Once-Through Cooling Interim Mitigation Program

Important Upcoming Events

August 13 – September 14:
Public comment period for draft Award Guidelines. Click here to download the draft Award Guidelines. Submit your comments by email to the Marine Protected Areas Program Manager, Tova Handelman (tova.handelman@resources.ca.gov), by 5:00 PM on September 14, 2018. 

Two informational webinars will be offered. The presentation will be the same in both webinars, and recordings of the webinars and a Frequently Asked Questions document will be posted on this website. Click the links below to register for a webinar.

October 25:
Award Guidelines presented to Ocean Protection Council for approval

November 2018 – February 2019:
Solicitation for proposals (pending Council approval of Award Guidelines)

May 15, 2019:
Select proposals recommended to Ocean Protection Council for approval



Once-through cooling (OTC) technology pulls water from the ocean to cool power plants. Marine animals, seaweeds, and billions of eggs and larvae of fish and invertebrates are taken in with the seawater and killed as they are subjected to thermal, physical, and/or chemical stresses. Larger organisms may also be pinned against seawater intake screens, causing injury or death. These impacts contribute to the decline of fisheries and the degradation of marine habitats near power plants using once-through cooling.

To address these damaging impacts, the State Water Resources Control Board established a Once-Through Cooling Policy (Policy) in 2010 requiring power plants to stop using once-through cooling technology. The Policy originally applied to 19 coastal power plants (including two nuclear plants) that had the ability to withdraw over 15 billion gallons per day from the State’s coastal and estuarine waters using OTC systems. Closed-cycle wet cooling has been selected as Best Technology Available and permittees must either reduce intake flow and velocity or reduce impacts to aquatic life comparably by other means. The Policy requires power plants that are not in compliance to make mitigation payments annually based on their annual intake volume of water until they come into compliance. To ensure grid reliability, final compliance dates were negotiated with each of the plants listed on the map after the name of each power plant (right).  Through closures of older plants, denoted by strike-through on the map, and retrofits to come into compliance prior to the payment program beginning, there are now 10 power plants that will be making payments until they come into compliance (highlighted in yellow). OPC will receive up to $5.4 million annually from these mitigation payments to fund to its OTC Interim Mitigation Program. Funds will decrease as power plants come into compliance with the Policy, and the Program is expected to end in 2029 when all power plants are required to be in compliance.

The policy gives a clear directive that funds received through this program will support “mitigation projects directed toward increases in marine life associated with the state’s marine protected areas in the geographic region of the facility”. To further implement the Policy and build out the OTC Interim Mitigation Program, OPC entered into a Memorandum of Understanding with the State Water Resources Control Board that allocates $5.4 million of the annual payments to mitigate the impacts of OTC on state marine protected areas (MPAs). The allotment amount was based on an interagency budget analysis conducted by the MPA Statewide Leadership Team of costs associated with the MPA Management Program that have a direct nexus with OTC impacts.

The Ocean Protection Council’s Once-Through Cooling Interim Mitigation Program directs mitigation payment investment through four critical components:

  1. Enforcement of MPA regulations statewide
  2. Outreach and education to improve compliance of MPA regulations statewide
  3. Research to understand how existing MPAs may be mitigating for OTC impacts
  4. Restoration that increases marine life in the geographic region of the facility

For more information on the impacts of OTC and how the MPA Management Program is linked to the OTC Interim Mitigation Program, click HERE.


Ocean Restoration Methods

The Ocean Protection Council Science Advisory Team (OPC-SAT) has just released a report entitled “Ocean Restoration Methods: Scientific Guidance for Once-Through Cooling Mitigation Policy”. This report provides scientific guidance on the types of restoration methods that can help offset the harmful effects to marine and estuarine life resulting from seawater intake structures used by coastal power plants (otherwise known as once-through cooling). This work is a continuation of California’s significant investment in the state’s network of 124 marine protected areas, which helps safeguard the long-term health of California’s marine life.

A Working Group of the OPC-SAT, convened by the Ocean Science Trust, applied the best science available to help identify projects that would meet the requirements of the Once-Through Cooling Policy to bolster marine life associated with the state MPA network. Their report determined that due to oceanographic currents connecting locations both inside and outside of MPAs, harmful effects of once-through cooling could extend hundreds of kilometers from a power plant’s intake pipe. Given the geographic extent of power plants still using once-through cooling, the findings of this report define the areas impacted as the entire coastline from San Diego to San Francisco, including the Channel Islands. This report provides essential guidance on the scientific principles needed to identify restoration projects that meaningfully offset the impacts of once-through cooling.


Tova Handelman
Marine Protected Areas Program Manager