About Coal Ash

Frequently Asked Questions

  1. What are CCPs?
  2. What are some of the beneficial uses of CCPs?
  3. Why does the use of coal ash reduce greenhouse gases?
  4. Are there other examples of the benefits of using CCPs?
  5. How much are CCPs worth?
  6. What are the barriers to CCP use?
  7. Are there technical standards that pertain to CCPs?
  8. What is Flue Gas Desulfurization (FGD)?
  9. Is coal ash hazardous?
  10. Are there hazards with skin contact with coal combustion products?
  11. Is coal ash radioactive?
  12. What’s the difference between coal ash, coal combustion “byproducts,” coal combustion “products,” and wastes from the combustion of coal?
  13. How much does it cost to dispose of coal ash?
  14. What are “avoided disposal costs?”

What are coal combustion products?

Coal combustion products (CCP) are the materials that remain after pulverized coal is burned to generate electricity.

Coarse particles (bottom ash and boiler slag) settle to the bottom of the combustion chamber. The fine portion (fly ash) “flies up” into the stacks with flue gases and is removed by electrostatic precipitators and fabric filter bag houses. These materials have a wide range of uses to the construction, manufacturing, environmental remediation, and other industries.

The U.S. Congress passed the Clean Air Act Amendments of 1990 (Public Law 101-549), which included stringent restrictions on sulfur oxide emissions. Most electric utilities in the Mid-Atlantic states use bituminous coal that has sulfur contents in the range of 2 percent to 3.5 percent. To meet the Clean Air Act emission standards, many utilities have installed flue gas desulfurization (FGD) equipment or other systems to remove or reduce the particulate and gas emissions of sulfur compounds. This process produces forms of FGD gypsum that are currently used in wallboard products or as a soil amendment in agriculture. At least 30 percent of wallboard manufactured in the U.S. comes from power plant gypsum.

For additional description, please click here.


What are some of the beneficial uses of CCPs?

The term “beneficial use” was coined by the U.S. EPA to emphasize recycling CCPs rather than disposing of these materials in landfills. The EPA considers industrial materials recycling a “national priority.”

Every year the ACAA reports the amount of CCPs produced and the amount recycled in its “CCP Production and Use Reports.” Fly ash in concrete accounts for the largest volume of CCPs recycled annually. Fly ash and bottom ash can be used to produce road base materials, manufactured aggregates, flowable fills, structural fills, and embankments. Coal ash is also used to replace natural materials in the production of portland cement. Other applications for CCPs include wallboard manufacturing, roofing tiles and shingles. CCPs are also used for waste stabilization, snow and ice control, soil modification, as mineral fillers, in agriculture and mining and for very specialized uses. For example some CCPs have properties suitable for metal castings in the aerospace and automotive industries.


Why does the use of fly ash reduce greenhouse gases?

For each ton of fly ash used in place of traditional cement a reduction of slightly less than one ton of carbon dioxide is achieved. To put this in perspective, one ton of carbon dioxide is equivalent to about two months’ emissions from an automobile. Estimating based upon the amount of fly ash used annually in concrete, approximately 13 millions tons of carbon dioxide is prevented from entering the earth’s atmosphere.


Are there other examples of the benefits of using CCPs?

Yes, another example of measuring the positive impact of CCPs is the elimination of one ton of landfill space through CCP use in concrete and in other building products, versus disposal. The amount of space required to dispose of one ton of coal ash is equivalent to that required for the solid waste produced by an average American in a 455-day period. This also does away with the need for trucks and pieces of equipment required to move and place the coal ash in a landfill thus eliminating additional carbon dioxide emissions.

Anytime CCPs are used in lieu of another natural material, like soil, sand or gypsum, a portion of the fossil energy required to mine, transport, place or process is reduced.  For example, using coal ash instead of natural soil in the construction of highway fills or embankments eliminates the need to remove soil from undisturbed areas, saving energy. The use of FGD synthetic gypsum (described below) provides a very efficient process to manufacture wallboard. This also avoids the energy intensive mining and processing activities when natural gypsum is used.


How much are CCPs worth?

The monetary value of CCPs is dependent on a number of factors and for that reason there is no single answer to this question. The type of CCPs, its market location and seasonal aspects all contribute to determining the value of CCPs.

