The harmful materials produced by electricity generation include:

• Fly ash: most commonly produced form of CCR consisting of fine particles that are carried up with the flue gases and collected by filters.
• Bottom ash: heavy CCR produced at the bottom of the furnace.
• Boiler slag: created when mold on bottom ash comes into contact with water.
• FGD materials: created when sulfur dioxide (SO2) emissions from the burning of coal are scrubbed from the flue gas using sorbents. Ex. Limestone.

Hazardous Contaminants in CCR

Although these CCR can be recycled and used in the construction industry, it is more often stored in surface impoundments or landfills. The handling and disposal of CCR pose environmental challenges, especially given the contaminants it contains. These hazardous contaminants include heavy metals, radioactive elements, and various organic and inorganic compounds. Some of the most concerning substances in CCR include:

1. Arsenic: A toxic metalloid that can leach into groundwater and cause serious health effects, including cancer, cardiovascular diseases, and neurological issues when ingested over time.
2. Lead: A heavy metal that is harmful even in low concentrations. Lead exposure is linked to developmental and neurological damage, particularly in children.
3. Mercury: A neurotoxin that can bioaccumulate in aquatic ecosystems. Mercury released from CCR can enter water bodies, affecting fish and other wildlife, and can ultimately reach humans through the food chain.
4. Chromium: Hexavalent chromium, found in CCR, is a known carcinogen that can enter the environment through leaching and inhalation of dust.
5. Selenium: Though a trace element essential in small amounts, elevated selenium levels can cause damage to wildlife and human health, particularly affecting reproductive systems.
6. Radioactive Elements: Some CCR contain trace amounts of radioactive elements like uranium and thorium. While the levels are generally low, long term exposure and concentration in certain areas may increase the risk of radiation-related health problems.

The leaching of these contaminants into groundwater is of particular concern. Many coal ash ponds are located near bodies of water which can lead to contamination if improper containment or breaches in storage occur.

Government regulations on CCR

The Environmental Protection Agency (EPA) established the Coal Combustion Residuals Rule under the Resource Conservation and Recovery Act (RCRA) in 2015. These national standards set a precedent for safe disposal of CCR in landfills and surface impoundments by requiring facilities to:

• Monitor groundwater for contamination
• Install protective liners
• Establish plans for the closure of ash ponds that pose environmental hazards

On May 8, 2024 EPA published “Legacy CCR Surface Impoundments” rule in the Federal Register, which becomes effective on Nov. 8, 2024.

Microscopic Analysis of CCR at Eurofins Environment Testing

Microscopic analysis of coal combustion residuals is a critical tool for understanding its physical and chemical composition. The microscopic analysis of CCR in soil and water can serve as a surrogate to determine the impact of coal ash impoundments on the surrounding environment. Through the use of various techniques, Eurofins Built Environment Testing can study the structure, morphology, and mineralogy of CCR particles to better assess their behavior and environmental impact.

1. Polarized Light Microscopy (PLM): PLM is typically the first step in evaluating the presence of CCR in soil or water systems. It is relatively fast and cost effective. Different types of coal ash can be classified, and the common minerals are also identified with this technique. The percentage of CCR in the soil can be reported by calibrated visual estimate similar to the EPA 600 method for asbestos. The reporting limit of CCR by this technique is at 1%.
2. Scanning Electron Microscopy (SEM): SEM is commonly used to examine the surface morphology of CCR particles. This technique allows researchers to visualize the shape, size, and surface features of the ash particles.
3. Energy Dispersive X-ray Spectroscopy (EDX): EDX, often coupled with TEM and SEM, enables the chemical analysis of individual particles. By identifying the elemental composition, researchers can detect the presence of hazardous metals like arsenic, lead, and chromium, as well as trace amounts of radioactive elements. This helps in understanding the distribution of contaminants and their potential release into the environment.
4. Transmission Electron Microscopy (TEM): TEM provides high-resolution images that can reveal the internal structure of CCR particles. It is especially useful in studying the crystallographic properties of ash and identifying nanometer-sized particles. These smaller particles pose a higher risk of airborne inhalation and can more easily penetrate living cells, leading to health concerns.
5. X-ray Diffraction (XRD): XRD is a powerful technique for determining the mineralogical composition of CCR. Fly ash, for example, contains various crystalline phases such as quartz, mullite, and magnetite, which affect its behavior in environmental settings. Understanding the crystalline structure can help predict how CCR interacts with water and how contaminants may be released under different conditions.

Microscopic analysis provides valuable insights into the composition, structure, and behavior of CCR. By combining these microscopic techniques, scientists can gain a more complete understanding of CCR’s properties, including how hazardous contaminants are bound within the material.