Proposed Basin Plan Amendment to Correct Errors in Freshwater Metal Water Quality Objectives, to Clarify the Basis to Establish Dilution Credits for Non-Priority Pollutants, and to Allow Establishment of Alternative Cyanide Dilution Credits and Mercury Concentration Triggers for Wastewater Treatment Operations


The San Francisco Bay Regional Water Quality Control Board (Regional 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); 2) clarify that other applicable policies, regulations, and guidance aside from the State Implementation Policy (SIP) may be used when developing dilution credits for non-priority pollutants; 3) allow establishment of alternative cyanide dilution credits and mercury concentration triggers to accommodate water recycling projects or to reflect material and substantial changes in wastewater treatment operations and conditions; and 4) clean up Table 3-4 to add clarifications and update obsolete information.

After the Regional Water Board adopts the Basin Plan amendment, it must also be approved by the State Water Resources Control Board (State Water Board), the Office of Administrative and Law (OAL), and U.S. Environmental Protection Agency (U.S. EPA) before the amendment language takes effect and incorporated into the Basin Plan.

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Silicon Valley Advanced Water Purification Center (Photo courtesy of

Regional Water Board Adoption

On December 13, 2023, the Regional Water Board adopted a resolution approving the Basin Plan amendment. The adopted resolution and final staff report can be found here: Other supporting documents for the Regional Water Board adoption, including Staff Summary Report, Response to Comments, can be found on the Board meeting agenda page.

State Water Board Approval Process

On January 12, 2024, the State Water Board published the Notice of Opportunity to Comment on the proposed approval of the Basin Plan amendment. The 30-day public review period ends by noon on February 12, 2024.

The State Water Board will consider approving the Basin Plan amendment at its April 17, 2024 meeting. Here is the Notice of the Meeting, where you can find details about when and where the meeting is to be held, how to attend the meeting, either in person or virtually, etc.

Documents for the State Water Board consideration, including the Agenda Item and the Draft Resolution, can be found on the meeting agenda (Item 3 under Wednesday, April 17, 2024, Board meeting)

Timeline and Important Dates

  • January 12 – February 12, 2024, public review for State Water Board approval
  • December 13, 2023 –Regional Water Board adoption
  • September 22 – October 7, 2023, public review for Regional Water Board adoption

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 “All Basin Planning/TMDL” or “Basin Planning/TMDL Projects by Area” 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 4/8/24)