Type of CCPs

Some CCPs, such as fly ash that meets concrete quality as defined by engineering standards, can not only lower the costs of construction, but actually improves the quality of the finished product. For example, the substitution of fly ash for Portland cement allows a contactor to replace some portion of the cement in concrete with fly ash, reducing the cost of the resulting concrete. The fly ash allows the concrete to be placed and finished more easily and usually contributes to higher strengths and resistance to certain types of wear. In many instances, fly ash that cannot otherwise be used in concrete due to its lower quality is often used to stabilize soils or wastes which makes this process less expensive. Other CCPs, such as synthetic gypsum, have value because they can meet technical requirements for use in wallboard, which avoids the processing required of natural gypsum. These examples also pertain to bottom ash, boiler slag and CCPs used instead of other manufactured or mined materials.

Market Location

The market place in which the CCPs are produced or going to be used has great impact on value.  If there are many sources of CCPs of similar type and quality are available in a market, then the value will be somewhat lower. Like any other product, supply and demand determines the value of CCPs, to some extent. Transportation is also a major factor in the cost of using CCPs. The method of transportation (rail, truck, pneumatic trailer, open trailer, accompanied by the loading and unloading methods all contribute to the cost of handling, which is reflected in the price of the CCP. For example, fly ash loaded directly into a truck at the power plant and delivered directly to the job site, may be less expensive than ash delivered by rail to a terminal, where it is transloaded into a truck for delivery to the job site, because more handling is required in the latter situation than in the former.

Seasonal Factors

The time of year may also contribute to pricing. In many parts of the country, the production of coal ash is very high during both the coldest and hottest months of the year – when people are heating and cooling their homes, offices and schools. These same periods of the year are often the slowest times for construction and other applications that beneficially use the ash. This sort of imbalance in the production and demand for CCPs can contribute to highs and lows in pricing. Many utilities and CCP marketing firms work to overcome this by using storage silos and sometimes large distribution networks.

Sample Prices

Recognizing that the factors above will vary greatly across the US, some of the typical 2003 price ranges one will find for various CCPs are as follows:

Concrete quality fly ash – $20 to $45 a ton

Self-cementing fly ash for soil stabilization – $10 to $20 a ton

Bottom ash for snow and ice control – $3 to $6 a ton

Fly ash for flowable fill – $1 a ton and up

Bottom ash and/or fly ash for road base – $4 to $8 a ton

Self-cementing fly ash for oilfield grouting or waste stabilization – $15 to $25 a ton


What are the barriers to coal combustion product (CCP) use?

There are many technical, economic, regulatory, and institutional barriers to increased use of CCPs. A lack of standards and guidelines for certain applications and new applications heads the list of technical barriers. Transportation costs lead the economic barriers, which limit the shipment of CCPs to within about a 50-mile (80 kilometer) radius of the power plants.

The industry’s ability to recycle CCPs may be limited by more restrictive environmental controls. In April 2000, the U.S. EPA stated that the use of CCPs does not warrant regulatory oversight but left the door open to stricter regulation of CCPs in the future. A few weeks later, the EPA nearly issued a ruling that would have classified CCPs as hazardous wastes under the Resource Conservation and Recovery Act (RCRA). However, in May 2000, the EPA reaffirmed its position that CCPs are non-hazardous.

Unfortunately, many of the environmental regulations placed on utilities under the Clean Air Act lead to quality problems in the resulting coal ash and thus limit the uses for the ash. One example in particular is the use of low-NOx burners and other NOx reduction techniques that leave a large amount of unburned coal in the ash and makes it unsuitable for concrete. In this situation the fly ash must be used in other applications or disposed of.

Other barriers to CCP use are: 1) the RCRA designation of CCPs as solid wastes, regardless of their composition, even when they are used as resources rather than disposed of; 2) the lack of governmental incentive; and 3) the lack of CCP knowledge among the user groups (engineers, contractors and regulators).

With industry and government cooperation, steps toward increasing CCP use can include: 1) the establishment of a research and development infrastructure to address the technical barriers to CCP use; 2) innovative methods to utilize Flue Gas Desulfurization (FGD) material; and 3) providing a method of disseminating objective scientific and technical information.


Are there technical standards that pertain to CCPs?

