Coal Ash Structural Fills

Coal ash structural fill is fly ash placed in construction projects and compacted as a base material. Fly ash (or coal ash) is produced primarily from the burning of coal in coal-fired power plants and other industries. It is a sandy to very fine, powdery material composed mostly of silica made from the burning of coal in a boiler.

When properly managed, a coal ash structural fill is closed and maintained to minimize the release of constituents to the environment and the potential exposure pathways of ingestion or inhalation; to ensure no groundwater standard violations occur and to prevent discharge into surface water.

Coal Ash Structural Fill Locations

Coal ash structural fill has been used to construct stable base layers for roads, bridges, airfields and large buildings across the state. Coal ash was widely used because it is considered stronger and easier to work with than other materials. The availability and often low cost of coal ash made the product attractive to developers and landowners, especially during the 1980s and 1990s. 

While DEQ has mapped the known locations of coal ash structural fills, there were few rules or records regarding the use of coal ash as fill prior to 1987. Coal ash used as structural fill was not required to be reported to the state environmental agency until 1994. The map below is a tool to assist with locating Structural Fill Projects as documented in the Division of Water Resources and Division of Waste Management database. An online documents folder for each project may be accessed by selecting the desired property and the link provided.

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Coal ash is produced primarily from the burning of coal in coal-fired power plants and other industries. Across the country, coal ash from power plants has been reused to produce cementitious products, like concrete. Other uses of coal ash (or coal combustion byproducts) include sand and gravel replacement in pavement production, gypsum replacement in sheetrock production and foundations for buildings or roadways.  

Coal ash and the construction of structural fills is regulated by two divisions in the Department of Environmental Quality – Division of Waste Management (DWM) and Division of Water Resources (DWR) – based on how the coal ash was originally handled at the power plant (either wet or dry).

Starting in 1987, the Division of Water Resources began issuing Distribution of Residual Solids (DORS) permits to the 14 individual coal-fired power plants owned by the predecessors to Duke Energy and Progress Energy as part of the coal ash reuse program. These DORS permits were issued to producers of coal ash for ash that was taken offsite – not to recipients of the coal ash product. The DORS permit:

  • Does not require tracking the final location of the ash.
  • Requires the use of ash does not result in any violations of water quality standards
  • Requires the use of ash involves no direct discharge to surface waters.
  • By statute, the records of distributions were only retained for 5 years.

In 1994, the 15A NCAC 13B .1700 Rules - Requirements for Beneficial Use of Coal Combustion Products became effective. These rules, enforced by the DWM, added the first regulations of the use of coal ash byproducts as replacement materials, as in structural fills. Under these rules:

  • A solid waste management permit was not required for structural fill management.
  • The Division of Waste Management must be notified 30-plus days before construction started with information about the property, the generator of the ash and the make-up of the ash for any project using coal ash as structural fill.
  • Structural fills according to the .1700 Rules had to be covered with a minimum of 12 inches of soil cover plus six inches of soil capable of supporting native plant grown.
  • If the structural fill contained more than 10,000 cubic yards, a construction plan, including a stability analysis, was also required to be submitted.
  • These rules contained no requirements to inspect structural fills. The Division of Waste Management inspected and monitored structural fills at the time of construction, and staff routinely conducted subsequent site visits.
  • Owners of land using a volume of more than 1,000 cubic yards of coal ash are required to file a statement with the county Register of Deeds.

In 1998, the power plants consolidated their individual DORS permits into a single permit covering ash distribution from all their facilities.

In 2009, the Division of Waste Management inspected every structural fill in its inventory.

In 2014, the North Carolina General Assembly passed the Coal Ash Management Act (CAMA) which requires coal ash structural fills to be permitted by the Division of Waste Management and added additional requirements for existing structural fills.

In 2021, the 15A NCAC 13B .1700 Rules - Requirements for Beneficial Use of Coal Combustion Products were repealed. NC Rule .1713 was readopted to maintain requirements for existing structural fills where coal combustion products were placed prior to September 20, 2014. Hence, only structural fills under CAMA may currently be permitted by the Division of Waste Management.

The Coal Ash Management Act or CAMA added additional rules for the use of coal ash, specifically, in structural fills and applied new rules to existing structural fills. The CAMA statute adds to and in some cases supersedes the existing rules regarding structural fills.

