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Biopiles wage new jet battle in Gloucester

contracts

THE GLOSTER aircraft factory may be no more but it entered the history books for its key role in the development of Britain's jet aircraft. The site known for building the Gloster Meteor, the first allied jet aircraft used during the Second World War, is being redeveloped as a residential housing estate.

But despite the Gloucester site's historic past, it has left a less than desirable legacy.

Production at the engine test bed site caused localised contamination of soil and perched groundwater by jet fuel. Petroleum hydrocarbon contamination was present in a shallow layer of made ground comprising limestone and clay fill but was contained by the underlying low permeability Lower Lias Clay.

Subcontractor Vertase won the £149,000 clean up contract from a consortium of housing developers, and opted for bioremediation on 6,000m 3of contaminated soil.

The 20 week job started with breaking out and crushing concrete hardstanding and tank bases, before the contaminated soil was excavated. The base and sides were checked on a 15m grid to confirm that all contaminated materials had been removed. Results confirmed that hydrocarbon concentrations were less than 200mg/kg, significantly below the site specific assessment criteria of 500mg/kg.

For biopile validation, Vertase subdivided the material into 20 areas, collecting samples from each for chemical analysis. Results showed mean concentration of the pile was less than 600mg/kg, significantly lower than the 1,000mg/kg remediation target.

Site-won material was split to enable 5,000m 3of secondary aggregate (crushed concrete) and 2,000m 3of clean fill to be stockpiled for re-use. This will be used to reinstate the site and to build a bund to screen off noise from the nearby M5.

However, disposal of contaminated water entering excavations was a problem, with no connection to a live foul sewer nearby, and the volumes making tankering off site for disposal too expensive.

The solution was a mobile oil water separator supplied by Siltbuster (see right) which removed in excess of 99% of the hydrocarbons from the water.

Conservation is also playing an important part on the project. Mature oak trees, home to barn owls, are to be retained and previously culverted water courses opened up.

Remediation was completed in autumn last year with the next phase of development beginning in early 2005.

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