Proposed Basin Plan Amendment – Chlorine Water Quality Objectives and Total Residual Chlorine Effluent Limitations for Wastewater Discharges


Wastewater treatment plants that use chlorine to disinfect their effluent or have the potential to discharge chlorine are subject to a technology-based effluent limitation of 0.0 milligrams per liter for total residual chlorine. Total residual chlorine refers to the sum of free and combined chlorine formed during wastewater chlorination process. Total residual chlorine is toxic to aquatic organisms at very low concentrations. To ensure compliance with this stringent effluent limitation, plant operators have routinely added excess dechlorination chemicals, normally sodium bisulfite, to neutralize any remaining TRC in the effluent. This use of excess chemicals results in extra operational cost and potential water quality concerns without providing environmental benefits.

Water Board staff proposed a Basin Plan amendment that would add chlorine water quality objectives to the Basin Plan, the same as the U.S. EPA’s chlorine national ambient water quality criteria, and replace the technology-based total residual chlorine effluent limitation with water quality-based effluent limitations developed from the new chlorine objectives. The proposed water quality objectives and effluent limitations would protect beneficial uses and provide economic and environmental benefits by minimizing the need for excess sodium bisulfate use.

The proposed amendment also includes some minor non-regulatory updates to harmonize the Basin Plan with “Part 2 of the Water Quality Control Plan for Inland Surface Waters, Enclosed Bays, and Estuaries of California—Tribal and Subsistence Fishing Beneficial Uses and Mercury Provisions,” or the Statewide Mercury Provisions, and to correct a previous error with regards to the applicability of the Oil and Grease effluent limits.
Clarifier at a wastewater treatment plant

Basin Plan Amendment Approval Process

The Office of Administrative Law approved this Basin Plan amendment on October 22, 2021 (OAL file number 2021-0910-01S).

The State Water Resources Control Board adopted the resolution (Order No. 2021-0016) approving this Basin Plan amendment on May 18, 2021.

San Francisco Bay Regional Water Board Adoption Process

The Regional Water Board adopted a resolution approving this Basin Plan amendment on November 18, 2020. Regional Water Board adopted resolution and supporting documents include the following:

Other Related Resources

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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