Because CCPs have many uses in engineering activities, there are a number of organizations that issue technical standards or guidelines for the use of CCPs.  These include, for example, the American Society for Testing and Materials (ASTM), the American Concrete Institute (ACI), the Federal Highway Administration (FHWA), the Federal Aviation Administration (FAA), the Army Corps of Engineers, the American Association of State Highway and Transportation Officials (AASHTO), the American Concrete Paving Association (ACPA), the National Ready Mixed Concrete Association (NRMCA), the American Society for Civil Engineers (ASCE) and many state departments of transportation (DOT).


What is Flue Gas Desulfurization (FGD)?

Flue gas desulfurization is a chemical process to remove sulfur oxides from the flue gas at coal-burning power plants.  Many FGD methods have been developed to varying stages of applicability.  Their goal is to chemically combine the sulfur gases released in coal combustion by reacting them with a sorbent, such as limestone (calcium carbonate, CaCO3), lime (calcium oxide, CaO) or ammonia (NH3).  Of the FGD systems in the United States, 90 percent use limestone or lime as the sorbent.  As the flue gas comes in contact with the slurry of calcium salts, sulfur dioxide (SO2) reacts with the calcium to form hydrous calcium sulfate (CaSO42H20) or gypsum.

Certain material produced by some power plants in an oxidizing and calcium based process for air emission scrubbing is called FGD (or synthetic) gypsum.  FGD gypsum is precipitated gypsum formed through the neutralization of sulfuric acid.  While the material may vary in purity, which is defined as the percentage of CaSO4?2H2O, it is generally over 94% when it is used in wallboard manufacturing. Because this material is very consistent when produced by power plants, wallboard manufacturers will often be located adjacent to the power plant to allow the FGD material to be delivered directly to the wallboard plants. This synergistic relationship not only is economically attractive, but it reduces the need to mine natural gypsum and therefore has a positive environmental impact.

FGD material can be wet or dry. Definitions related to FGD material can be found on this website by clicking on the tab “What are CCPs?” on the Home Page.  The PDF file “Glossary of Terms” can be downloaded.  As many different terms are used for FGD material, and operational differences between systems may create slightly different types of FGD, this Glossary of Terms is a reliable source of information.


Is coal ash hazardous?

Coal, like soil, rocks and other natural materials found in the earth’s crust contain trace amounts of heavy metal elements. The burning of coal results in some of these elements being oxidized in the coal ash that is produced. Typically, these heavy metals include arsenic, boron, cadmium, chromium, copper, lead, selenium and zinc.

Beginning in 1988 and continuing through 2000, the U.S. Environmental Protection Agency (EPA) studied extensively the risk that coal ash presents to the environment. First, in a report to Congress dated February 1, 1988 the EPA concluded that the ash resulting from the combustion of fossils fuels was not hazardous and did not need to be regulated as a hazardous waste under the Resource Conservation and Recovery Act (RCRA). In a Report to Congress dated March 1999, the EPA again confirmed that coal ash did not require regulation as a hazardous waste and encouraged the beneficial use of coal combustion byproducts. On May 22, 2000, the Federal Register published the EPA’s final determination “ Notice of Regulatory Determination on Wastes from the Combustion of Fossil Fuels.” This Federal Register is available on ACAA‘s website under “What are CCPs?”

As stated earlier, coal ash contains varying concentrations of these heavy metals.  Despite the large volumes of ash produced, the total quantity of heavy metals is relatively small, and an even smaller amount of these elements can be released to the environment.  Annually, utilities report the total quantity of metals and other materials released in to the environment through Toxic Release Inventory (TRI) reporting requirements.  For example, the largest quantities of heavy metals are in the form of manganese, barium and vanadium.    Much smaller amounts of copper, lead and other metals are reported under TRI.   The impact of these heavy metals is slight.  Studies conducted by the University of North Dakota indicate that for most heavy metals, even if released directly into groundwater, the concentrations are so low that they would not adversely affect drinking water quality.  A U.S. Geological Survey (USGS) fact sheet states that a “Standardized test of the leach ability of toxic trace elements such as arsenic, selenium, lead and mercury from fly ash shows that the amounts dissolved are sufficiently low to justify regulatory classification of fly ash as non-hazardous solid waste.”  Other regulations and standards regarding the use and disposition of coal ash are in place and vary by application from state to state.

However, it is important to note that despite these relatively low concentrations, if improperly managed, any waste can have a negative impact on the environment.  The United States and Canadian utility industry have implemented many methods of control and monitoring to ensure that when coal ash is disposed, there will be no adverse affect to human health or to the environment.  Environmental stewardship is an important part of the utility industry.


