What Are Coal Combustion Residuals (CCRs)?
Coal combustion residuals are the by-products remaining after the efficient combustion of coal in a PC or CFB boiler and are the residual rock and sand (inorganics) that do not volatilize in the combustion process. Most of the CCR is produced during the generation of electricity though some is produced in industrial facilities that produce their own energy production.
CCRs generally fall into four categories; Fly Ash, Bottom Ash, CFB Ash and FGD (fluidized gas de-sulfurization) and if combusted efficiently, can be beneficially used. The largest percentage of CCRs produced is fly ash (also known as pozzolans).
Currently, about 45% of CCRs are beneficially used in products from concrete to wallboard. The EPA has mandated that CCR be recycled and/or disposed of through environmentally sound methods promulgated by USEPA CCR management rules set forth in December 2014.
How Should CCRs Be Managed to Meet the EPA Coal Combustion Residual Rule?
Over the years, CCRs have generally been handled on power plant sites and sluiced into large wet impoundments. During the last 35 years, many plants have undergone dry conversion handling of CCRs to enhance beneficial use as market segments were developed. Approximately 70% of plants dry handle fly ash today, yet 90% still handle bottom ash by wet methods due to plant configuration limitations for equipment installations.
Due to some large-scale ash pond dam failures at power plants, the USEPA and current administration took the failure as an opportunity to seek alternatives to handle and store CCRs in impoundments. Thus, the EPA developed and promulgated the Disposal of Coal Combustion Residuals from Electric Utilities final rule on December 19, 2014, and it was published in the Federal Register (FR) on April 17, 2015.
Ultimately, the rule stipulates that most of the approximately 735 wet CCR impoundments will be closed via a clean closure or close-in-place strategy. The remaining wet sluiced plants will be required to convert to dry storage handling mechanisms and placed in lined landfills or commercial municipal fills.
Are CCRs Harmful?
By scientific definition and EPA regulatory rule, CCRs are defined as non-hazardous. The rule establishes technical requirements for CCR landfills and surface impoundments under subtitle D of the Resource Conservation and Recovery Act (RCRA), the nation’s primary law for regulating solid waste.
Like all soil around the country, CCRs contain elements of the 8 RCRA metals but almost never reaches limits of RCRA levels. However, due to the secondary metals and salts contained in CCRs, appropriate handling should be utilized to prevent any potential contamination above background levels of native soils and water sources.
Any material, including H₂O consumed at excess levels, can qualify as toxic. So responsible handling is always prudent to mitigate any risk to the environment or persons.
How Do Utilities and Power Plants Currently Manage CCR?
Currently, about 155 million tons of CCR are produced each year with approximately 45% recycled or beneficially used. Class F and Class C Fly Ash are used as a cement replacement in concrete if they meet ASTM C618 specifications, and all 50 state DOT’s specify 20% replacement of cement with pozzolans in all concrete work.
90% of all gypsum (CaSO₄• 2 H₂O) wallboard is produced with power plant FGD by-products. Many plants are now allowing FGD for use as a soil amendment for crops, which is a significant benefit to crop health and production.
If materials are not BU, then the by-products must be properly stored in current operating wet impoundments or dry landfill storage units. The EPA defines the critical timelines for the closure of the wet impoundments. Utilities are currently scrambling to work with consultants and internal design engineers to develop closure strategies.
What Are the Characteristics of a Competent Civil-Geotechnical Contractor?
There are several characteristics and factors that a utility must evaluate before selecting a trusted partner to successfully manage CCR pond/impoundment closure and ELG requirements:
- CCR Chemistry and Rheology Expertise
- Civil–Geotechnical Construction Expertise
- Multi-Discipline Skill Sets
- Risk Aversion
All of these requirements must be part of the decision to choose a competent contractor. Many civil contractors are good at moving soil from point A to point B but are not versed in the thixotropic nature of wet CCRs or complex risk mitigation strategies required to handle these projects and potential environmental impacts.
Looking to learn more about CCR? Get in touch with us, and we’ll lend our expertise to your current situation.