Proposed Basin Plan Amendment—Freshwater Water Quality objectives, Dilution Credits, and Mercury Triggers


Water Board has proposed an amendment to the Water Quality Control Plan for the San Francisco Bay Basin (Basin Plan), which would 1) correct errors in freshwater objective calculation formulas for selected metals to be consistent with the California Toxics Rule (CTR) or National Toxics Rule (NTR), from where these objectives originate; 2) clarify that additional applicable policies, regulations, and guidance aside from the State Implementation Policy (SIP) may be based on when developing dilution credits for non-priority pollutants; 3) allow establishment of alternative cyanide dilution credits and mercury concentration triggers to reflect changes in wastewater treatment operations that implement water recycling projects , water conservation, or use new materials in industrial production process; and 4) general cleanup to add clarifications, update obsolete information, and improve document formatting.

water tank

Silicon Valley Advanced Water Purification Center (Photo courtesy of

San Francisco Bay Regional Water Board Adoption Process

We are currently seeking public input on the proposed Basin Plan amendment.

The Public Notice and the draft Staff Report are available below in the section entitled, "Available Documents". The draft Staff Report includes a description of the proposed changes, the rationale for the proposed changes, a California Environmental Quality Act (CEQA) analysis, a demonstration of the consistency of the proposed amendment with federal and state antidegradation policies and antibacksliding requirements, and a CEQA environmental checklist, which serves in its entirety as a substitute CEQA environmental document.

The Water Board plans to consider a resolution approving this Basin Plan amendment at its December 13, 2023 Board meeting (agenda will be available one week before the meeting date).

Basin Plan Amendment Approval Process

After Water Board adoption of the Basin Plan amendment, it must also be approved by the state Water Resources Control Board, the Office of Administrative and Law, and U.S. EPA. The amendnent language is then incorporated into the Basin Plan. Relevant documents and key dates for each step of the process will be provided on this webpage.

Important Dates

September 22, 2023 – Start of 45-day public review period

November 7, 2023 – End of public review period

December 13, 2023 – Water Board hearing

Available Documents

Other Related Resources

Subscribe to Our Mailing List

The Regional Water Board maintains email notification lists. To ensure you receive future information on this and other Basin Plan amendments, please subscribe to the “All Basin Planning/TMDL” under “Basin Planning/TMDLs.” The instructions for subscribing to the list are provided on the subscription page, which you can reach by clicking here.

For more information contact:
Tong Yin, Ph.D., P.E.
Water Resource Control Engineer
San Francisco Bay Water Quality Control Board
1515 Clay Street, Suite 1400
Oakland, CA 94612
Phone: (510) 622-2418

  (Page last updated 9/21/23)