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CWA 316(b) Thermal Discharges-Cooling Water Intake Structures

Ocean Standards - CWA §316(b) Regulation


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 (Policy). The Policy became effective on October 1, 2010.

The 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 Policy applied to 19 existing power plants (including two nuclear plants) with the combined ability to withdraw almost 16 billion gallons 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).

The Policy is implemented through an adaptive management strategy by which the standards can be achieved without disrupting the critical needs of the state's electrical generation and transmission system. The Statewide Advisory Committee on Cooling Water Intake Structures (SACCWIS) reviews implementation plans and schedules to ensure the schedules take into account local area energy needs and grid reliability. SACCWIS provides recommendations to the State Water Board at least annually. The State Water Board considers SACCWIS’s recommendations and makes modifications to the Policy, as appropriate.

Eight plants have ceased their once-through cooling operations. In 2016, the eleven plants still operating once-through cooling systems withdrew slightly more than four billion gallons of water a day. These eleven 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.

Official Policy Documentation


Interim Mitigation Measures to the Water Quality Control Policy on the use of Coastal and Estuarine Water for Power Plant Cooling – Draft Determination for Encina Power Station

The State Water Resources Control Board (State Water Board) will accept public comments on draft determination to approve mitigation measures to comply with the Once-Through Cooling Policy for Encina Power Station. The draft determination is available to view or download by facility name on the State Water Board web site at: Interim Mitigation Measures.

Written comments must be received no later than 12:00 PM noon on January 2, 2018 and must be addressed to:

Jeanine Townsend, Clerk to the Board
State Water Resources Control Board
P.O. Box 100, Sacramento, CA 95812-2000 (mail)
1001 I Street, 24th Floor, Sacramento, CA 95814 (hand-delivery)

Comment letters may be submitted electronically, if less than 15 megabytes in total size, to the Clerk to the Board via e-mail at commentletters@waterboards.ca.gov.  If the file is greater than 15 megabytes in total size, then the comment letter may be submitted by fax at (916) 341-5620.  Please indicate in the subject line: "OTC Policy: Encina Power Station Draft Determination."

Couriers delivering hard copies of comment letters must check in with lobby security personnel, who can contact Ms. Townsend at (916) 341-5600.

Please direct questions about this notice to Katherine Faick at (916) 445-2317 or via email at Katherine.Faick@waterboards.ca.gov, or Mariela Paz Carpio-Obeso at (916) 341-5858 or via email at MarielaPaz.Carpio-Obeso@waterboards.ca.gov.



Public Meetings


Other Relevant Documents


The two committees listed below, were convened by the Executive Directory of the State Water board, as required by the 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 this Policy to ensure that implementation plans and schedules established by the 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
The Review Committee was established to oversee the special studies, which will investigate ability, alternatives, and cost for two nuclear-fueled power plants to meet the Policy requirements.  The special studies will be 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 Policy.  The Review Committee includes 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 Policy is implemented through National Pollutant Discharge Elimination System (NPDES) permits for coastal and estuarine power plants. The applicable Regional Water Boards are responsible for implementing the 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 Policy..  »»   Get more information …

Questions or Comments

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