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Keeping the sludge in

THE NIGHTMARE scenario for the new sludge dewatering plant is that the sludge escapes from it into the nearby countryside.To prevent this it was vital to ensure as many possible forms of protection were in place.

Once the sludge arrives on site it is stored in 8 m x 20 m tanks.Only two are needed for the daily requirements of the plant but the team has built six more.

Although this should be enough to cope with even the worst-case scenario, the team has also built a further lagoon for any overflow.

If this is not enough the team has also installed a 1,500 m earth bund around the site, which overlays a 1,200 m wall of bentonite that has been installed down to the clay below the site, meaning that the whole Iver South site is now impervious both to water entering (allowing a safe and dry site for construction work) and sludge escaping into the local environment.

'The bund and bentonite wall are designed for a one in 100 year flood, so you will not be seeing sludge cake floating off into the flood plain, ' says Costain Iver South project manager Colin Howe.