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Risk Sciences
Coal Combustion Products
Overview
After years of regulatory debate and analysis, on April 17, 2015 the US EPA published its final rule regarding the disposal of coal combustion residuals from electric utilities. The new rule, which upheld the classification of coal combustion products (CCPs) as Subtitle D waste under the Resource Conservation and Recovery Act (RCRA), contains several requirements that necessitate re-evaluation of how CCPs are currently handled. The Rule has introduced many new regulatory obligations related to wet storage of coal ash in surface impoundments. It also calls for increased monitoring of impoundments' structural stability and for evaluation of potential effects on groundwater from all types of waste management units. Although the Rule has introduced prescriptive requirements for disposal, it continues to support beneficial re-use of CCPs, which will likely expand CCP use.
Whether CCPs are disposed of as waste or recycled, Gradient has over a decade of experience evaluating environmental impacts and addressing human and ecological health concerns and regulatory issues associated with a number of constituents in CCPs.
Example Projects
Framework for Evaluating Relative Impacts of Surface Impoundment Closure Options
Full DescriptionGradient developed a decision tool using quantitative risk assessment that aids utilities in selecting closure plans that minimize potential human health and environmental impacts. The framework relies on a comprehensive, science-based assessment of possible impacts to traditional exposure pathways, including groundwater, surface water, and outdoor air, as well as impacts to green and sustainable remediation (GSR) metrics such as worker safety and resource use.
Coal Combustion Waste Probabilistic Risk Assessment
Full DescriptionGradient critiqued a recent US EPA risk assessment on the human and ecological health risks of CCPs drafted to inform a hazardous waste rulemaking. We evaluated the appropriateness of parameters used in the probabilistic risk assessment and the inputs selected for fate and transport modeling of metals.
Mercury Risks from Construction Materials Containing CCPs
Full DescriptionGradient evaluated potential mercury inhalation risks associated with the beneficial use and disposal of CCPs in building materials and structural fills. We calculated mercury releases from CCPs in wallboard, concrete, structural fills, and construction and demolition (C&D) landfills and compared the modeled mercury concentration in indoor and outdoor air to toxicity criteria to determine if potential exposures were above a level of concern.
Human Health and Ecological Risks of Constituents in Coal Combustion Products
Full DescriptionGradient prepared reports on the human health and ecological risks associated with several chemical constituents in coal combustion products (CCPs) including arsenic, thallium, selenium, and molybdenum. The reports included a summary of human epidemiology and key animal studies, focusing on the use of this information in risk assessment and current regulatory standards and criteria.
Surface and Groundwater Risk Assessment for Waste Impoundments
Full DescriptionWe evaluated the potential risk to surface and ground waters from coal combustion waste products stored in inactive, unlined surface impoundments around the country by conducting an analysis of a national surface impoundment database and statistically evaluating the duration of risk due to a potential surface impoundment structural failure. We developed an analytical approach simulating the leaching of coal combustion waste.