On October 28, the EPA published the Final Fifth Drinking Water Contaminant Candidate List. Under the Safe Drinking Water Act (SDWA), the EPA is required to publish a new Contaminant Candidate List (CCL) every five years. The CCL contains a list of contaminants that are currently not subject to any national primary drinking water regulations but are anticipated to occur in public water systems and may require regulation.
The CCL 5 lists 66 chemicals, three chemical groups, and 12 microbial contaminants. The list includes some of EPA’s emerging contaminants of concern, such as 1,4-Dioxane (which was recently the subject of an EPA risk evaluation under the Toxic Substance Control Act (TSCA)) and 1,2,3-Trichloropropane (for which EPA has already set a screening level in tap water).
The CCL 5 also includes per-and polyfluoroalkyl substances (PFAS) as a chemical group. The EPA noted that because there may be over 4,000 different types of PFAS chemicals, listing and considering PFAS as a class, rather than individually, will ease the administrative burden of gathering data, analyzing, and evaluating these chemicals. Notably, the two most infamous types of PFAS — PFOA and PFOS — are specifically excluded from the CCL 5 since they are already subject to an EPA regulatory action. Proposed national drinking water standards for PFOA and PFOS are currently pending interagency review with the Office of Management and Budget.
The CCL 5’s definition of PFAS appears to be broader than prior definitions that the EPA has recently used. For example, the CCL 5’s definition of PFAS includes more chemical structures than the definition of PFAS contained within a recently proposed rule under TSCA, which only includes around 1,364 out of the 4,000 different types of PFAS. EPA has indicated that it will eventually provide a list of the PFAS that meet the CCL 5 definition on its CompTox Chemicals Dashboard.
Although PFAS have been listed on the CCL 5 as a class, that does not necessarily mean that EPA will decide to regulate PFAS as a class under the SDWA. This is just the first step of a longer screening and evaluation process.