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Toxic waste plan raises hopes for Cardiff site

HYDER PLANS to spend £7M shifting nearly 1M.m3 of slag fill and toxic waste from its £180M Cardiff East wastewater treatment plant site in an attempt to resolve geotechnical problems dogging the project.

Design and construction of the high-tech sequential batch reactor facility has been on hold for several months while Hyder struggled to come up with a solution (NCE 16 October 1997.) And with the outfall now complete and work starting this week on the inlet tunnels, Hyder must have the first phase of the plant ready by 2000, or face considerable embarrassment.

Hyder originally planned to shift the unwanted fill to an area between the site and a planned M4 link road along the shores of Cardiff Bay. Cancellation of this road forced Hyder to apply for planning permission to dump the material on an existing landfill site nearby and landscape it to form a recreational area.

Hyder project manager Jeff Martin said: 'We hope to have planning approval by Easter, and begin work on the first phase of the SBR this autumn. This will keep us on target, with the second phase starting next winter.'

The 9m deep highly alkaline slag overlays soft alluviums and contains steel 'skulls' - huge ingots of waste from the former steelworks across the road - that effectively block a piled foundation design. Contractor Laing will have to remove up to 800,000m3 of this material, plus 100,000m3 of cadmium-rich flue dust, which will have to go to a contaminated waste tip.

A depth of around 2.5m of fill will be left under the SBRs. Martin said the weight of the remaining fill and the structures above must be the same as the original weight on the alluviums. 'Otherwise the alluvium will either compress if the weight is too high or expand if it is too low,' he added.

The landfill area targeted is currently used to tip the waste from recycled cars - mainly contaminated plastic and rubber scrap. This will take at least 500,000m3 of the surplus slag. The rest will go to landscape other amenity areas nearby.

Meanwhile on site, the first of three German-built tunnelling machines has started a £36M, 10km inlet tunnel which feeds the Cardiff East plant. The remotely controlled 2m diameter machine operates on a pipe jacking principle, and will be working at depths of up to 30m.

Dave Parker

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