In St Helier, Jersey, a surface water link and storage cavern are being constructed to alleviate surcharging of the town's sewerage system during periods of high rainfall. Foul sewers will discharge a stormwater/sewage mix into a 25 000 m3 cavern for temporary storage. The cavern will be emptied by pumping to a treatment works at a regulated rate.
As part of the site investigation for the work, an assessment of the levels of radon likely to be encountered during the construction and operation of the cavern was undertaken. Samples of borehole core were analysed in the laboratory to obtain values of radon emanation per unit surface area. These were then combined with design data to estimate radon concentrations in the void.
The method described provides a simple and effective way of assessing radon contamination at the site investigation phase of a project, enabling protection measures to be incorporated into the design at an early stage, so minimizing the exposure of staff to potential harmful levels of radon during both construction and operation.