Disposal of combustion ash generated by coal-fired power plants is a major concern for utility companies. Awareness of the issues related to design and maintenance of impoundments used to store this ash was elevated by the failure of a large ash impoundment at a TVA generation plant. D'Appolonia is experienced in the design of facilities for coal refuse and fly ash disposal and has been a pioneer in designing facilities for the co-disposal of these two materials.

Combustion ash and coal refuse impoundment for which D'Appolonia provided engineering services for the original design and subsequent expansion.

Descriptions of D'Appolonia projects related to evaluation and design of combustion ash impoundments are provided in the following:


Engineering Services Related to Coal Combustion Ash Disposal

Following the failure of a combustion ash slurry impoundment at the Tennessee Valley Authority's Kingston Fossil Plant, D'Appolonia served in a consultant role on a peer review team evaluating some TVA wet ash disposal facilities. Our scope of work included: (1) geotechnical investigations, (2) shear-strength characterization, (3) seepage analysis, (4) slope stability analysis, (5) seismic analysis, and (6) evaluation of stabilization plan constructability. Over its more than 50-year history, D’Appolonia has provided design and permitting services for numerous impoundments for coal refuse, combustion ash, and tailings disposal. D’Appolonia also provides inspections of dams and impoundments, and planning for expansion, decommissioning, and reclamation of these facilities.

Coal and Combustion Ash Refuse Impoundment Design and Expansion

D'Appolonia has been responsible for planning and design for a 160-acre coal refuse impoundment. The initial design was for a 60-foot-high diked impoundment constructed from coarse coal refuse. With increases in coal production and to accommodate co-disposal of refuse with combustion ash, the coal refuse disposal facility was expanded to a design height of 100 feet using upstream construction over areas of slurry deposition. D'Appolonia's responsibilities have also included support in obtaining permits and performing breach analyses related to preparation of an Emergency Action Plan. To accommodate expanded fly ash disposal projections by the mine’s primary power plants, a dedicated combustion ash impoundment was also designed and permitted. D’Appolonia’s responsibilities at the site have also included providing support in obtaining applicable federal and state permits. Based on Potential Failure Mode Analysis (PFMA), impoundment breach analyses were performed to identify potential downstream impacts, prepare inundation maps, and create an Emergency Action Plan (EAP). Various scenarios relative to the size of the breach and the quantity of tailings released were evaluated. D’Appolonia is also providing periodic review of construction and refuse material parameters at the facility.

Co-Disposal of Coal Mine Refuse and Combustion Ash

Following plant upgrades for a mine-mouth power station, the processed coal refuse was found to contain excess water that made placement and compaction difficult. D’Appolonia developed a testing program, prepared design modifications for the coal refuse facility, and provided permitting services related to the beneficial co-disposal of the wet coal refuse from the coal preparation plant combined with fly ash from the adjacent power plant. A testing program was developed for coal refuse/fly ash mixtures ranging from 0 to 60 percent fly ash by weight. The testing results provided a basis for selection of the amount of fly ash to be blended with the coal refuse at the disposal site and for monitoring the placement and compaction of the material consistent with regulatory requirements. D’Appolonia developed construction plan modifications for the disposal site that encompassed placement and compaction procedures, access road design, and internal and surface drain design. Surface and groundwater monitoring programs were modified in response to regulatory requirements, as part of permitting activities. The design modifications allowed the coal refuse disposal site to be trafficable year-round and enhanced facility access, final grading and site reclamation. In addition, the power plant benefitted from an increased life for its permitted fly ash disposal site.