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Tamdown win with bio

Tamdown Regeneration won Best use of a single remediation technique in the BB Remediation Innovation Awards for its treatment with bioremediation of a former gasworks in Surrey.

This project centred on the use of vented biopiles housed in poly-tunnels. This simple technique enabled the successful on-site treatment and re-use of 3,250 tonnes of gasworks-contaminated soils.

Tamdown undertook the remediation of the site for Explore Living Ltd, part of the Laing O'Rourke Group, to facilitate construction of residential apartments. Off-site disposal of all the soils (which were contaminated with BTEX compounds, TPH, phenols and coal tars) would have exceeded the client's remediation budget.

Tamdown therefore segregated 500 tonnes of grossly impacted soils at source for landfill disposal and treated the remainder on site by ex-situ bioremediation prior to re-use as backfill, thereby preventing the transportation and disposal of 200 lorry loads of hazardous waste to landfill.

Best practice

With remediation scheduled for September 2007 and a deadline for handover of the soil treatment area of January 2008, Tamdown sought to overcome the challenge of carrying out bioremediation in winter and also of operating on a restricted available footprint. Conventional methods (soil windrows) of biological treatment during winter are significantly hampered by lower temperatures and rainfall restricting biological activity, which can result in the need for longer treatment timescales.

To optimise the bioremediation process, Tamdown engineered a solution which involved poly-tunnels to promote a greenhouse effect, as well as the application of a blend of bio-stimulants (which had been successfully trialled at the field-scale by Tamdown on another project).

They also used a low vacuum extraction system to continually extract air through biopiles without the need for mechanical turning (this retains heat and minimises disturbance of the soil microbial populations) and engineered a system to provide an input of recycled warm air. These measures resulted in temperatures within the enclosures to be at least 15°C above ambient, and temperatures within the biopiles to be 25-30°C.

Reduction of pollution

The mean average time zero (T0) concentrations prior to bioremediation treatment were 2,410mg/kg TPH and 1100mg/kg total PAH respectively. On completion of soil treatment works after a 12-week period the mean concentrations had been reduced to 394mg/kg TPH and 218mg/kg total PAH respectively.

This represents a 90% reduction in overall contaminant loading - an achievement unlikely to have been possible in such a short timescale during winter months without the use of the poly-tunnel enclosures and recycled warm air input.

Cost effectiveness

The bioremediation and re-use of soils resulted in a saving of £195,000 compared to off-site disposal and importation of backfill, which equates to more than 50% of the total contract sum.

Communication and health and safety

Numerous stakeholders were involved in the assessment and remediation stages of the project and ongoing liaison was maintained with local residents and occupiers of adjacent commercial premises.

"An Imaginative and highly effective solution - creative simplicity at its best" John Campbell

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