Characterisation and Remediation of Beryllium Waste Pits in the Southern Storage Area at Harwell

The Southern Storage Area at UKAEA’s Harwell site was used from the late 1940’s through until the late 1980’s for the storage, packaging and disposal of various radioactive and chemical wastes. These included beryllium-contaminated wastes arising primarily from the decommissioning of redundant beryllium fabrication facilities. The latter were buried in five unlined, shallow trenches, each being ∼40–50 m long by 6 m wide and 3–4 m deep. An environmental assessment identified three feasible options for the future of these “Beryllium” Pits. These were full excavation with removal of their contents and surroundings, capping and long-term care and maintenance. These options were studied more extensively to select the best practicable environmental option (BPEO), which was excavation. This paper describes in detail the characterisation and remediation approaches used in identifying, planning and successfully implementing that option. It also compares the actual waste arisings in nature, form and quantities with the expectations from the characterisation investigations. At the project commencement limited information existed from records and past trial pitting on the form and contents of the pits. Thus much more extensive characterisation was necessary to determine their dimensions, identify waste types, volumes and disposal routes and quantify potential hazards for any excavations. The characterisation programme involved planning, setting up a site infrastructure, site clearance, non-intrusive surveying and intrusive characterisation by coring. The pit areas and their immediate surroundings were monitored for radiological contamination, followed by geophysical surveys using magnetometry and ground penetrating radar. Primary and secondary containment systems were then constructed over the pits before coring, sampling and analysis on a predefined grid. There was significant beryllium contamination in all pits with some limited contamination by heavy metals, including mercury, and radionuclides. There were also trace levels of volatile organic solvents. These data provided the basis for planning the remediation. The remediation was successfully undertaken to achieve as a minimum a set of remediation targets for residual chemical and radioactive contamination. These targets were determined from site-specific risk assessments, best practice and waste limits. Each pit was remediated within a sealed and ventilated primary containment inside a secondary weatherproof containment building. A horizontal mining approach was adopted to pit excavation with a small excavator initially placed in a launch pit constructed immediately outside the pit. The excavator worked along the pit removing thin layers of waste from an inclined face ahead of it. The waste was placed into bags on trolleys on rails. It was removed via a posting port. After removal of all of the contents and hazardous materials, the containment was removed. Any further excavation required to meet the remediation targets was undertaken in bulk in the open. After verification sampling the remediation was completed by inserting a low permeability barrier of clay and a bentonite geotextile into the base of the pit and backfilling with compacted clean soil. The remediation was completed with successful achievement of all remediation criteria and minimal impacts on the operators, public and environment.