Once-through Cooling

From Beachapedia


The US Environmental Protection Agency (“EPA”) currently allows power plants situated near water bodies to use a cooling system that sucks in and grinds fish, flattens them on screens - or, if they make it through that process, the fish still face boiling hot water through the “entrainment” process. Virtually no marine life survive the Once Through Cooling (“OTC”) system. In California alone, coastal power plants withdraw cold water and discharge hot water at a rate of about 16.7 billion gallons per day, killing at a rate of 88 billion marine lives a year. Nationally, power plants use up nearly 100 trillion gallons of ocean, lake and river water each year to absorb heat waste. A single plant can use more than one million gallons per minute. The killing of trillions of fish, shellfish, and other species at all life stages through this process has stressed and depleted our waters for decades and disrupts the food chain. EPA also identified 88 threatened or endangered species at risk from cooling water intake structures.

Section 316(b) of the Clean Water Act (“CWA”) specifies that standards governing the “location, design, construction, and capacity” of cooling water intake structures must “reflect the best technology available” for “minimizing [the] adverse environmental impact[s]”. The Surfrider Foundation does not think the OTC systems meet the requirements of 316(b) and call for a closed-loop cycle to be used for any necessary cooling water, which reduces marine life mortality by 95 to 98 percent.

After years of pressure from environmental groups including litigation, EPA released proposed regulations in 2011 governing cooling water intake structures for existing power plants under the Clean Water Act (“CWA”). The proposed rule impacts an estimated 1,200 facilities nation-wide, amounting to over half the water withdrawals in the entire nation. The proposal is designed to reduce the number of marine organisms that are killed by impingement or entrainment, but in Surfrider Foundation’s opinion, it does not go far enough.


In 2001, EPA issued national regulations identifying closed-cycle cooling as the best available technology for new power plants. But many older plants, typically those built more than 30 years ago, still rely on antiquated and damaging once-through cooling systems. The rule EPA proposed on April 20, 2011, is a step backward in collective efforts to safeguard ocean resources. Basically, EPA has chosen the path of least resistance by giving permitting authority to state agencies that too often lack the resources and the ability to stand up to industry pressure on this issue. The power companies have consistently resisted upgrading their cooling systems and have successfully avoided any regulations that would force them to modernize. Now more than ever, a clear, focused rule is needed to modernize power plants by halting the use of destructive once-through cooling.

Prior Litigation

Surfrider Foundation has been involved in a series of litigation battles to compel EPA to fully enforce the protections of the Clean Water Act and provision 316(b) relating to coastal power plants. On November 22, 2010, Surfrider Foundation, Riverkeeper and other environmental organizations signed a settlement agreement with the Environmental Protection Agency ("EPA") that resolved two lawsuits brought against the EPA in 1993 and 2006 addressing the agency’s failure to issue regulations implementing Section 316(b) of the Clean Water Act. This settlement agreement required EPA to draft these new regulations that are currently proposed for comment

Proposed Rulemaking

Without national standards, the EPA remains in violation of the Clean Water Act and states continue to lack the will and resources to impose use of better technologies on the power industry. An absence of national standards will create uncertainty and delays in the protection of water bodies.


UPDATE: EPA issued a final rule in May 2014.

This rule covers roughly 1,065 existing facilities that are designed to withdraw at least 2 million gallons per day of cooling water. EPA estimates that 521 of these facilities are factories, and the other 544 are power plants.

  • The facilities are required to choose one of seven options to reduce fish impingement.
  • Facilities that withdraw at least 125 million gallons per day must conduct studies to help their permitting authority determine whether and what site-specific controls, if any, would be required to reduce entrainment of aquatic organisms.
  • New units added to an existing facility are required to reduce both impingement and entrainment that achieves one of two alternatives under national entrainment standards.
  • EPA has concluded Endangered Species Act consultation with the Fish and Wildlife Service and the National Marine Fisheries Service.


The proposed rule covers existing cooling water intake structures at power-generating, manufacturing, and industrial facilities that:

  • withdraw more that 2 million gallons of water per day;
  • use at least 25% of that water exclusively for cooling purposes; and
  • have a National Pollution Elimination Discharge System (“NPDES”) permit or are required to apply for one.

The proposal addresses upper level impingement thresholds; entrainment thresholds; and requirements for new units at existing facilities.

Unfortunately, the current rule would exempt desalination plant intakes from the total volume of cooling water intakes in cases where power plants and desal plants are co-located. The proposed rule is also weak in its second recommendation for large facilities to conduct studies for permitting requirements. There have been dozens of studies on this technology already. Now is the time for tightening permitting requirements and halting the destruction of coastal resources, not for asking the industry to conduct further studies.

Furthermore, the “Commonly Asked Questions” document provided by the EPA on their website to explain more about the rulemaking is woefully misleading in its characterization of what the rule covers. In describing which facilities will need to comply with the new rules, the EPA states: “This proposed rule affects existing power plants and manufacturing facilities that generate electricity or manufacture other goods and that also withdraw at least 2 million gallons per day of cooling water.” However, as stated above, this rule will not apply to coastal desalination plants, even if they are co-located with power plants.

In addition to these shortcomings, EPA seems to be continually dragging their feet in publishing the final rules.

The benefits of strong 316(b) regulations are high, while the costs are low. Any changes to power industry intake technology would leave our public power grid virtually unaffected. Any increases in electric bills would be modest, costing consumers pennies or at most a few dollars per month on household electric bills. Only the most antiquated and marginal plants would choose to close down rather than upgrade to closed-cycle cooling. Meanwhile, requiring cooling system upgrades would create jobs, improve the economy, and may even clean the air. Transforming antiquated power plants into state-of-the-art, modern, and cleaner facilities will help the transition to a more sustainable energy supply that will help achieve our goal of healthy coasts.

California Regulations

On May 4, 2010 the California State Water Board adopted a Policy on the Use of Coastal and Estuarine Waters for Power Plant Cooling (Policy). The administrative record for the Policy was approved by the Office of Administrative Law (OAL) on September 27, 2010. The Policy became effective on October 1, 2010 when the California Environmental Quality Act Notice of Decision was submitted to the Secretary of Resources.

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 on marine and estuarine life. The Policy applies to the 16 existing power plants (note: San Onofre Nuclear Generating Station (SONGS) is on this list but Southern California Edison announced in June 2013 that it would permanently shut down the plant) that currently have the ability to withdraw billions of 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). In June 2016 Pacific Gas and Electric (PG&E) announced that they would be shutting down their Diablo Canyon Nuclear Generating Facility by 2025. So, as at SONGS, the end of OTC at Diablo Canyon will be a big win for the marine environment.

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. A Statewide Advisory Committee on Cooling Water Intake Structures (SACCWIS) has been established to review implementation plans and schedules and provide recommendations to the State Water Board at least annually. The State Water Board will consider SACCWIS’s recommendations and make modifications to the Policy, as appropriate. The permittees’ NPDES permits will be reissued or modified by the appropriate Regional Water Quality Control Board to conform with the Policy.

There have been several amendments to the Policy since it was first adopted in 2010. Read more about these regulations.

As is the case with the federal regulations, the California regulations do not appear to prohibit seawater desalination plants that may be co-located with coastal power plants from using the power plant's seawater intake and/or discharge structures and equipment to supply ocean water to the desalination plant and discharge concentrated brine back to the ocean. Therefore in these cases sea life mortality would continue even if the power plant switched to closed-cycle wet cooling or if the power plant shut down.

More Information

Contact Joe Geever or Rick Wilson at the Surfrider Foundation National Headquarters if you have questions regarding once-through cooling.