4 The record articles

Drinking Water and the CCL5

Posted: November 15th, 2022

Authors: Kayla T. 

The United States Environmental Protection Agency (U.S. EPA) has recently published an update to the Contaminant Candidate List (CCL) – this is the fifth time this list has been updated since it was first published in 1996, making this the CCL5. The CCL lists contaminants in drinking water that are known or are anticipated to occur in public water systems but are not currently subject to any national primary drinking water standards, as set forth by the Safe Drinking Water Act (SDWA). U.S. EPA is required to review and update the CLL on a 5-year cycle and to consider the effect of contaminants on different population subgroups who could be exposed. The most recent CCL5 includes the following:

  • 66 Individual Chemicals
  • Three chemical groups
    • Cyanotoxins
    • Disinfection byproducts (DBPs)
    • Per- and Polyfluoroalkyl Substances (PFAS)
  • 12 Microbial Contaminants

The CCL contains chemical groups, instead of only listing specific chemicals, because the chemical groups meet the CCL requirements and are also identified as priorities under other U.S. EPA actions. Just because a group is listed as a single line item, it does not mean that the group will be regulated as a whole in the future. For example, U.S. EPA plans to propose national primary drinking water standards for perfluorooctanic acid (PFOA) and perfluorooctane sulfonate (PFOS)—two specific subgroups of PFAS—in late 2022. These two substances were included in the CCL4 that was published in February 2021 and will soon be subject to a proposed regulation nearly two years later.

One of the major changes in the CCL5 is the expansion of the definition of PFAS as it pertains to the chemical group listed in the CCL. This update was championed by both U.S. EPA’s Science Advisory Board (SAB) and drinking water utilities. However, industry stakeholders have been cautious in expanding PFAS definitions since not all PFAS pose the same health and environmental risks.

The updated PFAS definition in CCL5 was authored specifically to target types of PFAS known to occur in drinking water. PFAS are classified by their molecular substructures, and the updated definition captures PFAS that have ether substructures or are highly branched. U.S. EPA has made it clear that as the science of PFAS is further explored, the definition of PFAS and how they are subcategorized is likely to evolve as well.

It is important to note that although a listing on the CCL is the first step in the regulatory process, it does not guarantee that any particular contaminant will be regulated in the future. The law requires that U.S. EPA make regulatory determinations for at least five contaminants from the most recent CCL within five years after the completion of the previous set of regulatory determinations. This ensures that emerging contaminants are being considered and that the CCL recommendations are further researched.

ALL4 recommends that facilities that engage in any of the following processes familiarize themselves with the CCL5 and note any listed contaminants that are likely present in either influent or effluent streams.

  • Industrial Wastewater Discharge
  • Industrial Stormwater Discharge
  • On-Site Drinking Water Treatment Plant
  • Process Water Treatment Plant

The SDWA ensures that drinking water standards and regulations are maintained as current, and ALL4 is tracking emerging contaminants of concern with regards to water quality. Please contact our EHS Practice Director, Heather Brinkerhoff (hbrinkerhoff@all4inc.com) with any question you may have.


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