Glossary

Deflector boom
A boom placed in a river to deflect a spill away from an environmentally sensitive area or deflect it to an area where the spill can be more effectively managed or recovered.

Discharge embayment
A bay of a river or reservoir into which wastewater or cooling water from a power plant is released.

Environmental Management System
A process-based method of managing environmental performance to maximize efficiencies and effectiveness through standardization and continuous improvement. The EMS enables TVA to factor environmental considerations into its business decisions and day-to-day performance, and provides a framework for continuous improvement and tracking of its performance.

Fine particles
Particulate matter (PM) suspended in the air that consists of very small liquid or solid “dust” particles. Fine particles, designated PM2.5, are 2.5 microns or less in diameter, which is less than the width of a human hair.

HERS (Home Energy Rating System)
An evaluation of the energy efficiency of a home. The home is compared to a computer-simulated reference house of identical size and shape that meets the minimum requirements of the Model Energy Code. The HERS rating is a score between 0 and 100, with the reference house assigned a score of 80. From this point, each 5 percent reduction in energy usage by the home results in a one-point increase in the HERS score. A home energy rating can qualify a homeowner or buyer for an energy efficient mortgage or an energy improvement mortgage.

Mercury speciation
Refers to the fact that mercury in the air is present in three forms: elemental mercury vapor, reactive gaseous mercury compounds (e.g., methyl mercury), and ionic mercury compounds in airborne particles. These forms have different chemical and physical properties that affect the length of time they remain in the air. This fact complicates research into mercury emissions.

Oil flow indicator
A device on a transformer that indicates whether oil is flowing through the transformer as designed. A lack of flow would indicate a malfunction that might lead to equipment failure.

Opacity
A measurement of the amount of light that is obscured by plant emissions. When there is no visible smoke, the opacity is 0 percent, meaning all of the light is able to pass through.

Oxygenation systems
Methods of increasing the concentration of oxygen in the tailwaters below hydropower dams. These methods include specially designed turbines, surface-water pumps, injection systems, weirs, and air compressors and blowers. Read more.

Riprap
Loose rock placed along the banks of a waterway to prevent erosion.

Skimmer boom
A large-diameter rope-like device made of oil-absorbent material that floats on top of the water and is used to capture oil and fuel spills to water.

Tailwater
The area of water immediately downstream of a dam.