Sellafield CPT set to start

Nirex announced last week that it is to test static cone penetration as an alternative to borehole drilling this summer, as part of its plans for an underground repository for low and intermediate level radioactive wastes in Sellafield, West Cumbria.

Cone Penetrometer Testing (CPT) will be investigated by the company as part of an intensive study of the Quaternary geological deposits in the Sellafield region. The investigations form part of Nirex's multi-million pound research programme to assess the suitability of Longlands Farm near Sellafield as a potential site for the repository.

CPT differs from traditional borehole drilling in that instead of erecting a drilling rig to bore a slim test well down to 50 metres depth, a probe containing monitoring instruments is pushed through soft ground at 20mm/second by hydraulic jacks on a six-wheel drive truck.

Nirex geologist Richard Heath said: "CPT is a quick and economical way to investigate near surface conditions in unconsolidated deposits. We will try this method along the 10km stretch of coastal flood plain between High Sellafield and the River Irt estuary to calibrate geophysical data acquired last year."

The CPT programme will be carried out at eight sites where stone content is sufficiently low to enable penetration to 30 or 40 metres depth. At two sites, a grid of CPT investigations with an electrical cone will be conducted over a 100 metre square area to measure deposits resistance and conductivity.

Piezometers will also be installed to enable monitoring of groundwater pressure and to improve the regional spread of near surface hydrogeological data. Push-in well screens will also be used to sampled groundwater for chemical analysis. Six other sites will see wire-line logging and standpipe piezometers installed, using standard near-surface drilling techniques.

The next step is Nirex's planned rock laboratory at Longlands Farm. It is expected that a report from the recent public inquiry into Nirex's application for the laboratory will be submitted to the Secretary of State for the Environment by the end of October.