ENVIRONMENTAL IMPACTS OF COAL COMBUSTION RESIDUES

Coal combustion residues account for 90% of all fossil fuel combustion wastes produced in the USA. It is Projected that by the year 2000 more than 150 million t of these materials will be produced in the USA each year. Presently, only about 20% of these wastes are utilized, with the remainder deposited in landfills or surface impoundments. This article reviews the information available concerning the environmental impacts associated with the disposal or utilization of coal combustion residues. The majority of the information available in the literature concerns the impacts of fly and bottom ashes; other coal combustion wastes have not received much attention. The major potential impacts of ash disposal on terrestrial ecosystems include: leaching of potentially toxic substances into soils and groundwater; reductions in plant establishment and growth due primarily to adverse chemical characteristics of the ash; changes in the elemental composition of vegetation growing on the ash; and increased mobility and accumulation of potentially toxic elements throughout the food chain. Ash disposal in landfills and settling ponds can influence adjacent aquatic ecosystems directly, through inputs of ash basin effluent and surface runoff, and indirectly, through seepage and groundwater contamination. Major impacts are generally associated with changes in water chemistry, including changes in pH and concentrations of potentially toxic elements. Using ash as a soil amendment can improve soil texture and water-holding capacity, increase soil pH, and enhance soil fertility. However, it may also result in excessive soluble salt concentrations, excess B, and increased concentrations of other potentially toxic trace elements; reduction in the concentrations and/or availability of soil N and P; elemental imbalances due to excessively high pH; and cementation or compaction of soil. Scrubber sludge and fluidized bed combustion waste may be used as soil amendments as well, but also may create problems due to high alkalinity and high salinity.