Design and Permitting of a FGD Landfill over an Existing Ash Reservoir

A large coal fired operating plant in the Ohio River Valley had a need to develop a disposal facility for residual waste from its newly installed Flue Gas Desulfurization (FGD) system. Siting studies were conducted resulting in the selection of a site located partially over an inactive fly ash reservoir (FAR 1) which was undergoing closure and partially over a remnant mine spoil disposal site. While the selected site would allow for environmental and operational advantages, significant engineering design and construction challenges had to be addressed. This paper provides information on the challenges that relate to the design and permitting of this residual waste landfill. Specific issues addressed include: (1) boundary issues (i.e., existing mining highwall, valley stream, and 45-m high dam); (2) potential for differential settlements of the foundation subsoils and effects on leachate collection and piping systems; (3) design of a subsurface drainage system to collect and transmit consolidation waters; and (4) impacts to landfill drainage systems resulting from liquefaction of the underlying fly ash during the design seismic event.