Highlights:
- Proposed: April 20, 2011
- Public comment period: Concluded August 18, 2011
- Final rule: Due July 27, 2012
- Compliance: 2020 - Impingement; Site-specific schedule (Entrainment)
Section 316(b) of the Clean Water Act (CWA) addresses cooling water systems at power plants and factories. Its goal is to protect aquatic ecosystems and addresses impingement and entrainment of aquatic species.
Definitions
Impingement - fish or other species become pinned against the screen of a cooling water intake structure.
Entrainment - small fish, eggs or larvae are drawn into the cooling water system and are affected by heat, chemical or physical stress.
Cooling water intake structures - the physical structures and any associated man-made waterways used to withdraw water from bodies of water for use in power plant cooling.
What - This rulemaking deals with existing facilities and supplements the 2001 rule for new facilities. To address impingement, U.S. Environmental Protection Agency (USEPA) proposes requiring facilities with a design intake flow greater than 2 million gallons per day, of which 25 percent or more is used exclusively for 
cooling, to reduce impingement mortality using one of two technological approaches. One approach involves upgraded intake screens and a system that gently returns fish to the original water body. The second option involves reducing the flow rate of the water intake to a level that allows fish to easily swim away.
To address entrainment, USEPA proposes a process for the permitting authority (such as state agencies) to determine entrainment controls on a site-specific basis, based on a study conducted by the facility.
How - Owners/operators will have the opportunity to demonstrate that they already
are meeting impingement mitigation requirements. The proposal provides for public input into determining site-specific requirements for entrainment.
The proposal identifies closed cycle cooling systems (cooling towers) as the best performing technology for controlling both impingement and entrainment mortality. However, USEPA does not propose mandating these systems for existing facilities. Cooling towers will be required on new units to be installed at existing facilities.
Who - The proposed rule covers existing large steam-electric generators, including nuclear, coal-based and natural-gas based plants, as well as existing small generators and manufacturers. It will apply to an estimated 1,260 facilities.
In general, the proposal may not significantly impact facilities already equipped with cooling towers.
When - Compliance for impingement is required within eight years. The schedule for
entrainment compliance will be set by the permitting authority.
