Geochemistry of leachate from fly ash disposal mound

Abstract

Leachate water was collected from the fly ash disposal mound in one of the major UK coal‐fired power station. The ash mound has been tipped since mid 1970's and is well engineered and managed, theoretically with no leaking of leachate generated within the ash mound into the underlain aquifer. The chemistry of the leachate shows high concentrations Ca, Na and SO₄, representing the chemical characteristics of fly ash. B, Li and As are the important trace elements recording the highest concentrations of 22. 3, 24.8 and 16.9 mg/1. Correlation of leachate water chemistry with the contents of the total dissolve solids implies most of the elements in the leachate, including Na, K, Ca, S, Pb, ? and Li, are derived from the dissolution of fly ash with infiltrating porewater. The rate of infiltration of porewater in the ash mound was calculated based on the chemical data from the porewater and fly ash. The result showed value of percolation rate of about 40 cm/year. The analytical result of the leachate water was processed with geochemical modelling program, WATEQ4F, and several potential concentration limiting solid phases were identified. Concentrations of As, Cd, SO₄, Cr, Pb and ? exceed the discharging limit set by the EC landfill directive or the National River Authority and this implies the leachate should be treated before discharge into surface water. There are well‐engineered sites built when the construction standard was not so stringent as is today, where potential groundwater pollution might take place by introducing leachate from the ash disposal mound.

Key words:

• Fly ash
• Leachate
• Landfill
• Groundwater pollution