Exploding a time bomb
A waste dump contaminated with chemicals, radioactivity and live munitions is certainly a place to tread carefully. Beverly La Ferla visits a site near Oxford that is coming to the end of a two-year remediation programme.
The first area that was of particular concern was the 18-acre SSA, an area known locally as the 'bomb dump' because the RAF used it as a munitions store during World War II when Harwell was an airfield. Since then the site has been treated as a waste burial ground, with a variety of waste entering the site, including chemical- and beryllium-contaminated material.
"Even before that the site was used to dump a quarter of a million tonnes of soil and construction waste from the building of the Harwell site itself," says Atyeo, "and then, during next thirty years, the site was used for the storage and handling of low level radioactive material wastes from the Harwell laboratories - contaminated gloves and bits of equipment from miscellaneous experimental work. What they did was dig a hole in the chalk and simply chuck the boxed waste in." The waste was dumped in the pits and piled up to 12 metres high, creating several small hills and on the whole forgotten about. The result: six chemical dumps and five beryllium pits.
A primary liability
As strong as steel but as light as aluminium, beryllium oxide is a white powder more toxic than asbestos and, if inhaled, can give rise to acute and chronic lung conditions. Not so great when the local primary school is situated downwind at one end of the SSA. "While the radioactive waste was easy to locate on-site and easy to deal with, the beryllium contamination can only be measured through laboratory tests. This, combined with the proximity of the primary school, is therefore the part of the project which we're managing most carefully as it has the most critical risk attached to it," says Atyeo.
The second area, the Catapult Pit, was constructed just before the war to be capable of launching a 30-ton bomber. Speculation abounds that the pit may have been intended as an alternative to building an airfield. Although built by 1938 and tested extensively, the Mark III Catapult was never used. When the UKAEA took it over in 1946, the chamber which held the catapult's machinery was used as a waste transit pit for the storage of radioactive materials, in particular unrefined uranium ore. Although the pit was cleaned and filled in during the 1950s, recent surveys revealed a small amount of uranium contamination.
Clean up of the SSA started in the late 1980s but progress occurred in fits and starts. Intensive remediation of the site started in June 2000 and initial surveys showed heavy metal contamination and chlorinated hydrocarbon contamination, as well as radioactivity. The site was divided up into a typical 20 metre grid and drilled at regular intervals before being swept with gamma radiation counters, and various surveys were conducted, such as metal surveys, soil/gas surveys, penetrating ground radar, and baseline surveys on air quality, groundwater, noise and local ecology. The same process was applied to the Catapult Pit which was enclosed in a double tented structure to contain airborne contamination.
Site clean up has been extremely thorough. Atyeo: "We peeled off layers one foot thick right down through the 12 metres of waste until we reached the base chalk. Each square inch was characterised for every determinand - chemical and radioactive - and then sorted, with contaminated material being put to one side. Material we verified clean was returned to the site. We estimated we had sifted through 250,000 cubic metres of soil at the SSA by the end! It was like the Time Team but on a massive scale."
About 1,000m3 of contaminated waste was generated, with the majority being chemical contamination. Areas contaminated with beryllium were enclosed in double tented structures, like the Catapult Pit, the inner tent being under negative pressure to ensure no leaks to the outside environment were possible.
To date all of the beryllium pits have been dealt with and half of the chemical pits. A total of 12,000m3 of exempt radioactive waste was generated, 4,500m3 of controlled waste, such as fill materials and scrap, and 250m3 of low level radioactive waste which has been sent to the special Drigg Repository in Cumbria.
Not all of the waste was quite as easy to deal with. "We found several other interesting items too. Live practice bombs numbering 1,100 were recovered together with 12,000 live round of small arms munitions," says Atyeo, "The best finds however were an unexploded 500kg German bomb and two 750kg bombs for which we had to call out a Bomb Disposal Unit! We also had to carry out 20 controlled explosions on-site."
Didn't the neighbours complain about bombs going off in their back yard? "Throughout the whole process we were in close consultation with local stakeholders - the local community, parish, parents of the primary school kids, the people who live in the nearby housing estate and farm - and regulators like the White Horse District Council, the Environment Agency and the Health and Safety Executive. We started up a regular newsletter with updates on the project's progress, e-mailed bomb explosion warnings, held meetings and also visited the school. We let the children do their own 'site survey' and when the site is returned to being a field," Atyeo chuckles, "I've promised each of them a tree to plant."
The Catapult Pit is due to be backfilled with fresh material and buried, although
the concrete outline will still be seen during summers as a region of poor grass
growth. The SSA has been earmarked as a football pitch when its remediation
programme comes to a conclusion this summer, and will form part of a new Science
and Technology Business Centre. Not quite as exciting as a 'bomb dump' but a
whole lot safer.