Pond contract in the pipeline

Wanganui wasterwater PHOTO/FILE

A contract to remove sludge from Wanganui's wastewater treatment ponds on Airport Rd is expected to be signed off in a matter of days.

A Wanganui District Council spokesperson confirmed on Friday the arrangements could be finalised soon after August 30 and that there were a "few processes" to be worked through yet before the contracts could be signed off.

Removing the toxic sludge from the ponds - expected to cost almost $4 million - is part of the $24 million remedial plan aimed at restoring the ponds to full working order.

It has been the sludge, loaded with heavy metals and other waste, that created the stench which has plagued the city, especially since December.

Council staff had earlier been getting prices from three contractors with the ability to remove the sludge, which had built up to about 5m deep in the main pond.

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Council infrastructure manager Mark Hughes said the options in dealing with the sludge were limited, mainly because of its composition.

Mr Hughes said it has to be dumped in a designated landfill, and while Bonny Glen (near Marton) can take some, the bulk would probably have to go to a landfill at Hampton Downs in Waikato.

He said the sludge would be dried out before being taken away. It cannot be composted or recycled because it contained too many heavy metals.

Planned changes to the plant mean the sludge would be removed on a regular basis and dehydrated before being taken off-site.

The $24 million cost would bring the system back within resource-consent guidelines.

Initially, lime slurry had been sprayed over the ponds as a first step in overcoming the stench and polymers were added to help take suspended solids to the bottom. Hydrogen peroxide had also been added at the Beach Rd pumping station to stop any sulphides getting into the system. The sulphides were responsible for the original odour coming from the ponds.