Are there hazards with skin contact with coal combustion products?

Most people never touch coal ash. Skin contact is generally limited to power plant workers and those who produce cement, concrete, autoclaved aerated concrete (AAC) or some other ash-based product.  However, some highway departments use bottom ash for snow and ice control, leaving deposits on roads and in gutters where people or their pets might touch it or track it into their houses.  Based on the experience of those who work closely with it, adverse health effects from skin contact with coal ash appear to be extremely unlikely.


Is coal ash radioactive? 

Radioactivity is present everywhere in North America. Naturally occurring radioactive material (NORM) is found in cities, in the mountains and everywhere. The levels of naturally occurring radioactivity will vary in different parts of the country.  Some western states have higher levels of NORM than are found in eastern areas. The United States Geological Survey (USGS) has published a fact sheet on radioactivity in coal ash “Radioactive Elements in Coal and Fly Ash:  Abundance, Forms, and Environmental Significance” which is available through ACAA and can be found under the website page “What are CCPs?” Trace elements in coal include uranium, thorium and the numerous decay products, including radium and radon. However, this USGS pamphlet concludes the “Radioactive elements in coal and fly ash should not be sources of alarm.  The vast majority of coal and the majority of fly ash are not significantly enriched with radioactive elements, or in associated radioactivity, compared to common soils or rocks.” Furthermore, “Limited measurements of dissolved uranium and radium in water leachates of fly ash and in natural water from some ash disposal sites indicate that dissolved concentrations of these radioactive elements are below levels of human health concern.”


What’s the difference between coal ash, coal combustion “byproducts,” coal combustion “products” and wastes from the combustion of coal?

More than thirty years ago, ash produced from the burning of coal in coal-fueled power plants was simply called “ash.”    More than two thousand years ago, the Romans discovered that the naturally occurring volcanic ash, when mixed with other materials could make a very strong, durable mortar or cement.  The Coliseum, Roman aqueducts and other structures used this pozzolanic ash in building.  In the 1960’s the utility industry realized that coal ash was a valuable product that could be used in many ways in commerce.   In 1968 the National Coal Ash Association was formed to help promote the use of coal ash and to provide information about the versatility of the material.  As the industry matured, it became obvious that coal ash needed to be categorized by types and uses.  Coal ash was classified by the type of coal burned, by the type of boiler in which it was produced, by its physical characteristics and by its end use, among other methods.  Fly ash, bottom ash, boiler slag, fluidized bed combustion (FBC) ash, flue gas desulfurization materials, cenospheres, and other terms began to be used commonly.

As these varieties of uses became better known to government and private industry, the overall terminology for the industry evolved.  The U.S. Environmental Protection Agency described these materials as the “waste products from the combustion of fossil fuels.”  But at the same time, the coal ash industry stressed the importance these materials had in commerce and referred to them as coal combustion by-products (CCBs).  Technically correct, these materials were the by-products of the generation of electricity in coal-fueled power plants.  While CCBs became widely used in the 1980s and 1990s, the American Coal Ash Association (formerly the National Coal Ash Association) and other organizations continued to promote the value of these materials.  Since coal ash could be used in many important applications, they truly were products that competed against other materials, both economically and physically.  Many producers, marketers and end users began to refer to these materials as coal combustion products (CCPs) to denote their value and ability to be used instead of other products (See the ACAA Glossary of Terms on this website under “What are CCPs?”)    In 2002, the U.S. EPA began referring to these materials as coal combustion products, as well.  This recognition by the EPA has helped to further promote the beneficial usefulness of CCPs.

In many settings, CCBs and CCPs are used interchangeably.  Neither use is incorrect and both terms convey that these are in fact materials that have many uses, have economic and sometimes physical and chemical advantages over using other materials.


How much does it cost to dispose of coal ash?

There is no easy answer to this question. There are multiple factors that go in to determining the cost of disposal of coal ash that cannot otherwise be used. The specific type of ash, location, transportation methods, climate and terrain, regulatory requirements and potential for future use all enter into determining disposal costs.

Type of material – Coal, when burned in a pulverized coal-fired boiler produces both fly ash and bottom ash. Approximately 80% of the material produced is in the form of fly ash and 20% is in the form of bottom ash.  Other boiler designs result in differing percentages of fly ash, bottom ash or other products.  Air emission control systems that create other types of CCPs, such as flue gas desulfurization material (wet or dry) also contribute to determining the method of disposal.

