Overview of the CCL 6 Approach

The methodology for developing the Sixth Contaminant Candidate List (CCL 6) is based on the three-step framework used previously for the CCLs (CCL 3, CCL 4, and CCL 5). The CCL 6 process closely mirrored the updates implemented during the most recent CCL 5 cycle that have allowed EPA to consider a larger number of contaminants, enhance transparency in the data being evaluated, and improve efficiency of transferring information compiled for CCL to other SDWA processes such as Regulatory Determination and UCMR activities.

The CCL framework consists of three steps: 

Step 1 identifies a broad universe of potential drinking water contaminants, called the CCL 6 Chemical and Microbial Universes. The EPA initially considered approximately 25,000 chemicals and 1,450 microbial contaminants.

Step 2 applies screening criteria to the CCL 6 Chemical and Microbial Universes. The EPA identified 240 chemicals and 36 microbial contaminants for further evaluation, called Preliminary CCLs (PCCLs), based on their potential to occur in public water systems and their potential for public health concern.

Step 3 selects chemical and microbial contaminants from each respective PCCL to include on the CCL 6 based on more detailed evaluation of occurrence and health effects and expert judgment. The CCL 6 process concluded with the selection of 75 chemicals, 4 chemical groups (disinfection byproducts (DBPs), microplastics, per- and polyfluoroalkyl substances (PFAS), and pharmaceuticals) and 9 microbes.