Your front page story (April 25) highlighted the use of fly ash, a by-product of coal-burning in concrete. Fly ash has been used as cement replacement in concrete in the UK for more than two decades.

The main benefits of its use include reduction in cost, re-utilisation of waste, and high workability and greater long-term strength of the concrete thus produced.

Despite all these benefits, fly ash produced by the Marsa power station for several years has been dumped in an un-engineered landfill in two disused quarries at Ben-għajsa in Birżebbuġa. This waste was eventually covered with a layer of soil to cover the bluish hue of the fly ash. This is clearly visible from the sea as shown in the accompanying photograph.

Landfilling of fly ash is problematic due to leaching of toxic waste that takes hundreds of years to be disposed of. Recent tests carried out on the fly ash landfilled at Bengħajsa showed a high level of radioactivity of the powdered ash.

Incorporation in concrete as cement replacement resulted in good quality concrete with similar radionuclide emissions to Maltese globigerina limestone used in most Maltese buildings. All these data have been reported in Waste Management (Camilleri et al. 2006).