A school of black perch swims through golden kelp in the Channel Islands

Scientific Guidance for Once-Through Cooling Mitigation Funds

A Working Group of the Ocean Protection Council Science Advisory Team

Just Released: New Report

Ocean Restoration Methods: Scientific Guidance For Once-Through Cooling Mitigation Policy

A new report by the Ocean Protection Council Science Advisory Team (OPC-SAT) provides scientific guidance on ways to restore coastal areas impacted by power plants using once-through cooling technology, helping safeguard the long-term health of California’s marine life.



California’s Once-Through Cooling Policy (Policy) was adopted by the State Water Resources Control Board, establishing technology-based standards to implement federal Clean Water Act section 316(b) to reduce the harmful effects associated with power plant cooling water intake structures on marine and estuarine life. The Policy requires power plants that were not in compliance by October 2015 to either perform or pay for mitigation activities to account for the negative impacts between October 2015 and the date of the plants’ full compliance with the Policy (interim mitigation). Section 3(e) of the Policy states, “It is the preference of the State Water Board that funding is provided to the California Coastal Conservancy, working with the California Ocean Protection Council (OPC), for mitigation projects directed toward increases in marine life associated with the State’s Marine Protected Areas in the geographic region of the facility.”

Scientific guidance from the OPC Science Advisory Team

As OPC considers how to design a funding program to disburse once-through cooling (OTC) funds, they seek the scientific guidance of the OPC Science Advisory Team (OPC-SAT) to scientifically define the spatial extent of OTC impacts and to help understand which common open coast mitigation strategies are supported by scientific evidence to likely achieve the goal of increasing marine life as defined in the Policy. To assist the State in developing the scientific guidance, OPC has asked Ocean Science Trust to convene a working group of the OPC-SAT.

Scope and purpose

Project timeline: January 2018 – June 2018

Per the Policy, mitigation funds must be spent on projects that are within the “geographic region of the facility.” However, the policy does not define what the geographical range is. Based on our understanding of currents, ecosystems, populations connectivity, larvae mobility, intake type, intake location, etc., what is the area of impact for each of the power plants? The Policy also states that mitigation funding should be spent on projects that lead to “increases in marine life associated with the State’s Marine Protected Areas.” Within these guidelines, the working group will provide scientific guidance on:

  • A discrete definition of  “geographic region” specific to the different types and locations of intakes of the ten power plants that are part of the program, and
  • The efficacy of common open-coast mitigation strategies or methods that may lead to increases in marine life associated with the State’s MPA network

Working Group Members

  • Richard Ambrose (Co-Chair),  OPC-SAT, UCLA
  • Peter Raimondi (Co-Chair), UC Santa Cruz
  • Adrian Stier, UC Santa Cruz
  • Christopher Edwards, UC Santa Cruz
  • Jennifer Caselle, UC Santa Barbara
  • Marissa Basket, UC Davis
  • Kerry Nickols, CSU Northridge
  • Mark Carr, OPC-SAT,  UC Santa Cruz
  • Nathalie Reyns, University of San Diego
  • Sean Anderson, CSU Channel Islands
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