We’ve made some changes to EPA.gov. If the information you are looking for is not here, you may be able to find it on the EPA Web Archive or the January 19, 2017 Web Snapshot.

Coal Ash Basics

On this page


What is coal ash?

Coal ash, also referred to as coal combustion residuals or CCRs, is produced primarily from the burning of coal in coal-fired power plants.  Coal ash includes a number of by-products produced from burning coal, including:

  • Fly Ash, a very fine, powdery material composed mostly of silica made from the burning of finely ground coal in a boiler.
  • Bottom Ash, a coarse, angular ash particle that is too large to be carried up into the smoke stacks so it forms in the bottom of the coal furnace.
  • Boiler Slag, molten bottom ash from slag tap and cyclone type furnaces that turns into pellets that have a smooth glassy appearance after it is cooled with water.
  • Flue Gas Desulfurization Material, a material leftover from the process of reducing sulfur dioxide emissions from a coal-fired boiler that can be a wet sludge consisting of calcium sulfite or calcium sulfate or a dry powered material that is a mixture of sulfites and sulfates.

Other types of by-products are:

  • fluidized bed combustion ash,
  • cenospheres, and
  • scrubber residues.

Top of Page


What do power plants do with coal ash?

Coal ash is disposed of or used in different ways depending on:

  • the type of by-product,
  • the processes at the plant and
  • the regulations the power plant has to follow.

Some power plants may dispose of it in surface impoundments or in landfills. Others may discharge it into a nearby waterway under the plant's water discharge permit.

Coal ash may also be recycled into products like concrete or wallboard.

Top of Page


How much coal ash is there?

Coal ash is one of the largest types of industrial waste generated in the United States. According to the American Coal Ash Association's Coal Combustion Product Production & Use Survey Report, nearly 130 million tons of coal ash was generated in 2014.

Top of Page


Why is coal ash reused?

Reusing coal ash can create many environmental, economic, and product benefits including:

  • Environmental benefits such as reduced greenhouse gas emissions, reduced need for disposing in landfills, and reduced use of other materials.
  • Economic benefits such as reduced costs associated with coal ash disposal, increased revenue from the sale of coal ash, and savings from using coal ash in place of other, more costly materials.
  • Product benefits such as improved strength, durability, and workability of materials.

For more information, visit the coal ash reuse Web page.

Top of Page


Why does EPA regulate coal ash?

Coal ash contains contaminants like mercury, cadmium and arsenic. Without proper management, these contaminants can pollute waterways, ground water, drinking water, and the air.

The need for federal action to help ensure protective coal ash disposal was highlighted by large spills near Kingston, TN and Eden, NC which caused widespread environmental and economic damage to nearby waterways and properties.

To address the risks from improper disposal and discharge of coal ash, EPA has established national rules for coal ash disposal and is strengthening existing controls on water discharges. For more information, visit the following Web pages.

Top of Page