Cone Penetration Testing of Radiologically Contaminated Burial Trenches
Authors: Walker Gareth , Jefferies Nick , Lennard Matt , Lightfoot Jeremy 
Published: December 2010

Golder Associates (UK) Ltd, in partnership with Serco Assurance (Serco), undertook targeted cone penetration testing (CPT) of a series of six parallel on-site burial trenches on a nuclear licensed site in the UK. The form and concentration of radioactive and chemical material within the trenches is unknown. CPT was used to confirm the location of the bund walls and to characterise the material within the trenches. The CPT technique involves hydraulically pushing rods fitted with specialist characterisation “cones” into the ground. CPT generates no solid or liquid waste, and allowed rapid investigation of the trenches and bunds while ensuring exposure of radiation and contamination to workers was kept to a minimum, or removed in entirety. As a result of the unknown nature of radiological contamination within the trenches and the potential of introducing contamination into the inside of the CPT truck, a purpose-built extraction rig was constructed to withdraw the CPT equipment from the ground. Extraction of the equipment assumed airborne radioactive contamination was a potential hazard. The CPT locations selected for the investigation were based on non-intrusive geophysical survey work and a radiation survey, which identified the approximate location of the trenches, anomalies within the material (e.g. metallic objects), and radiation hotspots. The results of the geophysical surveys were overlaid with the original as-built drawings of the trenches. During the investigation the following investigation cones were deployed: • Resistance/friction cone, which determines geology through measurement of the friction on the sleeve of the cone and resistance on the tip of the cone; this was used to investigate the geology of the bunds. • Total gamma cone, which was used to obtain total gamma radiation results (in counts per second); • Groundwater sampler (BAT Sampler™), which was used to obtain a water sample from beneath the trenches; • Video cone, which was used to obtain a visual recording of the material within the trenches; and • Conductivity cone, which was used to investigate the presence of and depth to bodies of water below ground level (e.g. perched water, regional groundwater). The investigation collected essential data from an area of the site that had not previously been investigated, while minimising potential radiological exposure to all workers, and producing no investigation-derived waste. The investigation therefore confirmed the efficacy of cone penetration testing as a valid site investigation technique in a high hazard area. The data acquired from the CPT investigation and geophysical investigation also allowed boreholes to be sited in the bund walls between the trenches. Siting of the boreholes was a major risk for the project and presented a significant potential hazard. Golder has successfully used CPT on nuclear sites in the UK: as an innovative site investigation technique to facilitate radiological characterisation of an area with variable ground conditions; to investigate organic solvent plumes; and for the installation of blind tubes as a way of conducting subsurface radiation surveys and as part of a leak detection system (work in progress in partnership with Serco).