Contributor: Sufian Khondker, PhD, PE, D.WRE
Cooling water intake structures adversely impact the environment by causing impingement and entrainment mortalities of fish, shellfish, and/or their eggs into a power plant’s screening system.
The Environmental Protection Agency (EPA) has put into effect regulations under 316(b) of the Clean Water Act, requiring that cooling water intake structures at large power plants (withdrawing more than two-million gallons per day) minimize adverse impacts to aquatic life.
Phase II—Large Existing Electric Generating Plants
Phase II regulations of 316(b) directs the EPA to establish the “best technology available” for cooling water intake structures to minimize adverse effects to fish and shellfish at existing power plants over the next 20 years.
Effects of 316(b) Phase II
The EPA estimates that this rule will affect about 550 facilities in the U.S. and will cost approximately $400-million annually to implement and administer. In order for power plant facilities to become compliant with the rule, impingement mortality (IM) must be reduced by 80-95 percent and entrainment mortality (EM) must be reduced by 60-90 percent.
1. IM Reduction – the result of organisms (aquatic life) pinned against the intake screens while a large volume of cooling water is withdrawn.
The owner or operator of an existing facility with a design flow greater than two MGD is subject to the IM standard. Compliance to the rule can be assured by redesigning the intake structure with thru-screen velocity of 0.5 ft/sec or implementing any of these EPA-approved best technologies available (BTAs):
- Wedgewire screens – passive screens with V-notch openings suitable for smaller intakes
- Barrier nets (fish nets) – water permeable barrier that keeps fish eggs, larvae, and other aquatic organisms away from intake structures. Barrier nets prevent both impingement and entrainment, however, have high potential of clogging
- Modified screens with fish return system
2. EM Reduction – affects aquatic organisms that pass through screen openings by heat from the condenser tubes.
The owner or operator of an existing facility with a design flow greater than 125 MGD is subject to the EM standard in addition to the IM standard. Compliance to the rule can be assured by reducing the entrainment of aquatic organisms by 60-90 percent by implementing any of these BTAs:
- Filter Barrier System – prevents transportation of aquatic organisms
- Wedgewire screens (with very small openings) – minimize transportation of aquatic life
- Traveling screens (with fish return system) – return screened aquatic organisms back to the water body before they could be passed through the condensers
- Velocity caps for offshore intakes – prevent the entrainment of aquatic organisms using the behavioral characteristics of various species. Velocity caps withdraw water in horizontal direction and most species avoid horizontal movement of water and swim away, thereby reducing the entrainment
Standard Practice in the U.S.
Velocity caps have been recommended as the best technology available by the EPA, as well as the best for intake for fish protection by the American Society of Civil Engineers. For large offshore intakes velocity caps reduces entrainment by 80-95 percent, far exceeding the EPA 316(b) Rule. Also, velocity caps do not cause any impingement.
Read Scott Ehrhardt’s blog, “A Pumped-Up Solution for Duke Energy,” for an example of our work at Belews Lake in North Carolina.