Existing and historical structural fills

The Coal Ash Management Act, or CAMA, requires structural fills constructed prior to 2014 that are greater than 10,000 cubic yards to be inspected annually. A list of structural fills greater than 10,000 cubic yards can be found at: This list includes sites from both DWR and DWM records.

Historical or existing structural fills less than 10,000 cubic yards are not addressed in CAMA. However, these structural fills are still required to be maintained with adequate cover according to the permit or rule governing their construction. Known structural fills containing less than 10,000 cubic yards are inspected as necessary.

New structural fill construction

There have only been two structural fills larger than 8,000 tons per acre permitted since the enactment of CAMA in 2014. However, only one permitted structural fill was utilized. There have been no structural fills less than 8,000 tons per acre permitted since CAMA.

Structural fills less than 8,000 tons per acre (80,000 tons per project)
Coal ash structural fills, involving less than 8,000 tons per acre or 80,000 tons per project, are to be permitted by the Division of Waste Management. The following information must be included in the application:

  • Purpose of project (or end use);
  • Start and end dates;
  • Estimated volume (if greater than 10,000 cubic yards engineering plans must be provided);
  • Toxicity Characteristic Leaching Procedure (TCLP) results which show leaching results of arsenic, barium, cadmium, lead, chromium, mercury, selenium, and silver below hazardous levels indicated below. [This analytical method simulates the leaching process that would occur naturally.]
  • Landowner statement; and
  • Ash generator information. 
Heavy Metal EPA Allowable Limits
Arsenic 5.0 ppm (mg/L)
Barium 100.0 ppm (mg/L)
Cadmium 1.0 ppm (mg/L)
Chromium 5.0 ppm (mg/L)
Lead 5.0 ppm (mg/L)
Mercury 0.2 ppm (mg/L)
Selenium 1.0 ppm (mg/L)
Silver 5.0 ppm (mg/L)


Structural fills more than 8,000 tons per acre (80,000 tons per project)
For structural fills greater than 8,000 tons per acre or 80,000 tons per project construction plans must be submitted which include all of the above items plus:

  • A liner,
  • Leachate collection system,
  • Cap,
  • Groundwater monitoring system which is certified by a licensed geologist or professional engineer to be effective in providing early detection of any release of hazardous constituents from any point in a structural fill or leachate impoundment to the uppermost aquifer, so as to be protective of public health, safety, and welfare, the environment and natural resources. 
  • Sufficient dust control,
  • Financial assurance that will ensure that sufficient funds are available for facility closure, post-closure maintenance and monitoring any corrective action required, and to satisfy any potential liability for accidental occurrences, and subsequent costs in response to an incident, and
  • A structural fill must not be:
    • Within the 100-year floodplain; it shall not restrict the flow of the 100-year flood, reduce the temporary water storage capacity or result of washout of the waste to pose a hazard to human life, wildlife or land or water resources.   
    • Within four feet of the seasonal high ground water table.
    • Within 25-feet of a property boundary, bedrock outcrop.
    • Within 50-feet of a property boundary, wetland, bank of a perennial stream or other surface water body.
    • Within 300-feet of a private dwelling or well.

Under the 1994 15A NCAC 13B .1700 Rules rules, coal ash byproducts could be used as a soil amendment or additive under the authority of the N.C. Department of Agriculture and Consumer Services. DEQ does not have records pertaining to those uses. 

A specific test is necessary to confirm the presence of coal ash particles, as it is often difficult to identify coal ash by sight.  

If you encounter a coal ash structural fill during a construction project, stop work immediately and contact DEQ’s regional office staff. A list of regional office phone numbers can be found at:

Regional DEQ staff will address proper, specific precautions with the individual on a case-by-case basis. General precautions that should be addressed when coal ash is encountered are as follows:

  • When removing coal ash material, reduce the amount of time the excavation stays open to mitigate exposure to both personnel and stormwater.
  • If ash material is staged for any amount of time, staging of excavated ash material should be conducted using best management practices.
  • Stormwater should be properly managed to keep coal ash from leaving the property or flowing into nearby surface waters.
  • Proper personal protective equipment should be used.

A list of structural fills greater than 10,000 cubic yards 

Specific project information can be found using the DEQ’s electronic document management system, Laserfiche: