Ocean Standards - CWA §316(b) Regulation

Cooling Water Intake Structures
Once-Through Cooling

On May 4, 2010, the State Water Resources Control Board (State Water Board) adopted a Policy on the Use of Coastal and Estuarine Waters for Power Plant Cooling (Once-Through Cooling or OTC Policy). The OTC Policy became effective on October 1, 2010.

The OTC Policy establishes technology-based standards to implement federal Clean Water Act section 316(b) and reduce the harmful effects associated with cooling water intake structures for power generating facilities on marine and estuarine life. The OTC Policy applied to 19 existing power plants (including two nuclear plants) with the combined ability to withdraw almost 16 billion gallons of water per day from the state’s coastal and estuarine waters using a single-pass system, also known as once-through cooling (OTC). Closed-cycle wet cooling has been selected as Best Technology Available (BTA). Permittees must either reduce intake flow and velocity (Track 1) or reduce impacts to aquatic life comparably by other means (Track 2).

Ten plants have ceased their once-through cooling operations. Eight of the remaining plants have informed the State Water Board that they are planning to comply by retiring their existing OTC plants’ equipment. In some cases, plants will repower their locations with modern non-water-cooled systems. Dynegy’s Moss Landing Power Plant is the only OTC plant that is complying with the OTC Policy through Track 2.

Once-Through Cooling – Current Version – Effective November 30, 2020

 » Go to the Official Policy Documentation


The Statewide Advisory Committee on Cooling Water Intake Structures (SACCWIS) will convene on March 26, 2021, to consider adoption of the Draft 2021 Report of the SACCWIS.  The Draft 2021 Report of the SACCWIS recommends extending the OTC compliance date for Redondo Beach Generating Station for two years from December 31, 2021, through December 31, 2023, for system-wide grid reliability.

The Draft 2021 Report of the SACCWIS is available on the SACCWIS webpage.

NEW!  The California Public Utilities Commission submitted the Procurement Report for the first quarter of 2021 to the State Water Resources Control Board on March 16, 2021. On November 7, 2019, the California Public Utilities Commission adopted Decision 19-11-016, implementing short-term procurement to enhance electric system reliability, including the procurement of 3,300 megawatts of capacity by 2023.  This report provides the status of procurement for those projects that are anticipated to come online by August 1, 2021, the targeted online dates, and any risks of delays.

Public Meetings

Annual Meeting of the Statewide Advisory Committee on Cooling Water Intake Structures
(SACCWIS) to Consider Adoption of the Draft 2021 Report of the SACCWIS

March 26, 2021
1:00 pm – 3:00 pm
Video and Teleconferencing Meeting Only
No Physical Meeting Location
(Authorized by and in furtherance of Executive Orders N-29-20 and N-33-20)
Video Broadcast available at: https://video.calepa.ca.gov/
For more information, please see documents posted on the SACCWIS webpage.

Other Relevant Documents


The two committees listed below, were convened by the Executive Director of the State Water Board, as required by the OTC Policy. The committees are subject to the Bagley-Keene Open Meeting Act.

Statewide Advisory Committee on Cooling Water Intake Structures (SACCWIS)
SACCWIS was established to advise the State Water Board on the implementation of the OTC Policy to ensure that implementation plans and schedules established by the OTC Policy are realistic and will not cause disruption to the State’s electrical power supply. SACCWIS includes representatives from the California Energy Commission, California Public Utilities Commission, California Coastal Commission, California State Lands Commission, California Air Resources Board, California Independent System Operator, and the State Water Board.

Review Committee for Nuclear Fueled Power Plants
This Review Committee was established to oversee special studies, which investigated ability, alternatives, and cost, for the two nuclear-fueled power plants to meet OTC Policy requirements. The special studies were conducted by an independent third party with engineering experience with nuclear power plants, selected by the Executive Director of the State Water Board, and paid for by the two nuclear-fueled power plants subject to the OTC Policy.  The Review Committee included representatives from the SACCWIS agencies, the nuclear power companies, the environmental community, and staffs of the State Water Board and appropriate Regional Water Boards.

Permitting of Affected Power Plants

The OTC Policy is implemented through National Pollutant Discharge Elimination System (NPDES) permits. The applicable Regional Water Boards are responsible for implementing the OTC Policy requirements in NPDES permits for existing coastal and estuarine power plants. The Water Boards determine requirements to implement best technology available for cooling water intake structures to be included in the permits. State Water Board staff provides technical support to the Regional Water Boards to ensure a high level of statewide consistency in implementing the OTC Policy.

»»   For more information on each power plant required to comply with the OTC Policy, visit the Power Plants That Are Affected page.

Questions or Comments

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