Project Specifics

In December 2008 a slope stability failure at a fly ash disposal facility in the United States caused significant environmental impacts to surface water. Consequently, the electric utility industry was concerned about static liquefaction of fly ash that could lead to failures at other facilities. The utilities, through the Electric Power Research Institute (EPRI), retained Geosyntec to conduct research into fly ash geotechnical properties and static liquefaction.

Further, the U.S. Environmental Protection Agency (EPA) proposed new coal combustion residuals (CCR) regulations that will cause power plants to likely close a large number of ash and flue gas desulfurization ponds during the next 10 years. The objective of this project was to provide information to help power companies meet the challenges presented by the evolving regulations. These challenges include multiple closures, premature closures, accelerated closures, long-term stability, construction materials, monitoring strategies, design of landfills on top of closed ponds, and reuse of closed pond properties.

Geosyntec Scope of Services

First, Geosyntec completed literature and laboratory research to compile seminal information on the geotechnical properties of fly ash and the potential for static liquefaction of hydraulically placed fly ash in ponds. Materials from 22 sites were involved in the research. Specimens were tested to evaluate the potential for static liquefaction or significant loss of strength upon undrained loading. The research report was completed at the end of 2012 and was provided to U.S. EPA in support of comments on the proposed CCR disposal regulations.

Second, Geosyntec provided EPRI with detailed guidance documents for: (i) dewatering and capping of CCR ponds and (ii) construction over closed or closing ash ponds. These two guidance documents assist the electric utility industry in meeting the challenges presented by evolving federal regulations. Developing the guidance required Geosyntec to obtain information from the utility companies funding the project, apply the firm’s experience at a number of sites, and conduct research. The final guidance documents have been submitted and are being finalized in early 2014.

Notable Accomplishments

Geosyntec brought its considerable experience to EPRI on these projects. The geotechnical research on fly ash indicated that even loosely placed fly ash specimens tended to dilate upon shear, a phenomenon that minimized the potential for static liquefaction. The two completed pond closure guidance documents provide the electric utility industry with comprehensive compendiums of experience that can be used by operators of coal-fired power plants to understand the technical aspects of ponded CCRs, methodologies for dewatering and capping ponds, design and construction of landfills on top of closed ponds, and what technical approaches work and those that should be avoided.

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