Location– The physical location of the power plant often has a great impact on disposal.  Plants located in urban areas may have no space for on-site disposal necessitating transport to other locations for disposal.  Many communities have permitted locations within their communities specifically for the disposal of ash.  However, as these locations are completely filled, new land must be found for disposal.  New permits often require extensive environmental reviews and regulatory hurdles.  In western states or parts of the country where the plant is located farther from population centers, there is often more land available for disposal.  Therefore the distance to the disposal site or the cost of land can influence disposal costs.

Transportation methods – if fly ash is collected in silos, it is often mixed with modest amounts of water (conditioned) during loading into a truck to prevent dusting and make handling easier.  In some situations, the fly ash is not mixed with water, but instead loaded directly into covered trucks or pneumatic tank trucks for transport.  If this material is disposed, then handling at the disposal site is normally more challenging due to potential dusting issues.   Bottom ash and other heavy ash material may be conveyed hydraulically using water in pipes to deliver the material to ponds.   In some cases these ponds are only temporary holding locations, from which the material is later excavated and transported to a final disposal site.  At some power plants, the material is transported to its final disposal location in these water filled pipes.  At still other plants, the wet material may be stacked and after it dries, be transported to a final disposal site.

Climate and terrain – The type of climate has a significant impact on methods of disposal.  In areas where water tables are high and where rain or snowfall is significant, precautions may be required to ensure that disposed material is contained.  To prevent leachates from leaving a disposal site, liners may be installed or other types of barriers implemented.  However, in arid climates, where water tables are far beneath a disposal site and annual rainfall is low, few barriers, if any, may be required.  The need for barriers and liners, therefore impact the construction of disposal locations and affects the cost of disposal.

Regulatory requirements – Often related to the geography of an area, some states regulate the disposal of coal ash differently from other states.  If regulated in a manner comparable to municipal solid waste, a state may impose requirements that are more rigorous than a state that regulates the material as an industrial waste.  Again, climate and terrain come into play.  Disposal in an arid state protects the environment in ways differently than in an area where heavy rains, snow or flooding can potentially impact a disposal location. Each of the requirements imposes different design requirements on a disposal facility and will impact cost commensurately.

Future use– In some cases, the material disposed may potentially have future value.  For example, some sites actually serve as stockpiles for material that can be used in future construction, such as in structural fills, highway projects or industrial developments.  Since construction is seasonal, these sites are not disposal areas but instead temporary storage facilities.  Many utilities can also provide numerous examples of old disposal sites being “mined” to recover coal ash for uses not envisioned when originally placed.

Conclusion – As one can see, a variety of factors enter into determining disposal costs.  The lowest cost occurs when a disposal site is located near the power plant and the material being disposed can be easily handled.  If the material can be piped, rather than trucked, costs are usually lower.  In these types of situations, cost may be as low as $3.00 to $5.00 per ton.  In other areas, when distance is far away and the material must be handled several times due to its moisture content or volume, costs could range from $20.00 to $40.00 a ton.  In some areas, the costs are even higher.  If new sites are required and extensive permitting processes take place, the total cost of the facility may be increased, resulting in higher disposal costs over time.


What are “avoided disposal costs?” 

If a plant markets its CCPs into commercial applications, then disposal of this coal ash is not required.  Not only is a revenue stream created for the producer but also the need to dispose of the ash is avoided.  As discussed above, disposal is not just the transportation and placement of ash in a disposal site.  The need for future space is a concern.  If CCPs are marketed, then the need to develop future sites  (including land acquisition, permitting, design and construction costs) is avoided.

If a utility is unable to market or otherwise sell the CCPs produced at a plant, disposal is normally the final destination for the CCPs. The inability to sell fly ash, for example, is determined by physical characteristics (too high in carbon or the presence of air emission additives) or competition of other products in the market place.  However, the ash may still have purpose for lower value uses, such as in structural fills or reclamation activities.  It is not uncommon for a company to help offset the costs of transportation or placement at construction sites by providing the contractor or trucking firm a payment of some sort.  For example, if the cost of disposal at a plant is normally four dollars a ton, then the company may arrange a payment of four dollars or less to the contractors to cover transportation and placement costs.  The difference between the amount of this payment and the cost of disposal is also referred to as “avoided disposal costs.”

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