The Long-Term Leaching Behaviour of a Pulverised Fuel Ash Mound

The long-term leaching behaviour of a pulverised fuel ash (PFA) disposal mound at a British coal-fired power station was investigated. Samples of weathered PFA, taken from boreholes extending through a PFA mound were taken from locations representing different constructional age bands within the mound (1976, 1980 & 1985). Small-disturbed samples taken at lm depth intervals were analysed for natural moisture content and a range of chemical determinands. Permeability behaviour with change in depth from the mound surface was also investigated using undisturbed samples. Generally, the moisture content and degree of saturation were fairly constant with increasing depth within the mound and did not differ significantly from those at initial deposition and compaction. The permeability was relatively constant with depth, ranging from 1.23 × 10⁻⁷ ms^−l to 1.45 × 10⁻⁸ ms^−l, with a mean permeability of 5.43 × 10⁻⁸ ms⁻¹. There was no evidence of a saturated zone or potential wetting front within the mound. Arsenic, sulphur and boron were significant in relation to their toxicity and concentrations. Concentrations of boron, molybdenum, potassium and sodium showed a slight increase with depth, suggesting downward migration of leachate derived from PFA. Concentrations of all determinands within the silty clay located below the constructed drainage blanket beneath the mound were below the Environment Agency threshold levels. PFA leachate concentrations did not constitute an environmental hazard to groundwater beneath the mound.

• INTRODUCTION

• METHODS

• RESULTS

• DISCUSSION

• CONCLUSIONS

• Acknowledgements

• REFERENCES