NDWAC Sends Recommendations To EPA On Potential MDBP Rule Revisions

On December 14, the National Drinking Water Advisory Council (NDWAC) sent a letter to EPA Administrator Regan outlining the group’s recommendations for potential revisions to the Microbial and Disinfection Byproducts (MDBP) rules. In 2021, the NDWAC was tasked with developing and providing these recommendations, aiming for consensus whenever possible. The letter includes 13 total recommendations initially developed by the NDWAC MDBP Working Group, with 11 of these reaching full consensus.

The recommendations that received consensus address various topics: premise plumbing, addressing data and analysis gaps in DPBs of emerging concern, storage tank maintenance, chloramination, consecutive systems, source control, environmental justice, TMF capacity, primacy agency capacity, overall data gaps, and the Ground Water Under the Direct influence of Surface Water definition. These recommendations include using Safe Drinking Water Act (SDWA) authorities but also extend beyond the SDWA realm by recommending the use of the Clean Water (CWA), Clean Air Act (CAA), Toxic Substances Control Act (TSCA), and other regulatory and non-regulatory actions.

However, the NDWAC could not reach full consensus on two recommendations: numeric disinfectant residual and precursor control. Concerns were raised regarding the disinfectant residual, as the language included in the report might disrupt the balance between distribution residuals and DBP formation. Specifically, there were concerns about the proposed numeric value, potentially as high as 0.5 mg/L for free chlorine and 0.7 mg/L for total chlorine. As the precursor control recommendation, concerns were focused on maintaining a water system’s ability to explore several alternative compliance actions rather than mandating one potentially very expensive option.

Per the 2020 Waterkeepers Alliance v. EPA settlement agreement, EPA must propose revisions by summer of 2024. However, EPA might delay this proposal by 12 months due to its consultation with the NDWAC through the Working Group process. The final rule must be promulgated by September 30, 2027, unless EPA determines no revisions are needed.