Pulverised fuel ash (pfa) and furnace bottom ash (fba) are the principal solid wastes from modern coal fired plant. These residues are often handled and disposed of as slurries and pfa is frequently used for the reclamation of derelict land.
The disposal of excess water from the handling operation after the ash has been allowed to settle in a pond or lagoon is the first interaction with the aqueous environment that needs to be considered. In CEGB, the discharge of such effluents to rivers is governed by consents laid down by Water Authorities. The state of the art is such that the required conditions can be met in once-through handling systems without undue difficulty but one factor which requires careful management is the level of suspended solids in the outfall when a lagoon is nearly full.
Whether ash is disposed of wet, or merely conditioned with water to facilitate handling. there may be a further need to consider the percolation of water through the ash and its possible interaction with groundwater. This calls for knowledge or study of the ash itself, the size of the area to be reclaimed, the rainfall pattern and the local hydrogeology, including the size and rate of recharge of the aquifer. Each case needs to be considered on its merits. The basic CEGB approach to this aspect of ash disposal is discussed; it requires the combination of laboratory studies of percolate quality with hydrogeological assessment to evaluate the potential risk, if any. The actual consent to dispose of ash, taking such factors into account, is made by the Local Authority in consultation with the Water Authority.
The present view of ash disposal relative to the aqueous environment could be disturbed if legislation and the associated Codes of Practice were to become more stringent. Recent control measures which are pertinent to these activities are, therefore, considered and comment made on their content and application.