reporting obligations, including adding perchlorate to consumer confidence reports that water suppliers make available to their customers. EPA also provides a list of treatment technologies to achieve compliance with the proposed standards. These methods include non-treatment options that may be used in lieu of installing and operating new treatment methods (e.g. blending existing water sources, replacing a perchlorate-contaminated source of drinking water with a new source, or purchasing compliant water from another system).

In addition, EPA requests comment on the option of withdrawing its 2011 determination to regulate perchlorate based on updated studies suggesting that perchlorate is not present in high enough levels in public water systems to constitute a health concern. EPA suggest that only 0.03% of public water systems would have perchlorate present at even the lowest level of 18 µg/L, but the proposed MCLs and MCLGs would require more than 60,000 public water systems to monitor perchlorate levels. As a result, EPA is soliciting feedback on whether its proposed MCLGs and MCLs will have a meaningful impact on reducing perchlorate’s adverse health effects.