When ash is stored in a landfill, it is mixed or conditioned with water at the power plant to minimize dust, and the damp ash is transported to the landfill where it is compacted in layers. When the landfill is full, the surface is covered with topsoil, seeded and reclaimed for possible future use.
When ash ponds are used, the ash is mixed with water at the power plant and pumped as a slurry to the ash pond. The ash settles and clear water is decanted from the pond to the power plant where it is recycled. When the ash pond is full, it is often necessary to excavate the ash and transfer it to a landfill or permanent disposal site to create additional storage space in the pond. If this is not possible, it is necessary to construct an additional ash storage pond.
According to the DOE EIA, in 1999, there were 450 coal-fired power plants in the US. These plants operated 600 ash disposal or storage sites, half of which were landfills and the other half were ponds.
The average size of the landfills was 116 acres at a height of 43 ft, while for the ponds, the average size was 149 acres with a depth of 36 ft. When combined, these ash storage sites cover approximately 124 square miles.
In the US, 62% of all ash produced is stored in landfills or ponds. To compare that with our neighbors to the north, Canada landfills 69% of their ash. Utilities in Europe landfill 36% of their ash.
The advantages of using this resource, rather than storing it, are obvious. The cost of disposal is high and a significant amount of land is necessary. Any time land can be used for a more productive purpose than storage or disposal, it is better use for the land.