Cooling towers are heat removal devices that let off heat into the atmosphere through evaporation and/or heat transfer. They are used to cool circulating water in power plants, oil refineries, and chemical plants. The towers vary in size from 200 meters tall and 100 meters in diameter, to rectangular structures that can be over 40 meters tall and 80 meters long. 
The EPA is in the process of developing a rule that will define how States will establish standards for cooling water intake structures at large power plants. In July 2010, the U.S. Court of Appeals for the Fifth Circuit granted EPA's request to take back part of a rule on cooling water intake structures relating to existing facilities so it can consider what might be appropriate requirements (ConocoPhillips v. EPA, 5th Cir., No. 06-60662, 7/23/10).
In coal plants, cooling towers are used as a means to lessen thermal pollution from coal plants. Thermal pollution is the degradation of water quality by any process that changes ambient water temperature. A common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers. When water used as a coolant is returned to the natural environment at a higher temperature, the change in temperature impacts organisms by (a) decreasing oxygen supply, and (b) affecting ecosystem composition.
When a power plant first opens or shuts down for repair or other causes, fish and other organisms adapted to particular temperature range can be killed by the abrupt rise in water temperature known as 'thermal shock': most aquatic organisms have developed enzyme systems that operate in only narrow ranges of temperature, and can be killed by sudden temperature changes that are beyond the tolerance limits of their metabolic systems.
Section 316(b) of the Clean Water Act (CWA) requires the EPA to ensure that the location, design, construction, and capacity of cooling water intake structures reflect the best technology available (BTA) for minimizing adverse environmental impacts, including thermal pollution. According to the EPA, cooling water intake structures can cause adverse environmental impact by pulling large numbers of fish and shellfish or their eggs into a power plant's or factory's cooling system. There, the organisms may be killed or injured by heat, physical stress, or by chemicals used to clean the cooling system. Larger organisms may be killed or injured when they are trapped against screens at the front of an intake structure.
The EPA has therefore been in the process of developing a rule that will define how States will establish standards for cooling water intake structures at large power plants, expected to be published in the Federal Register in September 2010. The rule would apply to large existing power plants that withdraw 50 million gallons per day or more, and that use at least 25 percent of their withdrawn water for cooling purposes only - an estimated 422 fossil-fueled and 38 nuclear power plants representing over 308 and 52 GW of existing capacity, respectively. The rule has been repeatedly challenged by industry lawsuits, prompting states like CA to move forward with their own regulations.
In July 2010, the U.S. Court of Appeals for the Fifth Circuit granted EPA's request to take back part of a rule on cooling water intake structures relating to existing facilities so it can consider what might be appropriate requirements (ConocoPhillips v. EPA, 5th Cir., No. 06-60662, 7/23/10).
Effect of cooling regulations on coal phaseout
According to the Air and Waste Management Association, industries are particularly concerned about cooling requirements because of the high costs associated with retrofitting cooling towers. According to a 2010 report, "Special Reliability Scenario Assessment: Resource Adequacy Impacts of Potential U.S. Environmental Regulations" by the North American Electric Reliability Corp., an estimated 33 gigawatts to 36 gigawatts of generating capacity could be forced to be retired, depending on how stringent the cooling tower rule might be. A 2010 study by The Brattle Group, "Potential Coal Plant Retirements Under Emerging Environmental Regulations" found that 11,000 to 12,000 MW of coal power could retire if cooling towers are mandated. According to the report, if scrubbers and cooling towers are required, it could shut down every merchant coal plant (plants that sell power into competitive wholesale markets) in the Texas ERCOT region.
Environmental effects of outdated cooling equipment
In 2011, the Chicago Tribune accessed industry reports through the Freedom of Information Act, and discovered that numerous older power plants have been exempted from environmental regulations designed to prevent enormous industrial fish kills. These older plants, employing "once-through" cooling, pump massive amounts of water from lakes and rivers through the screens of water intake systems - some so powerful they could fill an Olympic swimming pool in less than a minute - and sucking up multiple fish. Dozens of older power plants that ring the Great Lakes kill hundreds of millions of fish each year as a consequence of employing outdated processes to cool their equipment.
The FirstEnergy Bay Shore Plant on the Maumee River shoreline near Toledo, Ohio, kills an estimated 46 million adult fish annually, as well as 2.4 billion eggs, larvae and young fish. Not far away, at the mouth of another important Lake Erie tributary, the Monroe Power Plant in Michigan kills more than 25 million fish and almost a half-billion fish eggs and other organisms each year. FirstEnergy's Bay Shore power plant also withdraws more than 749 million gallons of water per day from Lake Erie, using vast quantities of "once-through" water used to cool equipment exits, and creating prime growing conditions for bacteria that harm native fish habitat.
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- U.S. Environmental Protection Agency (EPA). Washington, D.C. "Cooling Water Intake Structures - Basic Information." EPA Website, accessed November, 2009
- "Technical Development Document for the Final Section 316(b) Phase III Rule. Chapter 2." EPA Website, accessed November 2009
- Andrew Childers, "Electric Companies Said to Need Time to Implement Environmental Rules" Air and Waste Management Association, 2010.
- "Thermal Pollution" Pollution Issues, accessed November 2009
- "Criteria and Standards for Cooling Water Intake Structures" EPA Website, accessed July 2010.
- Cassandra Sweet, "California Rules Restrict Power Plants' Marine Water Use" The Wall Street Journal, May 5, 2010.
- "EPA rules could spark $180bn in upgrades, 67,000 MW of coal-fired retirements" Power-Gen, Dec. 8, 2010.
- Doug Schmidt, "'Huge' fish kill, power plants linked: Toll at U.S. generating station water intakes called astronomical", The Windsor Star June 18, 2011.
- "Power Plant Cooling Water and Clean Water Act Section 316(b): The Need to Modernize U.S. Power Plants and Protect our Water Resources" NRDC, March 2011.
- "Energy Penalty Analysis of Possible Cooling Water Intake Structure Requirements on Existing Coal-Fired Power Plants" U.S. Department of Energy, October 2002.